Fallicambarus schusteri, Taylor and Robison

Taylor, Christopher A. & Robison, Henry W., 2016, A new burrowing crayfish of the genus Fallicambarus Hobbs, 1969 (Decapoda: Cambaridae) from the Red River Drainage of the southcentral United States, Zootaxa 4144 (4), pp. 575-583 : 576-583

Fallicambarus schusteri, Taylor and Robison new species

Figs. 1 , 2, Table 1

Diagnosis. Body and eyes pigmented. Carapace laterally compressed and deep. Rostrum triangular and deeply excavated, terminating in short acumen with small upturned spine, weakly decurved in lateral view; median carina absent. Rostral margins not thickened and of relatively consistent thickness throughout their length ( Fig. 1 I). Margins bordered mesially by punctations with tufts of short setae; margins straight and converging through the basalmost ¾ of their length, then angle more sharply towards base of acumen. Areola 36.2–41.0 % (x = 38.5, n = 25, SD = 1.3) of total length of carapace (CL = distance from distal tip of acumen to dorsocaudal edge of cephalothorax) and 42.0–46.8 % (x = 44.4, n = 25, SD = 1.4) of postorbital carapace length (PCL = distance from anteriolateral edge of cephalothorax immediately behind eye to dorsocaudal edge of cephalothorax). Areola obliterated ( Fig. 1 I). Postorbital carapace length 84.9–88.1 % (x = 86.5, n = 40, SD = 0.8) of CL. Cervical spines absent. Postorbital ridge low with smoothly rounded terminal ends ( Fig. 1 A). Suborbital angle absent. Antennal scale broadest distal to midlength, distal margin gradually sloping to midpoint of mesial margin, thickened lateral margin terminating in long corneous spine ( Fig. 1 K). Incisor region of mandible deeply indented with two large cusps. Cephalomedian lobe of epistome wide and bell-shaped with small, triangular cephalomedian projection; epistomal zygoma strongly arched ( Fig. 1 H). Ischia of third and fourth pereiopods of MI males with large hooks, hooks barely overreaching basioischial articulation in larger form I males only. Ischia of third pereiopods of larger form II males (MII) with weak hook. Coxa of fourth pereiopods of MI and MII males with large, ridge-like caudomesial boss. Chela with cristaform row of tubercles along mesial margin of palm, usually seven tubercles (range 6–8, mode = 7, n = 25, SD = 0.5) in row. Second row of three to five small tubercles found just lateral to row along mesial margin of palm. Opposable margins of dactyl and propodus with third tubercle from base enlarged; opposable margin of dactyl shallowly excavated basal to third tubercle ( Fig. 1 M). Dorsal surfaces of fingers with low longitudinal ridges ( Fig. 1 M). Lateral margin of palm of chela weakly serrate.

First pleopods of MI male symmetrical and continuous at bases, extending to midpoint of bases of third pereiopods when abdomen flexed. Proximomesial or basiomesial spurs on both pleopods. First pleopod of FI male terminating in three elements: corneous central projection strongly recurved caudodistally at an angle of approximately 140 degrees, thin and gradually tapering to an acute tip lacking a subapical notch, and reaching proximally to or just beyond distal tip of mesial process ( Fig. 1 B, 1C); mesial process non-corneous, thin and gradually tapering to an acute tip, width at it’s base equal to that of the central projection, proximal edge usually at 90 degree angle to main axis of pleopod. Large, triangular cephalic process located between bases of central projection and mesial process; process angled approximately 45–50 degrees to main axis of pleopod; distal half of process corneus. First pleopod of MII male non-corneous, both elements arched caudodistally at 90 degrees to main axis of pleopod and diverging; wide gap between distal tips of both elements ( Figs. 1 F, 1G). Annulus ventralis immovable, subrhomboidal but with a circular central region defined by strongly elevated edges surrounding a deep, central fossa; cephalic half with wide median trough; fossa well defined with tongue extending dextrally, disappearing under caudolateral wall; sinuate sinus running from center of fossa to caudal edge ( Fig. 1 J).

Description of holotypic male, form I. Carapace laterally compressed and deep, at widest point carapace wider than abdomen (15.9 and 11.0 mm, respectively). Greatest width of carapace slightly larger than height at caudodorsal margin of cervical groove (15.9 and 14.3 mm, respectively). Areola constituting 40.3% of length of carapace. Postorbital carapace length 86.0% of total length of carapace. Areola obliterated. Rostrum as described in Diagnosis. Acumen short and terminating in small corneous spine, reaching just posterior to distal margin of third antennal endopod. Postorbital ridge weakly developed, termini smoothly rounded and lacking spine or tubercle. Suborbital angle absent. Cervical spine or tubercle absent. Branchiostegal areas and lateral and dorsal surfaces of carapace smooth, covered with shallow punctations.

Abdomen shorter than carapace (28.9 and 33.5 mm, respectively). Anteriolateral and ventrolateral margins of pleura smoothly rounded. Cephalic section of telson bearing 2 spines in each caudolateral corner, more mesial pair movable. Proximal podomere of uropod lacking spines along distal edge. Dorsal surface of mesial ramus with strong centrally located ridge, distal termini of ridge rounded. Caudal margin of cephalic section of lateral ramus with 8 fixed spines and 1 movable spine in caudolateral corner. Dorsal surface of lateral ramus with two weak ridges. Dorsal surfaces of telson and uropods setiferous. Caudal edges of telson and uropods with long setae.

Antennal scale narrow and as describe in Diagnosis. Left antennal scale 4.0 mm long, 1.2 mm wide. Epistome as in Diagnosis.

Lateral margin of right chela nearly straight, with four low tubercles along middle section; mesial surface of palm with cristiform row of 6 tubercles, second row of 3 low tubercles lateral to mesial row; dorsodistal margin of palm region at base of dactyl inflated with cleft at midpoint of base of dactyl ( Fig. 1 M). Mesial and lateral surfaces of chela, dorsal and ventral surfaces of fingers, and opposable margins of fingers covered with shallow setiferous punctations. Dorsal surface of finger of propodus with low submedian longitudinal ridge flanked by setiferous punctations; basal half of opposable margin with four tubercles, third tubercle from base of finger damaged (third from base on left chela largest), one corneous tubercle at three-quarter point. Dorsal surface of dactyl with low submedian longitudinal ridge flanked by setiferous punctations; basal half of opposable margin concave with two tubercles of equal size, one large tubercle at distal end of concavity, three small corneous tubercles evenly spaced along distal half of margin. Finger of propodus and dactyl with subterminal corneous tip. Ventral surface of palm of chela covered with tubercles of varying size.

Right carpus with wide deep oblique furrow dorsally; mesial margin with one large spine and two small tubercles, large spine distal-most; ventral surface with one small centrally located spine and two small tubercles mesial to large spine. Distal half of dorsal surface of merus with row of tubercles and spines increasing in size proximal to distal; ventral surface with one large corneous spine at distomesial corner and mesial row of nine spines, distal most three spines corneous; lateral margin with row of seven non-corneous spines. Ischium with two small corneous spines along margin.

Large hooks on ischia of third and fourth pereiopods; hooks barely overreaching basioischial articulation and not opposed by tubercle on basis. First pleopods of form I male symmetrical and continuous at bases, proximomesial spurs found on both; extending to midpoint of bases of third pereiopods when abdomen flexed. First pleopod of form I male as described in Diagnosis( Figs. 1 B–1E).

Description of allotypic female. Differing from holotype as follows: Areola constituting 37.4% of length of carapace. Postorbital carapace length 87.5% of length of carapace. Mesial surface of palm of right chela with row of seven tubercles. Distal half of dorsal surface of merus with two large spines only. Caudal margin of cephalic section of lateral ramus of uropod with 10 fixed spines.

Sternum between third and fourth pereiopods narrowly V-shaped. Annulus as described in Diagnosis. Ishia of third and fourth pereiopods lacking hooks. First pleopod uniramous, barely reaching caudal margin of annulus when abdomen flexed.

Description of morphotypic male, form II. Differing from holotype as follows: Areola constituting 37.4% of length of carapace. Postorbital carapace length 86.1% of length of carapace. Mesial surface of palm of right chela with single row of seven tubercles. Given the small size of the morphotype, many of the spines found on the carpus and merus are not as large and developed as those on the holotype.

Hook on ischium of third pereiopod only, hook very short, not overreaching basioischial articulation. First pleopod as described in Diagnosis.

Size. The largest specimen examined is a 35.5 mm CL (30.8 mm PCL) female. Females (n = 10) range in size from 19.9 to 35.5 mm CL. Form I males (n = 9) range from 24.6 to 33.5 mm CL. Form II males (n = 3) range from 19.5 to 21.2 mm CL. Several juvenile males were collected on 23 April 2015 and ranged in size from 11.2 to 11.5 mm CL.

Color. Dorsal and lateral surfaces abdomen and dorsal surface of carapace carmel brown. Dorsal surface of carapace at cervical groove with dark brown bar, caudal margin of bar angled cephalically. Lateral surfaces of carapace bone or cream colored. Dorsal surfaces of chelae light brown to orange with pale irredescent blue patches along junction of dactyl and palm region and in dorsal furrow of carpus. Rostral margins slightly darker brown than carapace color ( Fig. 2). Dorsal surfaces of pereiopods 2–5 pale blue ( Fig. 2). Ventral surfaces of chelae, cephalothorax, and abdomen cream to white.

Type locality. Roadside ditches along Co. Rd. 2190, 0.4 mi SW town of Haworth , McCurtain County, Oklahoma (33.8376, -94.6608 NAD 83) ( Fig. 3 A). Ditches on both the north and south sides of road contained approxiately two inches of standing water and were vegetated with grasses and various sunflowers in the Family Asteraceae . Surrounding land use in the immediate vicinity of the type locality was pasture and silvaculture. The holotype, allotype and morphotype were dug out of burrows ranging from approximately 20 to 45 cm in depth.

Disposition of types. The holotype, allotype, and morphotype are deposited in the Illinois Natural History Survey Crustacean Collection as INHS 15360 , INHS 15362, and INHS 15361, respectively. Paratypes are deposited at the National Museum of Natural History, Smithsonian Institution , Washington, D. C. as follows: 1 MI, 1 MII, and 1 F , USNM XXXXX. The localities and dates of collection for paratypes and morphotype are provided in the following Range and specimens examined section.

Range and specimens examined. Fallicambarus schusteri , new species, is currently known to occur in flatlands draining south into the Red River from Idabel in southcentral McCurtain Co. Oklahoma to Ashdown in southcentral Little River Co . Arkansas ( Fig. 4 ). These flatlands occur between the low hills of the southern edge of the Athens Piedmont subdivision of the Ouachita Mountains and the Red River . This species is known from only four locations, however, we believe that additional sampling of roadside ditches for burrowing crayfishes between these known sites and to the west of the current known range of F. schusteri will likely yield additional locations. Regions to the north and east of the known range of F. s c h us t e r i in Arkansas have been heavily sampled ( Hobbs and Robison 1989, Rhoden et al. in press) and we feel that it is less likely for the species’ range to extend into those regions. The exact location of one of the four known locations for the species, and western edge of it’s range, is vague. We’ve interpreted and plotted the collection of a single F1 individual from “ Rachel’s Pond , Idabel , McCurtain Co., OK ” on 29 April 1940 to be centered in the town of Idabel ( Fig. 4 ). We were unable to confirm the location of “ Rachel’s Pond ” with maps and online queries of known structures or landmarks in and around Idabel. A total of 30 specimens has been examined from four locations in the Red River drainage in Arkansas and Oklahoma. Specific locations are as follows : ARKANSAS, Little River Co.: 1) roadside ditch approx. 0.8 km SW Ashdown, 33.86523, -94.1368 NAD 83, 23 April 2015 ( INHS 14734—2 MI, 2 F, 6 juv. F) ; OKLAHOMA, McCurtain Co.: 2) roadside ditch in front of Tom Baptist Church, in town of Tom , 33.7363, -94.5725 NAD 83, 23 April 2015 ( INHS 14732 — 1 MI, 2 MII, 2 F) , 15 April 2000 ( INHS 11 328—1 MI, 1 F); 3) roadside ditches along Co. Rd. 2190, 0.4 mi SW town of Haworth 33.8376, -94.6608 NAD 83 , 23 April 2015 (INHS 15360—holotype, INHS 15361—morphotype, INHS 15362—allotype, 3 MI, 1 MII, 5 F); 4) Rachel’s Pond, Idabel, lat./longs. unavailable, 29 April 1940 (USNM 307289—1 MI).

Etymology. Named in honor of Dr. Guenter A. Schuster. Dr. Schuster dedicated his life to the study of freshwater invertebrates and contributed greatly to our knowledge of the insects, unionid mussels, and crayfishes of eastern North America. Besides being a meticulous and productive researcher, Dr. Schuster improved the lives of countless undergraduate and graduate students at Eastern Kentucky University by his enthusiasum for teaching and conveying the wonders of biology for over 30 years.

Habitat and life-history notes. Fallicambarus schusteri , new species, has been found in roadside ditches ( Fig. 3 A, B). As a primary burrower, the species was dug from burrows ranging from 10 to 45 cm deep. At the time of our sampling visits, standing water was present in some portions of the ditchs and burrows of the species were usually found on the sloping sides of the ditches adjacent to the standing water or in areas of the ditch floor without standing water. Occupied burrows had low chimneys averaging approximately 8.0 cm in height. Ditches containing the species were well vegetated with grasses, clovers, and sunflowers and silt to silt loan soils. Burrows had one shaft extending straight down to the water table and occasionally at least one lateral tunnel extending for up to 0.5 m parallel to the surface at a depth of 5–10 cm. While we’ve collected at a limited number of locations, F. schusteri does appear to be somewhat tolerant of disturbance. At two sites, (#1 and # 2 in Range and Specimens Examined) the species occurred in ditches with vegetation comprised entirely of low, mowed grass and clover. Site #2 was in the front of church with a meticously maintained lawn, grass height at that site was approximately 10 cm or less ( Fig. 3 B). This ability to inhabit, and perhaps prefer, open mowed ditches has recently been documented in another species of Fallicambarus found in southwestern Arkansas (Rhoden et al. in press).

Given the small number of collections available, determining definitive life-history aspects is not possible. The species has only been collected in the month of April. Of those collections, form I males were common at sites. No ovigerous females have been collected or observed. The presence of juveniles in burrows with carapace lengths of 11.2 to 11.5 mm in these April collections suggest that young F. schusteri hatch in the early spring months of late February or March for this region of the United States.

Crayfish associates. The following species were collected from burrows in ditches containing F. schusteri , new species: Fallicambarus fodiens (Cottle) and Procambarus curdi Reimer. At one site, small P. acutus (Girard) occurred in the standing water near F. schusteri burrows.

Variation. Few ontogenetic variations have been observed in the small number of individuals of F. schusteri examined. Those that have pertain to the number and degree of development of spines found on appendages. Several specimens examined lacked the movable spine in the caudolateral corner of the cephalic section of the telson. Also, two specimens had only one spine on the dorsum of the distal end of the merus. Larger individuals had larger, more developed spines and/or tubercles in a row located along the dorsum of the merus. The number of spines located along the caudal edge of the cephalic section of the lateral element of the uropod was highly variable in the species, ranging from eight to 12. No pattern of variation was detected.

Comparisons. Fallicambarus schusteri , new species, differs from all other members of the genus Fallicambarus in possessing a unique combination of form I male pleopod, pereiopods, and chelae characters. Fallicambarus schusteri shares a cephalic process on the first pleopod of MI males with seven other species of Fallicambarus (Fallicambarus) : F. (F.) macnessei (Black) , F. (F.) harpi Hobbs and Robison , F. (F.) strawni (Reimer) , F. (F.) petilicarpus Hobbs and Robison , F. (F.) devastator Hobbs and Whiteman , F. (F.) houstonensis Johnson , and F. (F.) kountzeae Johnson. Fallicambarus schusteri differs from F. harpi and F. strawni in having hooks on the ishia of the third and fouth pereiopods and from F. macnessei in lacking a distomedian spine that overhangs the margin of the mesial ramus of the uropod. Fallicambarus schusteri differs from F. petilicarpus , F. houstonensis , and F. kountzeae in having a first pleopod of M 1 males with a long thin caudally directed central projection that tapers to an acute tip and a large, wide, triangular shaped cephalic process. Fallicambarus schusteri also differs from F. kountzeae in possessing sufflamen (i.e. Hobbs 1973) ( Fig. 1 L) on the cheliped and from F. houstonensis in possessing an antennal scale that is widest at its midpoint rather than distal to midpoint.

Fallicambarus schusteri is most similar to F. devastator in MI male first pleopod and antennal scale shape but differs from that species in possessing a sufflamen and by lacking wide, triangular chelae, a greatlyl enlarged tubercle just distal to the encision at the base of the opposable margin of the dactyl. Coloration also differs between the two species, F. schusteri having a carmel brown carapace color rather than off-white, ivory, or pinkish lavender found in F. devastator ( Hobbs and Whiteman 1991) .

Relationships. The state of phylogenetic relationships within the genus Fallicambarus is currently in flux. Recent molecular evidence provided by Ainscough et al. (2012) does not support the monophyly of the genus Fallicambarus nor one of the two subgenera in the genus, Fallicambarus . As the genus Fallicambarus and two subgenera are currently recognized by morphological features on the rostrum, chelae, and M1 pleopod as proposed by Hobbs (1973), the molecular results of Ainscough et al. (2012) calls into question the phylogenetic utility of some of those characters for subgeneric, and perhahps species level, recognition. The phylogeny presented by Ainscough et al. (2012), in most cases shows a pattern of relatedness between species in both subgenera more closely allied with geographic proximity of taxa. This may imply that gene flow between neighboring taxa has occurred. We have not conducted a phylogenetic analysis of where F. schusteri is placed within Fallicambarus and Ainscough et al. (2012) does not propose an alternative taxonomy for the genus using molecular characters. Given these two factors, and the disconcordance between morphological and molecular characters, we hypothesize relationships between F. schusteri and other Fallicambarus species based on morphological similarity.

Following Hobbs’ (1973) use of proximomesial spur on M1 gonopod as the primary character for assessing evolutionary relationships within the genus Fallicambarus , we assign F. schusteri to the subgenus Fallicambarus . Within that subgenus we believe that F. schusteri is most closely related to members of a clade of species occurring in eastern Texas and southern Akransas based on the presence of a cephalic process and hooks on the ishia of the third and fourth pereiopods. Members of this clade include F. petilicarpus , F. devastator , F. houstonensis , and F. kountzeae . Within that clade, F. schusteri is likely most closely related to F. houstonensis in that both possess a sufflamen on the cheliped and a M1 gonopod of overall similarity.

Our proposed relationships discussed in the preceeding paragraph are tentative. Future analyses using a combined data set of both molecular and morphological characters should help elucidate the relationships within the subgenus and help resolve the phylogenetic position of F. schusteri .

Suggested vernacular name. Carmel Crayfish, in reference to the carmel coloration displayed by the species along its dorsal and lateral surfaces.

Figures

FIGURE 1. Fallicambarus schusteri, new species: A, Lateral view of carapace; B, Mesial view of distal half of first pleopod of form I male, CP = central projection, MP = mesial process; C, Lateral view of distal half of first pleopod of form I male, CeP = cephalic process; D, Mesial view of first pleopod of form I male, S = basiomesial spur; E, Lateral view of first pleopod of form I male; F, Mesial view of distal half of first pleopod of form II male; G, Lateral view of distal half of first pleopod of form II male; H, Epistome; I, Dorsal view of carapace; J, Annulus ventralis; K, Right antennal scale; L, ventral view of lateral margin of ischuim-basis joint on the left first pereiopod, Suf = sufflamen; M, Dorsal view of right chela and carpus. A, B, C, D, E, H, I, K, L and M of holotype (INHS 15360); F and G of morphotype (INHS 15361); J of allotype (INHS 15362).

FIGURE 3. Habitat of Fallicambarus schusteri, new species: A) left image of type-locality; B) right image of site at Tom, McCurtain Co., OK.

FIGURE 4. Known range of Fallicambarus schusteri, new species, in southeastern Oklahoma and southwestern Arkansas, USA. Circles indicate known sites, star indicates type-locality, enclosed circle indicates site at which exact location in Idabel, Oklahoma was estimated by centering symbol over center of town.

Tables

TABLE 1. Measurements (mm) of Falli c ambarus schusteri, new species.

Holotype	Allotype	Morphotype
Carapace:
Total length 33.5	32.1	19.5
Postorbital length 28.8	28.1	16.8
Width 15.9	16.2	8.9
Height 14.3	12.8	5.6
Areola:
Width 0	0	0
Length 13.5	12.0	7.3
Rostrum:
Width 3.6	3.9	2.4
Length 5.5	5.0	3.2
Chela, right:
Length, palm mesial margin 8.2	8.6	4.6
Palm width 10.2	11.7	6.5
Length, lateral margin 23.2	22.9	12.1
Dactyl length 14.5	13.4	6.5
Abdomen:
Width 11.0	13.8	7.6
Length 28.9	33.3	18.6