Echinodermata. Actinozoa. Echinoidea
Living in marine habitats.
1) Internal anatomy of a regular sea urchin: Aristotle’s lantern, complex structure formed by five converging teeth and ossicles, controlled by muscles, digestive system. Stomach makes a complete counterclockwise tour and return bend of 180° connecting to the intestine which turns a complete clockwise tour. Gonad and radial canals of the water-vascular system are visible.
2, 6) Pedicellariae. 3) Spine. 4) Podium.
5) Internal view with Aristotle’s lantern, first portion of the digestive system, water-vascular system with stone canal opening in the madreporite at the aboral pole and radial canal with an extruded podium.
7) Sphaeridium, a possible georeceptor. 8) Aboral view. Skeletal theca with 5 double series of ambulacral and interambulacral plates. In the centre, the apical system with a soft periproct, with irregular plates, 5 genital plates, one of these is madreporite, at the interradia, and 5 radial plates.
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• Zoologia, Echinodermi, Tavola didattica
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