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Cuadernos de Investigación UNED

versión On-line ISSN 1659-4266versión impresa ISSN 1659-4266

Cuadernos de Investigación UNED vol.7 no.2 Sabanilla, Montes de Oca jul./dic. 2015

 

Articles

Extensionof thegenus Pseudopeas ( Dysopeas )(Gastropoda: Subulinidae) from Venezuela to Nicaragua

Adolfo López 1  

Janina Urcuyo 2  

Gabriel Vega 3  

1Universidad Centroamericana, Apdo. 69, Managua, Nicaragua; alosi@ns.uca.edu.ni

2Universidad Centroamericana, Apdo. 69, Managua, Nicaragua; janina@ns.uca.edu.ni

3Universidad Centroamericana, Apdo. 69, Managua, Nicaragua; gahiver77@hotmail.com

Abstract

The study of Nicaraguan land snails is fragmentary. Recent sampling produced specimens of an undetermined species of PseudopeasPutzeys, 1899. This genus was segregated from OpeasAlbers, 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 Dysopeasfor 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 Universidadde lasRegionesAutónomas 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.

Key words: Subulinidae; Pseudopeas ; Dysopeas ; genus extension; Nicaragua

Resumen

El estudio de moluscos continentales de Nicaragua es fragmentario. En el muestreo reciente se han colectado numerosos especímenes de una especie indeterminada del género PseudopeasPutzeys, 1899. Este es un género segregado de OpeasAlbers, 1850 debido a su escultura de cóstulas prominentes y posteriormente fue descrito de nuevo por Pilsbry (1906) dando prominencia a la escultura espiral característica de sus vueltas nepiónicas. Baker (1927) nombró un nuevo subgénero para ejemplares en los que las espirales de la protoconcha se extienden también por las restantes vueltas. Los especímenes de Nicaragua muestran perfil, escultura en la protoconcha y en las vueltas ulteriores que se ajustan exactamente a las descripciones e ilustraciones de Pilsbry y Baker para el conjunto Pseudopeas/Dysopeas. Desde el año 1999 se han colectado un total de 160 especímenes de este grupo en tres localidades: El Castillo de Río San Juan, las Isletas de Granada y el recinto de la universidad URACCAN de Bluefields, indicando una extensión bien establecida del género en el sur de Nicaragua. Su similitud con algunos rasgos de la estructura y desarrollo de la protoconcha con especies de Spiraxis, SubulinidaeoLamellaxispueden causar confusión en la determinación de Pseudopeas. Además de la característica escultura nepiónica, también son criterios de diferencia de género la escultura del cuerpo de la concha, su perfil, longitud y la estructura cristalina.

Palabras clave : Subulinidae; Pseudopeas ; Dysopeas ; extensión de género; Nicaragua

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).

Table 1: Collection sites in Nicaragua 

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% alcohol and soiled specimens cleansed in ultrasonic bath (MEDELCO, INC. MODEL MD5-115).

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.

UCA Mollusk Collection (UCACM) contains 10 lots of Dysopeassp. for a total of 160 specimens (Table 1).

Two voucher spms sent to LACM.

Previous mention: Pseudopeas sp. Twospecimens, Isleta de Ken, Isletas de Granada (Pérez 1999).

Accompanying fauna at typelocality: Lamellaxis micra, L. gracilis, Leptinarialamellata, L. guatemalensis, Cecilioidesconsobrinus, Bulimuluscorneus, Succineahyalina, S. recisa, Miradiscops opal, Thysanophora crinita.

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 Dysopeasthe 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/ Dysopeasis 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/Dysopeasin 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 Pseudopeasmislabeled Opeas, Subulina, Spiraxis, or Lamellaxis.

The nepionic sculpture of the Pseudopeasviviparum 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 (Figure 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 Dysopeastranslucidumprotoconch (Figure 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.

Altogether, the descriptions and illustrations by Miller (1879), Putzeys (1899), Pilsbry (1906; Figure 1A, 2A) & Baker (1927; Figure 1B, 2B) accurately match the protoconch and shell sculpture and profile of the Nicaraguan specimens in the genus Pseudopeas.

Figure 1:  A. (Pseudopeas)Dysopeasgenustype. El Castillo (Alosi SEM 9607). B. Same specimen, aperture & body whorl; weak spiral sculpture (Alosi SEM 2180).  

Figure 2: A. Ps. saxatile Pilsbry, 1906, protoconch (Africa). B. D. translucidum, protoconch; (Baker, lam. 23). 

Pseudopeasshares some sculpture traits and protoconch development with Spiraxidae like Micromena Baker 1939, Rectaxis Baker 1926 and even with Lamellaxisgracilis, 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/Dysopeasfrom these look-alikes, such as Spiraxisfunibus(Figure 3B) and S. alvaradoi, both described from Guatemala by Goodrich & van der Schalie (1937), which are common and widely length, whereas Pseudopeas grow to 8 mm. Another difference is that Spiraxidaeprotoconch spirals are dissected by the diagonal ribs into individual chevron-shaped segments, very characteristic of these species (Figure 3B). In Pseudopeas the spirals are continuous, though slightly raised at intersections with ribs (Figure 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 Dysopeasspecimens reveals it is formed by three successive layers spread in Nicaragua. Other similar Spiraxidae in the subgenus RectaxisBaker and Micromena (Baker, 1939) are also present in various localities.

One general difference between these small Spiraxidae and Pseudopeasis size, with Micromenabarely reaching 3 mm and other Spiraxidae attaining 5 to 6 mm maximum of orthorhombic interlaced crystals (Figure 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, (Figure 2A, 2B), which is totally absent in Spiraxidae (Figure 3B), Lamellaxis, Opeasand 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.

Figure 3:  A Pseudopeasgenus, Castillo. B. Spiraxisfunibus, Matagalpa, 3.14 x 2.7 mm. 

Figure 4: (X 900) Aragonite crystal structure. 

Acknowledgements

We thank Mark and Lara G. McKaye for field assistance, and Wayne Arendt, Jorge Huete, Marvin Torrez and several anonymous reviewers. UCA authorities generously contributed to expenses in transportation and maintenance over the years.

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Received: January 14, 2014; Revised: December 09, 2014; Accepted: April 21, 2014

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