Reexamination of Corvospongilla novaeterrae (Porifera, Spongillidae), an environmentally restricted freshwater sponge from eastern Canada

Abstract

Corvospongilla novaeterrae (Potts, 1886) (Demospongiae, Spongillidae) is known only from a few acidic lakes on the eastern coast of Canada. It is considered by some to be a sexual hybrid and thus an invalid species. This assumption is based upon an erroneous interpretation of C. novaeterrae's highly variable gemmoscleres and the abundant of foreign spicules (predominantly those of Duosclera mackayi) in the type specimens. We have examined a new specimen from Nova Scotia that has no foreign spicules and fits the original species description. We evaluate three hypotheses concerning this species' status: (1) it is a hybrid of Corvomeyenia everetti and another species; (2) it is an unusual ecomorphic form of C. everetti resulting from atmospheric inputs of sea salts; (3) it is a valid Corvospongilla species, closely related to C. seckti, C. volkmeri, and C. boehmi. Corvospongilla novaeterrae's morphologically variable gemmoscleres are quite similar to those of C. seckti, C. volkmeri, and C. boehmi, and appear to be evolutionary transients between birotulates and amphioxea (as in Radiospongilla and Pectispongilla). Other characters linking C. novaeterrae with other Corvospongilla species include (i) large gemmules (diameter > 1000 μm) with simple multiple foramina, (ii) a weakly developed or absent pneumatic layer, (iii) the size and shape of the birotulate microscleres, and (iv) the predominantly rod-shaped, tangentially arranged gemmoscleres. Evidence supports the acceptance of C. novaeterrae as a valid, environmentally restricted species.