Hymedesmia (Hymedesmia) barnesi, Goodwin & Brickle, 2012

Goodwin, Claire & Brickle, Paul, 2012, Sponge biodiversity of South Georgia island with descriptions of fifteen new species, Zootaxa 3542, pp. 1-48 : 17-19

Hymedesmia (Hymedesmia) barnesi sp. nov.

( Figure 10)

Type material: Holotype: BELUM Mc 7627. Sample in 95% ethanol, tissue section and spicule preparation on slides; Right Whale Bay, South Georgia (54°00.173’S, 37° 40.856’W); depth 18m; collected by C. Goodwin, J. Brown and S. Brown, 21 st November 2010.

Paratype: BELUM Mc 7677. Sample in 95% ethanol, tissue section and spicule preparation on slides; 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 .

Etymology: Named after Dr David Barnes of British Antarctic Survey, project leader of the ‘Mapping the Benthic Biodiversity of South Georgia’ Darwin Initiative, in recognition of his support of this work.

External morphology: In situ appearance: Thinly encrusting (<3mm), bright orange, crust with pore sieves. Star shaped patterns of exhalent channels also visible ( Fig. 10a). Encrusting on bedrock, patches up to 15cm in diameter.

Preserved appearance: Thin white crust.

Skeleton: Typical hymedesmoiid skeleton with a dense basal layer of primary and echinating acanthostyles with ascending columns of the ectosomal spicules 3–6 spicules thick. Thick ectosomal layer of chelae ( Fig. 10b).

Spicules: Measurements from Mc7627.

Primary acanthostyles: 272(317)392 by 22(29)39µm at head. Tylote head bearing short rounded spines. Spined up to 1/3 of the shaft ( Fig. 10c).

Echinating acanthostyles: 102(138)161 by 9.3(17.2)24.5µm at head. Entirely spined with conical pointed spines ( Fig. 10d).

Ectosomal spicules: styles/tornotes 188(249)276 by 5.1(6.8)9.5µm. Fusiform with the ends variable in form: the majority are styles with one rounded, sometimes slightly tylote, and one pointed end but in some spicules the rounded end is modified into a point ( Fig. 10e,f).

Chelae: 23.6(27.7)30.7µm ( Fig. 10g).

Remarks: The majority of Hymedesmia (Hymedesmia) species occurring in the Antarctic have much bigger spicules or they possess sigma microscleres ( Table 5). The size range of the spicules in this species is similar to H. gaussiana Hentschel, 1914 . Unfortunately the type specimen of this species (ZMH collection) was destroyed in the Second World War and so is not available for examination. However, it differs in having strongyles as ectosomal spicules and entirely spined large acanthostyles.