Pontiothauma transregna Criscione & Hallan, 2024, sp. n.

Pontiothauma transregna sp. n. (PSH P2) (Figures 5E–H, 6G) ZooBank: urn:lsid:zoobank.org:act: 14347001–685D-4DF3-83D7-970E94D43815 Material examined Holotype. Australia, NSW, Hunter CMR (− 32.575°S, 153.162°E), IN2017_ V03 _070, 2595– 2474 m (AMS C.571641). Paratypes. Same as holotype. 1 wet (AMS C.571641), 1 wet (AMS C.519398); Australia, NSW, Central Eastern CMR (− 30.098°S, 153.870°E), IN2017_ V03 _086, 2429–2518 m, 1 wet (AMS C.482289); AIOT, Christmas Island SE (− 10.556°S, 105.764°E), IN2021_ V04 _007, 3200– 3345 m, 1 wet (AMS C.593511). Etymology In reference to its (supported by molecular data) occurrence in at least two separate marine realms (#13 and #16 of Costello et al. 2017), derived from ‘trans’ (Latin = across) and ‘regnum’ (Latin = realm). Plural of composite noun of neuter gender and nominative case in apposition. Description Shell fusiform, moderately thin. Protoconch eroded. Teleoconch white, suture impressed. Whorl profile medium broad, with wide, lightly concave, oblique subsutural ramp, moderately demarcated from whorl periphery. Lower portion of whorl subcylindrical. Subsutural ramp sculpture of dense arcuate growth lines, reflecting shape of anal sinus, and dense spiral cords, more or less evenly covering entire whorl, including last adult whorl (which contains approximately 70 cords; difficult to count with precision due to significant erosion); intermittent grooves about half width of cords. Teleoconch axial sculpture of distinct but eroded opisthocline ribs below subsutural ramp (20 on last whorl), most prominent at shoulder, then weakening, progressively becoming subobsolete towards suture; microsculpture of growth lines. Last adult whorl shouldered, more or less evenly convex below shoulder, gradually tapering towards mildly attenuated siphonal canal. Aperture elongated, nearly half of total shell length; outer lip thin, unsculptured. Inner lip with distinct white callus, with spiral cords not extending onto rather straight columella. Anal sinus wide, moderately shallow, U-shaped. Anatomy (based on paratype AMS C.519398): animal cream; cephalic tentacles short, cylindrical; eyes not recorded. Penis moderately large, cylindrical. Testis and prostate extremely well-developed. Proboscis relatively small; radular sac large, elongate; venom gland very large, long, convoluted, situated obliquely and rather anteriorly in rhynchocoel and almost parallel with proboscis; muscular bulb large, bean-shaped, pearlescent. Radula of hypodermic teeth, loosely rolled, up to approximately 350 µm in length, relatively straight; two barbs, comparatively blunt, with extremely elongated adapical opening (about half length of tooth) situated posterior to barb most adjacent to tip; basal swelling moderately broad, texture rough; basal opening large, unconstricted. Remarks Pontiothauma transregna sp. n. can be differentiated from P. mirabile by the significantly larger size of the latter (cf. Figure 5L), with the latter also possessing a deeper suture and more prominent spiral cords than the former. It can be distinguished from P. pacei in that the latter has a wider subsutural ramp (more or less half the height of the whorl; see Figure 5J), a more angulated, clearly defined shoulder, a wider spire, and more prominent axial ribs. Pontiothauma transregna has a wide distribution, with molecular evidence of a range spanning at least from Christmas Island in the AIOT to southeastern Australia (Figure 1). While it is likely contiguous in its distribution between these two known regions, it has not yet been recorded from any other Australian deep-sea cruises in which other raphitomids have been found (see Criscione et al. 2021, 2021b; Hallan et al. 2021, 2021a). It occupies a known bathymetric range of ~ 2430–3350 m, and is potentially bathymetrically partitioned from P1, which has a known range of ~ 3780– 4480 m (Figure 7).