''Nepanthia belcheri'' is a
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
starfish
Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...
in the
family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
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 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. He received the Clarke Medal from the Royal Society of New South Wales in 1947. A son of UMass Amherst president William Smith Clark, he spent more than 40 years ...
, 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 Port ...
, 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, commonly known as Sydney Harbour, is a natural harbour on the east coast of Australia, around which Sydney was built. It consists of the waters of Sydney Harbour, Middle Harbour, North Harbour and the Lane Cove and Parramatta ...
in New South Wales.intertidal zone
The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...
down to a depth of about 45 m (150 ft).[
]
Biology
''Nepanthia belcheri'' is a hermaphrodite
A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic.
The individuals of many ...
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 ger ...
s, but in some, no spermatogenic material is present, so they function as ovaries
The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocr ...
, while others produce sperm
Sperm (: sperm or sperms) is the male reproductive Cell (biology), 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 ...
and function as testes
A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone.
The ...
. Sexual reproduction takes place in October and November. The eggs have large yolk sacs so the larva
A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
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.[
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 occasions.][
]
References
{{Taxonbar, from=Q2800726
Asterinidae
Starfish described in 1875