A new genus and species of stygobiontic dytiscid beetle, Comaldessus stygius (Coleoptera: Dytiscidae: Bidessini) from Comal Springs, Texas

A new genus and species of stygobiontic bidessine dytiscid beetle, Comaldessus stygius, from Comal Springs, Texas, is described and compared with the proposed sister epigean genus Uuarus and the only other known stygobiontic bidessine water beetles, Trogloguignotus concii Sanfilippo from Venezuela and Uvarus chappuisi (Peschet) from Africa. Distinctive characters of the adult are illustrated with pen and ink drawings and scanning electron micrographs. The new taxon is the second stygobiontic bidessine genus with rudimentary eyes known from the Western Hemisphere and the first known from North America. Introduction and northeast. I n the artesian zone, faulting of the water-bearing limestone against impermeable layThe new taxon described in the following acers causes the water to be forced to the surface as count was first collected during a survey by the artesian springs. According to Holsinger and Lonjunior author to examine the distribution of a gley (1980), this karst area has been subjected to recently described stygobiontic dryopid beetle, Styintense faulting and fracturing, w h c h probably goparnus comalensis Barr and Spangler (1992). has resulted in the development of many phreatic The survey was conducted for the U.S. Fish and reservoirs. The reservoirs, in turn, probably led to Wildlife Service in 1992 and involved several springs the isolation of aquatic populations and the extenof the Edwards Aquifer (Balcones Fault Zone). sive speciation (43 species and subspecies) reported Among the springs examined were Comal Springs from the artesian zone of the aquifer by Bowles and a t New Braunfels, Texas, the type locality of Arsuffi (1993). For additional details of the fauna S. comalensis and this previously unknown dytisand geology of the Edwards Aquifer see Barr and cid. Additional specimens of Comaldessus stygius, Spangler (1992), Bowles and Arsuffi (1993), new genus, new species, were collected in 1993 Brune (1981), Holsinger and Longley (1980), Klemt during the Habitat and Flow Requirements Study et al. (1979), Longley (1981, 1986), Ogden et al. for the Comal Ecosystem by the U.S. Fish and (1986), Pearson et al. (1975), and Rothermel and Wildlife Service. Ogden (1987). Comal Springs emerge along the base of the Balcones Escarpment and are fed by the Edwards Aquifer (Balcones Fault Zone) of south-central Texas. The aquifer extends for 282 km in a crescent from Bracketville in Kinney County to Kyle in Hays County, and ranges from 8 to 48 km in width. Water enters the aquifer in the recharge zone where streams cross exposed, porous limestone. The underground water is subjected to increasing hydrostatic pressure as it flows towards the east Collecting Methods Using drift nets a t four sites, Barr sampled spring water discharge over a continuous period of about 100 hours. Drift nets used a t outlets with large volumes were 0.30 m X 0.45 m, had a mesh size of 363 microns, and had a plexiglass collection bottle. Barr used standard aerial and aquatic insect net bags as improvised drift nets a t springs with 302 Volume 9, nos. 3-4, September-December, 1995, INSECTA MUNDI low flow. Material trapped in the nets was preserved in alcohol in half-pint jars for later examination. Similar drift collection techniques were employed by R. Stanford of the U.S. Fish and Wildlife Service, who used plankton tow nets with a diameter of 200 mm., mesh of 118 microns, and set for approximately 24 hours.