CHRISTENSEN, A.B. *; DEAN, D.K.; Lamar University; Lamar University: Population structure in a fissiparous ophiactid brittlestar possessing hemoglobin

A small fissiparous brittle star, belonging to family Ophiactidae, was collected from South Jetty, Port Aransas, TX. While it was found in a variety of sponge and algal species, the densest aggregations were found in the colonial tunicate, Eudistoma carolinense (75 dl^-1). In the January 2002 collection, a total of 537 individuals were collected. The medium size class, 2-3 mm disc diameter, was dominant (67%) and 58% of the population was nearly full or fully regenerated. In contrast, the June 2002 collection yeilded 378 individuals, 78% belonging to the small size class (< 2mm disc diameter)and 75% of the sample was in some stage of regeneration. This brittlestar possesses hemoglobin containing coelomocytes (RBCs) in its water vascular system; the hemoglobin has a low affinity of oxygen (P50 = 27.9 mmHg). The amount of RBCs per individual varies from those with many RBCs (evidenced by bright red tube feet) to those with few RBCs whose tube feet appear almost colorless. The most numerous type collected were those possessing bright red tube feet. The redness of the tube feet was not correlated to size or regeneration state of the animal. The screening of genomic DNA using RAPDs revealed a high frequency of genotypes. This indicates that despite the large numbers of regenerating animals in a colony, fission is not the primary means of reproduction in this population.