Caecum iricolor n. sp.

(Figs 2 E-H; 4 A, B; 5 A, B)

urn:lsid:zoobank.org:act: 4FFA7AA6-0863-48AB-ACF1-451AD99D0347

TYPE MATERIAL. — Holotype. Mayotte • dd (length 2.33 mm, Figs 2 E-F, 4A and 5A); Mozambique Channel, W Mayotte, BIOMAGLO Stn DW4854; 12°56’S, 44°58’E; 455-465 m depth; 4.II.2017; MNHN-IM-2000-38696.

Paratypes. Mayotte • 1 dd; same data as for holotype; MNHN-IM-2000-38697 • 3 dd; Mozambique Channel, NW Mayotte, BIOMAGLO Stn DW4860; 12°31’S, 44°55’E; 486-646 m depth; 5.II.2017; MNHN-IM-2000-38699 .

TYPE LOCALITY. — Indian Ocean, Mozambique Channel, W Mayotte, 12°56’S, 44°58’E, 455-465 m depth.

OTHER MATERIAL EXAMINED. — Îles Éparses • 1 dd; Mozambique Channel, Banc du Geyser, BIOMAGLO Stn DW 4789; 12°22’S, 46°25’E; 340-342 m depth; 22.I.2017; MNHN.

Mayotte • 1 dd (fragm); Mozambique Channel, NW Mayotte, BIOMAGLO Stn DW 4860; 12°31’S, 44°55’E; 486-646 m depth; 5.II.2017; MNHN • 2 dd; Mozambique Channel, S Mayotte, BIOMAGLO Stn DW 4826; 13°05’S, 45°07’E; 489-496 m depth; 27.I.2017; MNHN • 1 dd (fragm); Mozambique Channel, NE Mayotte, BIOMAGLO Stn DW 4871; 12°44’S, 45°19’E; 462-486 m depth; 8.II.2017; MNHN .

DISTRIBUTION. — Known only from Mayotte and Banc du Geyser.

ETYMOLOGY. — Derived from Latin adjective iricolor due to the iridescent appearance of the surface.

DESCRIPTION

Shell of average size for the genus, tubular, smooth, colourless, semitransparent, iridescent.Tube cylindrical, gradually tapering toward the apex. In ventral view, tube appearing slightly dextrally twisted. Surface covered by fine growth lines, sometimes showing shallow wavy longitudinal grooves. Macula absent. Aperture somewhat inclined, preceded by a distinct swelling forming a rounded varix crossed by growth lines, then contracting and ending with a clearly reflected lip. Septum dome shaped without mucro, lying on the cutting plane. Traces of temporary septum visible at the boundary of the septum with the tube. No traces of periostracum detected. Young stages, protoconch, operculum and soft parts unknown. Holotype: length 2.33 mm, max diam 0.44 mm, min diam 0.33 mm.

REMARKS

Caecum iricolor n. sp. is very similar to C. biomaglo n. sp. and may at first sight be confused with it. However, C. iricolor n. sp. is more fragile and is easily distinguished due to the more slender shape of the tube, slightly twisted and more gradually tapering toward the apex, the smaller and more protruding septum and the more gently rounded swelling and more clearly reflected lip. Furthermore, C. biomaglo n. sp. shows a fine longitudinal microsculpture (Fig. 4), while C. iricolor n. sp. has no true microsculpture apart from growth lines and only longitudinal shallow wavy grooves occasionally occur.

Caecum iricolor n. sp. is also similar to C. succineum, which however is much smaller and shows several distinct rings in the abapical portion of the tube.

Iridescence of the tube is not unique to C. iricolor n. sp. and occurs in several other species of Caecum, all sharing a smooth and colourless tube, e.g., C. glabrum (Montagu, 1803), C. subannulatum de Folin, 1870, C. subcylindratum Pizzini, Raines & Vannozzi, 2013, C. maraisi Vannozzi, Pizzini & Raines, 2015 and C. biomaglo n. sp.