PHYLUM: ARTHROPODAPHYLUM: ARTHROPODA (arthron = joint + podos = foot) Arthropods are a vast...
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Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 29 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.
Transcript of PHYLUM: ARTHROPODAPHYLUM: ARTHROPODA (arthron = joint + podos = foot) Arthropods are a vast...
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 29
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.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 30
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.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 31
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.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 32
SUBPHYLUM - CRUSTACEA
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 33
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.
