Caecum wakense, Raines & Vannozzi, 2024

Raines, Bret K. & Vannozzi, Angelo, 2024, Caecum wakense: a new Caecidae (Gastropoda: Caenogastropoda) from Wake Atoll (Pacific Ocean), Zootaxa 5496 (1), pp. 147-150 : 147-148

Caecum wakense sp. nov.

Figures 1A–D , 2A–C

Type material. Holotype, LACM 2905 ; Paratype lot, LACM 2906 , 2 shells .

Type locality. Along the western coastline of Wake Atoll, sublittoral zone .

Etymology. This species is named for the type locality, Wake Atoll.

Distribution. Currently known only from Wake Atoll at 20 to 30 m.

Description. Protoconch paucispiral (about 1.2 whorls), planispiral, smooth, transition to teleoconch I marked by pronounced sinuous line ( Figs 1A , 2A ). Teleoconchs I and II short, surface smooth except for faint longitudinal microsculpture ( Fig 2B ), transition to teleoconch III marked by very slight axial line ( Figs 1B , 2A ). Teleoconch III surface smooth except for fine longitudinal microsculpture and occasional axial growth striae, transition to teleoconch IV marked by incised axial line ( Figs. 2A, C ). Teleoconch IV small for genus [Tol 1.4–1.6 mm], tubular, thin, narrow, moderately and regularly arched [Larc: 0.48–0.52 mm; Arc: 0.13–0.14 mm], subcylindrical, semi-translucent ( Figs. 1A–B ). Surface with axial growth striae, and occasionally fine longitudinal microsculpture is visible, especially on ventral side ( Fig. 2C ). Posterior [Dpe: 0.23–0.24 mm] with squared shoulder ( Figs. 1A–B ). Septum low, slightly recessed, without mucro ( Figs.1 A–B ). Aperture [Da: 0.33–0.35 mm] slightly inflated, with two fine annuli. No varix. Lip smooth. Periostracum not observed. Operculum and soft animal unknown. A conceptual reconstruction of the growth stages is shown in Fig. 2 .

Remarks. Caecum succineum de Folin, 1880 , which occurs throughout the entire Indo-West Pacific, is similar due to its small size, smooth tube and low dome-shaped septum. However, it is characterized by the presence of several clear rings close to the aperture and a microsculpture of fine collabral rings due to the periostracum, while no longitudinal striation is observed ( Pizzini et al. 2013; Vannozzi 2023). Caecum japonicum ( Habe, 1978) from Japan and the Indo-West Pacific is easily distinguished due to the color pattern, which is unusual for the family, including annular or zigzag stripes, although colorless specimens do occur ( Pizzini et al. 2013). However, it can be also distinguished due to the tapering apex, the inclination of both aperture and cutting plane, as well as the swelling in the last part of the tube preceding the aperture. Caecum dakuwaqa Pizzini, Raines & Vannozzi, 2013 from Fiji, Vanuatu and northeastern Papua New Guinea has a bell-shaped aperture and a clearly twisted tube. Caecum subcylindratum Pizzini, Raines & Vannozzi, 2013 from Vanuatu has a clearly subcylindrical teleoconch and a thick shell. Caecum lapita Pizzini, Raines & Vannozzi, 2013 from Fiji, northeastern Papua New Guinea and north Sulawesi has a similar smooth tube and recessed septum but the aperture is bell-shaped ending with a few strong annuli. Caecum bathus Pizzini, Raines & Vannozzi, 2013 from New Caledonia, Fiji and French Polynesia has a slender shell with bell-shaped aperture and worm-like microsculpture. Caecum neoguineanum Vannozzi, 2019 is different due to the more recessed septum and the aperture having a broad swelling lacking the annuli. Caecum frugi Vannozzi, 2019 from northeastern Papua New Guinea has a shorter tube, dome-shaped septum with low mucro and a granulated periostracum. Caecum restrictum Vannozzi & Renda, 2024 has a shorter tube and a swelling before the aperture with very fine and even annuli. Caecum miliarium Vannozzi & Renda, 2024 has a similar overall aspect but has a multispiral protoconch and a microsculpture of longitudinal furrows visible throughout the teleoconch. Caecum lozoueti Vannozzi & Renda, 2024 has dome-shaped, slightly recessed septum, a conspicuous longitudinal microsculpture and a simple aperture. Caecum temporale Vannozzi & Renda, 2024 is shorter, with a slight but clear swelling just before the aperture and the persistence of parts of the temporary septum.

Further comparisons can be made with two species never recorded after their description. Caecum crystallinum de Folin, 1880 from Hawaii was described from a fragmentary specimen without an apex, therefore the morphology of the septum is unknown. The holotype has a slight swelling before the aperture without annuli and a clear worm-like microsculpture throughout the tube. Caecum maori Pizzini & Raines, 2006 described from Kermadec Islands. Caecum maori has a sculpture of fine, somewhat irregular rings, not visible in the new species. Furthermore, Oliver’s description mentions the presence of a hemispherical septum with abrupt shoulder at the junction of the shell, likely alluding at the occurrence of a mucro, absent in the new species.

Figures

FIGURE 1. Caecum wakense sp. nov.: A–B. Holotype, LACM 2905, C–D. Paratypes, LACM 2906.

FIGURE 2. Conceptual reconstruction of growth stages of Caecum wakense sp. nov.: A. Protoconch to teleoconch IV. B. Surface of teleoconchs I and II. C. Surface of teleoconchs III and IV. White dots indicate transition points.