Phylum: Echinodermata (Echinoderms: Starfish, Sea Cucumbers etc.)

"Echinoderms — from the Greek for spiny skin — are invertebrates that exclusively inhabit marine environments. Most species have a five-fold radial body plan. Echinoderms are monophyletic and comprise a sister-group to the hemichordates (acorn worms). There are approximately 7,000 extant echinoderm species which fall into five well-defined taxonomic classes (Figure 1): Crinoidea (sea lilies and feather stars); Asteroidea (starfishes); Ophiuroidea (basket stars and brittle stars); Holothuroidea (sea cucumbers); and Echinoidea (sea urchins, sand dollars, and sea biscuits). This group has left an exceptional fossil record dating back to at least the Cambrian; this well defined fossil record allows comparative molecular studies to be made over a wide range of relatively well documented divergence times.

Echinoderms have several shared features that distinguish them from other animals, including a water vascular system and a characteristic form of calcium carbonate endoskeleton called stereom. Most echinoderms begin life as larvae and undergo complex metamorphosis to form an adult. As a group they display a diverse array of life history traits. Most have a sexual mode of reproduction, although some can reproduce asexually. Their larvae are primitively free-living and planktonic, and show a considerable diversity in morphology and function, some of the traits being clearly shared with the larvae of certain hemichordates.

Nearly all echinoderm adults adopt a benthic adult form following metamorphosis, though a few deep-water holothuroids are pelagic or epibenthic swimmers. Adult echinoderms are radially symmetrical, usually pentameric, with intricate internal skeletons of calcium carbonate ossicles, supported by a characteristic array of collagenous ligaments. When present in larvae, skeletons take the form of elaborate rods which are independently derived in Ophiuroidea and Echinoidea (and absent in larvae of the other three echinoderm classes)."

Source: Amemiya, Chris T., Miyake, Tsutomu and Rast, Jonathan P. (2005). Echinoderms. Current Biology 15(23): R944-R946. https://doi.org/10.1016/j.cub.2005.11.026

Class: Asteroidea (Starfish or Sea Stars)

Order: Forcipulatida

Family: Heliasteridae

Order: Paxillosida

Order: Valvatida

Family: Oreasteridae

Family: Poraniidae

Class: Echinoidea (Sea Urchins or Urchins)

Order: Camarodonta

Family: Temnopleuridae

Order: Cassiduloida

Family: Cassidulidae

Order: Clypeasteroida (Sand Dollars)

Family: Clypeasteridae

Order: Spatangoida

Family: Brissidae

—No subordinate taxa

Family: Loveniidae

Class: Holothuroidea (Sea Cucumbers)

Order: Dendrochirotida

Family: Ypsilothuriidae

Order: Elasipodida

Family: Elpidiidae

Order: Molpadiida

Family: Caudinidae

Statistics

<< Back to the Recently Extinct Animals database