Crustaceans and Arachnids

Spiders, snakes, ticks and mites all belong to the same class, Arachnida. They are covered with sensory hairs so tiny that they cannot be seen by the naked eye. In greek mythology, Arachne was a woman who challenged the goddess Athena to weave faster than she herself could. This angered the goddess, who turned Arachne into a spider, forcing her to weave forever. That is where these creatures get their name. Within the world of crustaceans, well-known animals such as shrimp, lobster and crab are also discussed in this chapter. You will find details about their anatomy, their differences and similarities and the way in which they live that will surprise you. Some species breathe through gills and also breathe through their skin.

Colourful Armour

Even though they inhabit all known environments, crustaceans are most closely indentified with the aquatic environment. That environment is where they were transformed into arthropods with the most evolutionary success. Their bodies are divided into three parts: the cephalothrorax, with antennae and strong mandibles; the abdomen, or pleon; and the back (telson). Some crustaceans are very small: sea lice, for instance, are no larger than 0.25mm (1/100 in). The Japanese spider crab, on the other hand, is more than 3 m (8 ft) long with outstretched legs, because it has legs in both the abdomen and the thorax in addition to two pairs pf antennae.

Sharp Front Legs

Crustaceans have appendages that generally branch in two directions and are adapted to aquatic life. A characteristic shared by all crustaceans is their articulated shell, which leaves two pairs of antennae uncovered. They also have a pair of mandibles, two pairs of maxillae and a pair of appendages in each segment of the body. Their pencers have enough strength so hey can trap their prey and feed themselves. The class Malacostraca includes lobsters, crabs, shrimp and prawns, among other animals.

In the Middle of the Chain

Zooplankton include thousands of distict species belonging to very different groups. Among these species are protist, coelenterates, worms, crustaceans and other small, weakly swimming organisms. Unicellular, eukaryotic protists contitute a large group of species of zooplankton. They constitute an extensive and varried community in the food network. The phytoplankton, which are capable of photosynthesis, provide food for the zooplankton. Phytoplankton, which for echinoderms, crustaceans and larval-stage fish. Once they grow up, the larvae serve as food for schools of small fish, which are in turn, food for larger fish, including plankton-feeding whales that sometimes eat these small fish.

A Special Family

Arachnids make up the largest and most important class of chelicerata. Among them are spiders, scorpions, fleas, ticks and mites. Arachnids were the first arthropods to colonize terrestrial environments. The fossil remains of scorpions are found beginning in the Silurian period, and they show that these animals have not undergone major changes in their morphology and behaviour. The most well-known arachnids are the scorpions and spiders.