Strongylodesma australiense Kelly & Goudie 2020, sp. nov.

Strongylodesma australiense sp. nov. (Fig. 1, Table 1)

urn:lsid:zoobank.org:act: 57C54719-52A3-454E-9C51-302E6503416E

Material examined. Holotype NMVF246384, Wasp Island, New South Wales, Australia, 35.668° S, 150.308° E, 15–20 m, coll. Rob Capon, SCUBA, July 1994.

Type location & distribution. Wasp Island, New South Wales, Australia, 15–20 m.

Description. Holotype irregularly hemispherical in life with a single, flush, oscule visible, and a low mounded surface that suggests the porefields in life: 5.5 cm long, 4 cm wide, 2.5 cm thick. Texture firm, compressible. Colour in life, dark reddish brown, purple brown in preservative (Fig. 1A, B).

Skeleton. Ectosomal skeleton a mass of strongyles orientated paratangentially, 220–300 µm deep, with a thin, clear, collagenous region below (Fig. 1M). The choanosome contains massive primary tracts, 120–400 µm diameter (Fig. 1N), between which lie interstitial strongyles in loose groups (Fig. 1M).

Spicules. Megascleres (Fig. 1 C–L; Table 1) are strongyles, larger spicules slightly sinuously curved, slightly thinner at one end (Fig. 1 C–E), smaller spicules sharply bent proximally (Fig. 1F, G), with faint tylote (Fig. 1C, E, J), centrotylote (Fig. 1L), and ‘shepherd’s crook’ (Fig. 1H, I) modifications: 398 (230–539) µm long, 8 (5–12) µm wide, n = 30.

Substrate, depth range and ecology. Attached to a silted rocky reef, 15– 20 m.

Etymology. Named for the first record of the genus in the Australian region.

Remarks. As for all Strongylodesma species, S. australiense sp. nov. possesses strongyles with ‘shepherd’s crook’ modifications, a diagnostic character for the genus. These modifications also occur in species of Batzella Topsent (Poecilosclerida, Chondropsidae Carter), which have strongyles of a similar length to those of Strongylodesma species, but in the former, there is no special ectosome and the choanosomal skeleton is plumose. Moreover, the discovery of the pyrroloquinoline alkaloid Damirone A (compound 15 in Antunes et al. 2005), in the holotype of S. australiense sp. nov. (R. Capon, pers. comm.), strongly supports assignment of S. australiense sp. nov. to Strongylodesma, rather than to Batzella.

Megasclere dimensions, ectosome thickness and choanosome structure are the primary differentiating characters for Strongylodesma species. The South African species S. aliwaliensis is closest to S. australiense sp. nov. in possessing the longest strongyles in the genus (S. aliwaliensis up to 590 µm long; S. australiense sp. nov. up to 539 µm long; Table 1) but those of S. aliwaliensis are much longer overall (S. aliwaliensis mean length 428 µm: S. australiense sp. nov. mean length 398 µm). Both species possess large internal tracts that are about the same thickness, but those of S. aliwaliensis are thicker (S. aliwaliensis up to 490 µm; S. australiense sp. nov. up to 400 µm thick) and form a notable, convoluted, honey-comb structure visible to the unaided eye (Samaai et al. 2004).

Strongylodesma tongaensis also has massive internal tracts but much smaller strongyles (mean length 295 µm, maximum length 330 µm); all other species have much smaller spicules (see Table 1), thin ectosomes and insubstantial choanosomal tracts by comparison. Note that citing an accessioned paratype (BMNH 2003.4.10.1) for S. tongaensis in Samaai et al. (2009) from Palau, was a mistake; we can confirm here that the distribution of this species is restricted to the Kingdom of Tonga.

The discovery of Strongylodesma australiense sp. nov. is significant as it is the first record of the genus in the Southwest Pacific, bridging the disparate primary locations in which the genus is recorded: the Tropical Western and South Atlantic Ocean, and the Western Pacific Ocean.