Caecum restrictum, Walter & Renda, 2024

Walter, Angelo Vannozzi & Renda, Walter, 2024, Sampling the depth: New data on the Caecidae (Mollusca, Gastropoda) from northeastern Papua New Guinea, Zoosystema 46 (14), pp. 327-347 : 334-335

Caecum restrictum n. sp.

( Fig. 4 )

urn:lsid:zoobank.org:act:73675C26-F3E9-4D3A-A4A9-828A4C35CAC0

TYPE MATERIAL. — Holotype. Papua New Guinea • sh (length 1.9 mm, Fig. 4 A-D); New Ireland, KAVIENG 2014 Stn DW4486; 2°28’S, 149°54’E; 272-276 m depth; 5.IX.2014; MNHN-IM-2000-38944 . Paratypes. Papua New Guinea • 2 sh worn; same data as for holotype; MNHN-IM-2000-38945 .

TYPE LOCALITY. — Pacific Ocean, Papua New Guinea, New Ireland, 2°28’S, 149°54’E; 272-276 m depth.

OTHER MATERIAL EXAMINED. — Papua New Guinea • 1 sh; Off Bougainville; 5°02’S, 154°29’E; 615-632 m depth; 13.X.2010; BIOPAPUA Stn DW3754; MNHN .

DISTRIBUTION. — Known from northeastern PNG (western New Ireland and eastern Bougainville Island).

ETYMOLOGY. — The specific epithet is derived from the Latin adjective restrictus (restricted) to indicate the adapically constricted tube. The epithet alludes also to the restricted distribution of the species.

DESCRIPTION

Shell small for the genus, tubular, smooth, colourless, semitransparent. Protoconch unknown. Teleoconch tubular, arched, almost smooth. Early teleoconch unknown. Adult shell tubular, cylindrical, clearly tapering close to the apex, straight in ventral view. Surface smooth. Microsculpture of evenly-spaced growth lines defining fine flat rings visible in the abapical half. Macula none detected. Aperture preceded by a strong varix-like swelling crossed by coarse growth lines, then contracting and ending with a fine reflected lip. Septum low dome shaped without mucro, slightly recessed below the cutting plane. Traces of temporary septum visible at the boundary of the septum with the tube. Periostracum none detected. Operculum and soft parts unknown. Holotype: length 1.9 mm, max diam 0.4 mm, min diam 0.3 mm.

REMARKS

This species is known from a few specimens. The two paratypes, originating from the type locality, although smaller and worn, display the characters shown by the holotype and have been designated accordingly.

Caecum restrictum n. sp. can be compared with C. succineum de Folin, 1880 , C. biomaglo Vannozzi, 2023 and C. iricolor Vannozzi, 2023 , all of them showing smooth shells with dome-shaped septum without mucro. Caecum succineum , described from Cape York, NE Australia, but recorded throughout the IWP, is smaller and slenderer, is not clearly constricted close to the apex and shows several rings close to the aperture. Caecum biomaglo , described from Mayotte, is larger and stouter and shows a longitudinal microsculpture. Caecum iricolor , also described from Mayotte, is larger and shows a slightly twisted iridescent tube, sometimes with longitudinal grooves.

Figures

FIG. 4. — Caecum restrictum n. sp.: A-D, holotype MNHN-IM-2000-38944; E, F, paratypes MNHN-IM-2000-38945 from type locality; G, specimen from Stn DW3754 (MNHN). Scale bar: 1 mm, details not to scale.