Myxilla (Ectyomyxilla) kerguelensis

Myxilla (Ectyomyxilla) kerguelensis (Hentschel, 1914)

(Figure 14)

Synonymy: Ectyomyxilla kerguelensis Hentschel, 1914.

Myxilla kerguelensis (Hentschel, 1914).

Crellomyxilla intermedia Dendy, 1924.

Not Myxilla tornotata Brøndsted, 1924.

Material: Samples in 95% ethanol, tissue section and spicule preparation on slides; BELUM Mc 7589, BELUM Mc 7591, BELUM Mc 7595 and BELUM Mc 7596. Prion Island Site 2, South Georgia (54°001.862’S, 37° 15.032’W); depth 18m; collected by C. Goodwin, D. Poncet, and P. Brewin, 19 th November 2010. BELUM Mc 7684. Green Island, Stromness, Site 1, South Georgia (54°09.448’S, 36° 39.752’W); depth 17.4m; collected by C. Goodwin, P. Brickle and S. Cartwright, 27 th November 2010.

Comparative material examined: ZMH S2325 Ectomyxilla kerguelensis, S2319 Acanthoxa werthii

External morphology: In situ appearance: Thickly encrusting orange sponge, some specimens very thick and mounded. Scattered large oscules up to 0.5cm in diameter. Surface with a honeycomb appearance due to patches of ostia (Fig. 14a).

Preserved appearance: Very firm, pale yellow, crust with some inclusions of grey sediment grains. Spaces visible in choanosome. Ectosome is glassily smooth but is not easily detachable.

Skeleton: Choanosome: Dense reticulation of bundles of 2–3 acanthostyles, predominantly large acanthostyles but some small acanthostyles are scattered through the bundles. Sigmas and chelae scattered abundantly through the tissue. Ectosome: Palisade of tornotes covered with tangential crust of the small acanthostyles (Fig. 14b).

Spicules: Measurements from Mc7589.

Choanosomal acanthostyles: 203(226)245 by 15(19)25µm. Parallel sided acanthostyles with large, conical spines. End terminates in an abrupt, unspined point (Fig. 14c).

Ectosomal acanthostyles: 74(91)109 by 7(10)13µm. Similar in form to the choanosomal acanthostyles but with much larger spines relative to the shaft (Fig. 14d).

Ectosomal tornotes: 174(190)210 by 7(9)12µm. Fusiform tornotes with mucronate points (Fig. 14e).

Chelae: 18(20)23µm (Fig. 14f).

Sigmas: 18(24)29µm (Fig. 14g).

Remarks: The specimen appears to be a good match for the type description. There is a slight difference in that the type specimens are reported as massive and ‘mostly in rounded form’ with the largest piece 11.5cm wide and 7cm high, rather than thickly encrusting. However, it seems that specimens might be quite variable in form, as samples collected in this survey range from thickly encrusting to massive mounds (Mc7596 and Mc7684 were approximately 10cm high). Hentschel (1914) reports that some of his specimens were found on whale bones which may indicate that they were actually very thickly encrusting. In terms of speculation, the chelae (12.5–19µm), small acanthostyles (56–75µm) and sigmas (17–22µm) reported from the type are slightly smaller than those of our specimens. However, Boury-Esnault and Van Beveren (1982) described a larger size range in their specimens, similar to that found in ours. It was not possible to examine the type as the type specimen jar was found to contain a specimen of Acanthoxa werthii Hetschel, 1914 (now reassigned to Spanioplon werthi (Hentschel, 1914).

The species Crellomyxilla intermedia Dendy, 1924, described from New Zealand (Dendy 1924), is currently regarded as a synonym. This has similar sizes spicules and ectosomal acanthostyles to the type specimen of M. kerguelensis. Dendy describes two categories of chelae, but Burton (1929) on re-examination of the type found only one category. Burton (1929, 1934) also considered Myxilla tornotata Brøndstedt, 1924 a synonym, despite noting it differed in having microspined ends to the tornotes. However, the two species can be separated by the size of the sigmas and the size and form of the ectosomal spicules (Lévi 1956; Boury-Esnault and Van Beveren 1982) and have been recorded sympatrically from the Kerguelen Islands (Boury-Esnault and Van Beveren 1982).

Distribution: Other than the type locality, Kerguelen (Lévi 1956; Boury-Esnault & Van Beveren 1982), this species has been recorded from McMurdo sound (Burton, 1929), although these specimens differ from the type description in that they are flabellate specimens with chelae up to 33µm, and New Zealand (as Crellomyxilla intermedia) (Dendy 1924). There are no previous records from South Georgia.