Starfish first appeared in the fossil record in the Cambrian. The first known asterozoans were the Somasteroidea, which exhibit characteristics of both groups. Starfish are infrequently found as fossils, possibly because their hard skeletal components separate as the animal decays. Despite this, there are a few places where accumulations of complete skeletal structures occur, fossilized in place in Lagerstätten — so-called "starfish beds". By the late Paleozoic, the crinoids and blastoids were the predominant echinoderms, and some limestones from this period are made almost entirely from fragments from these groups. In the two major extinction events that occurred during the late
Stichodactyla toxin Stichodactyla toxin Stichodactyla toxin (ShK) is a 35-residue basic peptide from the sea anemone "Stichodactyla helianthus" that blocks a number of potassium channels. An analogue of ShK called ShK-186 or Dalazatide is in human trials as a therapeutic for autoimmune diseases. "Stichodactyla helianthus" is a species of sea anemone (Phylum: Cnidaria) belonging to the family "Stichodactylidae". "Helianthus" comes from the Greek words helios meaning sun, and anthos meaning flower, which corresponds to the species' common name "sun anemone". It is sessile and uses potent neurotoxins for defense against its primary predator, the spiny lobster. The venom contains, among other components,