Ascoleuceta plana, Klautau & Lopes & Tavares & Rizzieri & Sorokin & Fromont & Goudie & Crowther & McCormack & George & Wahab, 2025

AscoleuceTa plana sp. nov.

( Figs 15, 16; Table 8)

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

Etymology: For the flat shape of the body (Latin = planus).

Diagnosis: Ascoleuceta oval and flat, with a single osculum. Cortex with large and small triactines. Choanocyte tubes with small triactines and tetractines. Atrial skeleton with small triactines and few small tetractines.

Type material: Holotype, SAMA S1874, GAB, 34°16 ʹ 33″S, 132°41 ʹ 29″E, depth: 209 m, coll. GABRP, site IN2015 _ C02_179, 7 December 2015. GoogleMaps

Colour: White to light grey in ethanol ( Fig. 15A). Morphology and anatomy: Sponge massive, approximately oval, flat, formed by regular and tightly anastomosed tubes on its external surface ( Fig. 15A). Internally, these tubes are larger and less anastomosed and run in parallel mostly near the cortex ( Fig. 15B). Te osculum is a single, large and lateral aperture. Underneath it, there is a true wide and smooth atrial cavity ( 1.8 cm in diameter). Te body wall is thin ( 0.15 cm thick). Aquiferous system solenoid.

Te body is entirely covered by a continuous cortex composed of large and small triactines ( Fig. 15C, D). Te inhalant apertures surrounded by the triactines give the cortex a beehive appearance ( Fig. 15C). Tese apertures are sometimes surrounded by a few tufs of trichoxeas. In the choanosome are found small triactines and tetractines. Near the atrium, the exhalant canals are surrounded by the tetractines ( Fig. 15E, F). Tey project their thin (needle-like) apical actines into the lumen ( Fig. 15E). Te atrial skeleton is composed mainly of triactines, but there are also a few tetractines ( Fig. 15F).

Spicules ( Table 8)

Large triactines: Regular (equiangular and equiradiate). Actines are slightly conical, with blunt tips ( Fig. 16A). Size: 262.0 (±65.6)/25.5 (±6.2) µm.

Small triactines: Regular (equiangular and equiradiate). Actines are cylindrical and undulated, with blunt to sharp tips ( Fig. 16B). Size: 121.1 (±20.9)/10.5 (±2.2) µm.

Small tetractines: Regular (equiangular and equiradiate). Actines are cylindrical, with blunt to sharp tips ( Fig. 16C). Te apical actine is very thin (needle-like), sometimes undulated, with a sharp tip ( Fig. 16D). Tey are so thin that sometimes they are similar to trichoxeas. Size: basal, 131.4 (±31.0)/12.0 (±2.3) µm; apical, 66.1 (±22.1)/4.2 (±1.0) µm.

Geographical distribution: Currently known from only the type locality in the GAB.

Ecology: Tis species was found at a depth of 209 m on the edge of the continental shelf (in fine sand and silt).

Remarks: Te DNA of Ascoleuceta plana was published in the study by Lopes et al. (2018) as being from Ascoleuceta compressa . Although both species are morphologically very similar, they can be differentiated by the size ( Table 8) and shape of the small triactines and tetractines, which are cylindrical in Ascoleuceta plana and conical in Ascoleuceta compressa . In addition, the new species has almost the same amount of triactines and tetractines, or triactines are more abundant, whereas the small tetractines are much more abundant than the small triactines in Ascoleuceta compressa .

Considering the other three new species described in this study, Ascoleuceta plana can be differentiated from Ascoleuceta gabensis by the size of the huge triactines of the later ( Ascoleuceta gabensis , 512.4/53.8 µm; Ascoleuceta plana , 262.0/25.5 µm). Moreover, the atrial skeleton of Ascoleuceta gabensis has only triactines, whereas Ascoleuceta plana has triactines and tetractines. Te species can be differentiated from Ascoleuceta globularis by the shape of the body, which is globular in Ascoleuceta globularis and flater in the present

Calcinea from deep-sea South Australia • 27 species, and by the abundance of triactines in the present species, whereas Ascoleuceta globularis has more tetractines in the choanocyte tubes and abundant tetractines in the atrial skeleton. Comparison with Ascoleuceta parallela indicates that the most important differences are the presence of large tetractines and boomerang spicules in the later species.