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The Paleozoic echinoderms were globular, attached to the substrate and were orientated with their oral surfaces facing upwards. These early echinoderms had ambulacral grooves extending down the side of the body, fringed on either side by brachioles, like the pinnules of a modern crinoid. Eventually, except for the crinoids, all the classes of ...
Ctenocystoidea is an extinct clade of echinoderms, which lived during the Cambrian and Ordovician periods. Unlike other echinoderms, ctenocystoids had bilateral symmetry, or were only very slightly asymmetrical. They are believed to be one of the earliest-diverging branches of echinoderms, with their bilateral symmetry a trait shared with other ...
Ambulacraria / ˌ æ m b j uː l ə ˈ k r ɛər i ə /, or Coelomopora / s iː l ə ˈ m ɒ p ə r ə /, is a clade of invertebrate phyla that includes echinoderms and hemichordates; [1] a member of this group is called an ambulacrarian. Phylogenetic analysis suggests the echinoderms and hemichordates separated around 533 million years ago. [2]
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.
Water vascular system. The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. [1] The system is composed of canals connecting numerous tube feet. Echinoderms move by alternately contracting muscles that force water into the tube feet ...
Sea urchins or urchins (/ ˈɜːrtʃɪnz /) are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres (16,000 ft; 2,700 fathoms). [ 1 ] Their tests (hard shells) are round and spiny, typically from 3 to 10 cm (1 to 4 ...
Helicoplacus. Helicoplacus (often misspelled Helioplacus) is the earliest well-studied fossil echinoderm. Fossil plates are known from several regions. Complete specimens were found in Lower Cambrian strata of the White Mountains of California. The animal was a cigar-shaped creature up to 7 centimetres (2.8 in) long that stood upright on one end.
Cincta is an extinct class of echinoderms that lived only in the Middle Cambrian epoch. [1] Homostelea is a junior synonym. [2] The classification of cinctans is controversial, but they are probably part of the echinoderm stem group. [1][3] Cinctans were sessile, asymmetrical animals with a skeleton made of stereom plates and a racquet-shaped ...