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

description: Orconectes (Gremicambarus) castaneus
Pecan Bayou Crayfish
new species
Figs. 6, 9–13, Table 2
Diagnosis. Body pigmented, eyes well developed. Rostrum with marginal spine, lacking median carina. Carapace with single cervical spine. Areola obliterated, constituting 32.1 to 36.9 (mean 33.8 ± 1.6) percent of total carapace length and 40.7 to 49.2 (mean 43.8 ± 2.7) percent postorbital carapace length. Suborbital angle weak. Ischium of third pereiopod in first form male with simple strong hook not overreaching basioischial articulation. Gonopod of first form male with two processes, reaching midlength of coxa of second pereiopod when abdomen flexed; central projection corneous, mesial process not; cephalic shoulder near base of central projection absent or weak; central projection constituting 32.3 to 35.7 (mean 33.5 ± 1.3) percent of appendage length, longer than mesial process; both processes curved caudally with tips directed approximately 90 degrees to axis of shaft. Annulus ventralis immovable, subrhomboid in outline, with well-defined cephalomedian fossa and sinus winding sinuously from fossa to caudal margin.
Holotypic male, form I. Cephalothorax (Fig. 9, 10 a, b) subcylindrical, slightly depressed. Abdomen slightly narrower than cephalothorax (12.6 and 14.6 mm, respectively). Areola obliterated. Cephalic section of carapace 2.1 times as long as areola, latter comprising 32.1% of total length of carapace (41.5% of postorbital carapace length). Surface of carapace punctate dorsally and both punctate 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, bearing punctations; acumen relatively long with upturned tip. Postorbital ridges strong, grooved dorsolaterally, terminating cephalically in divergent spines. Suborbital angle obtuse. Brancheostegal spine weak.
Abdomen longer than carapace (34.2 and 30.5 mm, respectively). Cephalic section of telson with two spines on left and three on right, lateral ones fixed. 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 slightly anterior to midlength. Antennal peduncle with well developed spine on both basis and ischium; flagellum reaching slightly beyond telson. Antennal scale (Fig. 10 j) 2.6 times as long as broad, widest slightly distal to midlength. Third maxilliped extending slightly distal to spine on ventral surface of proximal podomere of antennule.
Right chela (Figs. 10 c–f) depressed, palm inflated; palm about 1.8 times as broad as length of mesial margin; latter comprising 23% total chela length; dorsal surface of palm covered with punctations with a few weak tubercles mesially. Mesial margin of palm with two irregular rows of tubercles, dorsal row of 7 and ventral row of 8. Lateral and ventral surfaces of palm weakly punctate. Immovable finger dorsally covered with puncations and bearing grooves bordering inside and outside margins; lateral margin with well defined single row of punctations bordered on both sides by apunctate low ridges; ventral surface with punctations; opposable margin with 10 tubercles on proximal two thirds, with minute denticles on distal third, proximal third bearing plumose setae. Dactyl dorsally punctate, 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; ventral surface with low apunctate median ridge, otherwise punctate; opposable margin with row of 16 tubercles along proximal 80%, with minute denticles on distal third.
Carpus of cheliped longer than broad; dorsally with oblique furrow, flanked mesially by turbercles and laterally by punctations; mesial margin with two tubercles, one large and spiniform; ventral surface with scattered poorly developed tubercles and punctations and two spiniform tubercles on distal margin; lateral margin punctate. Dorsal, mesial and lateral surfaces of merus weakly punctate; dorsal surface with two spiniform tubercles near distal margin; ventral surface (Fig 10 g) with two rows of tubercles, lateral row of 6 and mesial row of 11, tubercles increasing in size distally. Lower surface of ischium with single small tubercle, otherwise weakly punctate.
Hook on ischium (Fig 10 h) and gonopod (Figs. 11 a–c) as described in "Diagnosis".
Uropod (Fig. 10 i) with both lobes of basal podomere bearing single acute spines; mesial ramus with well developed median carina terminating in distinctly premarginal spine and strong distolateral spine.
Allotypic female. Differing from holotype, other than in secondary sexual characteristics, in following respects: areola proportionately longer (34.2% carapace length and 44.8% postorbital carapace length); cephalic section of telson with two lateral spines on right and left margins; flagellum reaching to midlength of telson; palm of right chela 1.5 times as broad as length of mesial margin, latter comprising 27% total chela length; opposable margin of fixed finger with 7 tubercles; opposable margin of dactyl with row of 12 tubercles; ventral surface of merus with lateral row of 5 tubercles and mesial row of 9; Annulus ventralis (Fig. 13 a) immovable, cephalic 40% uncalcified; margin broadly rounded caudally, subangular cephalically and tightly angled laterally; sinus originating in cephalomedian fossa slightly dextral to midline, extends laterally across midline, then curves sharply dextrally back to midline before forking near its termination near midline of caudal margin. Postannular sclerite 40% as broad as annulus. First pleopod present.
Morphotypic form II male. Differing from holotype, other than in secondary sexual characteristics, in following respects: cephalic section of carapace 1.7 times as long as areola, latter comprising 36.9% of total length of carapace (49.2% of postorbital carapace length); cephalic section of telson with two distolateral spines on left and right margins; third maxilliped extends to distal margin of proximal podomere of antennule; palm of right chela 1.4 times as broad as length of mesial margin; opposable margin of fixed finger with 11 tubercles on proximal two thirds; opposable margin of dactyl with row of 13 tubercles; carpus with 3 tubercles on mesial margin and additional spine ventromesially; ventral surface of merus with 5 tubercles in lateral row; hook on ischium of 3rd pereiopod weak. Gonopod (Figs. 11 d, e) with both processes noncorneous and much shorter and thicker than holotype, both curved caudally with tips projecting at approximately 45 degrees to the axis of shaft; free part of central projection comprising 15% of total appendage length.
Color notes. Holotype (Fig. 9): Basic colors light brown with dark brown markings, in the form of freckles and stripes. Cephalic section of carapace anterodorsally obscurely freckled, mandibular abductor and caudal gastric regions slightly darkened; laterally several oblique short stripes and freckles present. Thoracic section with two dark, lateral, longitudinal stripes, one on the ventral margin and the other at midheight; freckles cover dorsal surface and single larger diffuse spot dorsolaterally near the caudal margin. Ventral surface of carapace cream. Abdomen more finely freckled than cephalothorax; pairs of dorsolateral spots on pleura, most pronounced on first pleuron and progressively less distinct on more caudal segments; caudal margins of pleura and cephalothorax bordered with thin red band, which in turn bordered cephalically by thin dark olive band, latter progressively less pronounced caudally. Basic coloration of telson and uropod similar to abdomen; caudal margin of telson, caudal and lateral margin of mesial ramus of uropod, and caudal margins of both podomeres of lateral ramus red. Cheliped with background color similar to body, covered with black spots, both fingers with distal 10% red-orange and distal 50%–10% blue; tubercles cream, those on mesial margin flanked by red proximally; propodactyl articulation lined with red, ventral surface cream and unspotted; carpus and merus colored similarly to chela, merocarpal articular condyle red. Pereiopods 2–5, with background color similar to cheliped; merocarpal articular condyles and dactyl and propodus of pereiopods 2 and 3 slightly tinged with red.
Based on body photos of 25 specimens, color pattern deviates in minor respects from the holotype. Overall color varies from that of the holotype to a slightly greenish brown. The proximal half of the fingers and distal part of the palm are sometimes blue-green. In several specimens the caudal gastric region is a chestnut brown, and in one case nearly orange.
Type locality. Lake Brownwood near its spillway, Brown County, Texas (31.84319° N, 99.00236° W). The margins of the lake are lined with slabs of limestone ranging in size from 0.25 to 2.0 meters in diameter. No aquatic vegetation is present, but moderate amounts of algae cover the rocks. Water is slightly turbid and in full sun with no trees along the shore. All crayfish were found hiding under rocks and captured by hand or with a dipnet.
Disposition of types. The holotype, allotype and morphotype (ɗI, Ψ, ɗII) are deposited in the National Museum of Natural History (Smithsonian Institution), nos. 1145304, 1145306 and 1145307, 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 50.0 (postorbital carapace length of 39.2) mm. The largest and smallest first form males have carapace lengths of 37.2 (28.6) mm and 29.5 (23.6) mm, respectively. Ovigerous females or ones carrying young have not been collected.
Range and specimens examined. This crayfish has been collected at only four sites (Fig. 6). Brown County: (1) Type locality, 1 ɗI, 3 ɗII (2 raised to I), 3 Ψ, 1 Aug 2009, 4 ɗI, 5 ɗII (4 raised to I), 11 Ψ, 25 Sep 2009; (2) Lake Brownwood @ Rt. 279, (31.83302° N, 99.09890° W) 1 Ψ, 25 Sep 2009. Mills County: (3) Pecan Bayou @ Rt. 574 (31.45545° N, 98.69973° W), 1 Ψ, 31 Aug 2008. San Saba County: (4) Colorado River @ Rt 16 (31.35365° N, 98.67193° W), 1 Ψ, 31 Aug 2008.
Variations. Color pattern variations were previously noted in the "Color notes" section. The form I male gonopod (Figs. 11 a–b, 12a–h) shows little variation; the central projection varies from 32.3 to 35.7 percent of the appendage length; the amount of curvature of both processes shows slight variation. The annulus ventralis (Figs. 13 a–l) varies in the following respects: both caudal and cephalic margins vary from smoothly rounded to subangular; the position of the lateral margin angles varies from 25% to 40% of the annulus length as measured from the caudal margin; the fossa size and shape, sinus configuration and surface wrinkling all show minor variation; the left and right sides are flipped about half the time.
Relationships. The nearly identical color pattern and similar gonopod structure attest to the assumed close relationship between Orconectes castaneus and O. nais (Faxon, 1885). The former, however, differs in the following respects: The gonopod processes are slightly longer, the central projection constituting 32.3 to 35.7 (mean 33.5 ± 1.3) percent appendage length, compared to 27.8 to 30.3 (mean 28.8 ± 0.7, N=20) percent in Texas O. nais specimens (compare Figs. 12 a–h with 12q–x). The areola is usually obliterated, but may be extremely narrowly open with no room for punctations; in O. nais the areola is always narrowly open, with room for 1 to 2 rows of puncations at its narrowed part. The annulus ventralis has a distinctly larger and deeper fossa and a more sinuous, branched sinus that deviates farther from the midline (compare Figs. 13 a–l and 13m –p). The coloration, based on a comparison with 35 O. nais body photos, is consistently less reddish (compare Figs. 9 and 15).
Although apparently most closely related to O. nais, O. castaneus keys out to O. p. longimanus (Faxon, 1898) with Hobbs' most recent key (Hobbs, 1972). O. p. longimanus, however, differs is the following respects: the color pattern is distinctly different (compare Figs. 9 and 16); its gonopod processes (Figs. 12 i–p) are longer, the central projection constituting 36.8 to 41.2 (mean 38.5 ± 1.5) percent appendage length (compared to 32.3 to 35.7, mean 33.5 ± 1.3); and the annulus ventralis has sinus that is less sinuous and forked in the caudal 40%, a usually more sinuous and narrow fossa, and a generally smoother surface (compare Figs. 13 a–l and 14).
Etymology. Castaneus (L.) = the color of chestnuts, brown; alluding to the color many specimens possess in the caudal gastric region.
Associates. No associates were found at the type locality or locality 2, both at Lake Brownwood; however, Procambarus clarkii was found with O. castaneus in the lotic environments of localities 3 and 4.
Conservation status. It is unclear whether this species is native to the Pecan Bayou/Upper Colorado region. Its range is rather small, which is often the case for introduced Orconectes species; and a large amount of recreational fishing takes place at the type locality at Lake Brownwood, providing ample opportunity for introducing Orconectes species. For conservation purposes however, until evidence is found that indicates otherwise, the species should be conserved as if native. With Orconectes virilis, O. nai s and O. deanae having been apparently widely introduced throughout the state, the chances of a species being introduced into the range of O. castaneus is great. In addition both Orconectes virilis and O. nais have already been introduced into the Colorado River system (Pedernales River) and may eventually migrate upriver to the Pecan Bayou region; although dams at Lake Travis, Lake LBJ and Lake Buchanan may impede dispersal. With this said, it is recommended the species be ranked as critically endangered.
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 11-19, DOI: 10.5281/zenodo.276049