Abstract: The achatinellid Pacificella variabilis Odhner, 1922, is reported for the first time since its original description from its type locality, Easter Island (Rapa Nui), South Pacific Ocean, Chile. Specimens were found living on the bark of a lemon tree in Hanga Roa town and among the endemic grass Paspalum forsterianum on Motu Nui Islet. A redescription of the shell based on scanning electron microscopy (SEM) is provided. This represents the first report of the habitat of the species on Easter Island.

Keywords: Rapa Nui, redescription, type locality, Polynesia, scanning electron microscopy, snail

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Easter Island or Rapa Nui, the easternmost Polynesian island, has a notoriously depauperate terrestrial mollusk fauna, represented by only nine land snail species, all of them nonindigenous taxa (Naranjo-Garcia and Appleton 1998, Boyko and Cordeiro 2001, Araya 2015). A single documented land snail species belonging to a monotypic genus is considered endemic: the extinct Hotumatua anakenana Kirch, Christensen & Steadman, 2009. There is also evidence of several fossil land snail species present in the island, which remain undescribed (Kirch et al. 2009). Among the land snails described for Rapa Nui, Pacificella variabilis Odhner, 1922, was originally considered native to the island (Odhner 1922). However, further records of identical shells coming from several Pacific localities led Pilsbry and Cooke (1933) to determine that P. variabilis may not be native to outlying Polynesian islands such as Palmyra or Easter Island. A subsequent work by Cooke and Kondo (1961) presented several new records for P. variabilis and a rather extensive distribution for the species, including several islands of the Pacific. Pacificella variabilis is now recognized as the achatinellid species with the largest known distribution. Although this species has been listed in several inventories of the fauna of Rapa Nui (Cooke and Kondo 1960, Boyko and Cordeiro 2001, Kirch et al. 2009), it has not been found in field collections in the island since its original description by Odhner (1922). As part of ongoing studies reviewing Chilean terrestrial mollusks (Miquel and Araya 2013, 2015, Araya and Aliaga 2015), here we present the rediscovery of P. variabilis on Easter Island and a new record for the species on Motu Nui Islet; a detailed description by scanning electron microscopy (SEM) of shells of the type locality is provided.

MATERIALS AND METHODS

Specimens of P. variabilis were collected from the bark of a dead lemon tree from the town of Hanga Roa (32 specimens; August 2016) and by sweeping, with an entomological net, the endemic grass Paspalum forsterianum at Motu Nui Islet (two specimens; August 2012) (Figure 1). The search time on this last locality corresponded to approximately 2 hr. Voucher specimens from Hanga Roa were deposited at the Museo Nacional de Historia Natural (mnhncl 203428) in Santiago, Chile. Shell measurements were made using a dissecting microscope with up to 100x magnification, and the microscopic structures were measured and examined from scanning electron microscope (SEM) images.

RESULTS

Systematics

Order Stylommatophora Schmidt, 1855

Superfamily Pupilloidea Turton, 1831

Family Achatinellidae Gulick, 1873

Genus Pacificella Odhner, 1922...