New indications of the phylogenetic affinity of Spongosorites suberitoides Diaz et al., 1993 (Porifera, Demospongiae) as revealed by 28S ribosomal DNA

Re-description of the Florida hermit-crab sponge Spongosorites suberitoides Diaz et al., 1993 by Sandford and Kelly-Borges (1997) found the sponge to be greatly more similar, morphologically and ecologically, to sponges in the Suberitidae (Hadromerida), than to Spongosorites (Halichondriidae, Halichondrida). Sponges in the genus Spongosorites have a crumbly, flaky texture, with a tangential ectosomal skeleton, and spongin-reinforced tracts of oxeas in the choanosome and are found in deep-water habitats, forming exclusive associations with vermetid gastropods, and displaying an aerophobic colour change on death or exposure to air. Suberitidae, on the other hand possess tylostyles, subtylostyles, strongyloxeas, and occasionally oxeas. Stylocordylidae and Polymastiidae are also known to possess oxeas but these never dominate the spicule complement. Despite the weight of morphological and ecological data for inclusion in Suberitidae, and the fact that oxeas are found in conjunction with strongyloxeas in Aaptos (Suberitidae), Sandford and Kelly-Borges (1997) reluctantly retained this species within the Halichondrida, which possess oxeas exclusively. The authors concluded that evidence additional to morphological and ecological data would be required to further indicate or resolve the phylogenetic affinities of Spongosorites suberitoides. A DNA sequence from the 5′ end of the 28S ribosomal RNA gene of S. suberitoides was compared with the same sequences from selected hadromerid and halichondrid species, in an attempt to resolve the phylogenetic affinities of this elusive taxon. Spongosorites suberitoides was strongly supported (>80%) within a clade containing members of the Suberitidae, Hadromerida, and internal topology of selected hadromerid families confirmed the earlier work of Kelly-Borges et al. (1991) using partial 18S rRNA sequences. Monophyly of Halichondrida remained unsupported, indicating that either the order is polyphyletic or that the 28S rRNA gene region sequenced is not capable of resolving the true relationships of this group. A new genus Pseudospongosorites n. g. is proposed for Spongosorties suberitoides, and a suggested transfer of this new genus from the Halichondriidae to the Suberitidae (Hadromerida).