Invertebrates Species: Phylum Echinodermata

Echinoderm (meaning Spiny skinned) is a diverse group of invertebrates belonging to the phylum Echinodermata. Phylum Echinodermata consists of five main classes that are divided into 7,500 extant species and approximately 13,000 known extinct species, including several classes that were discovered through fossils. The five main classes are proposed to have evolved from a common metazoan ancestor approximately 500 million years ago during the early Palaeozoic period (Britannica, 2014). Echinoderms are predominately benthic (bottom dwellers) and found only in marine ecosystems. They are the largest phylum to have no divergent terrestrial or fresh water organisms (Selden, P. A. 2001). This discussion looks at a variety of similarities and variances in the echinoderms body structure, feeding behaviours, the habitats they reside in and how they have achieved such diversity amongst marine habitats despite their seemingly primitive features. Characteristics Shared Between Classes

While these five classes are all derived from the same phylum, they are considerably unique to one another. Most of these classes do not look similar visually but there are multiple common features that determine their place amongst the phylum Echinodermata. Unlike most animals today, echinoderms still exhibit features that may consider them primitive. They show lack cephalisation (compartmentalization of particular areas of the body), pentamerous radial body organisation and symmetry amongst the adults and lack of specialised organs (Morris V.B, 2002). There is however some rather interesting features exhibited amongst the echinoderms such as some having the ability to regenerate and a unique feature exhibited only in echinoderms, called the water vascular syst...

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