''Nepanthia belcheri'' 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 ...

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 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 ...

Asterinidae The Asterinidae are a large family of sea stars in the order Valvatida. Description and characteristics These are generally small sea stars, flattened dorsally and bearing very short arms, often giving a pentagonal shape in the body ;example: ...

. It is found in shallow water in

Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...

and northeastern Australia. It is an unusual species in that it can reproduce sexually or can split in two by fission to form two new individuals. As a result, it has varying numbers of arms, and

Hubert Lyman Clark Hubert Lyman Clark (January 9, 1870 – July 31, 1947) was an American zoologist. The son of Professor William Smith Clark, he was born at Amherst, Massachusetts, and educated at Amherst College and Johns Hopkins University. From 1899 to 1905 he ...

, writing in 1938, stated, "It is a literal truth that no two of the 56 specimens at hand, nearly all from

Lord Howe Island Lord Howe Island (; formerly Lord Howe's Island) is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, part of the Australian state of New South Wales. It lies directly east of mainland P ...

, are exactly alike in number, size and form of arms".

Description

''Nepanthia belcheri'' is a small starfish with broad arms with rounded tips. Small specimens tend to have five arms, while larger ones have six or seven, although the number of arms can range from one or two to 10. When 12 months old, the length of an arm is typically , after two years it is , in the third year it reaches and in the fourth . ''N. belcheri'' is a muddy brown colour.

Distribution

''Nepanthia belcheri'' is native to the Pacific coast of Australia from the Low Islands in Queensland to

Port Jackson Port Jackson, consisting of the waters of Sydney Harbour, Middle Harbour, North Harbour and the Lane Cove and Parramatta Rivers, is the ria or natural harbour of Sydney, New South Wales, Australia. The harbour is an inlet of the Tasman Sea (p ...

in New South Wales. It also occurs in Southeast Asia and is found under boulders and rubble where conditions are muddy, from 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 ...

down to a depth of about 45 m (150 ft).

Biology

''Nepanthia belcheri'' is a

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

and can reproduce both sexually and asexually. The gonads generally produce

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...

s, but in some, no spermatogenic material is present, so they function as

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

, while others produce

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

and function as

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoster ...

. Sexual reproduction takes place in October and November. The eggs have large yolk sacs so the

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e are probably lechithotrophic, living on the nutrients already present in the eggs. Reproducing sexually allows the species to disperse to new locations in a way it could not do if it relied entirely on asexual reproduction. The lifespan is at least four years. During its second and third years, when it is actively growing and its arm length is either about 15 or 22 mm, ''N. belcheri'' can reproduce by fragmentation. A furrow appears on the disc which gradually deepens, and the two sides of the starfish pull away from each other. The disc is torn into two portions and over time, new arms grow on each section. As a result, the new individuals are asymmetric and often have six or seven arms of varying lengths. The original arms grow more slowly than the new ones so that, by the time the arm length reaches 27 mm, all the arms are much the same length. After fission, the gonads regress and individuals that previously had mature female gonads become masculinized, developing male-type gonads. Many larger individuals provide evidence from the varying lengths of their arms that they have divided by fission on several different occasions.

References

{{Taxonbar, from=Q2800726 Asterinidae Starfish described in 1875