Leucosyrinx derzellei Kantor, Fedosov & Puillandre, 2025, sp. nov.

Leucosyrinx derzellei sp. nov. urn:lsid:zoobank.org:act: A6BBDEE8-3B6A-4DBC-A96A-038324A0E155 Figs 5F, 8A–F Etymology The species is named after Alessandro Derzelle, member of the ERC “HYPERDIVERSE” team, for his contribution to the analysis of neogastropod genomes. Material examined Holotype (sequenced) SOUTH MADAGASCAR • 25°43′ S, 44°24′ E; depth 729–732 m; ATIMO VATAE, stn CP3597; MNHN-IM-2009-14986. Other material (all sequenced) NORTH-WESTERN MADAGASCAR • 1 lv; off Majunga; 15°25′ S, 45°55′ E; depth 943–950 m; MIRIKY, stn CP3253; MNHN-IM-2009-16918. SOUTH MADAGASCAR • 2 lv; 25°35′ S, 44°15′ E; depth 821–910 m; ATIMO VATAE, stn CP3595; MNHN-IM-2009-14814, MNHN-IM-2009-14833 • 3 lv; same data as for holotype; MNHN-IM-2009-14817, MNHN-IM-2009-14819, MNHN-IM-2009-14984. Description MEASUREMENTS (holotype). SL 33.3 mm, AL (with canal) 13.2 mm, AL (without canal) 8.6 mm, SW 10.5 mm. SHELL (holotype). Shell medium-sized, thin, fusiform, with high spire, tan in color, with slightly darker band on shoulder and lighter shell base and canal. Slightly over 10 teleoconch whorls. Paucispiral, of about 1.75 evenly rounded and microshagreened whorls protoconch. Protoconch-teleoconch transition indistinct, marked by emergence of shoulder keel, smooth initially but soon acquiring axial folds. Teleoconch whorls roundly angled at shoulder, with distinctly concave subsutural ramp. Shallow, impressed, and slightly wavy suture. 14 strong, oblique, broad, and rounded axial folds on shoulder of last whorl and 13 on penultimate whorl. Folds fade on subsutural ramp, strongly weaken towards lower suture, rapidly disappear on whorl periphery. Folds more closely spaced on five upper teleoconch whorls, on last whorl intervals between folds slightly broader than folds. Relatively distinct spiral sculpture is of low, rounded, and narrow cords over entire shell. On subsutural ramp and shoulder cords more closely spaced, with intervals narrower than cords themselves, broader spaced on shell base and canal, with intervals exceeding width of cords. Numerous thin, prominent on subsutural ramp growth lines. Shell base weakly curving, smooth transition to long and straight canal. Narrow, elongate-oval aperture, poorly differentiated from canal. Inner lip slightly convex. Columellar and parietal sides with narrow, distinct callus, slightly lighter than remaining part of last whorl. Moderately deep, subsutural, broadly arcuate anal sinus extends across subsutural ramp, confluent with large forward extension of outer lip. Lower margin of the sinus parallel to shoulder. RADULA (Fig. 5F; studied in MNHN-IM-2009-14833). Radula short, comprises around 25 rows of teeth, 8 nascent. Marginal teeth duplex, ~310 µm (2.6 % AL without canal). Major limb narrow lanceolate in dorsal view, curved. Accessory limb relatively broad, constitutes half of tooth width, ~0.75 of total tooth length, inserted into distinct deep socket on dorsal side of major limb. DNA diagnosis (based on 7 cox 1 sequences) ‘G’ in site 49, ‘A’ in site 307, ‘G’ in site 382, ‘A’ in site 554. Remarks The species is moderately variable in shell shape, length of the canal and degree of development of the axial folds. It is most similar to sympatric Leucosyrinx legalli sp. nov., differing in a relatively shorter canal and a higher spire. It is also very close to Leucosyrinx sp. 15 from the Philippines. None of the similar species is phylogenetically closely related to L. derzellei sp. nov. There is a certain similarity with Leucosyrinx melvilli (Schepman, 1913) from 918 m in Indonesia. The new species differs in a smaller size (35.8 vs 62 mm), less numerous axial folds (14 vs 22 on the last whorl) and a more angular shoulder. From sympatric L. madagascarensis, the new species differs in a slenderer shell with a less bulging shoulder as well as in less pronounced and more numerous spiral cords. Distribution From north-western to southern Madagascar, 729– 943 m.