PHYLUM: PLATHYHELMINTHES FLATWORMS Free living (living independently i.e. not attached) Bilaterally symmetrical with a definite front and back, and with left and right sides. Mobile creeping animals. Concentration of sensory organs at the front of body = eye spots Habitat Flatworms can be found gliding over rocks in rock pools. One species lives under the foot of the ocular limpet. Parasitic species include flukes and tapeworms. Flatworms generally remain hidden under rocks. Description Free-living marine forms are very flat leaf-like worms. They range in size from almost microscopic to 60 cm in length. Some are drab and others are very colourful. Flat worms are often mistaken for sea slugs. They prey on anything that is small enough or slow enough for them to catch e.g. small molluscs, crustaceans. Some flat worms eat sponges and hydroids. They are able to swallow the stinging cells of the hydroids without triggering the sting capsule. They may also scavenge on dead animals. Fishes are the main predators of flatworms. Two Oceans Aquarium Volunteer Manual Module 3 INVERTEBRATES 21
Did you know? Flat worms store food reserves in their cells and can go without food for long periods. When starved they begin to digest their own tissues, starting with their reproductive organs. The animal can shrink to a hundredth of its original size and still remain alive. When food is once again available, the worm grows bigger and regenerates the missing organs. 22 Two Oceans Aquarium Volunteer Manual Module 3 INVERTEBRATES
PHYLUM: SIPUNCULIDA PEANUT WORMS Soft bodied. Worm-like. Unsegmented. They have an enormously extensible front part of the body (the introvert), which can be shot out or rolled back into the body with equal ability. Habitat Sandy areas between rocks and shells. The majority are bottom-dwellers in shallow water. Description Peanut worms tend to have a dull appearance. They are light brown worms, which look remarkably like a peanut. The body consists of two main parts: - a cylindrical, bottle-shaped or sac-like structure, the trunk; - a more slender extendable introvert which can be completely withdrawn into the trunk. They feed on detritus (dead organic matter) that settles out under the rocks, algae and diatoms. The tentacles are used for gathering food. Fishes eat peanut worms. A B Figure: (A) withdrawn and (B) extended view of a peanut worm. Did you know? The introvert is used for both feeding and locomotion. The introvert can be extended up to four times the length of the worm s body. Two Oceans Aquarium Volunteer Manual Module 3 INVERTEBRATES 23
LONG, LONG AGO...... Six hundred million years ago, three kinds of animals appeared in the seas: Segmented creatures; Shelled animals; And others with five rays. They established four great groups of today s animals: Segmented Annelida and Arthropoda; Shelled Mollusca; And five rayed Echinodermata. PHYLUM: ANNELIDA Annule = ring shaped markings- segmented Segmented worms. Bilaterally symmetrical. There is a distinct head formation (cephalization). The heads have a variety of frills, jaws and feelers. CLASS: POLYCHAETA (poly = many; + chaetae = stiff hairs) This class includes the bulk of the marine worms and are characterised by having many bristle-like stiff hairs called chaetae. Two types of worms are described here - the active and free-living worms (e.g. the mussel worm) and the sedentary or tube dwelling worms (e.g. reef worms). 24 Two Oceans Aquarium Volunteer Manual Module 3 INVERTEBRATES
PHYLUM: ANNELIDA CLASS: POLYCHAETA Active. Uniformly segmented bodies. A pair of large paddle-shaped appendages (parapodia)on each segment with long bristles (called chaetae) Internal jaws. Well-developed sensory organs on head. 1. FREE-LIVING WORMS Habitat and description (structure) Mussel worm Wonder worm Scale worm Lives on rocks among Common under boulders, Common in rocky-shore mussels and seaweeds in especially where gravel pools, rock crevices and the intertidal zone. Used as bait species but its allows them to burrow. Large jaws inflict a painful beneath boulders from low shore to the shallow sub collection destroys large bite tidal. areas of mussel beds. Used as a bait species. Shoot out their jaws to catch small animals such as shrimps and other small worms. They are eaten by fish and crabs or even by other species of polychaetes. Two Oceans Aquarium Volunteer Manual Module 3 INVERTEBRATES 25
2. SEDENTARY WORMS Normally inactive, tube dwelling, with small parapodia. Head often modified with elaborate appendages that extend into the water for filter feeding. Lack (no) jaws. Habitat and description (structure) Tangle worm Spiral fan worm Reef worms Abundant everywhere, dotting most rocks in the shallow subtidal pools, on shells or sea plants. Lives in a mucous tube, which is decorated with sand or pieces of shell. Grooved tentacles extend to capture food particles that settle on them. Form extensive reefs on rocks at the mid-tide region, especially along the Atlantic coast. Cements sand grains to its tubes. Most of them are filter feeders. Others spread their long feeding tentacles over the sand or rock in a sticky web to catch small animals. Whelks and butterfly fish eat these sedentary worms. 26 Two Oceans Aquarium Volunteer Manual Module 3 INVERTEBRATES
Quick Review 1.Provide the Phylum and common name of the animals illustrated in the table below. 2. List TWO interesting facts for each of the following three worms. 2.1 Flatworm a. b. 2.2 Wonder worm a. b. 2.3 Spiral fan worm a. b. Two Oceans Aquarium Volunteer Manual Module 3 INVERTEBRATES 27