Taxonomy of the Neotropical freshwater crab family Trichodactylidae . VI . The genera Avotrichodactylus and Rodrigue-zia ( Decapoda : Brachyura : Trichodactylidae )

The taxonomy of two trichodactyline genera of the Neotropical freshwater crab family Trichodactylidae are revised. The genus Avotrichodactylus Pretzmann, 1968, includes two species, A. constrictus (Pearse, 1911) and A. oaxensis Rodríguez, 1992; the genus Rodriguezia Bott, 1969, also has two species, R. mensabak Cottarelli and Argano, 1977, and R. villalobosi (Rodríguez and Manrique, 1967). The taxonomic statuses of all the species are discussed and a short diagnosis is provided for each. A complete list of the material examined and a map of geographic distribution of the species are furnished.


Introduction
The four species of the trichodactylid freshwater crabs that occur in southern Mexico are included in the subfamily Trichodactylinae owing to similarities with the South American representatives of the genus Trichodactylus Latreille, 1828, in carapacial and gonopodal morphology (Pretzmann, 1968;Bott, 1969a;Rodríguez, 1992;Magalhães and Türkay, 1996a).The first two species described from this region were in fact assigned to this genus, viz., Trichodactylus constrictus Pearse, 1911, andT. villalobosi Rodríguez andManrique, 1967.However, these species have some peculiarities in the morphology of the first and second pair of gonopods, which led Pretzmann (1968) and to genus.This classification was maintained by Magalhães and Türkay (1996a) in their proposal of a generic system for the family, and more recently followed by other workers (see Ng et al., 2008;De Grave et al., 2009).
In this paper, we continue our ongoing taxonomic revision of the trichodactylid genera (see Magalhães and Türkay, 1996a, b, c;2008a, b) by presenting brief diagnoses and illustrations of the carapace and the male first pleopods for each species of Avotrichodactylus and Rodriguezia, as well as remarks about their intraspecific variability.A key to the species of both genera is also provided.

Material and Methods
The measurements are given in millimeters; measurements of the type and the largest specimen examined are usually provided.The terminology used for gonopod description is explained in Magalhães and Türkay (1996a); the number of anterolateral teeth of the carapace includes neither the exorbital angle (when toothed) nor the accessory tooth sometimes present at base of the exorbital angle.Type specimens of species were examined, except where noted otherwise.Synonymies presented include mainly references from 1969 onwards; see Bott (1969a) for synonymies prior to that year.Geographic distribution of the species was mapped on the basis of the records presented in this paper and from the literature.
Abbreviations: Measurements -cb, carapace breadth, measured across the carapace at its widest point; cl, carapace length, measured along the midline, from the frontal to the posterior margin.Repositories of the specimens -CNCR, Coleccíón Nacional de Crustaceos, Instituto
Remarks: Although the plp 2 is similar to that of Rodriguezia in being shorter than the plp 1, the tapered distal part of the plp 1 and its strong curvature in ventrolateral direction, as well as the fused III-V abdominal somites (as opposed to the straight plp 1 with broad apex, and all abdominal somites free in Rodriguezia), Distribution: Southern Mexico, in the states of Veracruz, Tabasco, Oaxaca, and Chiapas (Fig. 20).Additional records from these states were also provided by Rodríguez and Manrique (1967) and Rodríguez and Hobbs Jr. (1989).
Remarks: Bott (1969a) included A. constrictus in his newly-erected subgenus Trichodactylus (Rodriguezia) probable based on the geographical distribution of the species, as he did not have access to any male specimens of this species and, therefore, could not examine its gonopodal morphology.In the same paper, he described T. (R.) bidens and distinguished it from T. (R.) constrictus only by the number of teeth on the anterolateral margins of the carapace (2 versus 3, respectively), as both left and right gonopods of the holotype of T. (R.) bidens were already severely damaged, thus precluding an evaluation of gonopod morphology.Cottarelli and Argano (1977) also identified their specimens of T. (R.) bidens on the basis of the number of anterolateral teeth.
We have examined most of the specimens mentioned in the literature that were assigned to both taxa, as well as additional material from southern Mexico, and found a clear variation in the shape and number of the teeth on the anterolateral margins of the carapace.Usually, the second tooth is sharp as in the holotype specimen (Fig. 1), but it can be smaller, rounded, vestigial or even evanescent (Figs. 2,  Figures 1 -9.Avotrichodactylus constrictus (Pearse, 1911) (1, 2, 4-6);   5 mm (3); 2 mm (9), 1 mm (7, 8).3).Specimens from the state of Veracruz usually have three low and sharp teeth while there is a for reduction of the second tooth in those specimens from the states of Tabasco and Chiapas.This is particularly evident among the specimens from the lots NHM 1907.5.15.5-9 (Fig. 3a-h) and ZMH K-28323 (Fig. 3i).It is also rather common that the shape of the teeth vary between the left and right margins of the same specimen (for instance, a specimen from the lot CNCR 13385 -Fig.4).A few specimens can even bear four teeth on the lateral margin (for instance, some specimens of the lots CNCR 17084 and CNCR 12587 -Figs.5, 6), but usually the fourth pair consists of vestigial teeth (for instance, in the specimen of the lot CNCR 12587 -Fig.6, or in the holotype of A. constrictus itself -Fig.1).Rodríguez and Hobbs Jr. (1989) also recognized the variability in the anterolateral teeth of these taxa.
Moreover, the distal part of the plp 1 can be more or less tapered and the lateral and mesial patches of the subterminal spine field partially continuous in some specimens (Figs. 7, 8).The curvature of the plp 1's distal part is not so pronounced in immature males.Ojeda (2010), in an unpublished academic thesis on the distribution patterns of the Trichodactylidae from Mexico, presented a detailed morphological study of the carapace and gonopod of Avotrichodactylus constrictus and presumptive A. bidens from different river basins within their area of distribution.
He found great variability in carapace, third maxilliped and gonopod characters among populations of A. constrictus from different hydrographic basins, although no particular morphology could be associated with each basin or population (Ojeda, 2010).He also noticed a high degree of similarity between the specimens assigned to both species, but preferred to keep them separated until additional material can be obtained from the area of occurrence of A. bidens.
Our study of a good series of specimens (including adult male specimens with intact gonopods) from and near the type locality of T. (R.) bidens, the "Cueva de los Azufres", in Tapijulapa, state of Tabasco, has shown no taxonomically significant difference in the carapace and gonopod morphology to justify assigning specific status to them.Therefore, in spite of the impossibility of evaluating the gonopod morphology of the holotype of T. (R.) bidens, we propose that this species be considered a junior synonym of A. constrictus owing to the overlapping of their occurrences and overall similarities in morphology of the specimens, taking into account also that the characters used to separate both taxa are subject to strong variability as described above.Rodríguez, 1992 (Figs. 10 -14) Avotrichodactylus oaxensis Rodríguez, 1992

Diagnosis:
Carapace subquadrate; anterolateral margins of carapace with four to five teeth behind external orbital tooth.Abdominal somites III-V fused (segmentation between somites II-III and III-IV sometimes marked by pigmentation).Male plp 1 slender, with distal portion tapering and nearly straight or slightly bent in ventrolateral direction.Marginal suture running along mesial side of stem, not twisted to other sides.Subterminal spine fields well developed, situated on lateral and mesial sides, with latter broader and larger than former and both patches partially joined on dorsal side.Distal opening subcircular, very narrow, situated terminally and directed towards mesioventral side.Plp 2 about 0.6 times length of plp 1.
Distribution: Southern Mexico, in the states of Veracruz and Oaxaca (Fig. 20).
Remarks: Like the previous species, the shape and number of the teeth in the anterolateral margin of the carapace is also variable in A. oaxensis.Most of the examined specimens have four to five sharp teeth, but the fourth to fifth teeth can be more or less reduced in some specimens (Fig. 11); occasionally, a sixth tooth may be present (Fig. 10), but this seems to be an abnormal situation.
Avotrichodactylus oaxensis resembles A. constrictus in carapace morphology, but they can be distinguished from each other by the number of anterolateral teeth (4-5 in the former; 2-3 in the latter) and by the gonopod morphology (the plp 1 of A. oaxensis is nearly straight or weakly bent in a mesioventral direction, while it is strongly bent in a lateroventral direction in A. constrictus) (7)(8)respectively).Moreover, the molecular analysis made by Ojeda (2010) using two mitochondrial genes from individuals of one population of each species (A.oaxensis from laguna Majahual; A. constrictus from río Tuxtla) showed a clear genetic divergence between them: 8% for cytochrome oxidase I (COI) gene and 10% for the 16S rRNA gene.Rodríguez (1992) stated that the repository of the type material of A. oaxensis was the MNHN in Paris.In fact, only two male paratypes remain in the collection of this museum.The holotype, two males and one female paratypes have been returned to the ZMH in Hamburg, and the other male paratype has been deposited in the IVIC's collection.

Diagnosis:
Carapace subquadrate, regions well defined; frontal margin smooth, slightly bilobed.Anterolateral margins of carapace smooth, unarmed.Dactylus of pereiopods 2 to 5 covered by dense pubescence.Abdominal somites free.Male plp 1 with distal part straight, lateral borders with median constriction.Marginal suture straight, situated on mesial side.Subterminal spine fields well developed, discontinuous, with lateroventral and mesiodorsal patch, respectively.Apex simple and symmetrical, distal border rounded.Distal opening large, obliquely directed towards mesial side.Male plp 2 with lanceolate apex, reaching slightly beyond median constriction of plp 1.
Distribution: Southern Mexico, in the state of Chiapas (Fig. 20).An additional record from this state, San Juan Bosque [El Bosque] was provided by Rodríguez and Manrique (1967).
Remarks: The morphology of the carapace and the first gonopod of this species are very similar to that of Trichodactylus species, particularly to those with smooth anterolateral carapace margins (e.g., some forms of T. fluviatilis Latreille, 1828).However, the relative length of the male second pleopod and the zoogeographic distribution clearly distinguish this species from Trichodactylus species.
Remarks: This is the only truly troglobious species of Trichodactylidae, and most of its morphological features (ocular peduncle much reduced, very shallow orbit, absence of cornea, and very long and slender legs) are adaptations to a cavernicolous environment.Otherwise the male first pleopod shows a similar morphological structure to that of R. villalobosi and some species of the genus Trichodactylus.
The second male pleopod of R. mensabak has a very peculiar morphology.In this species, the plp 2 has a subtriangular apex, which is rounded distally, and bears minute spines on the mesial border (see Cottarelli and Argano, 1977: 208, fig. 1e), while in R. villalobosi the apex is lanceolate and sharp distally, and the subdistal part of the mesial border is smooth, without trace of spines (Fig. 16).(some symbols refer to more than one close set of localities).