Caecum galapagoense, Raines, 2020

Raines, Bret K., 2020, A Rosetta Stone for eastern Pacific Caecidae (Gastropoda: Caenogastropoda), Zootaxa 4827 (1), pp. 1-146 : 133-134

Caecum galapagoense species novum

Figures 117 A–H, 118A–M, 119A–B, 128B

Type material. Holotype, LACM 3754 ; paratypes, LACM 3755 (6 figured, 4 unfigured); SBMNH 637744 (3 figured, 1 unfigured); SBMNH 637745 (5 unfigured).

Additional material examined. NHMLAC: LACM 1984 - 47.16 , Academy Bay , Indefatigable Island, Galapagos Islands, Ecuador, intertidal to 1 m, 10 sh ; LACM 1972 - 196.28 , Espinoza Point , Fernandina Island, Galapagos Islands, 15–30 m, 8 sh . SBMNH: SBMNH 637744 , Cousins Rock , Galapagos Islands, Ecuador, 17–20 m, 1 sh ; SBMNH 618589 , Española Island (Hood), Galapagos Islands, Ecuador, 18 m, 7 sh ; SBMNH 637745 , Cormorant Point , Floreana Island, Galapagos Islands, Ecuador, intertidal, 2 sh .

Type locality. Academy Bay , Indefatigable Island, Galapagos Islands, Ecuador .

Diagnosis. Teleoconch subcylindrical, with slight increase in diameter from posterior end to aperture. Surface translucent white, glossy, sculptured with orange peel texture. Axial ribbing present posteriorly, which becomes obsolete. Septum mucronate, with low rounded mucro.Apertural end with 3–4 well-defined axial ribs. Periostracum thin, translucent brown.

Description. Protoconch unknown.Teleoconchs I and II without obvious separation ( Fig. 118A ), surface smooth ( Fig. 118B ), transition to teleoconch III marked by slight incised axial line ( Fig. 118A ). Teleoconch III sculptured with weakly-developed axial ribs ( Fig. 118C ), transition to teleoconch IV marked by incised axial line, followed by change in sculpture ( Figs. 118A, C ). Teleoconch IV with better developed axial ribs than previous stage ( Fig. 118G ), torqueing of tube may be present ( Fig. 117F ), transition to teleoconch V marked by suture, followed by increase in diameter ( Figs. 118D, F ). Teleoconch V axial ribs present posteriorly and aperturally, obsolete centrally ( Figs. 118H , J–K), transition to teleoconch VI marked by suture, followed by increase in diameter ( Fig. 118J ). Teleoconch VI (last growth stage) average size for genus [Tol 2.52–2.85 mm], larger than previous stage, tubular, mildly and regularly arched [Larc: 0.90–0.99 mm; Arc: 0.19–0.20 mm], subcylindrical, translucent white ( Figs. 117 A–C). Axial sculpture present posteriorly, comprised of rounded, closely arranged ribs, which become obsolete centrally ( Figs. 118 L–M). Axial interspaces shallow, narrower than ribs except those preceding aperture, which become wider ( Figs. 118 L–M). Surface with weak orange peel texture, glossy ( Figs. 117B , 118I ). Posterior [Dpe: 0.44–0.45 mm] with thin edge, rounded to squared shoulder ( Fig. 117E ). Septum mucronate, inflated ( Figs. 117 A–D). Mucro low rounded point, positioned on dorsal margin ( Figs. 117B, E ). Aperture [Da: 0.59–0.61 mm] with 3–5 well-defined axial ribs ( Figs. 118 L–M). No varix. Lip smooth, with slightly deflected peristome ( Fig. 117E ). Periostracum thin, smooth, translucent brown ( Fig. 117A ). Operculum thin, light brown; exterior surface with 7–8 concentric rings ( Figs. 117 G–H). Conceptual reconstruction of growth stages shown in Fig. 119A .

Etymology. The species is named after the type locality.

Distribution and Habitat. Currently only known from the Galapagos Islands. Intertidal, to 20 m. Uncommon on coarse sand and rocky substrates.

Remarks. Late stage subadult Caecum galapagoense can be mistaken for worn C. venustum . However, the larger size, axial ribs, weak orange peel microsculpture, and growth morphology of C. galapagoense easily separate it from C. venustum . Caecum semicinctum is the only other comparable species. Although C. semicinctum has axial ribs both posteriorly and aperturally, they are more pronounced than C. galapagoense . The surface of C. semicinctum is also completely smooth.

Figures

FIGURE 117. Caecum galapagoense sp. nov. A. Paratype, profile view with periostracum (SBMNH 637744). B. Paratype, profile view without periostracum (LACM 3755). C. Holotype, profile view (LACM 3754). D. Paratype, profile view (LACM 3755). E. Paratype, ventral view (LACM 3755). F. Paratype, subadult ventral view (LACM 3755). G. Operculum, exterior surface (LACM 3755). H. Operculum, interior surface (LACM 3755).

FIGURE 118. Caecum galapagoense sp. nov. shells at different growth stages. A. Teleoconchs I to IV (LACM 3755). B. Surface of teleoconchs I to II (LACM 3755). C. Surface of teleoconch III (LACM 3755). D. Teleoconchs III to V (LACM 3755). E. Teleoconch IV (LACM 3755). F. Teleoconchs IV to V (SBMNH 637744). G. Surface of teleoconch IV (SBMNH 637744). H. Surface of teleoconch V (SBMNH 637744). I. Surface of teleoconch VI (LACM 3754). J. Teleoconchs V to VI (SBMNH 637744). K. Teleoconch V (LACM 3755). L. Teleoconch VI (SBMNH 637744). M. Teleoconch VI (LACM 3754).

FIGURE 119. Caecum galapagoense sp. nov. A. Conceptual reconstruction of growth stages. B. Species distribution map.