Starfish

Any marine invertebrate of the class Asteroidea (phylum Echinodermata) with rays, or arms, around an unclear central disc is known as a sea star. They are not fish, despite their former common name. The estimated 1,600 live species of sea stars can be found in all oceans, with the highest diversity in the northern Pacific. The majority of species are 20 to 30 cm (8 to 12 inches) across; but, some are as little as 1 cm (0.4 inch) and others as large as 65 cm (25 inches).Sea star arms are hollow and covered with small spines and pedicellariae (pincerlike organs) like the disc; on the lower side are grooves with rows of sucker-tipped or pointed tube feet (see video of tube foot anatomy and physiology). One or more of a sea star's arms can be lost and replaced. It can move in any direction and stick to steep surfaces thanks to its tube feet.

         

  

Shark

Shark, any of the several predatory cartilaginous fish species that make up the order Selachii (class Chondrichthyes). Sharks, along with rays and skates, make up the Chondrichthyes subclass Elasmobranchii. Sharks, on the other hand, are distinguished from other elasmobranchs by their fusiform body shape and the placement of their gill clefts on each side of the skull. Sharks have thick skin that is drab grey in color and roughened by toothlike scales, though there are exceptions.A muscular, asymmetrical, upturned tail; pointed fins; and a pointed snout extending forward and over a crescentic mouth equipped with sharp triangular teeth are all common features. Sharks do not have a swim bladder, so they must swim constantly to avoid sinking to the bottom. According to various authorities, sharks are classified into 14–30 families, with over 400 species in existence. Humans are at risk from a number of larger animals. Sharks are fished commercially in large numbers. Overfishing in the late twentieth and early twenty-first centuries, on the other hand, drastically diminished the populations of some shark species.