BI 112 LAB: ACOELOMATE ANIMALS Acoelomate refers to animals that lack a true body cavity or coelom. A coelom is a real structure, often described as a bag, that forms a cavity that houses most of the organs within the bodies of higher animals. For example, our own abdominal cavity is a coelom that is lined by the peritoneum. The phyla we discuss in this lab, however, lack a coelom.

A quick overview of the major acoelomate phyla

Phylum Porifera (sponges)most primitive organization: no tissues; colonialnot multicellular; no gut (no mouth, no anus)

Phylum Cnidaria (jellyfish, hydrozoans, corals)true tissues but no organs, a blind gut (incompleteone opening)

Phlyum Platyhelminthes (flatworms=planaria/turbellaria, flukes, tapeworms)tissue & organs; flat and solid , blind gut (incomplete-one opening)

Phylum Nematoda (round worms)tissues & organs; an internal space (pseudocoelom=false body cavity), complete gut (mouth and anus)

Phylum Rotifer (wheel animals)2 ciliated wheels near mouth; complete digestive tract (mouth and anus), pseudocoelom

Phylum Gastrotrichaname means belly hair; covered with hairs and sometimes spines; resemble ciliates but have obvious organs; complete digestive tract and pseudocoelum

PHYLUM PORIFERA The sponges, or poriferans, are the simplest of the animals: they lack tissues and organs. Three basic cell types are present: surface cells, collar cells, and amoeboid cells. In addition, silica skeletal structures termed spicules (below, l), provide support, protection from predators, and are used by zoologists to identify species

. Sponges are filter-feeding organisms that move unicellular algae, bacteria, and fine particulate organic matter from the water for nutrition. Water is drawn into the sponge through 50-m holes pores by the collectively beating of flagellated cells called chonanocytes (collar cells). In ponds

well stocked with sponges, the entire volume of pond cycles through sponges in one week! Collar cells reside in pores and invaginations. Food particle are trapped in the collar of the collar cells and these cells transfer ingested food particles to archeocytes or amoeboid cells (above right x 1000) which digest the particles via phagocytosis, then expel undigested material into excurrent canals called oscula. In addition to carrying out digestion, amoeboid cells are totipotent, that is they can differentiate into any of the aforementioned cell types, depending on which tasks need to be carried out.

In addition to filtering particles, sponges also rely heavily (50-80% of growth in some species!!) on endosymbiotic green algae called zoochlorellae for nutrition. Zoochlorellae are housed within virtually all cell types and their chlorophyll is responsible for the bright colors found in many species of freshwater sponge. In some U.P. ponds, photosynthesis in sponges can equal that of the entire phytoplankton community!

Sponges reproduce asexually by producing

gemmules (a mass of amoeboid cells surrounded by a covering resistant to chemical and temperature extremes) in late fall when light availability for their symbionts decreases due to ice cover and reduction in day length.

1. FW sponge tissueUse your live samples of the common freshwater sponge, Spongilla lacustris to examine for the presence of spicules, amoeboid cells, and zoochlorellae. To do this, prepare a wet mount of a small piece of sponge tissue from a colony and examine under low & high power magnification. Spicules are easiest to see in the skeletal remains of defunct colonies that are often attached to the live fingers. Zoochlorellae are found within in amoeboid cells. In winter they are easiest to find in gemmules (see below)

2. FW sponge gemmules Sponges are not active during winter and you can see newly

forming gemmules, which look like greenish brown seeds within the colony (visible to the naked eye. Use a dissecting scope to get a full view of gemmules. If you make a thin slice of a gemmule with a razor blade. You can observe gemmulized amoeboid cells with their algal symbionts.

3. Marine spongesexamine preserved specimens of marine

& freshwater sponges on display PHYLUM CNIDARIA

The phylum Cnidaria includes the true jellyfish, hydrozoans, &

corals/sea anemones. Cnidarians have specialized encapsulated stinging thread cells called cnidocytes that are used for capturing 2

prey and defense against predators. They can also exist as 2 different feeding forms: 1) a motile medusa form; and 2) a generally sessile polyp form. True jellyfish spend the majority of their lives as medusae, whereas hydrozoans, such as freshwater Hydra (see diagram previous page) occur as polyps. Use a pipette and try to remove a hydra from the bowl. Observe it under scanning or low power without a cover slip. If available, try feeding Daphnia to the hydra and observe the use of cnidocytes and tentacles. Green hydras also possess endosymbiotic green algae (zoochlorellae) to supplement their nutrition.

1. Marine cnidariansdemo of various corals

PHYLUM PLATYHELMINTHES (flatworms)

Characteristics:

Flat & solid (no body cavity) Gut but no anus Bilateral w/distinct head organs

Groups: Class Turbellaria (Planaria)

Class Trematoda (Flukes) Class Cestoda (Tapeworms)

The phylum Platyhelminthes are known commonly as the flatworms. Most are parasites, but

some, such as the freshwater planarian Dugesia tigrina are predators of other aquatic macroinvertebrates. Prey items are engulfed using a protrusible pharynx (figure following page) and undigested food is expelled through the pharynx as well. Planarians are also highly negatively phototactic, and light is avoided by using its eyespots.

1. Planarian behaviorObserve live planaria under the dissecting scope. If food is available, observe how planaria uses its protrusible pharynx during feeding.

2. Observe examples of the two parasitic classes of flatworms, flukes and tapeworms, on display

PHYLUM NEMATODA (Roundworms) Characteristics

body cavity (unspecialized, unlined space)

complete gut w/mouth and anus 1. Observe various examples of roundworms on display. Make a wet mount of vinegar eels.

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2. Profile: Brainworm (Paralaphostrongylus tenuis) Paralaphostrongylus tenuis, commonly called brainworm, is a parasitic nematode of white-tailed deer. Although it has little apparent effect on its normal host white-tailed deer, it causes serious neurological disorders in other ruminants (abnormal hosts) such as moose (Alces alces), caribou (Rangifer tarandus), and elk (Cervus elaphus). For example, from 1985 to 1989, brainworm was responsible for 38% of the mortality in moose from the U.P. P. tenuis has a life cycle that requires both an intermediate and final host. Sexual reproduction occurs in the latter. The adult worms live in the subdural space closely associated with the venous sinuses of the brain into which the female worm releases her eggs. The eggs are carried to the lungs were they are trapped in the alveolar capillary beds, embryonate, and hatch into first stage larvae. First-stage larvae move into the alveoli and up the bronchial tree by ciliary action. When they reach the pharynx, the larvae are swallowed and eventually leave the host deer in the feces. Early larval development occurs in terrestrial gatropods (snails and slugs). In the external environment, first-stage larvae actively invade the foot of the gastropod either when the gastropod moves across the fecal pellet deposited by an infected deer or when the larvae are washed off the pellet and come in contact with a gastropod. The developing larvae molt twice within the gastropod before attaining infectivity as third-stage larvae. Deer and other ruminants acquire infection by accidentally ingesting an infected gastropod. The third-stage larvae emerge from the tissues of the gastropod in the abomassum of its new host, penetrates the gastrointestinal wall, crosses the peritoneal cavity and then invades the spinal cord via a peripheral nerve. The growing larvae migrate anteriorly in the neural parenchyma from the spinal cord to the brain until they reach the brain and subsequently the subdural spaces of the brain. Within about three months after ingesting the snail, the worms have settled into the subdural spaces, matured, copulated, and produces eggs. Adult worms are 2-4 long.

Procedure P. tenuis larvae will be harvested from the fecal pellets using a modified Baerman Technique.

A. Principle: larvae are stimulated to move out of the fecal pat by water but are unable to swim against the force of gravity. They collect at the bottom of the funnel

B. Protocol: 1. Place a funnel with an attached piece of rubber tubing in a ring stand.

Below this apparatus, place a bowl in case water is spilled or leaks. Fill the neck of the funnel and the closed-off tubing with tepid tap water. Check for leaks. 2. Place approximately 40 g of deer pellets in a double layer of cheese cloth and close with a rubber band or string 3. Place the fecal tea-bag in the funnel and add tepid water until the feces are just covered 4. Be careful not to let cheesecloth or string dangle over the edgeit will wick water out! 5. Let sit for 16-24 hours 6. Remove the clamp and collect the first 10-20 ml of water from the bottom--about 1 into a test tube.

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7. Importantlet the tube sit undisturbed in a rack for 30 minutes!! 8. Use a micro pipette and draw a few ml of the sediment from the BOTTOM.. 9. Add to slide with coverslip. Search for brainworms under low power. the brainworms whip back and forth, frequently coiling up or taking on a j-shape. You may also notice a dorsal spine on their posterior end.

Figure 1. Lifecycle of brainworm.

PHYLUM ROTIFERA

Rotifers are usually highly abundant microinvertebrates that are found in virtually all types of freshwater habitats. Rotifers are commonly referred to as wheel bearers because of the presence of a corona, which is a rotating wheel of cilia used in filter feeding and locomotion. Food particles are drawn in and processed in a gizzard-like organ called a mastax, which is lined with jaw-like structures. The pumping motion of the mastax is often very conspicuous. Find a rotifer in the jars. At first glance, rotifers resemble ciliates, but notice that rotifers have internal organs and jointed bodies (usually w/ a spike or two on their posterior).

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PHYLUM CNIDARIAPHYLUM PLATYHELMINTHES (flatworms)2. Observe examples of the two parasitic classes of flatworms, flukes and tapeworms, on displayPHYLUM NEMATODA (Roundworms)Procedure

PHYLUM ROTIFERA