Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 21

PHYLUM: PLATHYHELMINTHES

FLATWORMS

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.

Feeding 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.

Predators Fishes are the main predators of flatworms.

CHARACTERISTICS 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

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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.

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PHYLUM: SIPUNCULIDA

PEANUT WORMS

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bottle-shaped or sac-like structure, the trunk; - a more slender extendable introvert which can be completely withdrawn into the trunk.

Feeding They feed on detritus (dead organic matter) that settles out under the rocks, algae and diatoms. The tentacles are used for gathering food.

Predators Fishes eat peanut worms.

Figure: (A) withdrawn and (B) extended view of a peanut worm.

CHARACTERISTICS 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.

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.

A B

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PHYLUM: ANNELIDA Annule = ring shaped markings- segmented

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).

CHARACTERISTICS

Segmented worms.

Bilaterally symmetrical.

There is a distinct head formation (cephalization).

The heads have a variety of frills, jaws and feelers.

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.

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CHARACTERISTICS 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.

PHYLUM: ANNELIDA

CLASS: POLYCHAETA

1. FREE-LIVING WORMS

Habitat and description (structure)

Mussel worm Wonder worm Scale worm Lives on rocks among mussels and seaweeds in the intertidal zone. Used as bait species but its collection destroys large areas of mussel beds.

Common under boulders, especially where gravel allows them to burrow. Large jaws inflict a painful bite Used as a bait species.

Common in rocky-shore pools, rock crevices and beneath boulders from low shore to the shallow sub tidal.

Feeding Shoot out their jaws to catch small animals such as shrimps and other small worms.

Predators They are eaten by fish and crabs or even by other species of polychaetes.

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CHARACTERISTICS Normally inactive, tube dwelling, with small parapodia. Head often modified with elaborate appendages that extend into the water for filter

feeding. Lack (no) jaws.

2. SEDENTARY WORMS

Habitat and description (structure)

Tangle worm Spiral fan worm Reef worms 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.

Abundant everywhere, dotting most rocks in the shallow subtidal pools, on shells or sea plants.

Form extensive reefs on rocks at the mid-tide region, especially along the Atlantic coast. Cements sand grains to its tubes.

Feeding 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.

Predators Whelks and butterfly fish eat these sedentary worms.

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 27

Quick Review

1.Provide the Phylum and common name of the animals illustrated in the table below.

Phylum: __________________________ Common name:

Phylum:

__________________________ Common name:

Phylum: __________________________ Common name:

Phylum:

__________________________ Common name:

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.

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PHYLUM: ARTHROPODA (arthron = joint + podos = foot)

Arthropods are a vast assemblage of animals. At least 750 000 species have been described. This is more than three times the number of all other animal species combined.

The tremendous adaptive diversity of arthropods has enabled them to survive in virtually every habitat.

CLASSIFICATION OF ARTHROPODS

Taxonomists are constantly refining the classification of plants and animals.

Some university textbooks now group the crustaceans as a subphylum, because there are more than 42 000 known species in this group.

CHARACTERISTICS

All arthropods have jointed limbs.

The body is segmented and covered by a hard, jointed, external skeleton (exoskeleton) made of chitin, in some cases strengthened with calcium carbonate.

The exoskeleton cannot expand; therefore arthropods periodically shed the exoskeleton (moult) and can then rapidly expand.

Body is divided into a head, thorax and abdomen.

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CLASS: PYCNOGONIDA

SEA SPIDERS

Called sea spiders as they superficially resemble land spiders but are totally unrelated. Rarely seen due to their typically small size and cryptic colouring. Sluggish in their movement. Their many reproductive openings at the base of the legs give them their name pycno = great or multiple and gonas – reproduction.

Habitat Variety of habitats. Deep sea where the currents transport them over long distances. Amongst hydroids and bryozoan colonies, sea plants and sponges.

Description

Small body made up of a head and trunk.

o Abdomen reduced to a stub.

o Four pairs of long spindly legs.

Portions of the alimentary canal and reproductive system are partially displaced into the legs.

Use claws on end of legs to cling to substratum.

Males gather up the eggs with the ovigerous legs and carry them until they hatch.

Growth necessitates periodic moulting.

Feeding Preys on sponges, hydroids, sea anemones, polychaetes and bryozoans.

Predators The predators of sea spiders are poorly understood.

Did you know?

Nice Legs, but not just for show

Crawling among corals, anemones and sponges to suck their juices, sea spiders range throughout all the oceans. However, sea spiders have a problem. Their bodies are so tiny – usually just a few millimetres in diameter – that there is not room for all their internal organs. Therefore their legs serve as auxiliary storage, housing part of their digestive and reproductive systems. Males  carry  the  female’s  eggs  on  a  special  pair of legs, called ovigers, until they hatch.

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PHYLUM: ARTHROPODA

SUBPHYLUM: CRUSTACEA

A HOST OF SHRIMPS, LICE, CRABS and LOBSTERS.

SUBPHYLUM CHARACTERISTICS

Most crustaceans are marine.

Bodies are normally made up of a fused head (cephalus = head) and thorax - the cephalothorax plus a separate abdomen.

They have numerous jointed limbs, which are adapted for walking, swimming, feeding, respiration and reproduction.

Usually two pairs of antennae.

Complex compound eyes.

The exoskeleton may form a shield (carapace) that covers and unites various segments of the body.

The life cycle is complex. Most have several larval stages that form part of the zooplankton floating in the sea. The larvae are dispersed by currents.

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SUBPHYLUM - CRUSTACEA

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BRINE SHRIMP

Habitat

Brine shrimp (Artemia salina) exist in large numbers in brine pools and highly saline inland waters such as the salt lake in Utah, USA.*

Description

Adult size 15 mm.

Lacks a carapace but have a cuticle.

Has stalked eyes which are constantly on the rove

A discrete head.

Thorax has flattened, leaf-like limbs covered in hair-like setae.

Slender abdomen has no appendages.

Unusual for a crustacean it has haemoglobin in the blood, which varies in concentration inversely to the oxygen concentration in the surrounding water, i.e. when there is little oxygen there is much haemoglobin.

Fertilised eggs can survive long periods of drought.

Feeding

Feeds on phytoplankton that is filtered from the water by setae on the limbs.

Predators

Many brine shrimp are bred in the aquarium as food for such animals as: basket stars, seafans, seahorses, pipefish, comb jellies, sea cucumbers, barnacles, juvenile fish, butterfly fish and many more.

* Article researched by Bert Tucker Group 1 Volunteer

Did you know?

The dried fertilised eggs are purchased from overseas suppliers. They are small and brown and 1 gram contains 300 000 eggs.

A 417-g tin of cysts costs around R350 and 2-3 teaspoonfuls are put into an aerated aquarium where they hatch out in 24 -36 hours depending on the water temperature.

The animal is an anal water swallower and this is believed to act as an enema to remove unwanted material from the hind gut!

The brine shrimp is one of the most important foods in Aquaculture.