We report new occurrence records for stygobiontic invertebrates from the Edwards and Trinity aquifers in Blanco, Hays, and Travis counties of central Texas, USA. Our collection includes seven species from four families: Caecidoteareddelli (Steeves, 1968), Asellidae; Crangonyxnr.pseudogracilis Bousfield, 1958, Stygobromusbalconis (Hubricht, 1943), Stygobromusbifurcatus (Holsinger, 1967), and Stygobromusrusselli (Holsinger, 1967), Crangonyctidae; Sphalloplanamohri Hyman, 1938, Kenkiidae; and Cirolanides sp., Cirolanidae. Specimens of Caecidoteareddelli and Crangonyxnr.pseudogracilis are new records for Hays County and Travis county, respectively. Specimens of an undescribed species of Cirolanides were collected from a well in Hays County and from two localities in Travis County.

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A new freshwater ostracod genus, Bicornucandona gen. nov. and its type species (Bicornucandona fineganensis sp. nov.) are described from Finegan Springs, Texas, U.S.A. The new genus differs from the related genera in the presence of two horn-like structures on the dorsal margin of the left valve in both sexes. This is also the diagnostic character of the type species. Differences in the structure of the hemipenes and prehensile palps of the male, and the shapes of some other soft body parts also separate this genus from the related species. Taxonomic status of the new genus and species are compared and discussed with both living and fossil relatives.

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A new candonid genus,Schornikovdonagen. nov., with its type speciesSchornikovdona bellensissp. nov., is described from rheocrene springs of Bell County, Texas. It is designated to the tribe Candonini due to the smooth carapace surface, normal pore openings with sensory seta, the presence of a 5-segmented first antenna, two long sexual bristles on the second antenna in males, the narrowly fused terminal segment of the Md palp, a long penultimate segment of the Mxl palp, two long and one short setae on the terminal segment of T3, the absence of an “e” seta on T3, the presence of a posterior seta on the uropod, the presence of 5 + 2 rows of spines on Zenker’s organ, and other characteristics found in the tribe. The main diagnostic characteristics separating the new genus from the other genera in the tribe are the shape of the carapace, the reduced numbers of segments in the first antenna, reduction or absence of exopodial setae in the second antenna, asymmetrical clasping organs, the uropod with one rod-shaped claw, the different shape of the hemipenis, and differences in parts of the chaetotaxy. Based on these differences, we proposeSchornikovdonagen. nov. as a new genus, with the new speciesS. bellensissp. nov., in the subfamily Candoninae in the family Candonidae.

A new stygobitic groundwater amphipod species, Stygobromus bakerisp. nov., is described from 4 central Texas limestone karst springs; John Knox Spring (Comal County), Jacob’s Well (Hays County), Mormon Spring (Travis County) and Salado Springs (Bell County). This species belongs to the predominately western Nearctic hubbsi species group of Stygobromus and differs from other species in the group by gnathopod 1 with row of 4 to 5 setae posterior to the defining angle, pereopods 6 and 7 with broadly expanded bases and distinct distoposterior lobes, gnathopods 1 and 2 with 2 rows of 3 singly inserted setae on the inner palm, and uropod 3 with single, slightly distal peduncular seta. Habitat, sympatric groundwater species, and conservation issues are discussed.

The San Marcos River in Central Texas has been well studied and has been demonstrated to be remarkably specious. Prior to the present study, research on free-living invertebrates in the San Marcos River only dealt with hard bodied taxa with the exception of the report of one gastrotrich, and one subterranean platyhelminth that only incidentally occurs in the head spring outflows. The remainder of the soft-bodied metazoan fauna that inhabit the San Marcos River had never been studied. Our study surveyed the annelid fauna and some other soft-bodied invertebrates of the San Marcos River headsprings. At least four species of Hirudinida, two species of Aphanoneura, one species of Branchiobdellida, and 11 (possibly 13) species of oligochaetous clitellates were collected. Other vermiform taxa collected included at least three species of Turbellaria and one species of Nemertea. We provide the results of the first survey of the aquatic annelid fauna of the San Marcos Springs, along with a dichotomous key to these annelids that includes photos of some representative specimens, and line drawings to elucidate potentially confusing diagnostic structures.

A new ostracod genus, Tuberocandonagen. nov., was collected from Honeycut Hollow Springs, Texas, USA Morphological comparisons and cladistic analyses showed that the new genus displays several different features (e.g. presence of two tubercules on each of the valves, numbers of A1 segments, shape of A2 claws, shape and presence of two claw-like setae on the clasping organs, absence of d2 and dp setae on T2 and T3, absence of alpha and beta setae on Md, shape of hemipenis) from other genera of the tribe. Including the new species, the number of non-marine ostracods known from inland waters of Texas is now 118 species in 45 genera. With the aim of documenting ostracod biodiversity in Texas (USA) by including fossils, we sought documents published from 1927 to 2022 and were able to list 673 ostracod taxa belonging to 142 genera. Among the fossils, 73 ostracods were the oldest records during the Pennsylvanian period (ca. 310 mya), while there were only 42 taxa reported from the Holocene. The Eocene had the highest number of ostracods (126 taxa). In comparison, the living species had only 18 of 673 taxa that were considered nonmarine forms. There are only six species in common with the fossils and recent records. These results suggest the potential for relatively high ostracod species richness and diversity in Texas. This is indeed strongly supported by the present study and the described new genus and its type species (Tuberocandona leonidasisp. nov.).