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The phylum contains about 7,600 living species, making it the second-largest group of deuterostomes after the chordates, as well as the largest marine-only phylum. The first definitive echinoderms appeared near the start of the Cambrian. Echinoderms are important both ecologically and geologically.
The class Asteroidea belongs to the phylum Echinodermata. As well as the starfish, the echinoderms include sea urchins, sand dollars, brittle and basket stars, sea cucumbers and crinoids. The larvae of echinoderms have bilateral symmetry, but during metamorphosis this is replaced with radial symmetry, typically pentameric. [12]
A brittle star, Ophionereis reticulata A sea cucumber from Malaysia Starfish exhibit a wide range of colours. This List of echinoderm orders concerns the various classes and orders into which taxonomists categorize the roughly 7000 extant species [1] as well as the extinct species of the exclusively marine phylum Echinodermata.
Evechinus chloroticus has an annual breeding cycle. [12] It becomes sexually mature between 3.5 and 7.5 cm in diameter, depending on the population. [12] Gonads are ripe from October and individuals can spawn from November to February. [1] Swimming larvae complete development in the water column between 4 and 6 weeks. [13]
The aboral surface contains many small spines (ossicles) that are arranged in a netlike or pentagonal pattern on the central disk. The ossicles are no higher than 2 mm. [3] [4] In Pisaster the tube feet have suckers on their distal ends which allow them to attach to the rocky substrate and live in heavily wave-swept areas. [5]
Eleutherozoa is a subphylum of echinoderms. They are mobile animals with the mouth directed towards the substrate. They usually have a madreporite, tube feet, and moveable spines of some sort. It includes all living echinoderms except for crinoids. The monophyly of Eleutherozoa has been proven sufficiently well to be considered "uncontroversial ...
The tubercles are imperforate and do not have crenulate edges. There are few tubercles on the interambulacral plates. The buccal notches are reduced in size and, their most significant distinguishing feature, the pedicellariae are globiferous and have one or two pairs of lateral teeth on the narrow tubular blades. [2] [3]
Eucidaris tribuloides, the slate pencil urchin (named after slate pencil), is a species of cidaroid sea urchins that inhabits littoral regions of the Atlantic Ocean.As a member of the basal echinoid order Cidaroida, its morphological, developmental and molecular genetic characteristics make it a phylogenetically interesting species.