14 May 1986 PROC. BIOL. SOC. WASH. 99(1), 1986, pp. 121-136 HADOCERAS TAYLORI, A NEW GENUS AND SPECIES OF PHREATIC HYDROBIIDAE (GASTROPODA: RISSOACEA) FROM SOUTH-CENTRAL TEXAS Robert Hershler and Glenn Longley Abstract. ?Hadoceras taylori, a new genus and species of Hydrobiidae, Lit- toridininae, is described from three localities in Real County, Texas. This phreatic species may well range throughout the southern portion of the Edwards Plateau and into northern Mexico. The detailed morphological description provided for this species includes aspects of the shell, operculum, pallial cavity, digestive system, and reproductive system of both sexes. Generic separation of Hadoceras from similar-shelled late Tertiary Orygoceras is warranted by both morphological and ecological considerations. A suite of unique characters, including the uncoiled, horn-like shell and concentric operculum with ventral process, separates Hadoceras from other known phreatic littoridinines of south- central Texas and northern Mexico. Taylor's (1974) discovery of living phreatic snails from Roaring Springs, Texas referable to Orygoceras Brusina, 1882, a ge- nus previously known only as late Tertiary fossils from Idaho and southeastern Europe, ranks as a particularly exciting event in the recent history of freshwater malacology. The uncoiled, horn-like shell of Orygoceras is highly unusual among gastropods (Rex and Boss 1976) and the systematic placement of this genus has long been debated (Taylor 1974). Taylor (1974) concluded that living Orygoceras is a hydrobiid (Prosobranchia: Rissoacea), but did not describe this species. His morphological study was necessarily limited as he collected a single live speci- men, and various aspects of anatomy, in- cluding details of the male and female re- productive system critical to the systematic assessment of rissoacean snails, were not dealt with. As part of an ongoing survey and system- atic study of phreatic gastropods of south- central Texas (see Hershler and Longley, 1986) we collected more than 20 live Ory- goceras sp. (including a number of adults) from Roaring Springs and two other springs in Real County, Texas. We describe this snail as Hadoceras taylori, a new genus and species of Hydrobiidae; provide a detailed morphological description of this taxon, in- cluding aspects of the male and female re- productive systems; and discuss the system- atic relationships of Hadoceras, emphasizing comparisons with other members of the di- verse phreatic hydrobiid fauna of south- central Texas and northern Mexico. Localities.?Hadoceras taylori was col- lected during May 22-24, 1985 from the following three springs (see Fig. 1): a) Roar- ing Springs (unnamed on USGS topograph- ic sheets), about 7.6 miles W of Camp Wood (water temperature 21.0?; conductivity 319.2 ymHOS; 5/23); b) Unnamed spring in South Prong Canyon, 6.6 miles W of Camp Wood (temperature 21.0?; conductivity 415.0 ymHOS; 5/23); and c) Unnamed spring at Jo Jan Van Camp, 9 miles N of Vance. All three springs are moderate-sized rheo- crenes, with numerous orifices. They occur in the Nueces River drainage in the region where the southern edge of the Edwards Pla- 122 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON EDWARDS (Balcones Fault Zone) AQUIFER REGION Fig. 1. Map of the Edwards (Balcones Fault Zone) Aquifer Region showing the three localities from which Hadoceras taylori were collected. The localities are Roaring Springs (1), an unnamed spring in South Prong Canyon (2), and an unnamed spring at Jo Jan Van Camp (3). teau gives rise to the well-dissected Hill Country. The water-bearing unit feeding the springs is probably the Trinity group of low- er Cretaceous limestone (Ashworth 1983). Methods.? Three methods were used to collect H. taylori and other phreatic organ- isms at these localities. Sections of PVC pipe capped with fine (64 fi) mesh netting at one end were placed overnight in spring orifices to filter the water stream emerging from un- derground. Cotton gauze was placed over- night in the orifices to serve as an artificial colonization substrate for these organisms. Finally, sediments in the uppermost sec- tions of the spring runs were sifted using a fine hand sieve. Methods of morphological study are those of Hershler and Longley (1986). Usage of body surface references follows that of Fret- ter and Graham (1962). All morphological data presented are from individuals col- lected from Roaring Springs. Unless oth- erwise indicated, unrelaxed preserved spec- imens (initially fixed in formalin) were used for anatomical study. A total of six individ- uals was dissected. Family Hydrobiidae Subfamily Littoridininae Hadoceras, new genus Orygoceras Brusina, 1882 (in part):33. Diagnosis. ?Shell (Figs. 2-4) minute (maximum dimension, less than 2.8 mm), VOLUME 99, NUMBER 1 123 Fig. 2. Holotype (USNM 849000) of Hadoceras taylori (shell width, 2.37 mm). colorless, transparent, horn-like in shape with uncoiled teleoconch and simple aper- ture (Fig. 4B, H, I). Protoconch with pitted microsculpture (Fig. 4D), teleoconch with strong collabral growth lines (Fig. 4H). Operculum (Fig. 5) concentric, with a large, peg-like, non-calcareous process on ventral surface. Animal unpigmented and without eyespots (Figs. 6, 7). Ctenidium absent (Fig. 7). Intestine (In) with loop on right side of style sac (Fig. 10) and coil in roof of pallial cavity (Figs. 6, 7). Central tooth of radula trapezoidal in shape, with a single pair of basal cusps arising from lateral angles (Figs. 8, 9). Pallial gonoducts (Pr, Ag, Fig. 6) dis- placed ventrally. Gonads consisting of non- lobed mass, occupying 20-25% of total body length. Pallial portion of prostate less than 20% of prostate length; anterior vas defer- ens exiting from anterior tip of prostate (Fig. 10C). Penis simple, without lobes or spe- cialized glands (Fig. 10B). Capsule gland (Cg) with two tissue sections and terminal open- ing (Cga, Fig. 11). Albumen gland (Ag) loops posteriorly (around bursa (Bu)), with pos- terior tip joining oviduct (Ov, Fig. 11); sperm duct (Sdu) issuing from this juncture and connecting with anterior portion of sper- mathecal duct (Sd). Seminal receptacle ab- Fig. 3. Camera lucida drawings of shell outlines of H. taylori, including the holotype (A) and paratypes (D-H, USNM 849001). Note the variation in trans- lation rate along the coiling axis. sent; spermathecal duct and capsule gland opening jointly (Cga). Remarks. ?-The morphological ground- plan of Hadoceras clearly indicates that it is a member of the Hydrobiidae (see family definition in Davis 1979) and the presence of a spermathecal duct suggests placement in the Littoridininae (see Davis et al. 1982; Hershler 1985). Apart from its shell form, unique among hydrobiids, character-states distinguishing Hadoceras from other litto- ridinines include the concentric operculum with ventral process, unusual ventral dis- placement of the pallial gonoducts, and combination of minute adult size and sim- ple penis. There is little doubt that European Ory- goceras, which has been considered as either an uncoiled valvatid or planorbid (Wenz 1938-44; Papp 1962), is distinct from Had- oceras. The shells of the former are not only much larger (to 10 mm) than those of Had- oceras, but also differ in form, having a much larger whorl expansion rate, non-circular aperture, and (often) macrosculptural de- 124 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON VOLUME 99, NUMBER 1 125 velopment. The inferred habitat of Euro- pean fossil Orygoceras is lacustrine (Taylor 1974), as opposed to the phreatic habitat of Hadoceras. A similar set of arguments sug- gests generic distinction of Hadoceras from the Idaho fossil Orygoceras, which are as large as those from Europe, and are simi- larly found in ancient lake bed deposits (Ball 1924; Yen 1944; Taylor 1966). Type species. ?Hadoceras taylori (by original designation). Etymology. ?From the Greek words Hades and keras, meaning the god of the underworld and a horn, respectively, and referring to the subterranean habitat and horn-like shell of this genus. Gender neuter. Distribution.?Hadoceras taylori occurs in phreatic habitats associated with Creta- ceous limestone aquifers in Real County, Texas. Davis (1983) reports fresh shells re- ferable to this species from Williamson County, and it is likely that the species ranges throughout limestone aquifers in the south- ern edge of the Edwards Plateau. In addi- tion, live specimens of what appears to be the same species were collected by the se- nior author from groundwater outlets in the Cuatro Cienegas Basin, northeastern Mex- ico (Hershler 1985). Fossil shells in the 2- 3 millimeter range representing possibly a second Hadoceras sp. were collected by W. Pratt from an archaeological site in the Las Vegas Wash (Nevada) northeast of Hen- derson. The shells were radiocarbon dated as 400 years B.P. and the inferred fossil hab- itat at the site is a marshy spring area (W. Pratt, pers. comm. 1985). Habitat. ?The collection of living H. tay- lori by placing nets into groundwater out- lets, nets that cannot be entered by creno- biontic organisms, demonstrates that this species does occur in the phreatic environ- ment. It is also apparent from collections taken from the upper spring runs that the species also inhabits this epigean habitat. We do not concur with the assertions of Taylor (1974) and Davis (1983) that//, tay- lori is necessarily interstitial in habit. The Cretaceous limestone aquifers in south-cen- tral Texas are extremely porous, with open- ings ranging upwards in size to large caverns (Prune 1975), and there is no reason to sus- pect that the species is limited to interstitial habitats. The presence of much larger phreatic organisms in these aquifers, in- cluding vertebrates, attests to the use of non- interstitial habitats (Longley 1981). Associated fauna.? Phreatic organisms collected with H. taylori include another phreatic hydrobiid, Phreatodrobia sp. (Fig. 4C), as well as diverse crustaceans, includ- ing isopods, amphipods, and copepods. Hadoceras taylori, new species Figs. 1-12 Orygoceras sp. Taylor, 1974:93. Description.? Shell: For 8 (fresh) adult shells, height and width ranged from 0.946- 1.81 and 2.00-2.03 mm respectively (Table 1). The thin shell is transparent when fresh, but has an opaque, white aspect in older specimens. The protoconch has 1.0-1.12 whorls, a diameter of about 0.32 mm, and coils in the same plane as the beginning of the teleoconch (Fig. 4A, F). The junction between the protoconch and teleoconch is quite noticeable (Fig. 4D), often due to a sudden increase in diameter of the gener- ating curve, or sudden change in direction of coiling at the beginning of the teleoconch. The teleoconch typically gently curves away from and down the coiling axis with only a slight whorl expansion, producing the horn- Fig. 4. Scanning electron micrographs of shells of H. taylori (A, B, D-I) and Phreatodrobia sp. (C). The protoconch is shown from above (D), below (G), and from the side (F, 300 x). The aperture is shown from above (H, inner lip to the right) and below (I, inner lip above). 126 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. 5. Scanning electron micrographs of the operculum of//, taylori showing the ventral (A-E) and dorsal (F) aspects. VOLUME 99, NUMBER 1 127 like shell shape, but the rate and nature of whorl translation vary, as seen in Fig. 3 and reflected in the above data. Note that the teleoconch may initially translate slightly above the protoconch, or suddenly dip down the coiling axis. The teleoconch does not coil in a single plane, but is somewhat bowed (towards the viewer in Fig. 3). The aperture, while near-circular (diameter of 0.35 mm), does not lie in a single plane as the inner lip is rather advanced. While not noticeably flared, the aperture is sometimes slightly ex- panded at the outer lip (Fig. 4H). The te- leoconch growth lines are especially pro- nounced at the aperture. Operculum. ?The horny operculum is near-circular (Fig. 5B, D, F), with a typical diameter of 0.31 mm. The ventral process, centrally located, occupies a good portion of the operculum area. When viewed dor- sally, this central region appears depressed (Fig. 5F). The portion of the operculum pe- ripheral to the ventral process is also thick- ened and somewhat curved in the ventral direction (Fig. 5C, E). Of the 7-8 operculum whorls, which are arranged in near-concen- tric circles, the earliest 4 are located in the area occupied by the ventral process. Note that the distal end of the ventral process is concave, reflecting the progressive increase in process height from the first to fourth whorl. After the fourth whorl the process height then quickly decreases to the level of the peripheral portion of the operculum. General anatomy.? A set of anatomical data obtained from each of 4 specimens (2 males, 2 females) is given in Table 2. While lacking melanin pigment, the body of the snail does have black, spherical granules typically concentrated in 3 areas: on the right side of the digestive gland, where it covers the stomach and ventral to the gonad (Fig. 6A); and on the left side of the style sac (not figured). Apart from the red-pink color seen in the buccal mass and foot (due to hemo- globin), yellow-green color of the prostate (Pr), and yellow color of the ovary (Ova), Table 1.?Shell height and width (mm) for the eight adult specimens of Hadoceras taylori shown in Fig. 4. Shell height Shell width Holotype 1.20 2.37 Paratype 1.82 2.15 Paratype 1.12 2.00 Paratype 0.95 2.44 Paratype 1.81 2.41 Paratype 1.34 2.17 ? 1.20 2.63 - 1.27 2.06 the only other color visible in the animals is in the stomach, style sac and intestine, where the food contents and faecal pellets appear brown. The illustration of the head in Fig. 7 is based on examination of a single, somewhat damaged live specimen in a partly contract- ed state. In a more typical live individual the snout (Sn) is probably less squat and the tentacles (Tn) more elongate, as illustrated by Taylor (1974, fig. 1). Terminal setae on the tentacles, figured by Taylor (1974, fig. 1), were not visible in the contracted spec- imens examined. The inner base of the ten- tacles has a dense concentration of clear, crystalline granules (Fig. 7). As seen in Fig. 6, the pallial gonoducts (Pr, Ag) are situated more ventrally than is typical of hydrobiids (and prosobranchs in general), and actually lie over the oesopha- gus. The functional necessity for such a shift may be the need to accommodate the large kidney and intestinal loop on the style sac that lie dorsal to the gonoducts. This space constraint is also reflected in the unusual narrow nature of both gonoducts. Pallial cavity. ? The contents of the pal- lial cavity, which occupies 21-26% of the total body length, are shown in Fig. 7. While no trace of the ctenidium is seen, the large osphradium (Os), occupying 27-34% of the pallial cavity length, is found in its usual position. The intestine (In) makes a large, U-shaped loop that fills much of the pos- 128 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. 6. Male (A) and female (B, minus the head/foot) H. taylori, viewed from the right lateral aspect. Ag, albumen gland; Bu, bursa copulatrix; Edg, anterior end of the digestive gland; Ft, foot; In, intestine; Ki, kidney; Mc, mantle collar; Op, operculum; Ov, oviduct; Ova, ovary; Pr, prostate; St, stomach; Sv, seminal vesicle; Tn, tentacle; Ts, testis; Vdl, posterior vas deferens; Vd2, anterior vans deferens. terior portion of the pallial cavity roof, the loop actually bending back upon itself when the pallial cavity roof is viewed in its normal curved orientation (Fig. 6), and not flat- tened out as in Fig. 7. The anus is situated within 0.06 mm of the mantle edge. The pericardium (Pc) is rather small and narrow, whereas the kidney (Ki) is enlarged, with a simple, non-fleshy opening. Digestive system.? The radula of H. tay- lori is shown in Figs. 8 and 9. The gener- alized cusp formulae, based on examination of scanning electron microscope photo- graphs of 4 radulae, are as follows: central, 4(5)-l-4(5)/l-l; lateral, (4-6)-1-5; inner marginal, 17-21; outer marginal, 15-16. The width of the central tooth is about 0.0097 mm. Note that the central cusps of the cen- tral and lateral teeth are enlarged relative to other cusps on these teeth. Also note the relatively large basal cusps on the central teeth and the well-excavated basal process. The shape of the cusps on the central teeth varies from hoe-like (Fig. 8B) to dagger-like (Fig. 8D). The oesophagus (Oes) coils once imme- diately upon exiting from the head/foot mass (Fig. 7). The two stomach chambers (Ast, Pst) are poorly differentiated externally (Fig. 10A) and there is no caecal appendix. Two solid masses of digestive gland exit from the single opening of the stomach (Odg). The digestive gland lacks noticeable tubular swellings. The stomach is typically only slightly longer than the narrow style sac (Sts). Note that the intestine (In) exits from the VOLUME 99, NUMBER 1 129 left side of the style sac very close to where the latter joins the stomach. Male reproductive morphology. ?The seminal vesicle (Sv) exits from the anterior tip of the testis and consists of a tight mass of several coils, measuring about 0.2 by 0.2 mm, that fills the space between the testis and stomach. The prostate (Pr), which is 5 times as long as wide, overlies a portion of the anterior stomach chamber. Note that the vas deferens (Vdl) enters the prostate near its mid-line, which is considerably pos- terior to the end of the pallial cavity (Fig. IOC). The anterior vas deferens (Vd2) exits from the tip of the prostate as a thickened tube, which then travels 0.6-0.7 mm ante- riorly in the pallial cavity roof before turn- ing back posteriorly to enter the "neck" and travel a. similar distance to the base of the penis (Pn, Fig. 7). The penis (Fig. 10B) coils counter-clock- wise in a tight fashion, on the "neck" behind the snout. While lobes are absent, both edges of the penis have small folds, although the folds end on the inner edge at two-thirds of the penis length from the base. The vas def- erens does not coil greatly in the penis and is eversible at the penis tip. The single penis examined from a living individual (shown in Fig. 1 OB) lacked cilia, although columnar epithelia were seen along both edges. Single large spherical granules occur along the proximal two-thirds of the penis. Female reproductive morphology.?Large, spherical oocytes were seen in the posterior portion of the ovary of several specimens. Note that the anterior end of the ovary (Ova) abuts the posterior end of the stomach (St, Fig. 6B). The oviduct (Ov) exits from the anterior end of the ovary and disappears to the left side of the bursa and pallial oviduct (Bu, Ag, Fig. 6B). The pallial oviduct (Cg + Ag, Fig. 11) is unusually narrow along its entire length. The anterior section of the capsule gland is twice as long (but much narrower) as the posterior section, and clear rather than white. The Table 2.?Measurements (mm) of organs and struc- tures for four specimens of Hadocems taylori. M = male, F = female. Specimen 1 (M) 2(M) 3(F) 4(F) Shell width 2.54 2.51 2.51 2.57 Body length 2.04 1.92 1.96 2.26 Snout length 0.16 0.14 0.18 0.12 Tentacle length 0.16 0.14 0.18 0.14 Pallial cavity length 0.42 0.41 0.51 0.59 Osphradium length 0.14 0.14 0.14 0.16 Osphradium width 0.089 0.079 0.10 0.12 Stomach length 0.36 0.34 0.34 0.36 Stomach width 0.22 0.22 0.22 0.24 Style sac length 0.30 0.20 0.28 0.32 Style sac width 0.10 0.10 0.11 0.10 Gonad length 0.44 0.38 0.50 0.51 Gonad width 0.16 0.16 0.14 0.20 Prostate length 0.50 0.50 ? ? Prostate width 0.10 0.12 ? ? Pallial prostate length 0.10 048 - - Penis length 0.20 0.18 ? ? Pallial oviduct length - ? 0.87 0.83 Pallial oviduct width ? ? 0.18 0.10 Bursa length ? ? 0.42 0.59 Bursa width ? ? 0.12 0.14 albumen gland, which is thin, clear, tubular, and decidedly non-glandular; extends pos- teriorly to slightly overlap the stomach, and then loops anteriorly with its length slightly overlapping the right side of the bursa (Bu, Figs. 10B, 11). Although egg capsules were not found, we suspect that the species is oviparous and not ovoviviparous. The oviduct (Ov) has a single, swollen coil on the left side of the bursa. The coil has a pink sheen and is the probable site of sperm storage, given the absence of a seminal re- ceptacle. Just anterior to this coiled section, the oviduct opens into the albumen gland, the connection being difficult to recognize as the terminal portion of the albumen gland is extremely fragile and easily ruptured. The sperm duct (Sdu) issuing from this point is very narrow relative to the coiled oviduct, and extends anteriorly, looping back to the right side of the spermathecal duct (Sd) to enter the pallial cavity roof and finally join 130 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. 7. Head and contents of the pallial cavity of//, taylori. The length of the pallial cavity roof has been cut along the extreme left side and then flattened out to the right. The dashed line indicates the posterior end of the pallial cavity. The posterior portion of the prostate has been removed. In, intestine; Ki, kidney; Oes, oesophagus; Os, osphradium; Pc, pericardium; Pn, penial attachment area; Pr, prostate, Rpc, roof of pallial cavity; Sn, snout; Tn, tentacle; Vd2, anterior vas deferens. the spermathecal duct (Osdu) in the anterior portion of the pallial cavity. The bursa (Bu) is white and very solid (compared to the pallial oviduct). While the main body of the bursa is pear-shaped, it narrows anteriorly and then swells to form a vestibule (just anterior to the end of the pallial cavity), which then gives rise to the narrower sper- mathecal duct. The spermathecal duct is tightly appressed to the capsule gland, and the wide common opening of the two (Cga) is located anterior to the anus and close to the mantle edge. Holotype.-USNM 849000 (Figs. 2, 3A). Paratypes.-USNM 849001 (Figs. 3D- H), UF 67466. Type locality. ?Roaring Springs, Real County, Texas. Etymology. ?Named after Dwight W. Taylor, in recognition for his discovery of this species and immense contributions to the study of western American freshwater molluscs. Systematic Relationships among Phreatic Littoridinines With the description of H. taylori the known phreatic littoridinine fauna of south- central Texas and northeastern Mexico to- tals five genera and six species. A compar- ison between Hadoceras and the other four genera, involving 21 characters, is given in VOLUME 99, NUMBER 1 131 Fig. 8. Scanning electron micrographs of radulae of//, taylori. A-C, Sections of the radular ribbon; D, Close- up of central teeth. 132 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. 9. Scanning electron micrographs of radulae of H. taylori. A, Close-up of central teeth; B, Close-up of lateral, inner marginal and outer marginal teeth. Table 3. A phenogram, based on simple av- eraging of percent differences among generic pairs, is shown in Fig. 12. The most similar pair, linking at 33% dif- ference, are Paludiscala and Coahuilix, both endemic to the Cuatro Cienegas Basin, Mexico. The similarity between these gen- era extends to details of the anterior portion of the female reproductive system, with both taxa having a large-sized bursa (but no sem- inal receptacle) ventral to the pallial ovi- duct, and a sperm duct travelling from the right side of the bursa to enter the posterior portion of the albumen gland. While differ- ing in features involving shell form {Coa- huilix, planispiral; Paludiscala, elongate- conic), nature of the openings of the sper- mathecal duct and capsule gland (separate vs. fused), and site of sperm storage (albu- men gland proper vs. albumen gland pouch), the two taxa are probably part of the same local radiation and perhaps should even be considered congeneric. Stygopyrgus and Balconorbis, both occurring in the Edwards (Balcones Fault Zone) Aquifer in south-cen- tral Texas, link at 48% difference and have rather dissimilar groundplans of the ante- rior portion of the female reproductive sys- tem. We have speculated (Hershler and Longley 1986) that Balconorbis may be- long to the Paludiscala-Coahuilix group, despite differences in characters such as pro- toconch microsculpture type, as its arrange- ment of the anterior portion of the female reproductive system is derivable (involving loss of the bursa) from that of the latter group. In Stygopyrgus the oviduct loops on the left side of the albumen gland, and enters the anterior end of this gland, with the sper- mathecal duct arising from this juncture and then receiving the duct of the seminal re- ceptacle well into the pallial cavity. This unique arrangement, coupled with the mammiform penial glands seen in this ge- nus (versus bulbous apocrine glands in the above three genera), suggests that Stygo- pyrgus belongs to a second radiation of phreatic littoridinines. Hadoceras differs from the other four gen- era by 57-68% of the characters considered and has a number of unique character-states, including the horn-like shell, concentric operculum with ventral process, intestinal loop on the right side of style sac, lack of penial lobes, and ventral displacement of the pallial gonoducts. The anterior portion of its female reproductive system does not closely resemble the arrangements seen in either of the other genera considered: note the unusual nature of the albumen gland, which is slender, non-glandular, and loops around the periphery of the bursa, and the elongate sperm duct, which joins the sper- mathecal duct well into the pallial cavity. Given the diversity of unique character- states seen in Hadoceras, we conclude that VOLUME 99, NUMBER 1 133 Fig. 10. Stomach (A), penis (B), and prostate (C) of//, taylori. The right aspect is shown in A and B, and the ventro-right lateral aspect shown in C. The dark, curving line in C indicates the posterior end of the pallial cavity. Ast, anterior stomach chamber; In, intestine; Odg, opening of digestive gland; Oes, oesophagus; Pr, prostate; Pst, posterior stomach chamber; Sts, style sac; Vd, vas deferens; Vdl, posterior vas deferens; Vd2, anterior vas deferens. Sdu Oov 0.50 mm Fig. 11. Left lateral aspect of the anterior portion of the female reproductive system. The posterior portion of the intestine (In) has been removed. The thick curving line indicates the posterior end of the pallial cavity while the dashed line (to the left) indicates the mantle edge. Ag, albumen gland; Bu, bursa copulatrix; Cg, capsule gland; Cga, common opening of the capsule gland and spermathecal duct; In, intestine; Oov, opening of the oviduct into the albumen gland; Ov, oviduct; Osdu, opening of the sperm duct into the spermathecal duct; Sdu, sperm duct; Sd, spermathecal duct. 134 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Table 3. ?Comparison of phreatic littoridinine gen- era involving 21 characters. B = Balconorbis, S = Sty- gopyrgus, P = Paludiscala, C = Coahuilix, and H = Hadoceras. Data for genera other than Hadoceras are from Hershler (1985) and Hershler and Longley (1986). Table 3.?Continued. Character Germ: Character B s P c H Shell 1. Maximum dimension >2.0 mm (0, 1) 0 0 1 0 1 2. Shell form: 0 1 1 0 2 a) planispiral (0) b) elongate-conic (1) c) horn-like (2) 3. Protoconch micro- sculpture: 0 1 1 1 1 a) spiral lines (0) b) punctate (1) 4. Teleoconch sculpture: 0 0 1,2 2 2 a) spiral lines (0) b) collabral costae (1) c) absent (2) Operculum 5. Operculum concentric (0,1) 0 0 0 0 1 6. Operculum with ven- tral process (0, 1) 0 0 0 0 1 Nonreproductive anatomy 7. Ctenidium present (0,1) 0 0 1 0, 1 0 8. Intestinal loop on style sac (0, 1) 0 0 0 0 1 9. Intestinal loop in pal- lial cavity roof (0, 1) 1 1 0 1 1 Reproductive morphology 10. Pallial gonoducts dis- placed ventrally (0,1) 0 0 0 0 1 11. Number of penial lobes: 1 2 1 1 0 4 0(O b) i (i) 4 2(2) 12. Position of lobe(s): 0 1 0 0 - a) outer curvature of penis (0) b) inner curvature (1) 13. Penial gland type: 0 1 0 0 - a) apocrine (0) b) mammiform (1) 1 0 14. Anterior coil of oviduct: 0 1 2 a) ventral to pallial oviduct (0) b) on left side of pallial oviduct (1) c) absent (2) 15. Oviduct opens into: 0 2 1 a) posterior tip of al- bumen gland (0) b) posterior section of albumen gland (1) c) anterior end of al- bumen gland (2) 16. Albumen gland with posterior loop (0, 1) 17. Bursa copulatrix present (0,1) 0 0 1 18. Seminal receptacle present (0, 1) 19. Openings of sper- mathecal duct and capsule gland: a) fused (0) b) separate (1) 20. Number of capsule gland tissue sections: 0 0 4 2?% b)3(D 21. Capsule gland opening muscularized (0,1) 0 1 10 0 0 1 1 1 0 1 0* 0 0 0 0 0 10 1 0 0 1 0 * Secondarily-derived seminal receptacle present. this genus represents yet another separate phreatic invasion within the Littoridininae. Epigean littoridinines having either a sim- ple penis, or a penis having mammiform or apocrine glands are known from Texas and northern Mexico (see Hershler 1985) and represent possible ancestors of the three phreatic radiations mentioned above. Fur- ther study of the diverse epigean littoridine fauna of the region will be necessary, how- ever, before the above phylogenetic specu- lations can be tested. VOLUME 99, NUMBER 1 135 Paludiscala Coahuilix Balconorbis Stygopyrgus Hadoceras 0.9 0.7 0.5 0.3 0.1 Fig. 12. Phenogram showing similarities among Hadoceras and other phreatic littoridinines from Texas and northeastern Mexico. Data used to generate the phenogram are given in Table 3. Acknowledgments We thank the owners of the Roaring Springs Ranch, Maly Ranch, and property at Jo Jan Van Camp for permission to sam- ple springs on their property. Mr. Ivan Woodard, of the Roaring Springs Ranch, was especially cooperative and even al- lowed the senior author to camp by the springs. Mr. Kevin Kuehn helped with the fieldwork. The senior author thanks W. Pratt for sharing both his ideas concerning the systematic position of Orygoceras and al- lowing us to cite his exciting discovery of Hadoceras sp. from a Nevada archaeolog- ical site. J. Koke and K. Auffenburg assisted with the scanning electron microscopy. The senior author acknowledges the receipt of a generous contract from Southwest Texas State University (Account # 29665), with- out which the project could not have been completed. 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