''Asterias forbesi'', commonly known as Forbes sea star, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of starfish in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Asteriidae The Asteriidae are a diverse family of Asteroidea (sea stars) in the order Forcipulatida. It is one of three families in the order Forcipulatida. Genera The World Register of Marine Species lists these genera within the family Asteriidae (in a ...

. It is found in shallow waters in the northwest Atlantic Ocean and the Caribbean Sea.

Description

left, Underside of ''Asterias forbesi'' ''Asterias forbesi'' usually has 5 arms but occasionally has 4 or 6. Like many starfish species, the upper surface is covered in blunt conical projections giving it a rough feel. Some of these are

pedicellaria A pedicellaria (plural: pedicellariae) is a small wrench- or claw-shaped appendage with movable jaws, called valves, commonly found on echinoderms (phylum Echinodermata), particularly in sea stars (class Asteroidea) and sea urchins (class Echi ...

e, minute pincers that can grip objects. The arms are plump, broad at the base and tapering to a blunt tip. This starfish grows to about in diameter with an arm length of about . The

madreporite The madreporite is a light colored calcareous opening used to filter water into the water vascular system of echinoderms. It acts like a pressure-equalizing valve. It is visible as a small red or yellow button-like structure, looking like a smal ...

is usually pink and is visible near the edge of the disc. There are several rows of

tube feet Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on britt ...

on the underside on either side of the

ambulacral groove Ambulacral is a term typically used in the context of anatomical parts of the phylum Echinodermata or class Asteroidea and Edrioasteroidea. Echinoderms can have ambulacral parts that include ossicles, plates, spines, and suckers. For example, sea ...

that run down the centre of each arm. The colour of the upper side is variable, ranging from brown or tan to reddish-purple and the underside is usually pale brown. Near the tip on the underside of each arm there are small eyespots. These are not set on short stalks as they are in the otherwise similar ''

Asterias rubens The common starfish, common sea star or sugar starfish (''Asterias rubens'') is the most common and familiar starfish in the north-east Atlantic. Belonging to the family Asteriidae, it has five arms and usually grows to between 10–30 ...

'' with which this species can be confused.

Distribution

''Asterias forbesi'' is found in the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

of rocky shores on the Atlantic coast of North America from

Maine Maine () is a state in the New England and Northeastern regions of the United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Canadian provinces of New Brunswick and Quebec to the northeast and north ...

southwards to the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

. ''Asterias rubens'' has a more northerly range, being found from

Labrador , nickname = "The Big Land" , etymology = , subdivision_type = Country , subdivision_name = Canada , subdivision_type1 = Province , subdivision_name1 ...

southward to

Cape Hatteras Cape Hatteras is a cape located at a pronounced bend in Hatteras Island, one of the barrier islands of North Carolina. Long stretches of beach, sand dunes, marshes, and maritime forests create a unique environment where wind and waves shape ...

, most commonly north of

Cape Cod Cape Cod is a peninsula extending into the Atlantic Ocean from the southeastern corner of mainland Massachusetts, in the northeastern United States. Its historic, maritime character and ample beaches attract heavy tourism during the summer mont ...

living in colder, deeper waters.

Behaviour

''Asterias forbesi'' feeds on

bivalve molluscs Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

and other marine invertebrates. It can open shells by gripping the two halves with its tube feet and forcing them apart. It then inserts its stomach, turning it inside out in the process, and secretes enzymes, digesting the body of the mollusc in situ. Starfish can locate their prey by

chemoreception A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...

. In a trial, sixty ''Asterias forbesi'' that had not been fed for a week were used. The bait was a piece of

mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...

flesh in a tank of slowly circulating water. Test starfish were placed in the downstream odour plume, one metre (3 ft 3 in) away from the food source and the movements of each starfish were recorded on videotape. A control was provided using the same flow conditions but without an odour being present. 12 of the test starfish (20%) moved towards the target and got within of it in the allotted 15 minute timespan. The direction of movement became more accurate as the distance from the bait shortened. The rate of movement was slower than that of the control starfish and it was thought that this slower speed might improve the ability of the starfish to taste the water and make accurate comparisons of odour concentrations. None of the control starfish moved purposely in any direction, tending to move in random directions, circling and crossing their previous paths. It was proposed that more starfish would have moved towards the bait if they had previously been starved for a longer period. Other similar trials have involved starving starfish for two months prior to the experiment and this provides greater motivation to seek

prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

. The sexes are separate in ''Asterias forbesi''. Sperm and eggs are liberated into the sea and fertilization is external. The starfish in any area may synchronise their emission of gametes which will increase the chance of fertilization taking place. The eggs hatch into

bipinnaria A bipinnaria is the first stage in the larval development of most starfish, and is usually followed by a brachiolaria stage. Movement and feeding is accomplished by the bands of cilia. Starfish that brood their young generally lack a bipinnaria st ...

larvae which form part of the

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

and develop over a period of about three weeks before settling on the seabed and undergoing metamorphosis into juvenile starfish.

Ecology

The ciliate parasite ''

Orchitophrya stellarum ''Orchitophrya stellarum'' is a species of single-celled marine ciliates, a member of the class Oligohymenophorea. It is found living freely in the north Atlantic and Pacific Oceans but is also parasitic, being found inside the gonads of starfish ...

'' has been found in the gonads of up to 20% of male ''Asterias forbesi'' in

Long Island Sound Long Island Sound is a marine sound and tidal estuary of the Atlantic Ocean. It lies predominantly between the U.S. state of Connecticut to the north and Long Island in New York to the south. From west to east, the sound stretches from the Eas ...

. They feed on the tissue of the gonad and effectively castrate their host. A small number of females were also found to contain the parasite.

References

{{Taxonbar, from=Q770124 forbesi Animals described in 1848