where does water enter the vascular system of a starfish
Water vascular system In sea stars, water enters the system through a sieve-like structure on the upper surface of the animal, called the madreporite. This overlies a small sac, or ampulla, connected to a duct termed the stone canal, which is, as its name implies, commonly lined with calcareous material. The stone canal runs to a circular ring canal, from which radial canals run outwards along the ambulacral grooves. Each arm of a sea star has one such groove on its underside, while, in sea urchins, they run along the outside of the body.[11]:933â€“939
Operculum (fish) The opercular series contains four bone segments known as the preoperculum, suboperculum, interoperculum and operculum. The preoperculum is a crescent-shaped structure that has a series of ridges directed posterodorsally to the organisms canal pores. The preoperculum can be located through an exposed condyle that is present immediately under its ventral margin; it also borders the operculum, suboperculum, and interoperculum posteriorly. The suboperculum is rectangular in shape in most bony fishy and is located ventral to the preoperculum and operculum components. It is the thinnest bone segment out of the opercular series and is located directly above the gills. The interoperculum is triangular shaped and borders the suboperculum posterodorsally and the preoperculum anterodorsally. This bone is also known to be short on the dorsal and ventral surrounding borders.[2]