E.J. Beglinger

Skeletons in confusion: a review of astrophorid sponges with (dicho–)calthrops as structural megascleres (Porifera, Demospongiae, Astrophorida)

Abstract We present a review of astrophorid species possessing calthrops megascleres as structural megascleres (including species with dichotriaene modifications, but excluding mesotriaene and trichotriaene bearing species). Radiating oxeas characteristic of most astrophorids are lacking in such sponges, but auxiliary oxeas are apparently present in some species. These sponges are currently assigned to two families, Pachastrellidae with four nominal genera Dercitus, Stoeba, Dercitancorina, Halinastra (the latter two generally considered junior synonyms of Stoeba), and Calthropellidae with nominal genera Calthropella, Corticellopsis (usually considered a junior synonym), Pachataxa and Pachastrissa. Our review of many original specimens and extensive new material demonstrates the existence of considerable morphological similarity in megasclere shape and arrangement, and possible overlap of some microscleres of these sponges: pseudasters in Dercitus resembling euasters in Calthropella, ataxasters and other modified types in Calthropellidae resembling rhabds in a species of Dercitus. Pachastrellid representatives are proposed to be united in a single genus Dercitus, recognizable as (dicho–)calthrops bearing sponges with sanidaster–like microrhabds. Three subgenera, Dercitus s.s., Stoeba and the revived Halinastra are distinguished to accommodate species groups sharing additional characters. Dercitancorina is merged with Dercitus (Stoeba), because the type species, Dercitus lesinensis was found to be barely distinct from Dercitus (Stoeba) plicatus. Similarly, the calthropellid representatives are proposed to be united in a single genus Calthropella recognizable as calthrops bearing sponges with oxyasters. Three subgenera, Calthropella s.s., Pachataxa and Corticellopsis are distinguished to accommodate species groups sharing additional characters. The calthropellid genus Pachastrissa is considered a junior synonym of Calthropella s.s. because its type species, Pachastrella geodioides, is barely distinct from the type species of Calthropella, Calthropella simplex. Two species previously assigned to Dercitus or Stoeba (Dercitus loricatus and Stoeba natalensis) are excluded from the genus Dercitus as they do not fit with the emended and improved definition of the genus. One species assigned to Calthropella, Calthropella digitata, is excluded from that genus and assigned to the ancorinid genus Stelletta. Based on the similarity of the megascleres and their structure-less arrangement, we predict that the two reviewed genera will be found to be closely related and eventually will need to be accomodated in a single family, but independent molecular evidence is awaited before changes in the family classification, including a verdict on the validity of the family Calthropellidae, will be proposed. Our review included 38 valid species among which fourteen species and one subspecies appear to be new to science. Four of these were represented by insufficient material for a proper description, but the remaining ten are described as new species: Dercitus (Stoeba) senegalensis sp. n., Dercitus (Stoeba) verdensis sp. n., Dercitus (Stoeba) fijiensis sp. n., Dercitus (Stoeba) bahamensis sp. n., Dercitus (Halinastra) berau sp. n., Dercitus (Halinastra) japonensis sp. n., Dercitus (Halinastra) arubensis sp. n., Dercitus (Halinastra) sibogae sp. n., Calthropella (Calthropella) xavierae sp. n., and Calthropella (Pachataxa) pyrifera sp. n. The new subspecies, Dercitus (Dercitus) bucklandi lusitanicus ssp. n. is described for southern East Atlantic populations of the nominal species. Several specimens assigned to existing species were found to be deviating to the extent that they are likely members of further undescribed species. These are briefly discussed to facilitate further studies of the diversity of the two genera. Species of both genera and the six subgenera, including deviating or insufficiently characterized specimens belonging to species not yet properly described, are keyed out. Distribution patterns are discussed.

New bioeroding sponges from Mingulay coldwater reefs, north-west Scotland

The relatively shallow coldwater coral reefs growing off the eastern coast of Mingulay, north-west Scotland, are excavated by five sponge species, three of which, Alectona millari, Pione vastifica and Cliona lobata, were known previously from Scottish waters. The other two species are new to Scotland and Great Britain. One species is here described as new to science: Cliona caledoniae sp. nov. The species shows a superficial resemblance in colour (orange) and spiculation (possession of tylostyles and knobby microscleres) to Cliothosa hancocki described disjunctly from the Pacific Ocean and the Mediterranean Sea, but it differs clearly in lacking the characteristic Cliothosa amphiasters with branching rays. The Scottish species only possesses peculiar thick-rayed streptasters, which at first glance appear rather similar to the second microsclere type reported for Cliothosa hancocki, knobby-rayed amphiasters. However, the majority of the microscleres in the Mingulay species appear to be genuine spirasters (not amphiasters), and exhaustive search for true amphiasters, branching or otherwise, was in vain. The new species is extensively illustrated. Furthermore, we also report the first occurrence in British waters of Spiroxya levispira, originally described from Azorean deep waters, and subsequently reported from Madeira and several Mediterranean localities. It was found to occur not uncommonly in the Mingulay reefs, and additionally also in reefs of the Rockall Bank, west of Ireland. The spicular characters generally match those of the southern locations. The newly recorded species is described and amply illustrated.