Kuma blacki sp. nov. (Figs. 11, 12) Type Material. Holotype. USNM 1096768, one set of 2-µm-thick serial frontal sections of epoxy-embedded specimen stained with toluidine blue. Type Locality. Isla Bastimentos (9°20.898’ N, 82°9.959’ W), from subtidal, clean, coarse-grained, wellsorted sand surrounded by Thalassia sp. Other Material Examined. Living specimens in squeeze preparations; two sets of 2-µm-thick serial sections. Etymology. Species name honors Prof. Steven D. Black of Reed College, Portland, Oregon, who generously provided lab space and equipment to M.D.H. for the completion of this project. Description. Mature specimens ~720 µm long and ~120 µm wide (Figs. 11 A, 12A). Anterior end rounded; posterior end blunt. Epidermis without obvious coloration, but digestive syncytium with orange coloration in transmitted light. Epidermis completely ciliated. Few scattered rhabdoids present in body wall. Frontal organ well developed (Figs. 11 B, 12A). Mouth opening on ventral surface, anterior half of body. Ovaries paired, ventral; extend from mouth posteriorly to middle of body. Testes paired, lateral to ovary, compact; extend posteriorly from middle of body. Immediately behind ovary, testes fuse to form single mass that extends posteriorly to seminal vesicle (Figs. 11 A, C, 12A, B). Female gonopore, vagina, and seminal bursa absent. Male gonopore terminal at posterior end of body (Figs. 11 B, D, 12B). Gonopore opens to ciliated antrum with muscular wall (Figs. 11 D, 12B, C). Antrum wall appears to have a few gland cells that empty into antrum. Proximal end of antrum ringed by a rosette of erythrophilic gland cells that appear granular in living specimens (Figs. 11 D, 12C). Elongated seminal vesicle positioned proximally to antrum and gland cells; seminal vesicle wall lined with tissue but not muscle. Sperm within seminal vesicle aligned in parallel (Figs. 11 D, 12C). Remarks. Species in the genus Kuma are distinguished from those in Haploposthia by having separate rather than combined germinal centers for sperm and eggs. Kuma blacki stands apart from the other six known species in the genus in having paired testes that fuse together to form a single mass in the posterior half of the body, and in having an elongated seminal vesicle with sperm aligned in parallel. The male antrum of Kuma blacki is apparently capable of considerable contraction in its length. The live specimens we examined had only a very short antrum—almost nothing more than an indentation in the epidermis. However, in the histological sections of three specimens we examined, the antrum length was approximately 50 µm.

Published as part of Hooge, Matthew D. & Tyler, Seth, 2008, Acoela (Acoelomorpha) from Bocas del Toro, Panama, pp. 1-40 in Zootaxa 1719 on pages 14-16, DOI: 10.5281/zenodo.181066