Two new species of Chaco Tullgren from the Atlantic coast of Uruguay (Araneae, Mygalomorphae, Nemesiidae)

Abstract We describe two new species of the nemesiid spider genus Chaco from Rocha Province, Uruguay. These new species are diagnosed based on genital morphology, male tibial apophysis spination, and burrow entrance. We test cospecificity of one species, Chaco costai,via laboratory mating experiments. The new species are diagnosed and illustrated and habitat characteristics, and capture behavior are described. We conduct a cladistic analysis based on a previously published morphological character matrix that now includes the newly described species.


Material and methods
Specimens were examined using an Olympus SZH stereomicroscope. The description of color was based on live organisms when possible. Abbreviations: AME anterior median eyes, ALE anterior lateral eyes, PME posterior median eyes, PLE posterior lateral eyes, OQ ocular quadrangle, P prolateral, R retrolateral, D distal, STC superior tarsal claw, ITC inferior tarsal claw, FCE-MY Collection of Facultad de Ciencias, Entomología -Mygalomorphae. All measurements are in mm and were taken with an ocular micrometer. Total body length excludes chelicerae and spinnerets. Lengths were measured along a dorsal longitudinal line and widths were taken at maximum values. The OQ length was measured from the anterior edge of ALE to the posterior edge of PLE; the sternum length from the posterior angle to the labium edge (Goloboff 1995). Terminology for spination is modified from Pérez-Miles and Weinmann 2010. The formula gives the number of spines in the following order: dorsal-prolateral-retrolateral-ventral (p indicates a pair of spines that occur at this position). Spermathecae were cleared with clove oil and illustrated in dorsal view. Left male palpal bulb was removed from the cymbium and illustrated in prolateral and retrolateral views. Specimens were photographed using a Lumenera INFINITY 3 camera.

Cladistic results
Analysis of the morphological data using implied weighting and implicit enumeration resulted in 2 most parsimonious trees. Topologies were stable across K values 1-6 (62 steps, CI= 0.61, RI= 0.65, K=1, fit= 8.75, K=6, fit= 2.79; Fig. 5A-B). The genus Chaco was recovered as monophyletic including the two new species, supported by 4 characters: PE row procurved (1), strong rastellum (10), spination of male patellae I-II (17) and the presence of male palpal tibial spur (21). The main difference between the topology of the two recovered trees was: C. socos + C. tigre is the sister group of C. obscura + C. tucumana in one tree, while in the other C. socos + C. tigre is the sister group of (C. teka (C. patagonica, C. sanjuanina)). The consensus tree (Fig. 5C) recovers a polytomy for C. castanea, C. obscura, C. tucumana, and the clades ( C. obscura, C. tucumana) and (C. teka (C. patagonica, C. sanjuanina)). Based on these data the monophyly of the genus Chaco appears to be well supported with the inclusion of the new species; the addition of new characters in the future will be necessary to improve the resolution of relationships among several species. Regarding the biology of C. costai, the flap-like door of the burrow may be explained as an adaptation to sandy soil habitat.

Natural History
Chaco costai specimens are typically found in sandy soils of oceanic and river coastal areas associated with psammophyte vegetation (Fig. 2F). Individuals were collected from tubular vertical burrows of about 100mm length; the entrance diameter is about 10mm. The spider closes the burrow entrance with sand and silk when disturbed. Chaco patagonica, C. costai make a burrow that is covered with a thin, flaplike door (Fig. 2E). The door actually consists of a prolongation of the silk layer lining the interior of the burrow, covered by grains of sand; it is flexible and loosely articulated. According to field and laboratory observations, the spider begins foraging at night by standing at the top of the burrow with legs I-III extended lying in the substrate (Fig. 2E); similar to that reported by Bond and Coyle (1995) for Ummidia. After a prey item is captured, the spider returns to the interior of the burrow to feed; the burrow entrance remains open until later when the spider returns to the entrance to repair and close the flap-like-door.
A copulation event observed in the laboratory occurred over an eight minute time period at 18 °C. The male appeared to initiate courtship with body vibrations and pulling silk threads with his chelicerae. Body vibrations were caused by spasmodic contraction of legs I and II. The male approached the female burrow entrance and opened it with his chelicerae; the female then emerged from the burrow. Copulation took place at the burrow entrance; the male clasped his tibial apophysis with female chelicerae. The male performed 23 palpal insertions, alternating right and left palps. The mean duration of the insertions was 21.09±12.73 seconds. After copula the male retreated with legs I extended and female retreated in the burrow but maintained her first legs out towards the entrance. After 17 minutes the female closed the burrow flap-door. Etymology. The specific epithet is a noun taken in apposition (chestnut) and is in reference to the brownish coloration of this species.
Diagnosis. Males (Fig. 1A) uniquely possess a tibial apophysis with 4 spines (Fig. 3D). Chaco castanea males differ from C. tigre and C. socos males by having a palpal organ with a sinuous spermophor and parallel longitudinal ridges (Figs 3A-C,) and by having a PME and AME that are subequal in diameter. Females of C. castanea (Fig. 1C) differ from the other known Chaco species by the presence of a large reniform spermathecal receptacle in combination with a short sinuous duct (Fig. 3E).
Distribution. Uruguay, Rocha, Perla de Rocha and Cabo Polonio.   Etymology. The specific epithet is a patronym in honor of Fernando G. Costa, a recognized Uruguayan arachnologist who greatly contributed to the knowledge of spiders and has inspired many colleagues and students.
Diagnosis. Males of C. costai ( Fig. 2A) differ from the other species of the genus, except C. obscura, by the presence of numerous spines (7-10) on tibial apophysis (Fig. 4D); they can be distinguished from C. obscura by having a shorter embolous (Figs 4A-C). Female C. costai specimens (Fig. 2C) differ from most species of Chaco by having spermathecae with a sinuous neck (Fig. 4E). The species is distinguished from the geographically proximate species C. castanea by having a longer spermathecal neck and from C. obscura by the sinuous neck. Chaco costai differ from all other species of the genus (except C. patagónica and C. tecka) by having a flap door that covers the burrow (Fig. 2E).