Cushion star

Patiriella parvivipara

ORDER

Valvatida

FAMILY

Asterinidae

TAXONOMY

Patiriella parvivipara Dartnall, 1972.

OTHER COMMON NAMES

None known.

PHYSICAL CHARACTERISTICS

One of the world's smallest known sea stars, measuring up to 0.4 in (1 cm) in diameter with stout arms. They are conspicuous yellow-orange color. Morphologically, they are similar to a co-occurring species Patiriella exigua.

DISTRIBUTION

Among sea stars, this species has the most restricted distribution. Currently found only within the coastal waters of southern Australia.

HABITAT

In either sheltered or exposed shores, usually under small boulders. At low tide, they remain covered with a few centimeters of water, although occasionally they are completely exposed.

BEHAVIOR

Slow-moving and spends most of their time beneath the underside of boulders to avoid predators and desiccation at low tide.

FEEDING ECOLOGY AND DIET

Opportunistic feeder, consuming essentially algal growth and detritus, although small epifaunal organisms and decaying animals are also eaten.

REPRODUCTIVE BIOLOGY

Unusual life-history. It is simultaneous hermaphrodite (self-fertilizing), has intragonadal fertilization, and incubates its young in the gonads. The strategy is to produce few eggs and small amounts of sperm at any one time. The advantage is a higher survival rate of offspring compared to the more usual strategy of broadcasting species. Cannibalism by juveniles feeding on other juveniles is common in this species. Most juveniles crawl away from the parent when sufficient size is reached. Emergence of juveniles appears to be influenced by temperature increases during the summer months.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS None known. ♦

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