Extension of the genus Pseudopeas ( Dysopeas ) ( Gastropoda : Subulinidae ) from Venezuela to Nicaragua

The study of Nicaraguan land snails is fragmentary. Recent sampling produced specimens of an undetermined species of Pseudopeas Putzeys, 1899. This genus was segregated from Opeas Albers, 1850 by reason of its prominent rib sculpture and later re-described by Pilsbry (1906) for the characteristic spiral sculpture of its nepionic whorls. Baker (1927) named a new subgenus Dysopeas for species where the spiral sculpture covers the entire shell, not only the nepionic whorls. The Nicaragua specimens show nepionic and body sculptures that precisely match descriptions and illustrations given by Pilsbry and Baker for the complex Pseudopeas/Dysopeas. Since 1999, a total of 160 specimens have been collected from El Castillo on Río San Juan, Isletas de Granada and the Universidad de las Regiones Autónomas de la Costa Caribe Nicaragüense (URACCAN) in Bluefields. Similitude with some sculpture traits and protoconch development with species of Spiraxidae, Subulinidae or Lamellaxis might cause confusion in the determination of Pseudopeas. Besides the critical protoconch sculpture and profile, additional discriminatory differences from these look-alikes are dimensions, sculpture pattern and crystalline structure.

The study of Nicaraguan land snails is fragmentary.Since the year 1992 some 160 specimens of a small Opeaslike gastropod have been collected in Nicaragua that correspond to Baker's description of genus Pseudopeas (Dysopeas) with spirals extended to all whorls.The first site was at El Castillo on the San Juan River in Southern Nicaragua, among volcanic building blocks, dislodged from the castle ramparts (López, 1992).A second location was at the Isletas, a group of islands in Cocibolca (Nicaragua) Lake near the town of Granada and a third on the Campus of the URACCAN university by the town of Bluefields on the Caribbean coast (Table 1).
Collecting was done in humid surroundings, close to bodies of water among gravel and sandy soil, under stones or wood debris (López 1992;López & Pérez 1996, 1998;López, & Urcuyo, 2009).Surrounding soil was gathered in bags for later observation under a stereoscope (NIKON, SMZ-10A) to detect minute specimens and accompanying fauna.Live specimens were placed in 70% Lots recorded in ACCESS tables are numbered by two digits separated by a colon, the first digit for the year and the second for the order of sequence in that year.Thus, 92:02 is the second lot found in 1992.Each entry also contains the number and dimensions of specimens, location coordinates and date, as well as other details.
• Two voucher spms sent to LACM.
According to Pilsbry (1906) the presence of the characteristic spiral protoconch sculpture sufficiently determines his genus Pseudopeas.Baker's additional condition (1927) that the protoconch spiral sculpture extends over the remaining whorls also sufficiently determines his subgenus (P.) Dysopeas.The difference between the two is not a different protoconch sculpture, but only that in Dysopeas the characteristic spirals extend beyond the initial whorl onto the body whorls.And the reason why this protoconch spiral sculpture is necessary and sufficient for determination of the complex Pseudopeas/ Dysopeas is simply that no other known genus has it.Pilsbry himself (1906) mentions that although on some specimens of Paropeas, like P. achatinaceum, there are two or three very weak protoconch spirals, they are actually only folds between whorls and not sculpture as in Pseudopeas (Naggs, 1994).
It has been objected that to date no previous mention has been made of the complex Pseudopeas/Dysopeas in Mesoamerica.This would seem to be a good reason in favor of a recent genus extension, as here reported.However the extension might not be so recent if one fails to observe the characteristic nepionic sculpture.A revision of private and public collections may well reveal specimens of Pseudopeas mislabeled Opeas, Subulina, Spiraxis, or Lamellaxis.
The nepionic sculpture of the Pseudopeas viviparum Miller protoconch is described by its author (1879) as of one whorl "minutely decussate", and by Pilsbry (1906) as one and a half whorls with very delicate, close, striate spirals.Pilsbry adds (1906) that Pseudopeas has a protoconch of some two whorls "spirally striate" and figures P. saxatile (Morelet, 1885) from West Africa (Fig. 2A) with typical apical sculpture of Pseudopeas, spiral and granulate.Although Pilsbry does not mention the granulation, it is clearly shown in his figure.Baker (1927) figures Dysopeas translucidum protoconch (Fig. 2B) and describes it as globose, of 2 to 2.5 convex whorls separated by a deep suture with a sculpture of very weak growth lines some 35 in number near the beginning of the second whorl.
Pseudopeas shares some sculpture traits and protoconch development with Spiraxidae like Micromena Baker 1939, Rectaxis Baker 1926 and even with Lamellaxis gracilis, which might cause confusion.In Pilbry's opinion the spirally striated protoconch firmly determines the genus Pseudopeas, without need of further criteria such as dissection or radula study, described as 13-1-13 by Baker (1927).Additional reasons like dimensions, body sculpture pattern, profile and crystalline structure further distinguish the complex Pseudopeas/Dysopeas from these look-alikes, such as Spiraxis funibus (Fig. 3B) and S. alvaradoi, both described from Guatemala by Goodrich & van der Schalie (1937), which are common and widely  (Baker, 1939) are also present in various localities.
One general difference between these small Spiraxidae and Pseudopeas is size, with Micromena barely reaching 3 mm and other Spiraxidae attaining 5 to 6 mm maximum length, whereas Pseudopeas grow to 8 mm.Another difference is that Spiraxidae protoconch spirals are dissected by the diagonal ribs into individual chevron-shaped segments, very characteristic of these species (Fig. 3B).In Pseudopeas the spirals are continuous, though slightly raised at intersections with ribs (Fig. 3A), thin and weak in Spiraxidae, but thick, sturdy, porcelain-like in Pseudopeas and other Subulinidae.Crystal structure seen in small punctures or corroded areas of Dysopeas specimens reveals it is formed by three successive layers of orthorhombic interlaced crystals (Fig. 4) which determine the tough aragonite material of the shell (Callil & Mansur 2005), in contrast with the weaker structure of Spiraxidae and Subulinidae.But as mentioned, the most important and definitive discriminating trait is the characteristic nepionic sculpture, (Fig. 2A, 2B), which is totally absent in Spiraxidae (Fig. 3B), Lamellaxis, Opeas and all other recognized genera.Independently of protoconch sculpture presence or absence, its profile also discriminates the genus.In Pseudopeas, it is dome-like, whereas in Spiraxis it is bulbous.