Survey of Invertebrate Phyla

Background Information on Kingdom Animalia:

Kingdom Animalia includes about 35 phyla (depending on whose classification scheme is being used). When many people think of animals, they only think of mammals, yet Class Mammalia is only one class in Subphylum Vertebrata, which is only one subphylum within Phylum Chordata. We tend to lump all the other phyla and other taxa within Vertebrata into a catch-all pseudo-group, the “invertebrates,” but this is about 95% of all animals! There are more species of insects than all other plants and animals together (The more conservative estimates are that there are over one million species of just insects.). Mammals are only a minuscule piece of the picture.

Animals live practically everywhere on this Earth. Insects, alone, inhabit nearly all possible environments on Earth with the exception of deep in the ocean, yet their close relatives, the crustaceans have representatives that live there. Many other animals in many phyla live in the ocean and in just about every terrestrial habitat.

In general, animal reproduction includes flagellated sperm and a larger egg which join in fertilization to form a zygote. This grows by mitosis to form a blastula (blasto = bud, sprout), an embryonic stage that resembles a hollow ball, then on to other embryonic stages. From this point, if the young resemble the adults, it is said that the embryo grows into young, which grow into adults. If the young are very different from the adults, it is said that the embryo grows into a larva (larva = ghost, specter) which grows and metamorphoses into an adult. Caterpillars and tadpoles are larvae, which, as is typical of larvae, have different food, habitat, and appearance than the corresponding adults. A larva undergoes metamorphosis (meta = between, with, change; morpho = form; -sis = the act of) to become an adult.

Before discussing the various animal phyla, it is useful to introduce some of the terminology which will be used to describe these animals. The back or top side of an animal is its dorsal (dorso = back) side, and its belly or bottom side is its ventral (vent(er) = underside, belly) side. The head or front end is called the anterior (ante = before) end, and the tail or back end is the posterior (post = behind, after). Animals with radial symmetry (radia = spoke, radius; sym = with, together, metr, -metry = measure, measurement) do have distinct top and bottom sides, but have no distinct left and right. Starfish, jellyfish, and sea anemones are examples of animals with radial symmetry. Animals with bilateral symmetry (bi = two; later = side) do have distinct left and right sides, and most animals with which we are familiar, such as earthworms, ladybugs, and dogs, have bilateral symmetry.

The body of an animal is made up of several layers of tissue. Ectoderm (ecto = out, outer, outside; derm = skin) is the outer layer of tissue. The epidermis (epi = upon, over), or skin, other outer layers, and the nervous system in vertebrates (not in all animals) are formed from ectoderm tissue. Mesoderm (meso = middle) is the middle layers of tissue. Mesoderm forms the muscles and most other internal organs. Endoderm (endo = within, inner) forms the inner layers, including the lining of the digestive tract in all animals and the liver and lungs in vertebrates. Often animals have a space in their bodies between several of these layers. Animal groups, like flatworms, with no such space are referred to as acoelomates. Animals, such as roundworms, which have a space between the mesoderm and the endoderm are called pseudocoelomates, and the space is called a pseudocoelom. Animals, including earthworms, insects, and humans, which have the space in between several of the mesoderm layers are called coelomates, and the space is called a coelom.

Background Information on Invertebrates:

In this lab, you will become familiar with the characteristics of a variety of invertebrate phyla. While Phyla Annelida, Phylum Arthropoda, and Phylum Chordata – Subphylum Vertebrata will be covered in subsequent labs, this lab will survey some of the other invertebrate animal phyla. Some of the characteristics of each phylum are listed below. Depending on what specimens and slides and how much time are available, your instructor may choose to focus on a more-limited subset of these organisms. A whole course could be spent on comparative invertebrate anatomy, so this lab designed to just “skim the surface” and provide an introduction to these organisms.

As time allows, examine any microscope slides, plastic mounts, preserved, dead, and/or live specimens of these organisms which are available. Take notes on everything you see, draw pictures of each, and label all the parts, systems, and organs that are visible. Include labeled drawings of external and internal anatomy for as many of these animals as you are able to view.

Phylum Porifera

(pori = pore, small opening; fer = to bear, carry)

The members of this phylum are commonly known as the sponges. This is the most primitive group of animals, and it is thought that they evolved separately from all other animal groups. Interestingly, they share many characteristics in common with some forms of colonial protozoans. Sponges have no symmetry.

The body consists of two layers of cells: the outer dermal epithelium and the inner gastral epithelium which lines the central cavity. Between these two layers of cells is a jelly-like substance, and embedded in that, a skeletal framework, often consisting of spicules of varying chemical composition.

There are many pores in the body wall, hence the group name, “Porifera”. In general, water, along with potential food, flows into these pores, and out through the main ostium or excurrent opening.

Sponges are hermaphroditic, that is, they have both sexes in one body. This term is derived from the myth in which Hermes (Mercury) and Aphrodite (Venus) got together and had a son, who they named Hermaphroditus, who while swimming one day, somehow became united in one body with a water nymph. Sponges can reproduce sexually via eggs and sperm (which are just released into the water), with the resulting zygote giving rise to a multicellular, free-swimming larva. Sponges can also reproduce asexually by budding (a piece breaks/pinches off and forms a new colony of sponge. As adults, they are sessile (attached to one place).

Class Calcarea

Grantia sp., longitudinal section (too big to fit under low power all at once)

This photograph is a longitudinal section (l.s.) through a small sponge called Grantia, and exhibits the body structure typical of sponges. (This slide is not in your slide box, and we will not be examining it during lab, but it is included here so that you can better understand how a sponge’s body is put together.) Not visible in this microscope slide is the excurrent pore, the opening at the top of the “body” of this sponge. Below is a close-up view of a portion of the upper left corner of the above photograph.

Enlarged view of a portion of Grantia sp.

The central cavity in the “body” is called the gastral cavity. Notice how the body wall zigzags back and forth forming a number of canals. Incurrent canals open towards the outside, and are, thus, lined with dermal epithelial cells. Radial canals open toward the gastral cavity, and are lined with gastral epithelium. Notice that there are many small pores that connect the incurrent and radial canals. Water (carrying food, etc.) flows into the incurrent canals, through the pores into the radial canals, then into the gastral cavity. The cells of the sponge filter out, eat, and process the food, then excrete the wastes into the water in the gastral cavity. From there, the water is released via the excurrent canal at the top of the sponge.

Class Demospongiae

Spongia officinalis — Commercial Sponge
The body plan of these large sponges is arranged similarly to that seen in Grantia, but much more complex, consisting of a very complicated network of interconnecting canals. These sponges are collected from the ocean, then left to dry, so all the cells died long ago, and what is left is the “skeleton” of the sponge, made of fibers of a chemical called spongin, which is a type of protein and is chemically similar to the collagen in our bodies. (Some other types of sponges also contain a skeletal structure called spicules which are “spiky” and glasslike.)

Examine the skeleton of a commercial sponge and note the complex network of canals of which it is comprised. Also, observe any available plastic mounts of sponges. (A side note: the cellulose “sponges” that we all use, now, were designed to mimic the looks and water-absorbing ability of real sponge skeletons.)

Phylum Coelenterata or Cnidaria

(coelo = hollow; entero = intestine, gut; cnida = stinging nettle)

This phylum includes animals like jellyfish (Class Scyphozoa), coral and sea anemones (Class Anthozoa [anthe = flower; zoa = animal]), all of which are marine, plus Hydra, a freshwater genus (Class Hydrozoa). These animals have radial symmetry.

The body wall consists of two layers of tissue: ectoderm/epidermis on the outside, and endoderm/gastrodermis lining the gastrovascular cavity, with a non-living, jelly-like mesoglea in between them.

They have a digestive cavity with one opening, which thus is called a gastrovascular cavity (gastro = stomach; vascul = a little vessel). The name “Coelenterata” refers to the gastrovascular cavity, so named because it serves the functions of both digestion (similar to our digestive system) and distribution (similar to our circulatory system) of the food. Also, it has one opening which serves the functions of both a “mouth” and an “anus” (food, etc., in, wastes out).

While, overall, the bodies of these animals are similar, are all the same basic shape, they can take one of two forms, and thus, the bodies of cnidarians are described in one of two ways, depending on whether the opening of the gastrovascular cavity is dorsal (up) or ventral (down). Animals like Hydra and sea anemones, which are sessile (anchored to the substrate and not moving much, if any) and have the opening (mouth) and surrounding tentacles at the top of their bodies have a body shape called a polyp (polyp = many footed). Jellyfish, which float (or are free-swimming) and have the opening and surrounding tentacles at the bottom, have a body form called a medusa (medusa = a jellyfish).

This phylum is noted for the specialized stinging cells (cnidocytes or nematocytes) which are found only in this phylum and are located on the tentacles. The combination of tentacles and cnidocytes is used to capture and paralyze prey. The toxins in some jellyfish cnidocytes are irritating or toxic to humans.

Cnidarians have both sexual and asexual forms of reproduction. Hydra, for example, will periodically develop lumps on the sides of their bodies that are either testes or ovaries. These make and release sperm or eggs, which then join to form a zygote, which eventually grows into a new hydra. Hydra also reproduce asexually by a process known as budding in which a new, small Hydra begins to grow from the side of a large Hydra, eventually pinching off when it is fully formed.

Class Hydrozoa

Obelia sp. have both polyp and medusa forms in different stages of their life cycle. (This slide is not in your slide box, and we will not be examining it during lab, but it is included here so that you can compare the polyp and medusa forms.)

Hydra sp. — Hydra (all are polyp form)

Several Live Hydra
Live Hydra Hydra is the only common fresh-water coelenterate. They may be found in local streams, but due to their small size, probably wouldn’t be noticed unless someone was specifically looking for them.

The body of a hydra consists of a stalk, the bottom end of which is called the base or basal disc. The top end consists of the tentacles, and the hypostome (the area around the “mouth”), and the “mouth” itself (or oral opening). Hydra can move either by gliding on their bases or by turning somersaults.

Especially on the tentacles, hydra bear cnidocytes or stinging cells (hence the name of this phylum). These cells discharge to paralize and capture prey.

Hydra with Buds, wm, Actual View
Hydra with Buds, wm, Microscope View

Live Hydra with Bud (Actual Color) Hydra can reproduce asexually by budding, in which a new hydra grows on the side of an older one (as in these photos), then eventually pinches off.

View the prepared slide of a hydra budding (Carolina #Z615). Draw your budding hydra, and label all the body parts listed above.

Hydra with Spermaries, wm, Actual View
Hydra with Spermaries, wm, Microscope View
In sexual reproduction, hydra can form testes (a smaller “lump” that’s nearer the oral opening and sticks out more, as above), and/or ovaries (a larger “lump” that’s nearer the base and sticks out less, as below).

Hydra with Ovaries, wm, Actual View
Hydra with Ovaries, wm, Microscope View

View the prepared slides of hydra with spermaries (Carolina #E28) and with ovaries (Carolina #Z640). Draw each hydra and label all its parts.

Hydra, xs, Microscope View The body wall of a hydra consists of two layers of cells, the outer ectoderm and the inner endoderm. Note that, unlike our bodies, they do not also have a mesoderm layer. Also unlike our bodies, their ectoderm and endoderm layers are each only one cell thick. There is a jellylike substance called mesoglea between the ecto- and endoderm. The ectoderm is comprised of epitheliomuscular cells which serve both as a body covering and contain muscle fibrils for movement. Periodically interspersed among the epitheliomuscular cells, and especially numerous on the tentacles, are a few cnidocytes or stinging cells, which can only function once, then must be replaced. The most prevalent cells in the endoderm are nutritiomuscular cells, which aid in intake of food and body movement. Some bear flagella which help to circulate the contents of the gastrovascular cavity. In the endoderm there are also some gland cells which secrete digestive enzymes into the gastrovascular cavity. (This slide is not in your slide box, and we will not be examining it during lab, but it is included here so that you can better understand how a hydra’s body is put together.)

Class Scyphozoa

While some kinds of jellyfish are hydrozoans, many types of jellyfish are scyphozoans. All members of this class are of the medusa form. (This group is mentioned just because it fits in, here, but we will not be examining them.)

Class Anthozoa

Members of this class are of the polyp form. This group includes sea anemones and coral. Corals are colonial, secreting protective structures in which they live. These coral reefs area often very colorful. (This group is mentioned just because it fits in, here, but we will not be examining them.)

Phylum Platyhelminthes

(platy = broad, flat; helminth = a worm)

Members of this phylum are collectively known as the flatworms because their bodies are flat and ribbonlike. They have bilateral symmetry, but are acoelomates (have no coelom). They have a gastrovascular cavity with one opening. Most have no respiratory structures and “breathe” through their skin. Some of these are free-living (aquatic), and others are parasitic.

Class Turbellaria

This class includes a number of genera and species which are collectively referred to as Planaria, as well as other, closely-related organisms. They are all free-living, and there are both fresh- and saltwater forms (all are aquatic). Planaria typically are found in freshwater streams, including those here on campus.

Members of this class have a gastrovascular cavity with one opening. They have bilateral symmetry — they have specific dorsal and ventral sides, anterior and posterior ends, and right and left sides.

This is the first group of animals in which all three tissue layers are present. Externally, there is a layer of epidermis or ectoderm, the ventral surface of which bears cilia. These enable a gliding motion. Internally, there is a layer called the endoderm or gastric epithelium or gastrodermis which lines the gastrovascular cavity. This is the first group of animals in which a layer of mesoderm is found in between those two layers. This consists of layers of muscles just under the epidermis, as well as a layer of mesenchyme tissue, which takes up most of the space in the body.

Planaria, Actual View of Slide
Labeled Planarian The first picture is an actual photo of the microscope slide of two stained planarians, the others are microscopic views. These are stained whole mounts. The green-stained one shows the extent of the digestive system. Note the pharynx and the light-sensitive eyespots.

The pigment within the eyespots in the “head” region is light-sensitive, but these “eyes” do not see images like our eyes do. The lateral extensions in the head region are called auricles.

In the middle of body, on the ventral side there is a pharynx which may be extended or retracted. This serves the dual purposes of taking in food and elimination of waste. Since, once again, there is only one opening to the body cavity (digestive system), that is, again, referred to as a gastrovascular cavity.

Planarian
Planarian Stained to See Digestive System Planaria are reported to feed on algae and the dead bodies of snails and other aquatic organisms. When kept in captivity, they are often fed bits of liver.

Planarians have an excretory system made up of a network of tubules with flame cells at the ends (this system may be visible on specially-stained, prepared slides) to eliminate water, CO₂, and nitrogenous wastes.

They have a well-developed nervous system to coordinate feeding, movement, etc. This is a “ladder-like” nervous system with nerve cords running down each side and “rungs” connecting them. There are a number of ganglia, including a larger ganglion (“brain”) in the head region. There are also sensory structures, including the “eyes.”

Planaria have sexual reproduction. They are hermaphroditic (have both male and female gonads/genitalia) and cross-fertilize when they mate with another. They can also reproduce asexually by pinching apart, and each half regrowing the missing portions. A common lab demonstration that is done is to cut apart a planarian in various regions of the body to observe its regenerative capabilities, and that is a “hot” research topic because, if we could understand how they are able to regenerate missing parts, it is reasoned that perhaps that would give us a way to turn those genes on in humans. (Other experiments have also been done to study their learning ability.)

View the prepared slide of a whole mount (wm) of stained planarians (Carolina #Z915) under low power (the slide is too thick and will crack if you attempt to use higher powers of magnification. Draw and label all body parts. Notice that the gastrovascular cavity has one anterior branch and a pair of posterior branches (for a total of three branches/parts).
Observe any plastic mounts of planaria.
If live planaria are available, watch one move. If available, try adding some “food” to the water, and see if the pharynx is extended.

Bipalium kewense — Land Planarian (© 2016 by Eric Stein)

Here’s a planarian relative that, if you live here in the US, you may not see. (It certainly is not one I was told about back when I was in school!) These are sometimes called “hammerhead slug” or “hammerhead worm,” but they are not slugs, and they are not related to earthworms.
They are thought to be from somewhere in Indo-China, and are not native to the US, but were first seen here in 1901, in greenhouses. In greenhouses, they live in the moist environment in potted plants, and thus, can be spread when the potted plants are shipped to somewhere else. In some warmer areas of the US, they have become established outdoors, while elsewhere, they may be present seasonally (due to planting new plants in whose pots they were living). This individual was photographed in June 2016 in my brother’s yard in the Smoky Mountains in Tenn.
Our native planarians are typically in the vacinity of 1 cm long and aquatic. These planarian-relatives are terrestrial, and can grow to over 10 in (25 cm) long. True to some of their common names, their head (to the left in this photo) is “hammerhead”-shaped.
Like our local, aquatic planaria, they may have eyespots (again, not true eyes) on their head.
Also, as described above, they both feed and eliminate wastes via a pharynx midway down their body. Like our local planaria, they are also carnivores, with earthworms being a favorite food (people who own earthworm farms and are raising earthworms for money don’t like them), though according to one Web page, the will also eat slugs and some types of insect larvae.
Like our local planarians, they’re really good at regeneration. While they do reproduce sexually, apparently reproduction via the end of the “tail” pinching off is more common... and, just like the locals, if someone cuts one into several pieces, each piece can grow into a new Land Planarian. They move by secreting a mucus trail, along which they can glide by using cilia.

Class Trematoda

Clonorchis sinensis — Chinese Liver Fluke

The members of this class are known as flukes. They are parasites in the liver, lungs, intestines, or blood of various animals, and have complex life cycles needing specific hosts. One of the most frequently-studied is the Sheep Liver Fluke, Fasciola hepatica, a parasite in the liver of sheep. (Note that the prepared slide, above, is of a different species. This slide is not in your slide box, and we will not be examining it during lab, but it is included here so that you can better understand what a fluke looks like.)

The Sheep Liver Fluke has an anterior sucker to feed on the liver of its host. About a fifth of the way down the body from the anterior end is the ventral sucker which is used to attach to host tissue. Midway between these two suckers is the genital pore. At the posterior end is an excretory pore, the opening of the excretory system.

The digestive tract has two lateral branches running posteriorly down each side. Flukes are hermaphroditic. The flame cells of the excretory system are very difficult to see without a specially-stained prepared slide.

Interestingly, flukes have no epidermis (ectoderm) layer. Rather, the mesoderm muscle tissue is directly covered by a non-living cuticle.

Several species in genus Schistosoma are known as “blood flukes” and are parasites whose life cycle involves both humans and snails. A human who is infected with them is said to have schistosomiasis. Schistosomiasis ranks second, after malaria, in terms of the number of people (many in third-world countries) who are infected. The flukes parasitize blood vessels in the mesentaries (the membranes which surround the intestines). Members of genus Schistosoma are unusual, compared with other flatworms and even other trematodes, because they are dioecious — they have distinct, separate male and female flukes (remember other flatworms are hermaphroditic). Eggs are eliminated in either the person’s urine or feces, depending on the species of Schistosoma involved, and then the larval stage must parasitize a snail host. Then, humans become infected when they wade in snail-containing water in tropical areas where this fluke occurs, and a next-larval-stage organism burrows right through their skin. Just as a major component of malaria prevention is based on treating water supplies to eliminate mosquito larvae, so also, a major component of prevention of schistosomiasis is treating water bodies to eliminate snails. There is also a drug that may be given to humans who are already infected, and often, if in a particular village, a large number of children are showing symptoms, the simplest thing to do is to just treat everyone in the village, which also helps to eliminate re-contamination of the local water supply. Also, simple preventative measures can be taken: just as the use of bed nets eliminates mosquitoes’ ability to get to humans (children) to spread malaria, so also educating people (children) to avoid going in the water (no swimming) can cut down on the number of people infected with this parasite.

Observe any plastic mounts of flukes that are available.

Class Cestoda

The members of this group are known as tapeworms due to their shape, and are all parasitic. Their bodies are made of a number of segments called proglottids, each of which is pretty much on its own and separate/independent from the rest. These proglottids don’t need a digestive system because they absorb pre-digested food from the host’s digestive tract and don’t need a respiratory system because they absorb dissolved air (O₂), again, from the fluids in the host’s digestive tract. Thus, these segments are mostly reproductive system (imagine each segment as a very prolific female!). The segments break off and are passed out with the host’s feces. Other animals who accidentally ingest some of the infected feces (cattle eating grass near where other cattle have defecated) can acquire the parasite. Tapeworms can grow very large (long) and absorb so much food from their host’s digestive tract that they cause nutritional deficiencies.
One commonly-studied example is the Dog Tapeworm, Taenia pisiformis.

Anterior Segments and Scolex
Close-up of Scolex

Labeled Scolex The first segment of the body is called the scolex, and the rest are called proglottids. The proglottids closest to the scolex are the newest, youngest ones, and those farther away are older. The purpose of the scolex is attachment. It has a ring of hooks plus four suckers to attach to the wall of its host’s intestine.

Mature Proglottids
Close-up of Mature Proglottid

Labeled Proglottid While these structures may not be easily distinguishable, in the proglottids, a nerve cord and an excretory tube run along each side. The excretory system has one cross-connection posteriorly in each segment.

Neither the organism as a whole, nor the individual segments has any kind of mouth or digestive tract. Mature proglottids contain essentially no other body organs than (or lose all but) a reproductive system (each segment has its own) with a lateral genital pore. They are hermaphroditic, and may self-fertilize, or may copulation with another proglottid when the “chain” folds back on itself bringing proglottids into contact with others.

Once fertilization occurs, as the eggs develop and mature, all other systems disintegrate, so the older proglottids are, essentially, just egg sacs. Those at the end of the chain break off and are passed out with the host’s feces. Those eggs may, then, be ingested by another host animal who eats, for example, grass from near where those feces were deposited. If dog tapeworm eggs are ingested by rabbits, they hatch and burrow into the rabbit’s muscle, and form a cyst. If that rabbit is subsequently eaten by a dog, the tapeworm comes out of the cyst form, attaches to the dog’s intestine, and grows there.

View the prepared slide of a tapeworm (Taenia sp.) scolex (Carolina #Z971) and the prepared slide of tapeworm (Taenia sp. mature proglottids (Carolina # Z973b). Draw what you see and label all body parts that are visible. Also, view (and draw) any plastic mounts that are available.

Phylum Nematoda

(nema, nemato = a thread)

Members of this phylum are called roundworms because their bodies are cylindrical. Some are free-living in aquatic habitats (including damp soil), while others are parasitic. They have bilateral symmetry. For the first time, here, we’re seeing animals with a “tube-within-a-tube” body plan, in that they have both a mouth and an anus, and food travels through the digestive system from one end to the other. They have all three layers of tissue: ectoderm, mesoderm, and endoderm with a pseudocoelom (false coelom), a cavity between the meso- and endoderm (a true coelom is between meso- and more mesoderm). All muscle fibers in their bodies run longitudinally, so only they can only do thrashing movements. There are free-living (in water and in moist soil) and parasitic forms which range in size from microscopic to several feet in length. They have sexual reproduction with definite males and females.

Class Secernentea

One commonly-studied roundworm is Ascaris lumbricoides, a parasite of pigs. The smaller male has a curled posterior end and the larger female is straight. They are unsegmented and have no conspicuous appendages or sense organs.

On the female, the posterior end is more pointed than the anterior, and has a slit-like anus near the tip on the ventral side. The anterior end has three “lips” surrounding the mouth. About a fourth of the way down, on the ventral surface, is a genital pore. There is a faint lateral line on each side, indicating the lateral excretory canal. There are also less-distinct dorsal and ventral lines, indicative of the dorsal and ventral nerve cords.

Ascaris lumbricoides, x.s., Intestinal Region Ascaris lumbricoides is a roundworm that is parasitic on pigs. This is a cross-section through the female (left) and male (right) showing the uterus full of eggs/embryos in the female and other internal organs in both.

Ascaris lumbricoides, x.s., Esophageal Region This slide shows the internal organs in the region of the esophagus.

(These two slides are not in your slide box, and we will not be examining them during lab, but they are included here so that you can better understand what roundworms look like.)

Class Adenophorea

Male and Female Trichinella Worms, w.m. Trichinella spiralis (trichin = a hair; -ella = small) is a parasitic roundworm that infects muscle tissue in mammals that happen to consume some of them, and seems to be especially prevalent in pigs. The worms form cysts in the host’s muscle tissue. The infection is called trichinosis (trichin = a hair; -osis = diseased condition or state), and can be transferred to humans via consumption of (especially) pork that has not been cooked thoroughly enough to kill the parasites that have encysted in the pig’s muscle tissue.
Thorough cooking at high temperatures kills the parasites, but microwaving often does not get the center of a piece of meat hot enough for a long enough time to be effective. Because of this, while it is OK to reheat pork in a microwave, it should never be cooked that way for the first time. If a person ingests living Trichinella in undercooked meat, in the person’s intestines, the parasites will develop from larvae into adults and reproduce. Mated females will bore into the person’s intestinal muscles, where they will produce a new generation of larvae. These new larvae, in turn, either travel through the person’s lymph system or burrow through his/her body tissue to reach his/her muscles and other tissue where they will live.

Encysted Parasites in Muscle Tissue
Close-up of Worm in Cyst in Muscle

Parasitic roundworms also include pinworm and hookworm. School children frequently contract pinworm from doorknobs, etc. at school because infected classmates don’t wash their hands after wiping feces from their anal areas. Pinworms live in the rectum and lay their eggs around the anus, thus one main sign of a pinworm infection is when a child frequently scratches his/her anal area. A classic test for pinworm infection is to touch a piece of scotch tape to the child’s anal area, followed by microscopic examination of the tape to check for the presence of pinworm eggs.

Many roundworms are free-living, but need to live in an aquatic environment of some sort, which can include damp soil. Many soil nematodes are beneficial and are important decomposers, but there are some which can be found in garden soil that damage desirable plants.

View the prepared slide of Trichinella spiralis in muscle (Carolina #PS2430). Find a “good looking” encysted parasite to draw and label.

Phylum Rotifera

(rota = wheel, revolve; fer = to bear, carry)

These organisms are frequently seen when examining pond water under a microscope. They may be identified by their characteristic rings of cilia around the mouth which, when beating, look like rotating wheels, hence the group name. These direct food into the mouth.

One of the most commonly-seen forms has a telescoping body and a forked “foot” at the posterior end, but other configurations also occur. They are all microscopic, but multicellular, and there are both fresh- and saltwater-dwellers.

They also have a pseudocoelom like the nematodes. They have a tube-within-a-tube body plan with a mouth and an anus. They have an excretory system similar to flatworms. Frequently, they reproduce parthenogenetically (partheno = a virgin, without fertilization), that is, the females produce more females without fertilization by males. While smaller and not as common, males do exist.

(This group is mentioned just because it fits in, here, and this may be something you might see in pond water, but we will not be examining them in this lab.)

Phylum Annelida

Taxonomically, Phylum Annelida would fit here. More information on them can be found on the earthworm Web page.

Phylum Onchyohora

(onycho = a claw, nail; phora, fer = to bear, carry)

Macroperipatus torquatus from Trinidad © M. K. Busching Phylum Onchyophora includes the velvet worms (also called “walking worms”) in genera Peripatus (peri = around, -patus = a walk, path) and Macroperipatus (macro = large, long). This photo of Macroperipatus torquatus, a larger species from Trinidad, was taken by Milan Busching, Curator, Emeritus, of Invertebrates at the Cincinnati Zoo.
This phylum is of interest because its members share some traits in common with the Annelida, and other traits in common with the Arthropoda, and thus, many biologists feel that, evolutionarily, this phylum is midway between and may be an evolutionary link between those two phyla. They do also have unique traits of their own that are not shared with either the annelids or the arthropods.

One prevalent theory is that Onychophora is thought to have evolved from a marine worm-type ancestor, with the parapods evolving into unsegmented legs. Onychophorans have one pair of these unjointed, cone-shaped appendages per segment, and those appendages are muscular and can move, but are not jointed as in the arthropods. This theory regards onychophorans as a sort-of “missing link” on the way to the evolution of insects (Other biologists believe that arthropods arose directly from annelids through some jointed-legged ancestor.). Onychophorans’ walking legs have a pair of claws at the tips. At the anterior end of their bodies is a pair of antennae plus a pair of oral papillae, and in the mouth, a pair of “jaws,” all three of which are modified appendages, similar to the condition in arthropods.

Onychophorans are predatory and shoot sticky, mucus/saliva to tangle their prey. They have a tubular digestive system. They are bisexual (have males and females) and are live-bearing (viviparous). There is a pair of simple eyes on the “head.” The nervous system is simple, consisting of a “brain” and paired, ventral nerve cords without distinct segmental ganglia.

Their excretory system consists of paired, segmental nephridia like annelids, and locations of these corresponds to the locations of the legs. They also share the presence and structure of their cuticle, their ciliated reproductive tract, and their musculature with Phylum Annelida. However, their respiratory system of tracheal tubes which distribute oxygen directly to the various organs, paired appendages with claws at the tips, open circulatory system, and chitinous exoskeleton which must periodically be molted are shared with Phylum Arthropoda.

View the plastic mount of Peripatus.

Phylum Arthropoda

Taxonomically, Phylum Arthropoda would fit here. More information on them can be found on the crayfish Web page, the eyelash mite Web page, and the insect Web page.

Phylum Mollusca

(mollusc = soft)

There are several classes of mollusks:

• Class Polyplacophora (poly = many; plakos = flat plate, tablet; phora = bear, carry) which includes the chitons
• Class Gastropoda (gastro = stomach; poda = foot) which includes snails and slugs
• Class Bivalvia or Pelecypodia (bi = two) which includes oysters and clams
• Class Cephalopoda (cephalo = head) which includes octopus (octa = eight), squid, and chambered nautilus

Mollusks are soft-bodied and have a true coelom. Many have shells made primarily of calcium carbonate: chitons have a shell made of eight plates, snails have one, spiraled shell, clams have a shell composed of two, hinged halves, squid have small internal “shells,” and the chambered nautilus has a chambered shell (spiraling in living species but straight in many fossil forms).

The general body structure includes a ventral, muscular structure, the foot, which is involved in locomotion. Dorsal to that is the visceral mass, including the internal organs. Covering part to much of the body is the mantle, which often secretes a calcium carbonate shell. In the anterior portion of the digestive tract is a radula (radul = a scraper), a rasping organ used to obtain food. Most don’t show much sign of segmentation, with the exception of the chitons. They have bilateral symmetry. Aquatic forms have gills for exchange of oxygen and carbon dioxide.

While snails and slugs have a radula (radul = a scraper), a rasping organ in their mouths to “scrape” bits of food into their mouth, most bivalves use their gills to filter small food particles, which are then directed toward their mouths. Cephalopods have beaklike jaws for biting and crushing their prey, and unlike members of the other classes, tend to be fast-moving carnivores.

Many mollusks have good eyes (snail, octopus, squid). Octopuses are famous for their well-developed nervous systems and brains (necessary to process the information from their sophisticated eyes), and they are known to be very intelligent.

Most mollusks have males and females, while certain kinds of garden snails are hermaphroditic.

Examine any plastic mounts that are available. Additionally, since many of these are used as food by humans, “samples” may be available from the seafood section of a local grocery store.

Class Gastropoda

(gastro = stomach; poda = foot)

This class includes the snails and slugs. Some are marine, some inhabit freshwater, and some are terrestrial.

Snail Eye At their anterior (head) end, snails and slugs have two pairs of retractable tentacles with eyes at the tips of the longest pair. Because snails have a one-piece shell, they are called univalves. As snails and slugs move, they secrete a layer of mucus upon which they glide (hence the slug trails seen on sidewalks). Some types of snails are hermaphroditic.

Snail Snails and slugs have a rasping radula that helps them ingest their food.

The visceral mass forms a dorsal hump, covered by the mantle which secretes the shell. The digestive system (and other internal organs) is modified to account for the position of the visceral mass, so it goes up into the portion of the body held within the shell, around, and back out, again, somewhat anteriorly. While marine forms have gills, terrestrial snails have the inner surface of the mantle cavity modified to form “lungs,” instead.

Out in California, there is a species of slug called a Banana Slug. These are large — approaching the size of a small banana — and bright yellow in color.

Cowrie Shell, Top Side
Cowrie Shell, Bottom Side Cowries are another type of gastropod. They are marine, and like snails, their bodies extend inside their shells. Humans from many cultures have found their porcelain-like shells to be attractive.

Class Pelecypoda

(pelecy = hatchet, axe — this name is due to the wedge-shaped foot)

Mussels at Low Tide This class includes mussels (note spelling), clams, scallops, oysters, and similar organisms. These have two-part shells, so are called bivalves. The two halves are held together by a tough ligament in the dorsal region. Due to the way the mantle secretes the shell as it adds to the shell, the shell has growth rings. The widest side-to-side, oldest part of the shell is called the umbo. Looking from the side, the shell is not symmetrical, and the umbo is displaced toward the anterior end, while the other end is posterior. The two valves of the shell open ventrally, and the foot extends from there.

Bivalve Shells Used for Decorative Craft The two halves of the shell are held shut by the large, anterior and posterior adductor muscles, located dorsally. Just inside the shell is the mantle, and under the mantle, the wedge-shaped foot and the visceral mass. Modifications of the mantle create an internal current with the mantle forming incurrent and excurrent canals. This current brings in food and carries away waste. There are also two pairs of gills, sheet-like structures attached to the dorsal part of the body on either side.

Along the anterodorsal margin of the foot are two pairs of flaplike labial palps, and the mouth lies midway between the palps.

They have an open circulatory system. In the visceral mass, the coelom is modified as a pericardial cavity. The heart is in that cavity, surrounding the intestine. It pumps blood both anteriorly and posteriorly into arteries, many of which open into blood sinuses rather than capillaries. While passing through the gills, the blood absorbs oxygen.

A nephridium lies near the pericardial cavity, and absorbs nitrogenous waste from the pericardial fluid and blood, then discharges that into the water flowing through the inside of the shell.

The nervous system consists of three pairs of ganglia: the head ganglia near the anterior adductor muscle, the visceral ganglia near the posterior adductor muscle, and the foot ganglia in the foot. These ganglia are joined by paired connectives.

These organisms are bisexual (have separate male and female organisms). There are both freshwater and marine species.

Humans enjoy using mollusk shells in craft projects. The doll in this photo is composed of pelecypod shells (and pipecleaners) as a “Souvenir of Washington D. C.”, probably from the 1930s or 1940s.

Class Cephalopoda

(cephalo = head)

This class includes squid, octopus, and nautilus. The class name comes from the fact that the foot is highly modified into a “head.”

Whole Nautilus Shell
Nautilus Cut Open to View Chambers

Holes Between Chambers While squid and octopus lack an external shell, the nautilus has a shell that’s divided into chambers, and the animal lives only in the most recent chamber. The nautilus shells in these photos have had the outermost, brown-and-white patterned layer of their shells removed to reveal the pearlescent layer underneath. Notice the row of holes between the chambers. These, or more correctly, the tube that would be passing through them, is/are called siphuncles and are involved in regulating bouyancy by changing the amount of water vs. air present in the sealed chambers of the shell.

The squid has a region with arms and eyes that’s called its “head.” If a fresh or preserved squid is available, note the number of arms and note the suckers on them. The two arms that are longer help to capture prey, are retractile, and may be called “tentacles.” In the center of the circle of arms is the mouth with a beak that’s shaped like that of parrot.

On the head, above the tentacles are a pair of well-developed eyes. Adjacent to the head, on one side, is a muscular tube, the funnel, with an opening at its tip (remember, the head and funnel make up the foot of the squid, thus, technically, are ventral with the head anterior and the funnel posterior).

The rest, the major portion, of the body is a dorsal hump, the mantle, which encloses the internal visceral mass. It is extended laterally to form a pair of triangular fins. Near the head, the mantle forms a loose collar around the visceral mass. The gills lie in the mantle cavity.

Water from the mantle can be forced out the funnel for propulsion. Also, a sac in the mantle cavity contains an inky substance, which can be expelled in the jet as the squid or octopus is fleeing from a predator.

Cephalopods have a well-developed nervous system, especially a large brain with several pairs of ganglia between the eyes. They have excellent vision, and octopuses are extremely intelligent and good at problem-solving — as in, seeing the feeder fish in the aquarium next door, lifting the lid to squeeze through the filter and get out of the home aquarium, using one’s suckers to walk across the wall to travel to the neighboring aquarium, getting into that neighboring aquarium, eating all the fish, then going back home, and remembering to close the lid so those pesky humans can’t tell who ate the fish. Octopuses have demonstrated tool use.

Octopus blood contains hemocyanin, the center of which is a porphyrin ring with a copper atom in the center. This gives the blood a blue color.

If available for examination, compare squid and octopus — how are they similar, and how are they different?

Phylum Echinodermata

(echino = hedgehog, sea urchin, spiny; derm = skin)

This phylum includes

• Class Asteroidea (aster = star) which includes the starfish and sea stars
• Class Ophiuroidea which includes the brittle stars
• Class Echinoidea which includes the sea urchins and sand dollars
• Class Crinoidea which includes the sea lilies or crinoids
• Class Holothuroidea (holo = whole) which includes the sea cucumbers

Members of this phylum share several traits in common with, and thus, it is believed are evolutionarily more closely related to the chordates (vertebrates) than to other invertebrate phyla. They have an endoskeleton (internal skeleton — endo = within, inner) covered by a thin layer of epidermis (skin), vaguely reminiscent of our endoskeleton with skin on the outside. Also, the larval forms in these two phyla are similar to each other (and different from other animals). It is believed that these similarities are evidence of a close evolutionary relationship between these two phyla, even though that may not be obvious by looking at them.

All echinoderms are marine. The adults possess radial symmetry, but it is recognized that is secondary and is superimposed on the bilateral symmetry of the larvae (thus, is not a primitive trait). Their larvae have bilateral symmetry, but metamorphose to adults that have secondarily radial symmetry (have lost bilateral symmetry, rather than never had it).

An important characteristic of this phylum is that the members possess an unique hydraulic system, including external, suction-cup-like tube feet connected by internal “plumbing.” By pumping fluid from one part of the hydraulic system to another, echinoderms can create a strong suction in the tube feet, aiding in locomotion and feeding.

Examine any plastic mounts and/or skeletons of echinoderms that are available.

Class Asteroidea

Young Starfish, w.m.
Starfish Ray, x.s. The young starfish in the left picture is unusual among starfish in that it has six arms, rather than five. Many of its tube feet and its sieve plate are visible. Especially noticeable in the photo on the right are some of the tube feet.

Members of this class are called starfish (aster = star), having five arms radiating from a central disk. The oral surface (the side bearing the mouth) is the “bottom,” and that side has furrows extending from the center out into each of the arms. On the aboral surface (top), between two of the arms on the central disc, is a whitish sieve plate which opens into the water vascular system, the hydraulic system that enables the tube feet to function. In the center of the sieve plate is a tiny anal opening.

On/in the skin, between the spines, are small skin gills and pincer-like structures that help keep the skin free of debris (but these are both very small and hard to see).

On the oral surface, rows of tube feet (which are part of the water vascular system) extend from the ambulacral grooves (the furrows in which they originate). The tip of each tube foot is a “suction cup.” There are moveable spines along the margin of the grooves. As previously mentioned, the grooves converge toward the central area, and there, the mouth is found, surrounded by a soft, circular membrane.

Starfish feed on bivalves, such as oysters and clams. They use hydraulic pressure in their tube feet to pull open the shells of these bivalves. The starfish fastens onto the shell of the bivalve with its tube feet and pulls the shell open, and since this doesn’t involve the use of any (or at least extremely few) muscles, the hydraulic system of the starfish doesn’t “get tired,” and since they have so many tube feet, those can “take turns” so the tiny muscles in them can rest. In contrast, the bivalve must use the previously-mentioned anterior and posterior adductor muscles to try to keep its shell closed, and muscles can’t work forever without getting fatigued, so eventually those muscles tire and relax, and the starfish is able to open the shell. After the starfish has succeeded in opening the shell, the starfish’s stomach, a large, membranous sac, is everted through the mouth to cover the fleshy part of the bivalve. The stomach secretes digestive juices that break down the bivalve, and the mostly-digested food is taken into the stomach for further digestion. Since little indigestible food is taken into the stomach, the remainder of the digestive tube and the anus don’t have a lot to do, and thus, are are very small.

The digestive organs, etc., lie within a coelom filled with coelomic fluid. The nervous system is simple, consisting of a ring of nerves with nerves radiating into each arm.

Starfish can also reproduce asexually by regeneration from chopped off arms. Starfish prey on oysters (valued as a human food source), and years ago before their regenerative powers were realized, the oyster fishermen would “destroy” any starfish they found by chopping them up, then tossing them back into the water. The chopped up starfish arms would just regenerate whole new starfish, and the “problem” with starfish eating the (desirable-to-humans) oysters intensified.

Starfish are either male or female. They release large quantities of eggs and sperm into the open water, where fertilization takes place. Starfish larvae are bilaterally symmetrical and look nothing like the adults. They are free-swimming. Eventually, each larva attaches itself to a convenient substrate and metamorphoses into an adult starfish.

Other Classes

Other classes in this phylum include Class Ophiuroidea = brittle stars, Class Echinoidea = sea urchins, Class Crinoidea = the sea lilies and feather stars, and Class Holothuroidea = sea cucumbers. While live sea lilies (AKA crinoids) are not very numerous or common, now, and are found only deep in the oceans, they were abundant in the Paleozoic Era and are commonly-found fossils.

Phylum Chordata

There are other subphyla besides Vertebrata within Phylum Chordata! These include Subphylum Hemichordata = tongue worms, Subphylum Tunicata = the tunicates and Subphylum Cephalochordata = the lancelets. While many of the traits in these groups vary, there are several things, common to all chordates, that they and members of Subphylum Vertebrata all share. At least in some stage in their life cycles, all possess a stiff axial rod called the notochord, hence the phylum name. Additionally, all chordates possess, at least in some stage of their life, a dorsal, hollow, nerve cord and pharyngeal slits.

The nerve cord is worth special mention here. Annelids and arthropods have a nerve cord that is ventral, solid, and of mesodermal origin. Thus the fact that the chordate nerve cord is dorsal, hollow, and arises from an invagination of ectoderm tissue points to a considerably different evolutionary history.

Subphylum Cephalochordata

Note that members of this subphylum are in Phylum Chordata, but are not in Subphylum Vertebrata — not all vertebrates are chordates! In general, members of this subphylum are known as lancelets or lancets for their resemblance, shape-wise, to that medical tool. The best-known member of this subphylum is Amphioxus (Branchiostoma lanceolatum; amphi = on both sides, double; branchi = gill, fin, hoarse; stoma = mouth), which lives in shallow marine waters, buried in the sandy bottom with only its anterior end protruding.

Like other chordates, members of this subphylum possess, at least in some stage of their life cycles, a) a stiff axial rod called the notochord, b) a dorsal, hollow nerve cord that is formed by invagination of ectoderm tissue, and c) pharyngeal slits.

Class Leptocardii

Amphioxus, w.m., Unlabeled and Labeled

Running down the sides of an Amphioxus are segmental, V-shaped muscles called myotomes. The body is more flattened (side-to-side) ventrally than dorsally. The head end is more flattened and somewhat less pointed than the posterior end.

The membrane called the oral hood makes up the anterior part of the head. Its “bottom” border is fringed with tentacles, and the area enclosed by the hood and tentacles is called the buccal cavity.

There is a median dorsal fin that runs all the way down the back. Ventrally, from the oral hood to about two-thirds of the way to the posterior end of the body run a pair of metapleural folds. Ventrally, at about two-thirds of the distance, posteriorly, is the atriopore, and the median ventral fin continues posteriorly from there.

At the posterior end, the median dorsal and median ventral fins expand to form the tail fin. The anus opens just anterior to the tail fin, near the ventral fin.

Sometimes, in the anterior regions, ventrally, below or at the bottom ends of the myotomes, whitish masses may be seen — these are the gonads.

Internally, the mouth is at the rear end of the buccal cavity, surrounded by velar tentacles. From the mouth to about half-way down the body are the pharynx and pharyngeal gill slits. Behind the gill slits, the digestive tract narrows to form the intestine, which extends back to the anus. In the region where the pharynx intestine meet, extending anteriorly, is a dead-end tube that is the liver. Above the digestive tract, extending end-to-end is a rod that may appear yellowish on a prepared slide — this is the notochord. Just above that, also extending end-to-end is the dorsal nerve chord, which is smaller in diameter than the notochord, and is hollow. It bears some pigmented spots (near anterior end) which may be light-sensitive. Ventrally and between the pharynx and body wall, and also behind pharynx is a body chamber called the atrial chamber. This collects water that has passed through the gill slits, and empties it to the the outside via the atriopore.

Amphioxus, x.s. of Pharyngeal Region
Amphioxus, x.s., Labeled The view, above, is a cross-section through the pharyngeal area, and shows many of the body parts mentioned, above. Throughout much of the pharyngeal area, the atrial chamber is more expanded below and somewhat to the sides of the pharyngeal area, itself, while this slide/photo is from an area where the atrial chamber looks like a relatively “thin” area between the pharynx and the outer layers of muscle and skin. Also, a cross section from another portion of the pharyngeal area would show paired gonads to each side of the pharynx, but in this view, there is only a small area on the right that might be the “end” of one of the gonads. Notice how the pharyngeal slits and branchial bars alternate around the pharyngeal cavity. The bars are for support/structure, while the slits allow water to flow from the pharyngeal cavity into the atrial chamber (and, eventually, out the atriopore). For comparison, while we do not have pharyngeal slits as adults, we do have them during a portion of our embryonic development.

Examine the plastic mount of a whole Amphioxus. Examine the prepared slide of a whole mount of Amphioxus (Carolina #Z2706) and of a cross section through the pharyngeal region (Carolina #Z2720). Draw and label all parts that are visible.

Amphioxus has its own song! A number of recordings of this song are available online. For example, see

• http://www.youtube.com/watch?v=LNoHBU1He1o
• http://www.youtube.com/watch?v=iGMuEDXaoRs
• http://evolution.gs.washington.edu/amphioxus/
• http://bullhead.us/mp3/LongWayFromAmphioxus.mp3
• http://bscd.uchicago.edu/content/long-way-amphioxus
• http://www.traditionalmusic.co.uk/song-midis/Its_a_Long_Way_From_Amphioxus.htm
• ... and others...

Subphylum Vertebrata

Taxonomically, Subphylum Vertebrata would fit here. More information on them can be found on the cat Web page.

Other Things to Include in Your Notebook

Make sure you have all of the following in your lab notebook:

• all handout pages (in separate protocol book)
• all notes you take as you read through the Web page and/or during the introductory mini-lecture
• all notes and data you gather as you perform the lab
• labeled drawing(s) (yours!) of any/all organisms examined
• all plastic mounts
• all microscope slides
• all live, dead, and/or preserved specimens
• answers to all discussion questions, a summary/conclusion in your own words, and any suggestions you may have
• any returned, graded pop quiz