Sea stars don’t look like fish, or swim like fish, and really aren’t fish at all. They belong to the Echinoderm Phylum. Scientists chose the new name, sea star, because sea stars look like a star and live in the sea. But starfish remains a popular name for the sea star to this day.

The star fish has two surfaces. Aboral, the surface (Fig. 13.1) directed upwards in natural position and oral (Fig. 13.2) directed down­wards. The two arms between which the madreporite lies are the bivium and the remaining three, trivium.

Sea stars (group name Stelleroidea) are sometimes called starfish, though they are not real fish (they lack both vertebrae and fins). There are two sub-types of sea stars: Asteroideas: these are the true sea stars and sun stars. Ophiuroideas: these are the brittle stars and basket stars.

THE STARFISH PHYLUM ECHINODERMATA CLASS ASTEROIDEA PART ONE – EXTERNAL ANATOMY. 1. Distinguish the oral side from the aboral side. 2. Locate the central disk and the aboral madreporite 3. A pair of arms, the bivium, borders the madreporite. The other arms form the trivium. 4. The anus is a fine pore in the center of the aboral surface. 5.

The common species of starfish used for classroom observation and discussion is Asterias forbesi. Below is the complete taxonomy of the common starfish. KINGDOM: Animalia. PHYLUM: Echinodermata. CLASS: Asteroidea. ORDER: Forcipulatida. …

the arms of the star fish; ... Other three rays are referred to as the Trivium. Eye spots (ocelli) detect light located on the tip of each ray. Central Disk. located in the middle of the starfish on the Aboral Side. Madreporite. a perforated plate by which the entry of seawater into the vascular system of an echinoderm is controlled.

Starfish have mesodermal endoskeleton (endo- meaning the skeleton is inside) with small calcareous ossicles (bony plates). Their bones are very flexible, allowing them to move around freely. Ossicles in the skin provide support, protection from predators, and wave action allowing the starfish to move all directions.

Sea stars (group name Stelleroidea) are sometimes called starfish, though they are not real fish (they lack both vertebrae and fins). There are two subtypes of sea stars: Asteroideas are the true sea stars and sun stars.

From the intestine, and close to the anus, arise two diverticula. They bear several irregular caecal ampullae and reach a short way into two interradii, the interradius between the central and left ray of the trivium and the interradius between the left rays of the bivium and trivium respectively.

Apr 4, 2024 · Trivium: The three rays that are furthest away from the madreporite of the sea star. Bivium: The two rays nearest to the madreporite of the sea star. Anus : At the end of the digestive tract of a sea star lies the area where waste is expelled.