Orconectes (Buannulifictus) occidentalis
Creators: name: Johnson, Daniel P.
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Cambaridae
Orconectes
Orconectes occidentalis

description: Orconectes (Buannulifictus) occidentalis
Western Freckled Crayfish new species
Figs. 6, 17–24, Tables 3, 4
Cambarus palmeri longimanus, Faxon, 1898 [in part]
Orconectes palmeri longimanus, Hobbs, 1942 [in part]
Orconectes (Buannulifictus) palmeri longimanus, Fitzpatrick, 1987 [in part] Diagnosis. Body pigmented, eyes well developed. Rostrum with marginal spine, lacking median carina. Carapace with single cervical spine. Areola obliterated and constituting 33.1 to 35.3 (mean 34.2 ± 0.8) percent of total carapace length (42.6 to 46.8, mean 44.7 ± 1.6, percent postorbital carapace length). Suborbital angle obtuse. Ischium of third pereiopod in first form male with simple strong hook reaching level of basioischial articulation. Gonopod of first form male with two processes, reaching caudal margin of coxa of first pereiopod when abdomen flexed; central projection corneous, mesial process not; cephalomesial shoulder near base of central projection weak or absent; central projection constituting 37.1 to 46.0 (mean 42.8 ± 2.1) percent of appendage length, longer than mesial process; both processes curved caudally with tips directed from 60 to 90 degrees to axis of shaft. Annulus ventralis immovable, outline subelliptical to subcircular in shape with broadly rounded cephalic and caudal margins and angled lateral margins, sinus sinuous along most of length with cephalic half open forming sinuous fossa. Coloration heavily mottled, postorbital ridge brown-orange.
Holotypic male, form I. Cephalothorax (Fig. 17, 18 a–b) subcylindrical, slightly depressed. Abdomen slightly narrower than cephalothorax (13.2 and 15.3 mm, respectively). Areola obliterated. Cephalic section of carapace 2.0 times as long as areola, latter comprising 33.6% of total length of carapace (44.3% of postorbital carapace length). Surface of carapace punctate dorsally and granulate laterally.
Rostrum with margins slightly converging, not distinctly thickened, and terminating in well-developed, upturned marginal spines; upper surface deeply concave, lacking median carina, marginal row of heavy punctations otherwise weakly punctate; acumen relatively long with upturned tip. Postorbital ridge strong, grooved dorsolaterally, with anterior spine. Suborbital angle obtuse. Brancheostegal spine strong.
Abdomen slightly longer than carapace (33.4 and 32.7 mm, respectively). Cephalic section of telson (Fig. 18 i) with two spines on each margin, lateral ones fixed (left lateral spine damaged). Cephalic lobe of epistome campanulate, with slightly thickened irregular margins; main body of epistome with distinct, elongate fovea.
Ventral surface of proximal podomere of antennular peduncle with spine at two-thirds distance from base. Antennal peduncle with well developed spine on both basis and ischium; flagellum reaching midlength of 6th abdominal segment. Antennal scale (Fig. 18 j) 3.1 times as long as broad, widest slightly distal to midlength. Third maxilliped extending to distal margin of proximal podomere of antennule.
Right chela (Figs. 18 c–f) depressed, slightly gaping; palm inflated, about 1.5 times as broad as length of mesial margin; latter comprising 24% total chela length; dorsal, lateral and ventral surfaces of palm covered with punctations with a few weak tubercles dorsomesially. Mesial margin of palm with two rows of seven tubercles. Immovable finger strongly punctate on dorsal and ventral surfaces; lateral margin with well-defined single row of punctations bordered on both sides by apunctate low ridges; dorsal surface with pronounced groove bordering mesial margin and weak groove bordering lateral margin; opposable margin with row of 10 tubercles on proximal two thirds and minute denticles on distal half, base bearing minor plumose setae. Dactyl dorsally and ventrally punctate, dorsum with broad relatively apunctate low median ridge, and low groove bordering opposable margin; mesial margin with three rows of tubercles, those of middle row largest, dorsal row smaller and ventral row poorly developed; ventral surface with broad low apunctate median ridge; opposable margin with row of 15 tubercles along proximal 4/5ths, with minute denticles on distal half.
Carpus of cheliped longer than broad; dorsally with oblique furrow; all surfaces weakly punctate with simple tubercles dorso- and ventromesially; spiniform tubercles are at the following locations: 3 on mesial margin, 1 on distal ventral margin and 1 on ventrolateral articular condyle; dorsal, mesial and lateral surfaces of merus weakly and sparsely punctate; ventral surface (Fig 18 g) with two rows of tubercles generally increasing in size distally, lateral row of 7 and mesial row of 13; additional spiniform tubercles are found at the following locations: 2 on distal half of dorsal surface and 1 on the ventrolateral distal margin. Lower surface of ischium with 4 small tubercles, otherwise weakly punctate.
Hook on ischium (fig. 18h) and gonopod (figs. 19a–c) as described in "Diagnosis". Uropod (fig. 18i) with both lobes of basal podomere bearing single acute spines; mesial ramus with well developed median carina terminating in distinctly premarginal spine; distolateral spine well developed
Allotypic female. Differing from holotype, other than in secondary sexual characteristics, in following respects: cephalic section of carapace 1.9 times as long as areola; acumen relatively short with tip not distinctly upturned, possibly due to damage; abdomen distinctly longer than carapace (35.0 and 29.9 mm, respectively); flagellum reaching distal margin of cephalic section of telson; palm of right chela 1.3 times as broad as length of mesial margin; latter comprising 28% total chela length; opposable margin of fixed finger with row of 9 tubercles on proximal two thirds, plumose setae at base more pronounced; opposable margin of dactyl with row of 13 tubercles; ventral surface of merus with lateral row of 5 tubercles and mesial row of 12; lower surface of ischium with 5 small tubercles. Annulus ventralis (Fig 21) immovable, cephalic 40% uncalcified; margins broadly rounded cephalically and caudally, and obtusely angled laterally; sinus originates at midline near cephalic margin, extends and opens up dextrally, curves sinistrally to sinistral side, then curves dextrally back to midline where it closes, then continues sinuously before terminating at midline of caudal margin. Postannular sclerite 0.81 times as wide as annulus with cephalic margin semicircular and caudal margin slightly convex. First pleopod present.
Morphotypic form II male. Differing from holotype, other than in secondary sexual characteristics, in following respects: acumen without spine due to damage; flagellum reaching slightly past distal margin of telson; third maxilliped extending to two thirds length of proximal podomere of antennule; palm of right chela about 1.2 times as broad as length of mesial margin; latter comprising 28% total chela length; mesial margin of palm with dorsal row of 6 tubercles; proximal half of opposable margin of immovable finger with distinct plumose setae; opposable margin of dactyl with row of 9 tubercles; ventral surface of merus with lateral row of 4 tubercles and mesial row of 8; lower surface of ischium with 2 small tubercles; hook not evident on ischium of 3rd pereiopod. Gonopod (Figs. 19 d,e) with both processes noncorneous, thicker and relatively shorter than holotype; central projection comprises 24.4% total appendage length, both tips curved caudally with tips directed at approximately 45 degrees to axis of shaft.
Color notes. Holotype (Fig. 17): Basic colors light brown with dark brown markings, primarily in the form of freckles. Anterior gastric region gray with dark freckles; caudal gastric and mandibular adductor regions dark, hepatic region with poorly defined dark stripes; postorbital ridge, rostral margin and eye stem margin orange-tan; cervical groove gray surrounded by suffusion of orange-tan. Thoracic region heavily mottled, well defined kidney-shaped blotches just caudal to cervical groove; ventrolateral and caudolateral margins dark gray. Abdomen finely and obscurely freckled; caudal third of terga dark brown. Chela, carpus and distal merus with slight greenish cast; well-defined black spots on dorsal surface of carpus, palm and proximal third of fixed finger; tips of fingers tan, bordered by pale blue-gray proximally; tubercles cream. Venter and proximal third of pereiopods cream.
The color pattern varies as follows, based on photos of paratypes and specimens from other locations: anterior gastric region background color in some specimens is tan rather than gray; in the majority of specimens, the abdomen and tail are distinctly speckled and most specimens in general are more freckled than the holotype (Fig. 24); in some individuals the dark marks on the caudolateral margin of the carapace extend onto the abdomen; in very young specimens, the fingers of the chela have red on the tips, which is in turn bordered proximally by yellow then vivid blue.
Type locality. Guadalupe River @ Rt. 1376, Kendall County, Texas (29.95760° N, 98.71735° W). The region is underlain by limestone bedrock and the river contains an abundance of rocks and occasional accumulations of decaying leaves, stick and logs, the latter being the favored microhabitat for this species. Water is clear, rapidly flowing, with many sections less the 30 cm deep. Cypress trees are scattered along the banks.
Disposition of types. The holotype, allotype and morphotype (ɗI, Ψ, ɗII) are deposited in the National Museum of Natural History (Smithsonian Institution), nos. 1145308, 1145309 and 1145310, respectively. Paratypes are deposited in the Illinois Natural History Survey Crustacean Collection.
Size. The largest specimen examined is a female with a carapace length of 40.8 (postorbital carapace length 30.8) mm from the Guadalupe River in Kendall County. The largest and smallest form I males have carapace lengths of 39.6 (29.7) and 20.5 (14.7) mm, respectively. Neither ovigerous females nor ones carrying young have been collected.
Range and specimens examined. As part of this study, a total 66 form I males, 50 adult females, and an uncounted number of form II males and juveniles were examined. The species has been collected at 91 sites in 22 counties (Fig. 6) spanning the Colorado, Guadalupe, Medina, Frio and Nueces basins, as follows (number of sites in parentheses): Bandera (3), Bastrop (1), Blanco (4), Burnet (3), Comal (5), Edwards (1), Gillespie (7), Gonzales (2), Guadalupe (3), Kendall (5), Kerr (10), Kimble (14), Llano (4), Mason (5), McCulloch (3), Medina (2), Menard (5), Real (2), San Saba (5), Sutton (1), Travis (3), Uvalde (3). Prior to this study, this crayfish was known (as O. p. longimanus) from only 6 counties (Johnson and Johnson, 1998).
Variations. Considering the species spans five basins, the amount of geographic variation is remarkably small. The only population with characteristics notably different from the others is that of the San Saba River and adjacent upper Colorado River which it feeds. There the gonopod processes (Figs. 20 s–x) are shorter, with the central projection comprising 39.2 (mean) percent of the appendage length, compared to 42.6 to 44.6 percent for other regions; and the cephalic margin of the annulus ventralis (Figs. 23 q–x) is more tightly curved on average.
For the rest of the range the gonopod process lengths (Figs. 19 a–b, f–m, 20a–x) increase slightly from eastern to western drainages (Table 4, Fig. 7). In a few specimens, the mesial process is markedly shorter than the central projection, possibly as the result of damage. The degree of separation and curvature of the processes is variable. The tip of the mesial process may be directed anywhere from 45 to nearly 90 degrees from the appendage axis. Aside from the previously noted region, the annulus is remarkably uniform in general form (Figs. 22 a–s, 23a–x), but does show minor variations: the width/length ratio ranges from about 1.26 to 1.6, the smaller values correlating with larger specimens; the sinus opening ranges from narrow to wide, and in a few cases a distinct subcircular fossa is present. While the sinus is always clearly sinuous, the length of the lobes is variable. The caudal margin shape varies from broadly rounded to straight, and in some cases a small angular protrusion is present at the midline. The surface may be smooth, contain a few dimples or wrinkled. The sinistral and dextral sides are reversed about half the time.
Relationships. The nearly identical gonopod, similarities in many color pattern elements and proximity of ranges allude to the presumed close relationship between O. occidentalis and O. texanus. The two, however, differ in the following respects:
The annuli ventralis of all O. texanus populations (Figs. 32–34) are distinctly different from the subcircular to subelliptical form of 90% of the O. occidentalis females examined (Figs. 22 a–s, 23a–x). The remaining few annulus ventralis variants (e.g. Figs. 23 h, q, w), mostly from San Saba River specimens, are clearly less rhombic in outline than that of the nearest populations of O. texanus (Fig. 34). Characters useful for distinguishing annuli ventralis of other O. texanus populations are as follows: the annulus ventralis of the Trinity basin always has a definite cephalic fossa with a narrow cephalic rim; and that of the Sabine basin always has a cephalic pillow-like structure. A few of the annuli from the Neches basin cannot be definitively distinguished from the aforementioned few subrhombic annuli of O. occidentalis. That basin is, however far removed from the range of O. occidentalis and the similarity of the few annuli is unlikely to be due to a close relationship.
Although the gonopods appear to be nearly identical, the degree of taper of the central projection (Fig. 1 c) is statistically different (although overlapping): it ranges from 13% to 20% (mean 17% ± 3%) in O. texanus and 18% to 26% (mean 23% ± 3%) in O. occidentalis. In addition the gonopod of O. texanus of the Navasota River (Figs. 30 h–o), the most proximal population, has a higher ratio of central projection caudal offset (Fig. 1 a) to total appendage length than in O. occidentalis.
The color pattern of O. texanus (compare Fig. 25 with Figs. 17, 24) is much less mottled; the dark caudal rim of the carapace is unbroken dorsally; the caudal dark margins of the abdominal segments are much more distinct; and the postorbital ridge, merocarpal articular condyles, and telson/uropod margins are bright red. These color pattern differences, based on body photos of 52 O. occidentalis and 78 O. texanus specimens, in addition to examination of hundreds of living wild specimens of both species by the author, are consistent.
The ranges of O. occidentalis and O. texanus are separated by a gap of approximately 120 km (75 miles, Fig. 6), with the only occurrence of either species in the Brazos basin being the Navasota population of O. texanus.
Apparently more distantly related is O. palmeri longimanus, to which O. occidentalis was previously assigned. It differs in the following respects: the annulus ventralis (Figs. 14 a–p) is subrhombic and its sinus is simpler with fewer lobes; the color pattern (Fig. 16) is very different, with the body never freckled, widely scattered red marks present, and the kidney-shaped blotch caudally flanking the cervical groove absent or obscure; and the gonopod processes (Figs. 12 i–p) are slightly shorter with a 38.4 mean ratio of central projection length to total appendage length, compared to means of 44.6 to 39.4, for the geographic regions of O. occidentalis.
O. p. palmeri (Faxon, 1884) is distributed east of the Mississippi River and as such is presumably not closely related; however, its gonopod and its color pattern are more similar to O. occidentalis than that of O. p. longimanus. The gonopod processes are longer, matching more closely the range of O. occidentalis. The color pattern is described as heavily freckled (Pflieger, 1996) and photos of specimens from relatively near the type locality (Pflieger, 1996; Taylor and Schuster, 2004) show the presence of kidney-shaped blotches caudolaterally flanking the cervical groove and no bright red markings. O. palmeri palmeri differs from O. occidentalis, however, in color pattern and annulus ventralis characteristics. The typical annulus ventralis of O. occidentalis with its broadly rounded margin and highly sinuous sinus has not been seen in any of the O. palmeri palmeri annuli examined (Figure 35). Furthermore nearly all of the annuli of O. palmeri palmeri examined possess characters which differ from those seen in O. occidentalis. Three annuli (Figs. 35 a–c) have large, deep, crosswise elongate fossae similar to that of O. virilis. Another annulus (Fig. 35 d) has a sinus with a long narrow lobe restricted to the cephalic third. Another two (Figs. 35 e–f) differ in having simpler sinuses, especially in the caudal third. The annulus in Figure 35 g is not clearly distinct from that of some specimens of O. occidentalis from the San Saba basin.
Only a single photo of O. p. palmeri from relatively close to the type locality and east of the Mississippi River could be found (Taylor and Schuster, 2004). This specimen shows characters never seen in O. occidentalis including a dark lateral longitudinal stripe and a dark blotch laterally flanking the caudal section of the branchiocardiac groove. Pflieger (1996) illustrates a specimen of O. palmeri from Dunklin County, Missouri. This location is also relatively close to the O. p. palmeri type locality (80 km), but is west of the Mississippi River and as such may be considered to be in the so called O. p. palmeri / O. p. longimanus intergrade zone as defined by Williams (1954). This specimen also shows what appears to be a broken lateral carapace stripe.
Given the limited number of character differences between O. occidentalis and O. p. palmeri, the possibility that the former is an introduction of the latter must be considered. This is especially important considering the few photos and museum specimens of O. p. palmeri available for examination and the high variability of annulus ventralis structure known for O. palmeri and close relatives. Against O. occidentalis being an introduction of O. p. palmeri are the following arguments. The crayfish has long been known from the area, with it being recorded in the Colorado system in 1951 (USNM 115562) and in the Guadalupe system in 1958 (Penn and Hobbs, 1958). The crayfish occurs in five different adjacent drainages, with no other isolated populations of this crayfish having been found in the state despite suitable habitat being widely available. Fifty nine years after the first Texas record of O. occidentalis, no evidence can be found of introductions of O. p. palmeri anywhere, indicating that it is not gathered and sold in significant quantities by the bait industry and probably infrequently collected and used by individual fishermen. Gonopod and annulus ventralis structure show geographic variation, as previous discussed in "Variations", indicating most probably a native distribution.
O. p. creolanus (see Walls, 2009) shares a strikingly similar color pattern to that of O. occidentalis. It, however, differs in having shorter gonopod processes and a different annulus ventralis.
O. castaneus differs from O. occidentalis in having a very different color pattern (Fig. 9), much shorter gonopod processes (mean ratio of central projection to total appendage length of 33.5 versus 39.2 to 43.9 depending on region in O. occidentalis) and a different annulus ventralis structure (Figs. 13 a–l).
Etymology. Occidentalis (L.) = western; alluding to the relatively western distribution of the species compared to other members of its genus.
Associates. It has been found at one or more locations with the following crayfishes: Procambarus clarkii, Orconectes nais and O. virilis. The latter two are apparently recent introductions based on their limited distributions.
description: Published as part of Johnson, Daniel P., 2010, Four new crayfishes (Decapoda: Cambaridae) of the genus Orconectes from Texas, pp. 1-45 in Zootaxa 2626 on pages 19-31, DOI: 10.5281/zenodo.276049