Caecum microannulatum, 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 : 332

Caecum microannulatum n. sp.

( Fig. 3 A-E)

urn:lsid:zoobank.org:act:EEB17B92-D0B7-4383-9D42-C84739FB9C9A

TYPE MATERIAL. — Holotype. Papua New Guinea •sh (length 1.27 mm, Fig. 3 A-D); New Ireland, KAVIENG 2014 Stn DW4464; 2°43’S, 150°36’E; 140-214 m depth; 3.IX.2014; MNHN-IM-2000-38948 .

TYPE LOCALITY. — Pacific Ocean, Papua New Guinea, New Ireland; 2°43’S, 150°36’E; 140-214 m depth.

OTHER MATERIAL EXAMINED. — Papua New Guinea • 1 sh (juv); same data as for holotype; MNHN .

Japan • 1 sh (ph); Okinawa, 1 km E of Onna Village ( Horseshoe South ); 26°29.7’N, 127°50.6’E; 43 m depth; B. Raines leg.; sand and coral rubble; LACM 1978-16.1 .

DISTRIBUTION.— Known from northeastern PNG and southern Japan.

ETYMOLOGY. — The adjective microannulatum is composted of the Greek µ ΙΚΡΌ (small) and Latin annulatus (ringed), due to the sculpture of the shell consisting of very small rings. The term µ ΙΚΡΌ also alludes to the small size of this species.

DESCRIPTION

Shell small for the genus, whitish, semitransparent. Protoconch unknown. Teleoconch tubular, slightly arched, with fine collabral rings. Early teleoconch conical. Adult shell cylindrical, tapering toward the apex, slightly dextrally twisted in ventral view. Surface covered by more than 60 collabral rings, separated by as-wide interspaces. Macula none detected. Aperture somewhat ventrally inclined, preceded by a strong varix-like swelling, crossed by faint annulations, then contracting and ending with a fine reflected lip. Septum low dome-shaped, bimamillated due to the presence of a strong, almost dorsal nail-like mucro, slightly lower than the septum. Periostracum none detected. Operculum and soft parts unknown. Holotype: length 1.27 mm, max diam 0.29 mm, min diam 0.22 mm.

REMARKS

A juvenile specimen ( Fig. 3E ), likely belonging to Caecum microannulatum n. sp., was found in the same station as the holotype and shows a clearly conical and twisted tube and an almost flat septum with pointed mucro, as usually shown by juveniles.

The new species can be compared with Caecum directum Vannozzi, 2019 , C. virginiae Pizzini, Raines & Vannozzi, 2013 and C. musorstomi Pizzini, Raines & Vannozzi, 2013 . C. directum , described from Kranket Island (Madang, PNG) shows a similar septum with strong almost dorsal nail-like mucro and a fine annulated sculpture. However, it differs by the larger size and more solid shell, the less prominent sculpture, the less curved tube and the very strong apertural varix which is oriented to the left side of the tube. C. virginiae , described from Fiji and reported from Kranket Is. ( PNG), shows a similar size as the new species. However, it differs by the subcylindrical tube, the finer annular sculpture consisting of more than twice the number of rings and a different shape of the septum. C. musorstomi , described from New Caledonia and reported from several localities in the SW Pacific, is slenderer, larger and shows a weaker and irregular annular sculpture, a narrower apertural varix and a lower septum with sharper mucro.

Figures

FIG. 3. — Caecum Fleming,1813 species from deep-water stations from northeastern PNG:A-D, Caecum microannulatum n. sp., holotype MNHN-IM-2000-38948; E, C. microannulatum n. sp., juvenile from type locality; F, C. musorstomi Pizzini, Raines & Vannozzi, 2013 from Stn DW4412, transitional growth stage. Scale bar: 1 mm, details not to scale.