They are opportunistic feeders and are mostly predators on benthic invertebrates.
, Each starfish arm contains two gonads that release gametes through openings called gonoducts, located on the central disc between the arms.
, Several species sometimes suffer from a wasting condition caused by bacteria in the genus Vibrio; however, a more widespread wasting disease, causing mass mortalities among starfish, appears sporadically. In particular, Oreaster reticulatus, with its easily accessed habitat and conspicuous coloration, is widely collected in the Caribbean. † Calliasterellidae The water vascular system serves to transport oxygen from, and carbon dioxide to, the tube feet and also nutrients from the gut to the muscles involved in locomotion. , Most species are generalist predators, eating microalgae, sponges, bivalves, snails and other small animals. A 2014 analysis of 219 genes from all classes of echinoderms gives the following phylogenetic tree.
The tropical crown-of-thorns starfish (Acanthaster planci) is a voracious predator of coral throughout the Indo-Pacific region, and the northern Pacific sea star is considered to be one of the world's 100 worst invasive species.
, There may also be papulae, thin-walled protrusions of the body cavity that reach through the body wall and extend into the surrounding water. The starfish does not have the capacity to plan its actions.  This species has a unique ability to absorb seawater to keep itself cool when it is exposed to sunlight by a receding tide.  In 2011, on further molecular evidence, Janies and colleagues noted that the phylogeny of the echinoderms "has proven difficult", and that "the overall phylogeny of extant echinoderms remains sensitive to the choice of analytical methods".
, An aboriginal Australian fable retold by the Welsh school headmaster William Jenkyn Thomas (1870–1959) tells how some animals needed a canoe to cross the ocean.
 The times at which the clades diverged is shown under the labels in millions of years ago (mya).  The term "keystone species" was in fact first used by Robert Paine in 1966 to describe a starfish, Pisaster ochraceus. These are composed of pigmented epithelial cells that respond to light and are covered by a thick, transparent cuticle that both protects the ocelli and acts to focus light. , The scientific name Asteroidea was given to starfish by the French zoologist de Blainville in 1830.  The Starfish and the Spider is a 2006 business management book by Ori Brafman and Rod Beckstrom; its title alludes to the ability of the starfish to regenerate itself because of its decentralized nervous system, and the book suggests ways that a decentralized organisation may flourish. The peripheral nerve system consists of two nerve nets: a sensory system in the epidermis and a motor system in the lining of the coelomic cavity. The mouth is located in the centre of the oral surface, where it is surrounded by a tough peristomial membrane and closed with a sphincter. This vessel has a blind end and there is no continuous circulation of the fluid within it.
The taxonomy of the group is relatively stable but there is ongoing debate about the status of the Paxillosida, and the deep-water sea daisies, though clearly Asteroidea and currently included in Velatida, do not fit easily in any accepted lineage.  There are eyespots at the ends of the arms, each one made of 80–200 simple ocelli. The existence of a drug “breaking down Black womens’ ovaries” would presumably have led to a greater incidence of birth defects being reported in African-American communities.
Experimental removals of this top predator from a stretch of shoreline resulted in lower species diversity and the eventual domination of Mytilus mussels, which were able to outcompete other organisms for space and resources. The vessels form three rings: one around the mouth (the hyponeural haemal ring), another around the digestive system (the gastric ring) and the third near the aboral surface (the genital ring). The original ball of cells develops a lateral pouch, the archenteron. , Several groups of starfish, including Valvatida and Forcipulatida, possess pedicellariae. These extend to contact the substrate.  The developing young are called lecithotrophic because they obtain their nutrition from the yolk as opposed to "planktotrophic" larvae that feed in the water column. 
Most can regenerate damaged parts or lost arms and they can shed arms as a means of defense.  The sensory component receives input from the sensory organs while the motor nerves control the tube feet and musculature. Apr 28, 2019 - 11,986 points • 279 comments - Some star fish can have birth defects that make them square - 9GAG has the best funny pics, gifs, videos, gaming, anime, manga, movie, tv, cosplay, sport, food, memes, cute, fail, wtf photos on the internet!
, Another area of research is the ability of starfish to regenerate lost body parts. When she releases eggs into the water, he is induced to spawn. These bulb-shaped organs are joined to tube feet (podia) on the exterior of the animal by short linking canals that pass through ossicles in the ambulacral groove. Starfish are also known as Asteroids due to being in the class Asteroidea. Starfish, such as the ochre sea star (Pisaster ochraceus) and the reef sea star (Stichaster australis), have become widely known as examples of the keystone species concept in ecology. Trendception: A master class in the use of spurious data to make bogus and self-referential political talking points unsupported by empirical evidence. , The lifespan of a starfish varies considerably between species, generally being longer in larger forms and in those with planktonic larvae.  The body fluid contains phagocytic cells called coelomocytes, which are also found within the hemal and water vascular systems. This type of tissue is called catch connective tissue and is found in most echinoderms. , Some species of starfish have the ability to regenerate lost arms and can regrow an entire new limb given time.
Brooding may be done in pockets on the starfish's aboral surface, inside the pyloric stomach (Leptasterias tenera) or even in the interior of the gonads themselves.
Sometimes at the full moon time, when the moon is really dazzling and hitting on the ocean, a starfish jumps out of the water and falls down.  Research into the efficacy of these compounds for possible pharmacological or industrial use occurs worldwide. These are honeycombed structures composed of calcite microcrystals arranged in a lattice.
Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface. Some of these species are grazers, but others trap food particles from the water in sticky mucus strands that are swept towards the mouth along ciliated grooves.
Oxygen is transferred from these to the coelomic fluid, which acts as the transport medium for gasses.
, In his 2002 book The Divine Mystery Fort, Sri Sai Kaleshwar Swami wrote, "An eighth type of supernatural power object is a starfish. (We have contacted the CDC seeking epidural usage rates between 2010 and 2014.). The interior of the whole canal system is lined with cilia.  Various species have been shown to be able to absorb organic nutrients from the surrounding water, and this may form a significant portion of their diet.
, While a starfish lacks a centralized brain, it has a complex nervous system with a nerve ring around the mouth and a radial nerve running along the ambulacral region of each arm parallel to the radial canal. The cardiac stomach is glandular and pouched, and is supported by ligaments attached to ossicles in the arms so it can be pulled back into position after it has been everted.  When a starfish finds itself upside down, two adjacent arms are bent backwards to provide support, the opposite arm is used to stamp the ground while the two remaining arms are raised on either side; finally the stamping arm is released as the starfish turns itself over and recovers its normal stance.  When such a larva senses that food is plentiful, it takes the path of asexual reproduction rather than normal development. , Starfish sometimes have negative effects on ecosystems. They remove debris from the body surface and wave around on flexible stalks in response to physical or chemical stimuli while continually making biting movements.