New evidence of brooding in the deep-sea brittle star Astrotoma agassizii Lyman, 1876 from a South Western Atlantic Canyon

Abstract

The reproduction of the brittle star Astrotoma agassizii was studied from deep waters of the South Atlantic Ocean, based on samples collected in August 2012, and May and September 2013. Ten samples from 800 to 1400 m depths off Mar del Plata Canyon were studied. The species was found to be a brooding simultaneous hermaphrodite. Hermaphroditic gonads contained testis and ovaries inside the same sacs. Both, ovary and testis contained different stages of gametogenesis development simultaneously. The largest oocyte recorded was 800 µm diameter. Gonads contained several stages of oocytes in different stages of gametogenesis. Free spermatozoa were observed in the lumen of the testis, together with spermatogenic columns. Five individuals, from a total of 30 examined, resulted brooding, and most contained mature ovotestis at the same time. Incubation occurs in five of the ten bursal sacs, containing 15 to 20 young juveniles each. Maximum disc diameter recorded for a brood was 1120 µm. Herein we hypothesize that Astrotoma agassizii could be continuous breeder species in the deep-sea.