Protected development in deep-sea invertebrates. The rule in the southwestern Atlantic?

RIVADENEIRA, PAMELA; GUIDO PASTORINO; TESO, VALERIA; MARIANO IGNACIO MARTINEZ; DANIEL LAURETTA; JUAN JOSÉ BERECOECHEA; MARTIN IGNACIO BROGGER; FLORES, JONATHAN; PERTOSSI, RENATA; SÁNCHEZ, NOELIA; PABLO ENRIQUE PENCHASZADEH

Simposio; Deep-Sea Biology Symposium; 2018

Biological deep-sea research off Argentina (beyond 1200 m)started since 2012 with focus in the Mar del Plata submarinecanyon (up to 3500 m). Many of the more than 200 species foundof benthic cnidarians, mollusk and echinoderms are being studiedand new species are being described. Previous studies fromdifferent authors have pointed out the unusual proportion of speciesshowing protective adaptations for its offspring in the SouthernSea, particularly in Antarctica. Many new cases were observed inthe study area in different phyla showing some kind of protecteddevelopment, with avoidance of a free swimming larval stage.Among Cnidaria, oocyte gigantism was found in the black coralDendrobathypathes grandis with a diameter of up to 1.5 mm, whenoocytes in Antipatharia are usually under 0.2 mm. Many deep-seagastropods show encapsulated direct development, by thepresence of supplementary food for the embryo as nurse eggs,adelphophagia (Buccinidae, Calyptraeidae), proteins in theintracapsular liquid (Naticidae, Volutidae), or by means of giganticeggs of about 1.8 mm in diameter (Cochlespiridae). Peculiar eggmass morphologies are reported, i.e. in the moon snail Bulbuscarcellesi where the egg capsules are the largest ever recorded forthis family (8.8?14.1 mm in diameter vs 3 mm of the largestpreviously known). Brooding is found in the five classes ofEchinodermata. The sea star Ctenodiscus australis protects itsbroods in the dorsal side between paxillae; the crinoid Isometravivipara shows two phases, one with eggs brooded in a marsupiumand a second phase in the cirrus. In some sea cucumbers(Cladodactyla crocea, Psolus patagonicus, and Psolus lawrencei)broods could be found in pouches, sole or brooding chambers. Thesea urchin Austrocidaris canaliculata, protect their young in theapical system. Brooding chambers have been also reported inophiuroids as Astrotoma agassizi and Ophiochondrus stelliger. Allthis new evidence contributes to the understanding of the sceneryfor so many cases of parental care and the avoidance of planktoniclarvae in the southwestern Atlantic.