''Parvulastra parvivipara'' is a very small
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 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 ;exampl ...
. It is a
viviparous species and gives birth to live young. It lives in rock pools on intertidal granite rocks in a limited area of South Australia.
Description
Adults of ''P. parvivipara'' can grow to a diameter of about and are an orange-yellow colour. They are the
smallest known starfish.
Distribution and habitat
''P. parvivipara'' is
endemic to the coast of South Australia, where it is found within of the
Eyre Peninsula. Its distribution is limited to intertidal
rock pools on
granite rocks.
Some seemingly suitable pools contain none of these starfish, while others have large numbers. Starfish favoured pools with little wave action, but with a considerable degree of
biodiversity. They also preferred pools low down the beach rather than high-level pools.
[
]
Lifecycle
''P. parvivipara'' has a very unusual lifecycle for a starfish.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 ...
s and the eggs are brooded within the gonad
A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...
s. No planktonic larval stage is seen, and the directly developing juveniles are cannibalistic, feeding on other embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
s and juveniles while in the brood pouch.[ When mature enough, they are released into the water in batches of up to 20, where they continue their lives, quite probably in the same rock pool as their parents.][ Because of the inability of this species to disperse in a typical starfish manner, it may experience some adverse circumstances in any particular pool, be exterminated there, and perhaps recolonize the pool later.
Some individuals breed in the autumn and winter, but most do so in the late spring and the summer, when the brood sizes are smallest and the juveniles are the largest when born. By varying size and number of offspring in this way, the starfish is thought to maximize the chances that its young will survive.]
See also
* List of marine animals of Australia (temperate waters)
References
{{Taxonbar, from=Q2161999
Asterinidae
Fauna of the Indian Ocean
Marine fauna of Australia
Endemic fauna of Australia
Animals described in 1978