Leucascus boomerang, Klautau & Lopes & Tavares & Rizzieri & Sorokin & Fromont & Goudie & Crowther & McCormack & George & Wahab, 2025

Leucascus boomerang View in CoL sp. nov.

( Figs 7, 8; Table 4)

Zoobank registration: urn:lsid:zoobank.org:act:

Etymology: For the peculiar shape of some spicules, which seem to be triactines and tetractines that lost one of the basal actines, becoming similar to a boomerang.

Diagnosis: Leucascus with cortical and atrial skeletons composed of triactines and common, but not abundant, tetractines. Choanosomal skeleton with the same proportions of triactines and tetractines. Deformed triactines and tetractines, with only two actines, are also present.

Type material: Holotype, SAMA S1886, GAB, 34°17 ʹ 30″S, 132°42 ʹ 24″E, depth: 283 m, coll. GABRP, site IN2015 _ C02_181, 7 December 2015 GoogleMaps . Paratype, SAMA S1953, GAB, 33°21 ʹ 56″S, 130°44 ʹ 52″E, depth: 198 m, coll. GABRP, site IN2015 _C02_398, 15 December 2015 GoogleMaps .

Colour: White in ethanol ( Fig. 7A).

Morphology and anatomy: Sponge massive, sof, subspherical to vasiform, formed by tightly anastomosed tubes surrounded by a continuous and smooth thin cortex ( Fig. 7A–C). Te osculum is single, apically located, and it is surrounded by a delicate membrane. Below it there is a large atrium with pinacocytes. Aquiferous system solenoid ( Fig. 7D).

The cortex ( Fig. 7C), the choanosomal tubes ( Fig. 7E), and the atrial membrane ( Fig. 7F) are composed of triactines; however, tetractines can also be found. They are not abundant and are present mainly in the interior of the tubes ( Fig. 7E). Given that the atrial membrane has mostly triactines, the atrium is smooth ( Fig. 7F). The size of the spicules is very variable, but it is possible to observe that the largest triactines are present mainly in the cortical membrane. Triactines and tetractines without one of the basal actines were also observed.

Spicules ( Table 4)

Triactine: Regular (equiangular and equiradiate), but it is also easy to find non-equiradiate spicules. Actines are conical, with sharp tips ( Fig. 8A). Sometimes there is a constriction at the middle of the actine. Under light microscopy, it is possible to see a mark at the centre of the spicules, forming a triangle. Tere are also spicules without one of the basal actines. Tey are similar to a boomerang ( Fig. 8B). Te size of these spicules is highly variable, some being larger and others being tiny (from 13.5/2.7 to 43.2/6.8 µm). Given that these tiny triactines could be young forms, we did not consider them to calculate the mean size of the spicules and did not include them in the table. Size: 116.9 (±21.3)/12.6 (±2.1) µm.

Tetractine: Regular (equiangular and equiradiate), but there are also non-equiradiate spicules. Actines are conical, with sharp tips ( Fig. 8C). Some spicules present a constriction near the middle of the actine. Under light microscopy, it was possible to see a triangle at the centre of the spicules. Boomerangs were also observed. Te apical actine is very thin (needle-like), frequently curved at the tip and covered with short spines ( Fig. 8D); however, several are smooth ( Fig. 8E). Although these spicules also have variable sizes, they vary less than the triactines. Size: basal, 101.5 (±19.8)/10.9 (±1.6) µm; apical, 54.2 (±11.5)/4.1 (±0.9) µm.

Geographical distribution: Currently known from only two localities in the GAB.

Ecology: Tis species was found in depths ranging from 189 to 283 m on the edge of the continental shelf (in fine sand and silt).

Taxonomic remarks: In Australia and nearby ( Indonesia and New Caledonia), three species of Leucascus with only triactines and tetractines have been described: Leucascus simplex Dendy 1892 , Leucascus flaous Cavalcanti, Rapp & Klautau, 2013 , and Leucascus neocaledonicus Borojević & Klautau, 2000 .

Leucascus simplex View in CoL was originally described from Port Phillip Heads ( South Australia; Dendy 1892), then reported from several other places in the Pacific, Indian, and Atlantic Oceans. Currently, its accepted distribution is (see Cavalcanti et al. 2013): Southeast Australia —Port Phillip Heads, Bass Straits, Port Jackson, and Watson’s Bay ( Dendy 1892); Western Australia —Shark Bay, Geraldton District, Fremantle District, and Bunbury District ( Row and Hôzawa 1931); New Zealand ( Kirk 1897); French Polynesia ( Klautau et al. 2020); and the Seychelles (Dendy 1913). However, it is still necessary to verify the identity of the specimens from the Seychelles and New Zealand because both have many tetractines, according to the authors, and those from Western Australia, because Row and Hôzawa (1931) did not give any description or figure.

Although the specimens in this study are morphologically similar to Leucascus simplex View in CoL , they can be differentiated mainly by the common presence of tetractines. Although tetractines are not abundant, they are not rare as in Leucascus simplex View in CoL . Another difference is the presence of a reduced atrium in Leucascus simplex View in CoL and a large one in Leucascus boomerang View in CoL .

Leucascus flaous is known only from Indonesia ( Sulawesi, Bali, and Ternate; Cavalcanti et al. 2013, Van Soest and De Voogd 2015). Tis species can be distinguished from Leucascus boomerang View in CoL by the presence of more tetractines than triactines in the atrial skeleton of Leucascus flaous .

Finally, Leucascus neocaledonicus View in CoL is most similar to Leucascus boomerang View in CoL . It is a shallow-water species, originally described from New Caledonia ( type locality; Borojević and Klautau 2000) and already reported for Australia (Great Barrier Reef; Wörheide et al. 2004, Dohrmann et al. 2006, sensu Cavalcanti et al. 2013). Both species have more triactines than tetractines, but tetractines are common, not rare as in Leucascus simplex View in CoL ; the atrial skeleton has many more triactines (tetractines are rare there and not abundant as in Leucascus flaous ), and actines are conical and sharp. Although Cavalcanti et al. (2013) have described the actines of Leucascus neocaledonicus View in CoL as blunt, we re-analysed the spicules of the type specimens and concluded that they are sharp, like those from the South Australian specimens. Another similarity between our specimens and Leucascus neocaledonicus View in CoL is the presence of a large atrium, whereas Leucascus simplex View in CoL has a reduced atrial cavity.

Although our specimens are very similar to Leucascus neocaledonicus , there are some differences between them. Leucascus neocaledonicus is lobate, with several oscula, whereas Leucascus boomerang is subspherical to vasiform, with a single osculum. Te spicules of Leucascus boomerang also have a different shape; some have a constriction in the middle of the actine and can have one reduced actine. Moreover, the apical actines of our specimens are thinner, more needle-like, and some of them are smooth. Consequently, we identify the specimens from the GAB as a new species.