Discorhabdella Dendy, 1924

Maldonado, Manuel, Carmona, M. Carmen, Van Soest, Rob W. M. & Pomponi, Shirley A., 2001, First record of the sponge genera Crambe and Discorhabdella for the eastern Paci ® c, with description of three new species, Journal of Natural History 35 (9), pp. 1261-1276 : 1268

Discorhabdella Dendy, 1924

Diagnosis. Encrusting poecilosclerids characterized by a category of small acanthostyles with a globate tyle and a short shaft with spines concentrated towards the end, along with a category of large choanosomal tylostyles with tuberose tyles, and a category of small ectosomal subtylostyles. A single category of anchorate-unguifer - ate isochelae occurs in all species, except one of the new species described herein. Microxeas and sigmas may also occur, depending upon species.

Remarks. The acanthostyle of Discorhabdella is highly characteristic in possessing a globate tyle, the hypertrophy of which is so important in some species that the spicule resembles an aster, and is termed a`pseudoastrose acanthostyle’ ( Dendy, 1924). SEM observations reveal axial canals within the spines of the globate tyle, indicating that the presumed spines are actually actines and suggesting that these peculiar acanthostyles have evolved from a polyaxonid spicule, an ancestor most likely shared with the aster-like desmas of Crambe ( Uriz and Maldonado, 1995; Maldonado and Uriz, 1996). The fact that Crambe and Discorhabdella share virtually identical spicule complement except for the aster-like desmas and the pseudoastrose acanthostyles is also consistent with the idea of aster-like desmas and pseudoastrose acanthostyle s being homologous spicules. The alternative hypothesi s that the pseudoastrose acanthostyles would not be non-polyaxonid in origin, but derived from regular diactinal acanthostyles is unlikely. From such an alternative view, the presence of axial canals in the aster-like tyles of Discorhabdella cannot be explained in agreement with the traditional actinal theory that distinguished between actines and spines in the spicules on the basis of the presence / absence of axial canals within the structure ( Sollas, 1888; Dendy, 1921b, 1926). Furthermore, if aster-like desmas and pseudoastrose acanthostyles are considered non-homologous, the enormous similarity between Crambe and Discorhabdella in composition, structure and arrangement of the remaining spicule set would have to be explained by evolutionary convergence. Such a process is clearly unrealistic in probabilistic terms, given the large number of skeletal traits and micro-traits that should have converged (e.g. pattern of axial canals, spicule micro-ornamentation, spicule sizes and arrangement, etc.). It is also unsupported from any anatomic evidence.