Although spiders are possibly the most familiar arthropod, lobsters, crabs, barnacles, and shrimps of the class Crustaceans are also in this phylum.
Arthropods are most closely related to the Annelids, or segmented worms. The five main groups in the phylum are Trilobita, Myriapoda, Chelicerata, Crustaceans, and Hexapoda.
Echinoderms
Echinoderms lack a head and have five-point radial symmetry. These fascinating animals live only in marine environments. They have an endoskeleton made of calcareous plates, which is often protected by hong kong email list spines. The plates that make up the endoskeleton often support the spines and enclose the coelom, an anatomical feature used for movement, respiration, food gathering, and as a sensory mechanism. The coelom also houses the reproductive organs and the alimentary canal.
Starfish, Lembei Strait, Suluwesi, Indonesia 2008Echinoderms can be found in all oceans in all areas with approximately 6,000 described species.
The two main subphyla in the phylum Echinodermata are Eleutherozoa and Pelmatozoa.
Subphylum Eleutherozoa contains the superclasses Asterozoa and Cryptosyringida.
Superclass Asterozoa contains the sea stars/starfish of the Class Asteroidea and the extinct Class Somasteroidea.
Starfish, Lembei Strait, Suluwesi, Indonesia 2006Superclass Cryptosyringida contains Class Echinoidea (heart urchins, sand dollars, and sea urchins), Class Holothuroidea (sea cucumbers), and Class Ophiuroidea (basket stars, brittle stars, and snake stars).
