ABSTRACT
External appendages (spines, tubercles and pedicellariae) of brood pouches of the congeneric spatangoid echinoids Abatus nimrodi and A. shackletoni were examined using SEM. Both species brood their eggs and juveniles in four marsupial pouches. Yolky eggs average 1.4 and 1.0 mm in diameter in A. nimrodi and A. shackletoni, respectively. Stage I juveniles have mean lengths of 2.0 and 1.6 mm, stage II juveniles of 4.3 and 2.8 mm, respectively. In both species, spination of brood pouches consists of two spine types: tall, distally enlarged and small layered cover spines, as well as slender brood-pouch-bottom-spines. Pedicellariae in A. nimrodi were represented by only the dentate type, which occurs in bi, tri, and quadrodentate form. A. shackletoni has two forms of tridentate, rostrate and globiferous pedicellariae. Both, Abatus nimrodi and A. shackletoni have morphologically similar brood pouch spination that differs significantly in density. Abatus nimrodi and A. shackletoni are found on the eastern and on the western sides of McMurdo Sound, respectively. Differences in spination density may be related to the dramatically distinct sediment characteristics in these respective habitats. Supported by Austrian Schrödinger PostdoctoralScholarship J0614 to GOS and by NSF EPSCoR R11 8996152 to JBM.
