Dercitus Dercitus bucklandi bucklandi (Bowerbank, 1858)

Van Soest, Rob W. M., Beglinger, Elly J. & De Voogd, Nicole J., 2010, Skeletons in confusion: a review of astrophorid sponges with (dicho-) calthrops as structural megascleres (Porifera, Demospongiae, Astrophorida), ZooKeys 68, pp. 1-88 : 9-11

Dercitus Dercitus bucklandi bucklandi (Bowerbank, 1858) Figs 2 A–D3A–E 5a-eTable 1

Halina bucklandi Bowerbank 1858: 288.

Hymeniacidon bucklandi ; Bowerbank 1866: 226; 1874: pl. 38 figs 9-12.

Dercitus bucklandi ; Gray 1867: 542; Topsent 1895: 528; Ackers et al. 1992 (2007): 52; Van Soest et al. 2008 (CD-ROM).

Pachastrella bucklandi ; Schmidt 1870: 76.

Dercitus niger Carter 1871: 3, pl. IV fig.1.

Battersbyia bucklandi ; Bowerbank 1874: 346, pl. 92 fig. 8; Bowerbank and Norman 1882: 93.

Material examined.

Schizoholotype (2 slides, one with dissociated spicules, the other with section at right angles to surface): NHM collection, Bwbk. 542 (labeled as Battersbyia bucklandi , Hymeniacidon bucklandi ), part of holotype BMNH 1877.5.21.142 (wet, fragment examined); locality presumed to be Abbey Bay, near Torquay, Devon, England (but this is not indicated on the labels).

Holotype of Dercitus niger Carter, 1871 (dry) BMNH 1895.4.27.1-6 (Fig. 3); dry schizotype ZMB 3046, (including 17 slides); locality Straight Point, Budleigh–Salterton, South Devon.

Description

(amalgamated from various descriptions of material from the British Isles and NW France). Cushion-shaped to massive-lobose (Figs 2A, 3A), filling crevices in vertical rock faces. Size frequently over 5cm2. Black to dark grey-brown externally. Surface smooth but often has ridges looking like stretch-marks. The surface is usually concave. Apertures (oscules?) are flush with the surface, variable in size and usually collected into groups towards the centre of the sponge. Consistency moderately firm but compressible and spongy when in situ, liver-like in preserved condition.

Skeleton: Main skeleton of confused, randomly arranged calthrops, a layer of sanidasters and many toxas occur near the surface, but these also occur in the choanosome. There are many large pigment cells (?) with black inclusions evident in sections.

Spicules: Calthrops, toxiform microscleres, sanidasters.

Calthrops (Figs 2B, 3 B–C), often with axial canals seen clearly, occasional bifid cladi or with angulated curve, rarely with 5 cladi, size of cladi: 80 –218.9– 305 × 12 –28.1– 48 µm, cladomes 120 –311.3– 480 µm.

Smooth toxiform microscleres (Figs 2C, 3D, 5 a–e), often slightly swollen near the apices, occasionally with irregular side branches (Fig. 2C): 51 –86.8– 111 × 1-2 µm.

Sanidasters (Figs 2D, 3E) relatively robust with strong spines in ‘mature’ condition: 22 –25.7– 31 × 0.5 –5.2– 7 µm (spines included in width).

Habitat.

In crevices in vertical rock faces in clean water. Particularly common on limestone substrata. From the extreme low water mark to a few meters subtidally in rock pools and caves.

Distribution.

British Isles (SW coast of England and N and W coast of Ireland), and France (Roscoff, Iles de Glénan). There is a record from the northern Gulf of Mexico ( Teerling 1975), but this has not been verified and is unlikely to be correct.

Etymology.

Named after Mrs. Buckland of Guernsey, who collected one of the type specimens (in fact the species should probably have been named “bucklandae” since the named person is female).

Remarks.

Bowerbank’s type specimen (a fragment, BMNH 1877.5.21.142, Fig. 2A) and slide (Bwbk. 542) and two of Carter’s (1871) types of Dercitus niger (BMNH 1895.4.27.1-6, Fig. 3A, and ZMB 3046) were reexamined (see also Table 1). Bowerbank’s material (Fig. 2) had calthrops with cladi 81-318 × 12-48 µm (cladome 120-480 µm), toxas 64-111 × 1-2 µm, and sanidasters 22-31 × 0.5-7. In the type material, the toxas showed some peculiar straight or curled side branches usually in the mid section (see below).

Carter’s type specimens (Fig. 3) possessed spicule sizes closely similar to those of Bowerbank’s type: calthrops 108-356 × 17-37 µm (cladome up to 472 µm), toxas 51 -103 × 1.5-3 µm, sanidasters 21-31 × 3-7 µm. However, there was a curious discrepancy in shapes of calthrops and the sanidasters between the BMNH and ZMB Carter type specimens. Presumably this conveys a large variability among specimens from the same locality.

Topsent (1895) gives the following measurements of specimens from the W coast of France: calthrops with cladi 310-320 × 38-45 µm (thicker than the types), toxas 75-90 (similar to the types), sanidasters 21-27 µm (similar to the types).

In view of some of the discrepancies we considered it worthwhile to investigate whether spicular differences of specimens within the known range of the species would yield a pattern that could explain some of the differences. We compared spicular data from the northern samples cited above with those of samples from areas in the southern part of the range, from the coasts and offshore localities of Portugal obtained from Dr Joana Xavier and examined spicule sizes and shapes. This led us to the conclusion that there are consistent differences between samples from these areas which should be recognized at the subspecies level.