Heleobia deserticola, Collado, Gonzalo A., 2015

Collado, Gonzalo A., 2015, A new freshwater snail (Caenogastropoda: Cochliopidae) from the Atacama Desert, northern Chile, Zootaxa 3925 (3), pp. 445-449 : 445-446

Species Heleobia deserticola sp. nov.

Holotype. ( MZUC 43067, Fig. 1A ). Collected by G.A. Collado from Aguada de Chorrillos, Chile (28 November 2011). Holotype measurements: SL 4.41 mm, SW 2.10 mm, AL 2.00 mm, AW 1.21 mm.

Paratypes. ( MZUC 43068–43077, Fig. 1B – K ). Snails from Aguada de Chorrillos, Chile, collected with the holotype by G.A. Collado. Morphometric data of the paratypes (n = 10): SL: 4.01 ± 0.31 (3.40 – 4.40); SW: 1.99 ± 0.13 (1.80 – 2.20); AL: 1.76 ± 0.19 (1.40 – 2.00); AW: 1.22 ± 0.15 (1.00 – 1.40); SW/SL: 0.50 ± 0.02 (0.46 – 0.53); AL/SL: 0.44 ± 0.04 (0.35 – 0.47); AW/AL: 0.07 ± 0.08 (0.61 – 0.86).

Description. Shell small, elongate – conic, thin, transparent, smooth, suture depth, closed umbilicus (imperforate). Adults with 6 to 7 convex whorls. Aperture ovate, outer lip thin. Operculum corneous, ovate, flat, thin, light brown, paucispiral ( Fig. 1L ). Foot, mantle and tentacles gray, head black, snout white, visceral sac yellow to light brown. Penis elongated, white – grayish; proximal portion with a wide base, with 5 – 6 cup – shaped apocrine glands on the border ( Fig. 1M – O ); distal portion tapers to an elongated conical tip. One or two additional aprocrine glands are located in the convex side of the penis.

Reproductive biology. This species is gonochoric, with direct development. Several individuals sampled in Aguada de Chorrillos bore single egg capsules attached to the shells with an embryo or a juvenile snail inside, depending on the stage of development ( Fig. 1P, Q ).

Type locality. Aguada de Chorrillos, a small spring located at the Pacific coast in the Atacama Desert, northern Chile ( Fig. 2 A, B), 5 m above sea level. The site is located several kilometers north of the mouth of the Copiapó River, which is separated from it by an arid desert. The water of the spring arises from the walls of a canyon about 10 m high that form pools ( Fig. 2 B) at the bottom of the ravine which eventually drains to the sea.

Distribution and habitat. The snails were collected from the small puddles of water (c. 10 cm depth) on soft substrate in the spring Aguada de Chorrillos. In November 2011 individuals of all size ranges from this locality were sampled.

Etymology. The name is a compound noun meaning desert dweller; it is derived from the area of origin of the new species.

Remarks. Heleobia deserticola sp. nov. can be distinguished from the other species of the genus by its particular penis morphology ( Fig. 1M – O ), including the wide portion of the base of the organ, several apocrine glands located around of the complete margin of the base and the additional aprocrine glands located in the convex side of the central portion of the organ. All these characters as a whole differentiate this species from other species of the group whose penis morphology is known (e.g. Hubendick 1955; Gaillard & de Castellanos 1976; Hershler & Thompson 1992; Collado et al. 2011; Ovando & De Francesco 2011; Collado 2012; Collado et al. 2013). The sister group of this species is an undescribed population from Carrera Pinto, northern Chile (Collado et al. 2013), a spring separated from Aguada de Chorrillos by over 100 km of arid desert. I did not treat these populations as conspecific because of differences in shell and penis morphology ( Fig. 1 R, S). The shell of the snails from Carrera Pinto has a band in the growing whorls not present in Heleobia deserticola sp. nov. while the penis has aprocrine glands only on the convex side of the base. The snails from Aguada de Chorrillos and Carrera Pinto belong to the clade including Heleobia transitoria ( Biese, 1947) , and a population from Quebrada El León in the Atacama Desert. These snails are not very close to Heleobia opachensis ( Biese, 1947) , Heleobia loaensis ( Biese, 1947) , Heleobia chimbaensis ( Biese, 1944) , Heleobia ascotanensis ( Courty, 1907) and Heleobia atacamensis ( Philippi, 1860) (Collado et al. 2013) described from northern Chile.

Comparison with the other Heleobia species. Heleobia deserticola sp. nov. fits well the morphological characteristics of the shell and penis of the genus as defined by Hershler & Thompson (1992), with the male copulatory organ possessing aprocrine glands. Additionally, the new species was also placed in the genus Heleobia based on a molecular phylogenetic analysis (Collado et al. 2013). Of the nominal species of Heleobia from northern Chile, Heleobia deserticola sp. nov. is the third representative described from the coast of the Atacama Desert after H. chimbaensis and H. transitoria . The shell of the new species is little differentiated morphologically from other regional congeners [see Collado et al. (2011), Collado (2012), Collado et al. (2013) for comparative purposes]. The closed umbilicus of the new species resembles that of H. atacamensis , H. loaensis , H. opachensis and H. transitoria . Heleobia deserticola sp. nov. has direct development, similar to the reproductive strategy employed by H. chimbaensis , Heleobia parchappii ( d’Orbigny, 1835) , Heleobia miaulis ( Marcus & Marcus, 1965) and Heleobia guaranitica ( Doering, 1885) ( Marcus & Marcus 1965; Gaillard 1973; Cazzaniga 1982; Collado & Méndez 2011); other species of Heleobia have indirect development (see Collado & Méndez 2011). The black pigmentation of the head of H. deserticola sp. nov. differs from that of Heleobia neveui ( Bavay, 1904) because the latter species in general is less pigmented ( Hubendick 1955). The gray pigmentation of the tentacles of H. deserticola sp. nov. differs from that of Heleobia compacta ( Haas, 1955) , Heleobia cumingii ( d’Orbigny, 1835) and Heleobia aperta ( Haas, 1955) from Lake Titicaca, which are almost black over all these structures ( Hubendick 1955). Heleobia is divided into two groups on the basis of the size ( Biese 1944, 1947). The group of Heleobia hatcheri ( Pilsbry, 1911) , which contains small species, with 4–5 shell whorls, and the group of H. parchappii , which contains larger forms, with 5–8 whorls. The new species belongs to the second group; adult individuals can reach up to seven whorls.

Heleobia deserticola sp. nov. is only known from the spring of Aguada de Chorrillos (Collado et al. 2013; present study). This oasis is an extremely small restricted habitat, surrounded by an arid desert and facing the sea. In northern Chile, several localities with populations of Heleobia are subjected to anthropogenic pressures, pollution or water scarcity ( Collado 2012). Recently, two species of Heleobia in the Atacama Desert, H. atacamensis and H. chimbaensis were declared Critically Endangered and Vulnerable, respectively ( Collado 2013a, b), according to the list of the threatened species of the Ministerio del Medio Ambiente, República de Chile. It is clear that some biological and population parameters need to be estimated by monitoring Heleobia deserticola sp. nov. because any alteration to the biotope could affect the population of these snails in Aguada de Chorrillos. There are currently no conservation measures for this particular place.

Figures

FIGURE 2. Aguada de Chorrillos, Atacama Desert, northern Chile, the type locality of Heleobia deserticola sp. nov. A. Panoramic view of the system, desert, beach and Pacific Ocean. B. Spring where the snails live.

FIGURE 1. A – Q. Heleobia deserticola sp. nov. A. Shell of the holotype (MZUC 43067). B – K. Shells of the paratypes (MZUC 43068 – 43077). L. Operculum (1.70 mm total length). M – O. Penes of three individuals (0.64, 0.70 and 0.90 mm total length, respectively). Operculum and penes were photographed from both sides. P, Q. Egg capsules of the new species. P. Egg capsules attached to the adult shells. Q. Pre – hatching capsule isolated with a shelled juvenile inside. R. Shell of an adult snail from Carrera Pinto (SL 3.51 mm, SW 1.55 mm, AL 1.35 mm, AW 0.97 mm. S. Penis of this individual (0.75 mm total length).