A new genus and species of deep-sea glass sponge (Porifera, Hexactinellida, Aulocalycidae) from the Indian Ocean

Abstract New hexactinellid sponges were collected from 2589 m depth on the Carlsberg Ridge in the Indian Ocean during deep-sea dredging. All fragments belong to a new genus and species, Indiella gen. n. ridgenensis sp. n., a representative of the family Aulocalycidae described here. The peculiar features of this sponge, not described earlier for other Aulocalycidae, are: longitudinal strands present in several layers and epirhyses channelization.

Etymology. The name of the genus is derived from its place of collection and refers to the Indian Ocean.
Definition. Aulocalycidae with fan (or funnel)-like body, epirhyses, and several regular layers of dictyonal strands located mainly on the atrial side.
Remarks. It is likely that the body is rather fan-like than cup or funnel-like since the fragments are flat, thus the funnel-like body shape should be of a very large diameter. The original shape of the body is already known in Aulocalycoidae: Leioplegma Reiswig &Tsurumi, 1996, while wide funnels are unknown. Basiphytous type of fixation to likely hard substratum is suspected since all other representatives of the family have it. The taxonomic affiliation of genus Cyathella (its attribution to the Aulocalycoida, Aulocalycidae with definition of a new subfamily Cyathellinae was made by Janussen and Reiswig 2003), possessing a rhizophytous type of fixation is unique for recent hexactinellids with rigid skeleton.
The walls in the new genus are relatively thick (in comparison with other representatives of the family). Usually the aulocalycoid skeleton is composed of large hexactins located approximately in a single layer, their rays are distributed in a single plane (the distal one and proximal are bent), fusion takes place at points of mutual contact, so the wall thickness includes an only dictyonal layer. The regular dictional strands are observed in Leioplegma only, they are present as a single layer of parallel units longitudinally distributed, and irregular aulocalycoid skeleton is situated among them (Reiswig and Tsurumi 1996). The walls in Euryplegma appear to be very complicated and their construction has no equivalent interpretation (Tabachnick and Reiswig 2000). Cyathella has similar framework construction with several layers of dictyonal strands, but it has no channels and likely no loose spicules.
The presence of epirhyses type of channelization is unique for the family. It is known in Euretidae (Hexactinosida), for instance, in Chonelasma (Reiswig & Wheeler, 2002). Among the other types of channelization in Aulocalycoidae, only schizorhyseslike ones are known in Euryplegma, meantime as in the case with complicated wall construction, they may be intercavaedia-like constructions between the atrial cavity and numerous small lateral oscula (Tabachnick and Reiswig 2000).
The loose spicules are typical for the family where few species possess scepters and uncinates. A more simplified spicule set is observed in Heterochone (Hexactinosida: Euretidae), which has no loose spicules other then discohexasters (Reiswig and Wheeler 2002).
The situation with aulocalycoid, paraulocalycoid and skeleton of Cyathella-like construction (Reiswig 2002 b;Janussen and Reiswig 2003) is becoming more complicated after finding in the dictional strands of Farrea numerous axial canals (Reiswig 2004), thus the definition of Aulocalycidae into subfamilies seems to be poorly established and the new genus is regarded as a representative of Aulocalycidae.

Indiella ridgenensis
Spicules framework is seems to be constructed of different elements: regular, longitudinally directed dictyonal strands, located mostly in the vicinity of the atrial surface (approximately 4 layers) and irregular hexactins fused to each other and to the regular elements at points of mutual contacts, at all levels of the wall thickness. All framework surfaces are covered by very small spines, the free outer ray ends are conically pointed. The dictyonal strands are easily observed, they have diameter 0.09-0.12 mm, beams between the strands are 0.03-0.07 mm in diameter. Free rays of the dictyonal strands are protruded atrially. The meshes between the dictyonal strands and their connecting beams are rather regular, usually rectangular, 0.3-0.5×0.5-0.8 mm. Adjacent hexactinic spicules located among the dictyonal strands are irregularly and sparsely distributed among their meshes, they are connected to the framework by a single ray (small hexactins with rays 0.07-0.12/0.003-0.006 mm) and often at points of mutual contact (large hexactins with rays about 0.5/0.012-0.018 mm). The meshes there are very irregular and of different sizes. The dictyonal strands may be also observed in the vicinity of dermal surface but due to numerous epirhyzes, they are not straight as those from the atrial surface.
Loose spicules: dermal and atrial pentactins are similar to each other, they always have a rudiment about 0.02 mm long instead of the ray directed outside the body, rough surface, their outer ends are clavate, rounded, lanceolate or sometimes conically pointed. Tangential rays of dermal pentactins are 0.102-0.432 mm long (Table 1), the ray directed inside the body is 0.048-0.258 mm long (Table 1), the diameter of these Figure 2. Indiella gen.n. ridgenensis sp.n. A view from the dermal side B view from the atrial side; (i) holotype, (ii) to (iv) paratypes rays is 0.002-0.009 mm. Tangential rays of atrial pentactins are 0.078-0.372 mm long, ray directed inside the body is 0.036-0.342 mm long (Table 1), the diameter of these rays is 0.004-0.009 mm.
Remarks. Since all these fragments of the holotype and of paratypes were collected from the same station, there is a great probability that they belong to a single specimen.

Remarks.
It is not obvious that the genus Euryplegma has schizorhyses, as postulated in the key of genera by Reiswig (2002); a possibility of lateral oscula and cavaedia (Tabachnick and Reiswig 2000) cannot be rejected. This newly suggested version of the key to genera of Aulocalycoidae family avoids this problem.