Pterygodermatites (Paucipectines) baiomydis n. sp. (Nematoda: Rictulariidae), a parasite of Baiomys taylori (Cricetidae)

Pterygodermatites (Paucipectines) baiomydis n. sp., an intestinal parasite of the northern pygmy mouse, Baiomys taylori (Cricetidae), collected in La Yerbabuena, Colima, Mexico, is described herein. Specimens were studied using light and scanning electronic microscopy. This is the 19th species of the subgenus Paucipectines described worldwide and the fourth collected in Mexico. It is differentiated from the remaining species in the subgenus by having 25 perioral denticles, arranged in a triangle (seven on each lateroventral margin, and eleven on the dorsal margin), and 10 pairs of caudal papillae.


Introduction
Cricetid rodents are one of the most speciose groups of mammals of the New World with approximately 600 species [25]. From the 141 species known to occur in Mexico [25], only 25 had been examined for helminths prior to this study. These surveys resulted in the inventory of 45 species of helminths [5].
As part of an ongoing project to describe the metazoan fauna associated with rodents from Mexico, we analyzed 27 cricetid taxa in seven localities from the Mexican states of Colima, Guerrero, Jalisco, Michoacán, and Oaxaca. The main goal of this paper is to describe a new species of the nematode subgenus Pterygodermatites (Paucipectines) Quentin, 1969, as a parasite of the northern pygmy mouse Baiomys taylori (Thomas, 1887) in Colima, Mexico.

Materials and methods
In December, 2011, two specimens of B. taylori were collected in La Yerbabuena (19°28 0 39 00 N, 103°40 0 46 00 W) in Comala, Colima, Mexico. Hosts were collected with permission (FAUT-0170), issued by Secretaría del Medio Ambiente y Recursos Naturales, Mexico. Rodents were anesthetized by isoflurane inhalation, euthanized by cervical dislocation, and examined for helminth parasites. Helminths were removed from the intestine and placed in 0.85% saline solution, fixed in hot 4% formaldehyde, and stored in 80% ethanol. Nematodes were cleared with Amman's lactophenol and temporarily mounted for morphological study. Population parameters follow Bush et al. [1]. Measurements, expressed in micrometres unless otherwise stated, are given as the range, followed by mean, standard deviation, and sample size in parentheses. Figures were drawn with the aid of a drawing tube. Specimens for scanning electron microscopy were dehydrated in a graded ethanol series, critical-point dried with CO 2 , and then coated with a gold-palladium mixture. Specimens   Etymology: The species is named after the host's generic name.

Description General
Medium-sized nematodes, body slightly widened at posterior end, with thick cuticle. Oral opening apical, surrounded by 5 pairs of papillae, 2 cephalic pairs, and 3 internal labial pairs (1 dorsal, 1 ventral and 1 lateroventral pair). Amphids lateral. Oral opening asymmetric, somewhat hexagonal, with thick margins. Seven denticles on lateroventral margins, and 11 denticles on dorsal margin; 3 internal pharyngeal teeth at bottom of buccal capsule, 1 dorsal and 2 lateroventral. Two subventral rows of cuticular projections along body, starting at end of buccal capsule and ending at anus in females and at level of ventral fans in males. A single type of cuticular projection present in males (combs), and 2 different types in females: simple spines and combs.
Esophagus divided into short muscular and long glandular portions.

Remarks
The morphology of the buccal capsule of the specimens described in this study, particularly the apical position of the oral opening, enables us to include them in the subgenus Pterygodermatites (Paucipectines) [3]. However, the number of prevulvar cuticular processes in P. (Paucipectines) baiomydis n. sp. (38-44) differs from the range described for the subgenus (29-39) by Quentin [19]. Because variations of this trait have been reported for other species included in the subgenus, for example P. (P.) kozeki (Chabaud and Bain, 1981), P. (P.) jagerskioldi (Lent and Freitas, 1935), and P. (P.) dipodomis (Tiner, 1948), all possessing more than 39 prevulvar cuticular processes, the diagnosis of this subgenus should be amended (Table 1).
To date, 18 species of this subgenus have been described as parasites of rodents (12 species), armadillos (1 species), bats (1 species), and marsupials (4 species) ( Table 1). Pterygodermatites (P.) baiomydis most closely resembles   (Quentin, 1967). All three species share traits such as the number of prevulvar combs and fans, unequal spicules, and all three parasitize rodents (Table 1). However, the number of denticles is greater in P.  (Cuckler, 1939), differ from the new species by the position of the vulva, which in those species is anterior to the esophago-intestinal junction, whereas in P. (P.) baiomydis it is situated 1190 posterior to the esophagointestinal junction. Moreover, the oral opening in P. (P.) peromysci and P. (P.) onychomis is a rounded oval, but hexagonal in the new species. In having fewer denticles, arranged in a trapezoid, P. (P.) chaetophracti (Navone and Lombardero, 1980) and P. (P.) azarai (Sutton, 1984) can be distinguished from the Mexican species (16-18 and 17-19, respectively vs. 25 disposed in a hexagon).
For most of the species of the subgenus, males are unknown or insufficiently described; for that reason, female morphological traits are commonly used in species differentiation, partially solving this problem. However, in species such as P. (P.) massoiai (Sutton, 1979), females are poorly described and the morphology of males is still unknown. Because of this, we only compared a few characters of this species with our material; nonetheless, the following traits are sufficient to distinguish them: body size 8.44-9.1 mm in Sutton's species vs. 18.35-21.41 mm in P. (P.) baiomydis; distance from the last spine to the tip of the tail (108 vs. 1660), and distribution (South America vs. North America).
Pterygodermatites (Paucipectines) baiomydis is the 19th species of the subgenus described worldwide and the fourth collected in Mexico. Since cricetid rodents are one of the most speciose groups of mammals of the New World with approximately 600 species [25], its helminth fauna is incompletely documented. From the 141 cricetid species known to occur in Mexico [25], only 26 have been examined for helminths. The surveys of more species of this host group could result in the description of numerous new species of helminths, including representatives of Pterygodermatites.