CLASS: CIRRIPEDIA BARNACLES They are highly modified crustaceans. Along the shore they live permanently attached to rocks in the balanoid zone. Can also attach themselves to other solid substrata, e.g. pier pilings, whales, bottom of ships, flotsam. A shield of calcareous plates encloses body. The shells of barnacles dot the rocks in the balanoid zone like small grey volcanoes or white stars. At low tide the barnacles seal the opening at the top of the shell with an operculum of four plates. Filter feeders. When the tide comes in and they are covered with water, they open up their shells and extend hairy cirri (leg-like structures) to comb food particles from the water. They catch plankton and suspended organic matter in the water. Carnivorous molluscs and reef fish prey upon barnacles. Goose Barnacles have a flexible stalk and occur in colonies attached to floating objects in the sea. Acorn barnacles live on ships, rocks and even whales. The animal inside the shell is actually standing on its head. The balanoid zone (an intertidal rocky shore zone) gets its name from a northern hemisphere barnacle, Balanus sp. 34
MANTIS SHRIMPS Live in burrows or in rock and coral crevices. The Cape mantis shrimp is common in Cape Town where it burrows into the soft sediment. Massive raptorial second thoracic limbs. Eyes are large and stalked A short carapace covers the front half of the thorax. They have a large segmented abdomen. Down each side are paddles that are used for swimming. Many are brightly coloured and defend their territories. 1. to hold food, 2. to catch food, 3,4,5, used to shred food Highly specialised predators Two functional groups occur: o Spearers: impale soft-bodied prey such as fish and shrimps. o Smashers: strike hard animals like crabs and molluscs with the elbow and stun them. Mantis shrimps are eaten by some species of fish, decapods (10-legged Crustacea) and some species of Molluscs. The strike force of a smasher approaches that of a bullet and can easily crack the glass of a small aquarium. 35
PHYLUM: ARTHROPODA SUBPHYLUM: CRUSTACEA Isopods (iso = same + podos = foot) are a diverse group of small crustaceans with over 270 species in southern Africa. They include the kelp louse, fish louse - parasitic on fish and the pill bug Tylos that burrows in sand. Amphipods (amphi = both + podos = foot) are also a diverse group of crustaceans with over 300 species occurring in southern African waters. They include beach-hoppers. Isopods: Found in all marine habitats from the intertidal to the deepest sea. Amphipods: Most crawl or burrow amongst seaweeds or in sediments. ISOPODA e.g. Beach-lice SIMILARITIES No solid exoskeleton Jointed segments Two unstalked eyes Seven pairs of legs. Certain species eat kelp. Thoracic brood pouch in female. AMPHIPODA e.g. Sand-hoppers ISOPODA DIFFERENCES AMPHIPODA Bodies flattened from top to bottom. Narrow bodies that are flattened from side to side. Shrimp-like creatures. Legs similar to one another. First two pairs of legs generally form nippers help with feeding. Remaining five pairs end in a simple claw. Some have a well-developed jumping ability (e.g. sand hoppers). Certain isopods and amphipods eat kelp. Some feed on detritus, while others filter food particles from the water. Fish, crabs and worms. 36
PRAWNS, ROCK LOBSTERS AND CRABS ROCK LOBSTERS Popularly called crayfish, they are correctly termed "spiny lobsters" or "rock lobsters" to avoid confusion with clawed freshwater crayfish. They spend the daytime hiding in holes under rocks. Small spiny rock lobsters may be seen in rock pools, but they normally stay in deeper water. Large, robust crustacean with a long abdomen ending in a well-developed tail-fan. Thorax and head covered by a single shield or carapace. None of the walking legs end in nippers. They have an elaborate life cycle involving 13 larval stages which drift in the sea for nearly a year before assuming the adult form and settling on the sea floor. Lobsters do scavenge, but seem to prefer fresh food. They live on mussels, limpets, sea urchins and scraps of food lying around. Young seals, dog sharks, octopus, fish and humans hunt them. Living Shores: Figure 264 37
SOME LOBSTERS ALONG OUR COAST * WEST COAST ROCK LOBSTER (Jasus lalandii) Body orange-brown. Tail fan orange, blue and green. Front carapace has two large spines and smaller projections between the eyes. Intolerant of low oxygen levels. They moult once a year, breed after 5 years and live up to 30 years. Males reach a carapace length of 190 mm and females 140 mm. Most important commercial species. SOUTH COAST ROCK LOBSTER (Palinurus gilchristi) Body orange. Legs and antennae have alternating pinky-orange and white bands. Broad plate between eyes flanked by two outer horns. Second most important commercial species. EAST COAST ROCK LOBSTER (Panulirus homarus) Brown to brick red; orange spines and blue-green markings on the head. Two sharp horns project forwards between the eyes. The abdomen has a scalloped groove on each of abdominal segments 2-5. Readily sheds some of its legs to distract predators. These legs can be re-grown later. The South and West Coast rock lobster fisheries are worth about R150 million rand a year and about 4 000 people are employed in the industry. Rock lobsters are not farmed, as it is not possible to rear the larvae. How far rock lobsters can travel One theory is that larvae are carried in the currents in a big circle around the Atlantic Ocean, north to the equator across to South America, south down the American coast and back across the ocean to South Africa. Many of them also probably remain and develop off the coast of South Africa. * Extract from Fact Sheet Crustacea 1 by Margo Branch, March 1997. 38