Caecum subaustrale Stuardo, 1970

Figures 87 A–G, 88A–J, 89A–B, 127F

Caecum (Micranellum) subaustrale Stuardo, 1970: 183, figs. 1b, 2b–c, holotype, Los Vilos, Provincia de Coquimbo, Chile (lost).

Caecum subaustrale — di Geronimo et al. 1995: 116, fig. 7; Mattano & Zelaya 2013: 170.

Material examined. In addition to the type material the following lots were examined. NHMLAC: LACM 1975 - 46.9, Chiloe Island, Los Lagos Prov., Chile, 3–7 m, 3 sh; LACM 1975 - 10.13, Iquique, Tarapaca Prov., Chile, intertidal, 3 sh; LACM 1975 - 28.14, Los Molles, Aconcagua Prov., Chile, intertidal, 5 sh; LACM 1975 - 37.8, Mehuin, Valdivia, Los Rios Prov., Chile, intertidal, 6 sh; LACM 1975 - 30.13, Montemar, Valparaiso Prov., Chile, 3–8 m, 20 sh.

Original diagnosis. “Concha tubular, curvada, con un díametro menor en el extremo septal, de color blanquecino-amarillenta, opaca, con períostraco de color amarillo-café claro. Escultura en los adultos formada por 44 a 59 anillos bajos (50 en el holotipo), algo aplastados, y separados por interspacios más estrechos casi rectangulares. Parte anterior del tubo más o menos expandida debido a la fusion de un número variable de anillos; estos son más estrechos en el lado concavo que en el convexo. Abertura circular. Septo generalmente erosionado, bastante elevado hacia el borde convexo de la concha y rodeado por un reborde poco elevado.” Stuardo (1970: 183).

Description. Protoconch multispiral (about 2.0 whorls), planispiral, smooth (Fig. 88A), transition to teleoconch I marked by well-defined apertural varix (Fig. 88A). Teleoconch I short, sculptured with axial bands of irregular reticular sculpture (Fig. 88B), transition to teleoconch II marked by change in sculpture (Fig. 88A). Teleoconch II about two times length of teleoconch I, sculptured with weak axial ribbing crossed by irregular longitudinal sculpture (Fig. 88C), transition to teleoconch III marked by incised line (Figs. 88A, D, F). Teleoconch III sculptured with low, rounded, axial ribbing and longitudinal striae in interspaces (Fig. 88E), transition to teleoconch IV marked by suture (Fig. 88F). Teleoconch IV sculptured with numerous, thin, longitudinal lines in interspaces of strong axial ribs (Fig. 88H). Teleoconch IV transition to teleoconch V marked by suture (Fig. 89A). Teleoconch V (last growth stage) average size for genus [Tol 2.37–2.56 mm], larger than previous stage, tubular, moderately and regularly arched [Larc: 0.76–0.86 mm; Arc: 0.19–0.26 mm], subcylindrical with slight increase in diameter from posterior to aperture, brilliant opaque white to tan (Fig. 87B). Surface sculptured of 40–60 low, flattened, wide, axial ribs (Fig. 88J). Axial interspaces narrow, shallow, with longitudinal striae varying in degree from quite pronounced to nearly obsolete; narrower closer to the apertural end (Fig. 88I). Posterior [Dpe: 0.42–0.44 mm] with moderately thick edge, squared shoulder (Fig. 87C). Septum mucronate, somewhat flattened (Fig. 87C). Mucro with rounded point, positioned on dorsal margin (Fig. 87C). Aperture [Da: 0.56–0.61 mm] with slight flare in diameter followed by abrupt constriction (Fig. 87J). No varix. Lip smooth, with well-developed deflected peristome (Fig. 87C). Periostracum thin, smooth, yellowish to light brown (Fig. 87A). Operculum thin, light brown; exterior surface with 5–6 concentric rings (Figs. 87 D–E). Conceptual reconstruction of growth stages shown in Fig. 89A.

Distribution and Habitat. From Iquique, Chile to Chiloe Island, Chile. Intertidal to 10 m. Uncommon on organogenic sand substrates.

Remarks. The illustration of Caecum subaustrale shown herein (Fig. 87G) is from Stuardo (1970). Sometime during the 1970s and 1980s, the holotype was transferred to MNHNCL. However, the museum has no record of it, and the holotype is now considered lost. In addition, the 100 paratypes mentioned by Stuardo (1970: 184) cannot be located at MZUC. Given that both the holotype and all paratypes of C. subaustrale are either lost or missing, a neotype is herein designated for taxonomic stability (LACM 3759, Fig. 87F).