Chonelasma sp.

aff. Chonelasma sp.

( Figures 1–2 View FIGURE 1 View FIGURE 2 )

Material. IORAS 5/2/2051; IORAS 5/2/2201: RV ‘Akademik Mstislav Keldysh’ —22, sta. 2316, trawl, N from the Piip Volcano , 55 o 36.08’–35.0’ N 167 o 23.04’–24.46’ E, depth 4294– 4200 m .

Body. Small broken lamellate fragments about 1.2 mm in thickness are present in the collection. The dermal surface has no channelization, the atrial surface has numerous regularly distributed aporhyses 0.06–0.07 mm in diameter arranged in regular quadrunx order, the walls between the neighboring canals are 0.013 –0.026 mm thick.

Farmework. The inner skeleton of the atrial surface is composed of dictyonal strands constructed from beams 0.009 –0.038 mm in diameter with numerous spines. These dictyonal strands construct the euretoid type of skeleton with rectangular meshes 0.03–0.34 x 0.06–0.65 mm. The outer skeleton from the dermal surface is constructed from hexactins fused to each other at points of mutual contact. They have smoother and shorter rays then the dictyonal beam spines, the rays of these hexatins are 0.03–0.12 x 0.006 –0.013 mm with conically pointed outer ends.

Megascleres. Sarules with 9–19 tines are 0.185 –0.248 mm long (n= 25, avg: 0.223 mm, std: 0.017 mm), the tines are 0.009 –0.022 mm long (n= 25, avg: 0.012 mm, std: 0.003 mm), the maximal diameter of the tines head is 0.013 –0.023 mm (n= 25, avg: 0.020 mm, std: 0.002 mm), the diameter of the shaft of the scopule is 0.002 mm. Unlike other scopules typical for Chonelasma , the sarules in this specimen have widened head and unusual number of tines situated circularly on the edge of widened head. Therefore, in their shape they are similar to anchorate clavules with turned out teeth. Dermalia and possibly atrialia too are pentactins with spiny rays and rounded outer ends. These spicules are very rare. The tangential rays of these pentactins are 0.259 –0.352 mm long (n= 4, avg: 0.324 mm, std: 0.044 mm), the ray directed inside the body is 0.370 mm (n= 1), the diameter of these rays is 0.017 – 0.037 mm. Various fragments of different diameter and large length of likely diactins with smooth shafts possibly belong to other hexactinellids from this station, moreover that they have no outer ends, while some fragments of uncinates may be autochthonous.

Microscleres. Microscleres have discoidal outer ends: discohexasters, discohemihexasters and rare discohexactins. The discohexasters and discohemihexasters with 1–3 secondary rays are 0.047 –0.089 mm in diameter (n= 25, avg: 0.064 mm, std: 0.008 mm), their primary rosette is 0.009 –0.022 mm in diameter (n= 25, avg: 0.015 mm, std: 0.004 mm). The discohexactins are 0.050 –0.068 mm in diameter (n= 25, avg: 0.061 mm, std: 0.010 mm).

Distribution. Bering Sea, Kommandor Basin at 4294–4200 meters depth.

Remarks. Fragments are very small. Specific features of this sponge are the presence of extremely spiny framework and specific sarules. The presence of aporhyses distributed in regular quadrunx order together with corresponding set of loose spicules suggests the the best allocation of these specimens to be in Chonelasma . The absence of channelization of the dermal surface may be owing to the poor preservation condition of the material, inferred also from the rarity of dermal or atrial pentactins in the investigated materials.

Another hexactinellid representative which has similarity to the described specimens is Cyathella luthea from the Caribbean area but they are similar only in structure of the framework: aporhyses are arranged in regular manner; outer layer is formed by hexactins with short rays and extremely spiny beams of the dictyonal skeleton. The taxonomic position of Cyathella is unstable: the latest publication ( Janussen, Reiswig, 2003) placed it in a specific subfamily Cyathellinae in the family Aulocalycidae , but many reasons and facts, especially the euretoid type of inner framework mentioned in the same publication, indicates that it rather belongs to Euretidae , Chonelasmatinae . The fact that Cyathella has only a single type of loose spicules—discohexasters, argues in favor of considering the newly found materials as a problematic representative of Chonelasma .

Some features of the loose spicules of this sponge have similarities with Eurete irregularis Okada, 1932 and several specimens described by Koltun (1967): onychoidal microscleres (onychohexactines; onychohemihexasters and onychohexasters 0.065 –0.095 mm in diameter): scopules (clavate scopules are figured by Koltun, 1967: Fig. 30 2; 3) 0.300 – 0.350 mm long with 4–8 tines 0.030 –0.045 mm, dermal pentactins have rough tangential rays 0.220 –0.250 mm long; uncinates are absent. An important difference is presence of aporhyses and extremely spiny dictyonal skeleton in the problematic Chonelasma sp. as well as some differences in the size of loose spicules. Finding of new, better preserved specimens is required to clarify the position of this strange sponge.