CHELICERATES, MYRIAPODS AND ANNELIDS
Chelicerates, myriapods and annelids are invertebrate animals (animals without backbones). Chelicerates and myriapods are arthropods (phylum Arthropoda) (animals with jointed limbs), while annelids are segmented or true worms of the phylum Annelida.
Chelicerates belong to the subphylum Chelicerata. Their body is made up of two major regions: the cephalothorax (fusion of head and thorax) and the abdomen. They are characterized by the structures called chelicerae, a pair of pincer-like appendages situated in front of the mouth.
Among the chelicerates in Malaysia are horseshoe crabs (or king crabs, class Merostomata) and arachnids (class Arachnida), which include spiders (order Araneae), scorpions (order Scorpionida), and ticks and mites (order Acarina). Malaysia has three of the worldÕs four horseshoe crab species; these are animals which have not changed in form for millions of years. Spiders are by far the most diverse and most widely distributed of the chelicerates. Although spiders are usually associated with webs, many Malaysian species do not make webs. These include the most primitive of the country's spiders, Liphistius spp., which live in burrows with a hinged door. Some live in mossy banks in forests; others live in limestone caves.
Myriapods are divided into two classes: centipedes (class Chilopoda) and millipedes (class Diplopoda). Centipedes are active predators, hunting small prey such as insects, spiders and worms. They paralyse their prey with venom from their 'poison claws', the modified first pair of legs. In contrast, millipedes are scavengers, feeding mostly on vegetable matter. However, many millipedes have a row of poison glands along each side of the body. Pill millipedes, shorter and stouter than most millipede species, defend themselves by rolling up into a spiral.
Annelids include earthworms (class Oligochaeta) and leeches (class Hirudinea). Both earthworms and leeches are hermaphroditic, each individual having both male and female reproductive organs. Visitors to Malaysia's rainforest often find themselves bitten by leeches, which thrive in the moist, tropical climate.
Despite their diverse backgrounds, chelicerates, myriapods and annelids all contain some members which can be harmful or hazardous to humans. Scorpions, some larger spiders and centipedes are potentially venomous; and, given the opportunity, leeches feed on human blood. But some kinds are beneficial to humankind. Earthworms, through their burrowing habit, help in improving the fertility of the soil. Tubifex worms are important as fish food in the aquarium fish industry. Many spiders are useful as they prey on insect pests. The blue blood of the horseshoe crabs is being utilized in medical research.
