Crustacea

From Palaeos.org

Introduction

With around 35,000 known species the Crustacea are a diverse group. They are so incredibly abundant in marine and freshwater habitats are they that they have been called the insects of the water. A majority of zooplankton are Crustacea - either larvae or tiny adults. A few Crustacea (slaters or sow bugs) even live on land, usually under old logs and leaf litter. The majority of crustaceans are marine and are herbivores, although there are also many species which are carnivores or scavengers

Most crustaceans have jointed appendages which serve as either walking or swimming legs, and some of which have been modified in some way to serve a special function, such as the claws of lobsters and crabs. The number of body segments varies widely among the different groups.

Crustacea are characterized by two pairs of antennae, three pairs of mouthparts, and a special type of larvae called the nauplius.

Crustacea generally also have a carapace and compound eyes. Most species are filter-feeders or scavengers.

The Crustacea are a very ancient group. They first evolved in the earlier Cambrian period, as part of the great radiation of coelomate animals that occurred at that time. By the Jurassic period Crustaceans looked pretty much like they do today. Shrimps and lobsters from the famous Solnhofen limestone are hardly distinguishable from modern forms

Phylogeny

The monophyly of the "Crustacea" as broadly defined is currently somewhat contentious. For the total group of crustaceans and hexapods (including insects), see Pancrustacea. For the crown group of crustaceans, see Eucrustacea.

Credits

MAK020505 (Intro); Christopher 10:45, 29 April 2009 (UTC) (phylogeny)