First record of Axinyssa Lendenfeld, 1897 (Demospongiae, Halichondrida) from the East Pacific Ocean, with the description of Axinyssa isabela sp nov.

A new species of Axinyssa Lendenfeld, 1897 (Halichondriidae, Halichondrida) is described from the Mexican Pacific Ocean, which constitutes the first record of the genus in the Eastern Pacific Ocean. Axinyssa isabela sp. nov. is an incrusting to massive cushion-shaped yellow sponge without ectosomal skeleton. The ectosome is simply a thin, translucent, partly detachable collagen layer. The collagen is also abundant in the choanosome, while spicular density is relatively low. The choanosomal skeleton is confused with ascending single spicules or spicules grouped in tracts. The tracts become slightly more organized towards the periphery, protruding on the surface in spicule bundles or in single spicules. Spicules are oxeas and derivates (styles and strongyles), 200 to 780 mu m long and 3 to 15 mu m thick. So far, despite the sampling of a large number of localities along the Mexican Pacific Coast during the last years, Axinyssa isabela sp. nov. has been found only at National Park "Isla Isabel" (Nayarit, Mexico), where it is relatively common, in vertical walls, small caves and overhangs at depths between 4 and 20 m.