Two brooding brittle stars (Echinodermata: Ophiuroidea) from Argentinean deep waters

BROGGER, M. I.; BERECOECHEA, J. J.; PENCHASZADEH, P. E.

Sopot

Conferencia; 9th European Conference on Echinoderms; 2016

Ophiuroids contribute a significant portion of biomass in marine environments, and in the deep sea can overcome other components of the benthic fauna. Approximately 2000 brittle stars species are known worldwide. The majority of ophiuroids are gonochoric, but at least 43 species are recognized as stable hermaphroditic, being all brooding forms. Although 10 species of ophiuroids have been characterized as protandric, this distinction is tricky to be confirmed. Despite their abundance and diversity, the mode of larval development has been documented for only 4% of all species, and studies of development for deep sea species are particularly scarce. The mode of reproduction of deep sea ophiuroids has been inferred from the approximate relationship between egg size and type of development. In Argentina almost 5 species are known as brooders and 4 of them reported as hermaphroditic. Here we study the reproductive biology of Astrotoma agassizii and Ophiochondrus stelliger from Argentinean deep sea, through histological examinations of the gonads and Scanning Electron Microscope (SEM). Astrotoma agassizii is abundant in the cold temperate Magellanic region of Argentina and has a circumpolar distribution. It can be found from 74 until 1000 meters depth. Ophiochondrus stelliger is a small species, and its distributions occurs from 37°S off Buenos Aires province to the Malvinas Islands (51°S). Therefore in this work we investigate and compare the reproduction biology of these two deep sea brittle stars known from Argentinean cold waters.Samples were collected at the Mar del Plata Canyon between 500 and 3500 meters during August 2012 onboard the RV ?Puerto Deseado?. Tissues were dehydrated in alcohol, embedded in resin and sectioned at 4 to 5 μm. We used haematoxylin and eosin to stain the sections. Stage maturity and size-frequency counts of the oocytes of the females are reported for each species. Oocytes were measured using a microscope scale and only oocytes that were sectioned through the nucleus were counted. Internal broods were transferred to aluminum stubs, metal sputter coated and observed under SEM.The preliminary results showed a maximum oocyte diameter of 0.85 mm in Astrotoma agassizii and 0.7 mm in Ophiochondrus stelliger. Embryos were found within the bursae in both cases. Herein we analyzed data on the incidence of brooding, the number and development of embryos in individuals from several samples. Observations of embryos on different developmental stages, appearance and position inside the bursae are also documented. Conclusions on maturity size of emergent juveniles and transfer of nutrient from parent to embryos are informed in both cases.