''Thromidia catalai'', sometimes called the heavy starfish, is a species of

starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...

in the family

Mithrodiidae The Mithrodiidae is a family of starfish in the order Valvatida. Members of this family are big to huge tropical sea stars with 5 arms, rounded in cross-section. List of genera and species * Genus '' Mithrodia'' Gray, 1840 ** '' Mithrodia br ...

in the order

Valvatida The Valvatida are an order of starfish in the class Asteroidea, which contains 695 species in 172 genera in 17 families. Description The order encompasses both tiny species, which are only a few millimetres in diameter, like those in the genu ...

. It is native to the Indo-Pacific region. ''Thromidia catalai'' is one of the largest and heaviest starfishes in the world. It is reported to weigh as much as and have a diameter of . This species was first described by the Australian biologists E. C. Pope and F. W. E. Rowe in 1977, the type locality being New Caledonia.

Description

''Thromidia catalai'' is a large starfish with five arms and a diameter of up to , weighing up to . The surface is covered with low tubercles, giving it a granular appearance. The arms are robust and cylindrical, not tapering much and having rounded tips. The disc is small, and both disc and arms are a pinkish-beige colour, apart from the tips of the arms, which are a dark orange-brown. In contrast to other members of the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

'' Thromidia'', the tips of the arms have small, widely spaced tubercles. The only other starfish with which this species could be confused is the closely related '' Thromidia gigas'', but that species, though a similar size, has paler arm tips and is only found in the southern Indian Ocean, around Madagascar, Réunion and South Africa.

Distribution and habitat

''Thromidia catalai'' is found in the tropical Indo-Pacific region, its range extending from Indonesia to Hawaii, and from southern Japan to New Caledonia and northern Australia. It is found typically in and between reefs in the places where

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

settles, at depths between about , but usually deeper than on the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

. Although seldom encountered, this may be because of the considerable depth at which it lives rather than its rarity.

Ecology

Little is known of the feeding habits of this

, but related species are carnivorous with a diet mainly consisting of molluscs and echinoderms. The starfish everts its stomach to blanket the prey, secretes enzymes and digests it. As with other starfishes, the sexes are separate and the eggs and sperm are liberated into the water column where fertilization takes place.

References

{{Taxonbar, from= Q3198119 Mithrodiidae Fauna of the Indian Ocean Fauna of the Pacific Ocean Animals described in 1977