Caecum lightfootanum, Raines, 2020

Raines, Bret K., 2020, A Rosetta Stone for eastern Pacific Caecidae (Gastropoda: Caenogastropoda), Zootaxa 4827 (1), pp. 1-146 : 126-128

Caecum lightfootanum species novum

Figures 108 A–F, 109A–G, 110A–B, 126J

Type material. Holotype: SBMNH 637734 ; paratypes: SBMNH 637735 (3 figured); SBMNH 637736 (3 unfigured).

Additional material examined. SBMNH: SBMNH 637737 , Playa Pocoma , Peru, intertidal, 30 sh ; SBMNH 100339 , San Pedro, Guayas, Ecuador, 6 sh .

Type locality. Playa Pocoma , Peru .

Diagnosis. Teleoconch subcylindrical, with increase in diameter from posterior end to aperture. Surface smooth, semi-translucent white in color. Septum mucronate, pronounced, but flattened and angled away from dorsal margin. Mucro low, heel-like, and usually covered by septum. Aperture rather ovate and oblique. No varix. Periostracum thin, smooth, translucent.

Description. Protoconch multispiral (about 2.2 whorls), planispiral, smooth ( Fig. 109A ), transition to teleoconch I marked by well-defined apertural varix ( Fig. 109A ). Teleoconch I short, sculptured with axial growth marks ( Fig. 109C ), transition to teleoconch II marked by incised axial line ( Fig. 109A ). Teleoconch II about two times length of teleoconch I, sculptured with numerous, very weak, thin growth lines ( Fig. 109E ), transition to teleoconch III marked by incised axial line, followed by increase in diameter ( Fig. 109A ). Teleoconch III with identical characters as previous stage, transition to teleoconch IV marked by slight incised axial line, followed by increase in diameter ( Fig. 109B ). Teleoconch IV smooth ( Fig. 109F ), transition to teleoconch V marked by slight incised axial line, followed by increase in diameter ( Figs. 109B , 110A ). Teleoconch V with identical characters as previous stage, transition to teleoconch VI marked by suture, followed by increase in diameter ( Fig. 110A ). Teleoconch VI (last growth stage) small for genus [Tol 1.45–1.80 mm], larger than previous stage, tubular, mildly and regularly arched [Larc: 0.43–0.60 mm; Arc: 0.09–0.10 mm], with increase in diameter from posterior to aperture, semi-translucent white ( Figs. 108 A–C). Surface smooth ( Fig. 109F ). Posterior [Dpe: 0.35–0.44 mm] with thick edge, squared shoulder ( Fig. 108D ). Septum mucronate, pronounced with flattened top, angled away from dorsal margin ( Fig. 108C ). Mucro low, heel-like, positioned on dorsal margin, usually covered by septum.Aperture rather ovate [Da: 0.40–0.50 mm], oblique, slightly constricted ( Fig. 108D ). No varix. Lip smooth ( Fig. 108D ). Periostracum thin, smooth, translucent ( Fig. 108A ). Operculum thin, light brown; exterior surface with 5–7 concentric rings ( Fig. 108F ). Conceptual reconstruction of growth stages shown in Fig. 110A .

Etymology. The species is named in honor of the late Joanne Lightfoot (1930 – 1993), for her lifelong work on Caecidae .

Distribution and Habitat. From Playa Pocoma, Peru to San Pedro, Guayas, Ecuador. Intertidal. Common on coarse sand substrates near the type locality, less so farther north.

Remarks. The apertural end of Caecum lightfootanum is rather ovate, and is especially noticeable in early stages and subadults. There is no doubt that with only casual observation C. lightfootanum could be mistaken for its most similar congener C. orcutti . However, the smoother sculpture, ovate aperture shape, and growth morphology of C. lightfootanum is quite different. Furthermore, the closest population of C. orcutti is over 4,800 km away and ocean currents do not support its dispersal or distribution to South America. There are also no fossil records that would suggest an earlier connection.

Cruz (2007) reported a species he referred to as Caecum cf. orcutti from Ecuador. However, his description is more consistent with the smoother form of C. chilense . It could also be a subadult C. lightfootanum , but the illustration is not detailed enough to make that determination.

Figures

FIGURE 108. Caecum lightfootanum sp. nov. A. Profile view with periostracum (SBMNH 637735). B. Profile view without periostracum (SBMNH 637735). C. Holotype, profile view (SBMNH 637734). D. Paratype, ventral view (SBMNH 637735). E. Paratype, subadult transition, ventral view (SBMNH 637735). F. Operculum, exterior surface (SBMNH 637735).

FIGURE 109. Caecum lightfootanum sp. nov. shells at different growth stages. A. Protoconch and teleoconchs I to III (SBMNH 637735). B. Teleoconchs III to IV (SBMNH 637735). C. Surface of teleoconch I (SBMNH 637735). D. Teleoconch V (SBMNH 637735). E. Surface of teleoconchs II to III (SBMNH 637735). F. Surface of teleoconchs IV to VI (SBMNH 637734). G. Teleoconch VI (SBMNH 637734).

FIGURE 110. Caecum lightfootanum sp. nov. A. Conceptual reconstruction of growth stages. B. Species distribution map.