Sea stars, sometimes known as a starfish, are echinoderms belonging to the class Asteroidea[2]. The names "sea star" and "starfish" are sometimes differentiated,[3] with "starfish" used in a broader sense to include the closely related brittle stars, which make up the class Ophiuroidea, as well as excluding sea stars which do not have five arms (have Many arms), such as the sun stars and cushion stars.
Sea stars exhibit a superficially radial symmetry. They typically have five "arms" which radiate from a central disk (pentaradial symmetry). However, the evolutionary ancestors of echinoderms are believed to have had bilateral symmetry. Sea stars do exhibit some superficial remnant of this body structure, evident in their larval pluteus forms.[4]
Sea stars do not rely on a jointed, movable skeleton for support and locomotion (although they are protected by their skeleton), but instead possess a hydraulic water vascular system that aids in locomotion.[5] The water vascular system has many projections called tube feet on the ventral face of the sea star's arms which function in locomotion and aid with feeding. Sea stars usually hunt for shelled animals such as oysters and clams. They have two stomachs. One stomach is used for digestion, and the second stomach can be extended outward to engulf and digest prey. This feature allows the sea star to hunt prey that is much larger than its mouth would otherwise allow. Sea stars are able to regenerate lost arms. A new sea star may be regenerated from a single arm attached to a portion of the central disk.[6]
Cuttlefish are marine animals of the order Sepiida belonging to the Cephalopoda class (which also includes squid, octopuses, and nautiluses). Despite their common name, cuttlefish are not fish but molluscs. Recent studies indicate that cuttlefish are among the most intelligent invertebrate species.[1]
The origin of the word cuttlefish can be found in the old English term cudele, itself derived in the 1400s from the Norwegian koddi (testicle) and the Middle German kudel (pouch), a literal description of the cephalopod's shape. The Greco-Roman world valued the cephalopod as a source of the unique brown pigment released from its siphon when alarmed. Hence, the word for it in Greek and Latin is sepia (later seppia in Italian).
Cuttlefish have an internal shell (cuttlebone), large W-shaped pupils, and eight arms and two tentacles furnished with denticulated suckers, with which they secure their prey.
Cuttlefish eat small molluscs, crabs, shrimp, fish, octopuses and other cuttlefish. Their predators include dolphins, sharks, fish, seals and other cuttlefish. Their life expectancy is about one to two years.
Turtles are reptiles of the order Testudines (the crown group of the superorder Chelonia), most of whose body is shielded by a special bony or cartilaginous shell developed from their ribs. "Turtle" may either refer to the Testudines as a whole, or to particular Testudines which make up a form taxon that is not monophyletic—see also sea turtle, terrapin, tortoise, and the discussion below.
The order Testudines includes both extant (living) and extinct species. The earliest known turtles date from 215 million years ago,[1] making turtles one of the oldest reptile groups and a more ancient group than lizards and snakes. About 300 species are alive today, and some are highly endangered.
Like other reptiles, turtles are ectotherms—varying their internal temperature according to the ambient environment, commonly called cold-blooded. Like other amniotes (reptiles, dinosaurs, birds, and mammals), they breathe air and do not lay eggs underwater, although many species live in or around water. The largest turtles are aquatic.
