MAY 9 2001 \ ;. I PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 113(3):579-589. 2000. The genus Hymerhabdia Topsent, 1892 (Porifera: Halichondrida: Axinellidae) with some remarks on related genera Jose Luis Carballo Institute de Ciencias del Mar y Limnologia, UN AM. Estacion Mazatlan. Apartado Postal 811. Mazatlan 82000. Mexico E-mail: carballo @ola.icmyl.unam.mx Abstract. — The genus Hymerhabdia hitherto contained the species H. typica, H. oxytrunca, H. intermedia, H. contracta, H. papillosa and H. topsenti. Based on our material, a new species is described, Hymerhabdia diversicolor, and H. typica and H. papillosa are redescribed. Moreover, it is proposed to synonymize H. oxytrunca and H. typica, and to assign H. topsenti to the genus Bubaris. The new species, H. diversicolor, is distinguished by having very particular anisodiametric oxeas, that is, one half tapering to a sharp lanceolate point, the other half uniformly thick and abruptly ending in a tip. This feature clearly distinguishes the species from other known species. The affinity of Hymerhab-dia to other closely related genera such as Axinysa, Collocalypta and Bubaris is discussed based mainly on their different types of spicules and choanosomal skeletons. Hymerhabdia and Collocalypta have a clearly plumose choanosomic skeleton, which consists of erect plumose columns of spicules in Hymerhabdia, from which spicule tracts in Collocalypta diverge. In the other genera the choanosomal skeleton is disorganised with spicules strewn in confusion and/ or composed of vaguely ascending tracts in Axinyssa, and with a condensed reticulation of flexuous or vermiform strongyles, with projecting bundles or individual styles ascending to the surface in Bubaris. Hymerhabdia is a small genus with spe-cies with a typically littoral Atlanto-Medi-terranean distribution (Sara & Siribelli 1962, Pouliquen 1972, Juan 1987). The ge-nus was erected by Topsent (1892) to in-clude encrusting sponges with a choanoso-mal skeleton that consists of erect plumose columns of spicules, with centrotylote ox-eas sharply curved at the middle and rhab-dostyles (Topsent 1904), although the most typical spiculation is formed by long styles that are sometimes sinuous and shorter ox-eas (Bergquist 1970). The diagnosis of the genus has been expanded a few times to include a new external morphological char-acteristic (with vertically ascending projec-tions) (Sara & Siribelli 1962), or some spic-ular type previously not found (rhabdos-trongyles, strongyles) (Sara & Siribelli 1960, 1962). In material from the Strait of Gibraltar (Southern Iberian Peninsula), we found a new species for the genus charac-terized by having anisodiametric oxeas which have one-half their length of the same width, and the other half progressive-ly decreasing in width towards a fine or lan-ceolated point. Besides the new species, there are six others: H. typica (Topsent 1892), H. oxytrunca (Topsent 1904), H. topsenti (Levi 1952), H. intermedia (Sara & Siribelly 1960), H. contracta and H. pap-illosa (Sara & Siribelli 1962), which share many characteristics with the family Axi-nellidae, in this work considered to be part of the order Halichondrida (van Soest et al. 1990). Moreover, some species of Bubaris,
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