We are to our final day of Fishmas. As you are now all professional ocean ID experts, I present one of the most difficult to figure out. It may take a little outside the box thinking but I think you can get it.Edited Photo: Brandon Smith
Did you guess starfish (sea star)?
Starfish are not fish at all but invertebrates and are now referred to as sea stars. They are in the phylum echinodermata, which means spiny skin. Also in this pylum are brittle stars, sea urchins, sand dollars, sea cucumbers and crinoids.
Sea stars have a water vascular system that pumps sea water through their veins instead of blood. Sea stars move with the use of tube feet, which are part of the water vascular system. By pumping water they can create suction with the feet for locomotion or feeding. Most sea stars feed on mollusks, with many focusing on bivalves (clams, mussels, etc.). They suction onto the shell of a bivalve with their tube feet and slowly pull the shell open. Sea stars only have to pull the shell partially open to feed on it due to the unique property of their stomachs. They they can evert their stomach outside of their body and insert it into the thin opening of the mollusc shell, digesting it outside their own body. While most feed on mollusks some are specialized feeders, like the crown of thorn sea star, which feeds on coral polyps.
Sea stars, like most echinoderms have the ability to regenerate lost limbs. Some can even regenerate into several organisms if cut up, as long as part of the central disk remains. It takes about a year for a limb to grow back completely and the sea star is more susceptible to infection when it first loses a limb. Some sea stars even reproduce asexually using this method by making their limbs easier to break during periods of abundant resources.