echinoderm - Physiology, Classification

A spiny-skinned marine invertebrate characterized by its typically 5-radial (pentamerous) symmetry; body enclosed by a variety of calcareous plates, ossicles, and spines; water vascular system operates numerous tubular feet used in feeding, locomotion, and respiration; includes starfishes, brittle stars, sea lilies, sea urchins, and sea cucumbers, as well as a diverse range of fossils. (Phylum: Echinodermata.)

iEchinoderms Fossil range: Late Ediacaran-Recent
Sea urchin
Scientific classification
Kingdom: Animalia Subkingdom: Metazoa Superphylum: Deuterostomia Phylum: Echinodermata Klein, 1734
Classes
Asteroidea Blastoidea (extinct) Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea

Echinoderms (Phylum Echinodermata, from the Greek for spiny skin) are a phylum of marine animals found at all depths. Five or six classes (six counting Concentricycloidea) are alive today:

Asteroidea (asteroids, starfish, or sea stars): about 1,500 species that capture prey for their own food.

Physiology

Echinoderms evolved from animals with bilateral symmetry;

All echinoderms exhibit fivefold radial symmetry in portions of their body at some stage of life, even if they have secondary bilateral symmetry.

Echinoderms possess a hydraulic water vascular system, a network of fluid-filled canals that function in locomotion, feeding, and gas exchange.

Many echinoderms have remarkable powers of regeneration: a starfish cut radially into a number of parts will, over the course of several months, regenerate into as many separate, viable starfish.

Classification

Echinoderms, like chordates, are deuterostomes and are therefore thought to be the most closely related of the major phyla to the chordates, being a sister group to chordates plus hemichordates. Caster, 1960 Class Homostelea Class Homoiostelea Class Stylophora Gill & Caster, 1960 Class Ctenocystoidea Robison & Sprinkle, 1969 Subphylum Crinozoa Class Eocrinoidea Jaekel, 1899 Class Paracrinoidea Regnéll, 1945 Class Cystoidea von Buch, 1846 Class Blastoidea Class Crinoidea Subphylum Asterozoa Class Ophiuroidea Class Asteroidea Subphylum Echinozoa Class Helicoplacoidea Class Edriosteroidea Class Ophiocistioidea Class Holothuroidea Class Echinoidea Leske, 1778