Antarctic Brittle Stars

Antarctic Ophiuroids (Echinodermata) 

• The ophiuroids are one of the five classes of echinoderms which has more than 2000 species.

Ophiactis asperula dorsal view

• They form an important group of benthic invertebrates in all seas and oceans, from tropical to polar regions and from coastal to abyssal waters.

• Like other echinoderms, they are exclusively marine animals.

• Their locomotion is based on the movement of the arms which are articulated by bony prats called vertebrae.

• Most are dioecious and their development is through a larva called ofiopluteus. There are many species that are hermaphrodites and also species with direct development and incubators.

• They are stealthy and elusive.

Ophiophragmus chilensis, ventral view

• They are predators, scavengers, detritivores or suspensivorous.

• Ophiuroids have a great capacity for regeneration, they are able to lose several of their arms  leaving the predator surprised and thus having a chance to escape.

Amphiura belgicae, dorsal and ventral view

• Ophiuroids are one of the major benthic groups, due to their biomass and diversity, in the waters surrounding Antarctica, many of their species are viviparous and have opportunistic eating habits.

Ophiacantha paramedea, arm spines dorsal view

Biology, Ecology, Taxonomy, Evolution

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Peculiarities of the Antarctic benthic fauna:

• The Antarctic Circumpolar Current causes isolation and homogenization.

• The absence of sharks and crabs means a low predation on groups such as echinoderms.

• Their food web is based on primary producers in summer and on independence from these in winter. Food shortages power omnivorous alimentation.

• In the areas covered by ice barriers there are food shortages.

• The drifting icebergs destroy benthic communities forcing ecological successions.

• There are many viviparous species with longer incubation time and a slower pace of growth that has resulted in very long-lived species.

• The low predation, little competition for food, and empowerment of reproduction in larger bodies favor gigantism.

• More than 4100 benthic species have been recorded in the Southern Ocean.

Astrotoma agassizii, dorsal and ventral view