Parvulastra parvivipara
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P. parvivipara
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| Parvulastra parvivipara (Keough & Dartnall, 1978)[1]
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Parvulastra parvivipara is a very small species of starfish in the family Asterinidae. 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 Parvulastra parvivipara can grow to a diameter of about 1 cm (0.4 in) and are an orange-yellow colour.[2] They are the smallest known starfish.
Distribution and habitat
Parvulastra parvivipara is endemic to the coast of South Australia where it is found within 200 kilometres (120 mi) of the Eyre Peninsula. Its distribution is limited to intertidal rock pools on granite rocks.[3] Some seemingly suitable pools contain none of these starfish while others have large numbers. Experiments showed that the 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.[3]
Life cycle
Parvulastra parvivipara has a very unusual life cycle for a starfish. The adults are self-fertilising hermaphrodites and the eggs are brooded within the gonads. There is no planktonic larval stage and the directly developing juveniles are cannibalistic, feeding on other embryos and juveniles while in the brood pouch.[4] When mature enough, they are released into the water in batches of up to twenty where they continue their life, quite probably in the same rock pool as their parent.[4] Most starfish disperse to new habitats during the planktonic larval stage but Parvulastra parvivipara is unable to do this. It is likely that it can only move to a new pool by chance when an individual is swept there by a wave.[3] Because of the inability of this species to disperse in a typical starfish manner, it may experience some adverse circumstance in any particular pool, be exterminated there, and perhaps recolonize the pool later.[citation needed]
Some individuals breed in the autumn and winter but most do so in the late spring and the summer at which time the brood sizes are smallest and the juveniles are the largest when born. It is thought that, by varying size and number of offspring in this way, the starfish maximises the chances that its young will survive.[5]
References
- ↑ 1.0 1.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 3.0 3.1 3.2 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 4.0 4.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
