Suborder Spongillina subord. nov.: Freshwater Sponges

Abstract

Spongillina subord. nov. (Demospongiae, Haplosclerida) consists of seven families of exclusively freshwater sponges together containing 45 genera: Spongillidae (21 valid genera), Lubomirskiidae (three genera), Malawispongiidae fam. nov. (five genera), Metaniidae (five genera), Metschnikowiidae (monogeneric), Palaeospongillidae (monogeneric), Potamolepidae (six genera), some geographically widespread and others highly endemic. A central body cavity is peculiar to Malawispongiidae. Skeletal network is typically multispicular alveolate-reticulate with scanty spongin in Metaniidae, Potamolepidae and Malawispongiidae, paucispicular irregularly reticulate in Palaeospongillidae, Spongillidae, Metschnikowiidae with a variable amount of spongin, multi- to paucispicular irregularly reticulate with an abundant amount of spongin in Lubomirskiidae. Smooth or variably ornamented megascleres range from oxeas to strongyles in Spongillidae, Lubomirskiidae and Metaniidae, but are exclusively oxeas in Malawispongiidae, Metschnikowiidae, Palaeospongillidae, and exclusively strongyles in Potamolepidae. Microscleres usually present in Spongillidae, Palaeospongillidae and Metaniidae, are rare in Potamolepidae, and absent in Lubomirskiidae, Malawispongiidae and Metschnikowiidae. Microscleres if present are oxeas, strongyles, aster-like, pseudobirotules. Larvae are always parenchymella. Gemmules are typical of Spongillidae, Metaniidae, Palaeospongillidae, rare and strictly adhering to the substratum in Potamolepidae, and absent in Lubomirskiidae, Malawispongiidae and Metschnikowiidae. Gemmular theca is monolayered in Potamolepidae, mono-, bi- or tri-layered in Spongillidae, generally tri-layered in Metaniidae. Gemmules usually armed by gemmuloscleres in Metaniidae, Potamolepidae and Spongillidae, are rarely naked in the latter. Gemmuloscleres are boletiform (tubelliform), parmuliform, pseudobirotules in Metaniidae, and oxeas, strongyles, birotules, pseudobirotules, club-like, botryoidal in Spongillidae. Three more genera incertae sedis are included. This work is a relatively critical synthesis of the literature, however, a critical phylogenetic revision of established taxa is still in progress.