Cambarellus (Pandicambarus) rotatus Schuster and Kendrick

Schuster, Guenter A. & Kendrick, Michael R., 2017, A new dwarf crayfish (Decapoda: Cambaridae) from floodplain swamps in central Alabama, Zootaxa 4238 (3), pp. 375-384 : 376-382

Cambarellus (Pandicambarus) rotatus Schuster and Kendrick , new species

( Figures 1–4 , Table 1 )

Diagnosis. Body and eyes pigmented. Rostrum dorsal surface flat, without carina; margins not thickened, straight, distinctly converging, terminating in long spines ( Figures 1 K&2). Acumen distinctly set off from rest of rostrum ( Figure 1 K), long, lanceolate. Areola length 28.6–46.2% (n=27, =33.5, SD=4.0) of TCL and 42.0–63.3% (n=26, =48.4, SD=4.8) of PCL; narrowest at midpoint, 3.1–5.4 (n=27, =3.8, SD=0.6) times as long as wide, with no punctations. One corneous well-developed, sharp cervical spine on each side of carapace. Postorbital ridge well defined, dorsally angular, ending in long sharp spine ( Figure 1 K). Suborbital angle obtuse. Carapace smooth, without tubercles or punctations. Antennal scale widest at midpoint, scale width 1.4–3.5 (N=26, =2.6, SD=0.4) times length, thickened lateral margin terminating in large corneous spine ( Figure 1 M). Ischia of pereiopods II and III of ♂ I with sharply pointed hooks, on leg II usually bifid, on leg III bifid or single ( Figure 1 J); hooks just reaching basioischial articulation. Coxa of fourth pereiopod of ♂ I with well-developed, rounded boss.

Chela without rows of tubercles along mesial margin of palm ( Figure 1 N). Dactyl length is 0.9–1.6 (n=25, =1.2, SD=0.2) times longer than palm length. Total length of chela 2.0–3.0 (n=24, =2.4, SD=0.2) times longer than dactyl length. Carpus surface smooth without spines or tubercles, usually with long spine at distomesial margin just mesial to joint with chela. Merus usually with single well-developed dorsal spine at distal quarter of segment.

Mandible with serrated incisor region. Cephalomedian lobe of epistome broadly triangular; epistomal zygoma ridged and moderately arched ( Figure 1 I).

Gonopods of ♂ I symmetrical ( Figure 4 A), extending to posterior edge of bases of third pereiopods when abdomen flexed. Gonopods distinctly rotated mesially, resulting in terminal elements of each gonopod directed mesiad ( Figure 4 A). Due to gonopod twisting, sperm groove in mesial view short, distinctly C-shaped ( Figures 1 H & 4B). Central projection corneous without subapical notch, only slightly curved; mesial process non-corneous, broad, triangular, slightly shorter than central projection; caudal process elongated, tubular, subequal in length to central projection. Gonopod length of ♂ I 1.9-3.0 (n=6, =2.3, SD=0.4). Gonopod of ♂ II non-corneous ( Figures 1 F & G), extending to posterior edge of bases of third pereiopods when abdomen flexed, sperm groove more elongated than in ♂ I. Gonopod length of ♂ II 1.3-2.0 (n=11, =1.7, SD=0.2). Central projection broadly rounded; mesial process bulbous, shorter in length to central projection; caudal process extending beyond central projection; all elements tapering with rounded tips ( Figures 1 F & G). Annulus ventralis freely movable along cephalic edge, narrow, wide oval-shape; sinus and fossa laterocaudally located, form broad upside down U-shape; fossa expanded, tear-shaped at one end of sinus ( Figure 1 L). Annulus ventralis width of non-ovigerous females 0.6-1.3 (n=4, =1.0, SD=0.3), for ovigerous females 0.8–1.0 (n=6, =0.9, SD=0.1). Annulus ventralis of some females may be mirror image of Figure 1 L.

Description of the holotype male, form I. Cephalothorax ( Figures 1 A & K) TCL 9.0 mm and PCL 6.7 mm; bullet-shaped laterally, somewhat vaulted anteriorly; maximum width equal to maximum height (4.0 mm, each). Abdomen slightly narrower than cephalothorax (3.9 and 4.0 mm, respectively). Abdomen length 10.0 mm. Areola 3.7 mm long, 0.9 mm wide ( Figure 1 K). Cephalic portion of cephalothorax 1.4 times longer than areola; areola comprising 41.1% of TCL (54.9% of PCL). Surface of carapace smooth dorsally and laterally, no obvious punctations ( Figures 1 A & K). Rostrum ( Figure 1 K) broadest at base (1.5 mm), 2.2 mm long; sides gradually converging to acumen; rostral margins not thickened, ending in well-developed spines at base of acumen; acumen distinctly set off from rest of rostrum, as very acute triangle, not ending in tubercle. Postorbital ridge ( Figure 1 K) strongly angled dorsally, ending anteriorly in sharp spine. Suborbital angle ( Figure 1 A) obtuse; branchiostegal spine sharply pointed, small. One small cervical spine.

Cephalic lobe of the epistome ( Figure 1 I) broadly triangular; main body of epistome rectangular in broad outline, zygoma broadly arched. Antennal scale ( Figure 1 M) 3.6 mm long and 1.0 mm wide, widest at midpoint; mesial margin with row of long, flexible setae.

Third maxilliped well-developed, ventral and lateral sides of basal segments covered with long flexible plumose setae; distal segments also with long setae, not as dense.

Cephalic section of telson with one movable and one immovable spine in caudolateral corners. Protopodite of uropod with spine extending over endopodite. Caudal margin of cephalic section of exopodite with numerous fixed spines (n=11). Cephalic section of exopodite with distinct median ridge, caudolateral corner with spine. Lateral margin of endopodite terminating in spine; endopodite with median ridge terminating in small premarginal spine. Dorsal surfaces of telson and uropods covered with short, translucent setae.

Right chela ( Figure 1 N) total length 5.8 mm, dactyl length 2.8 mm, dactyl and propodus each smoothly rounded without strong dorsomedian longitudinal ridges. Opposable margins of dactyl and propodus with no large tubercles, with numerous small denticles. Palm length greater than palm width (2.9 and 1.3 mm, respectively); mesial margin of palm smooth without tubercles or plumose setae. Carpus of cheliped smooth, without tubercles or spines. Merus surface smooth, without tubercles or spines, with single distolateral marginal spine. Bifid tubercles with sharp hooks on ischium of second and third pereiopods, just reaching basioischial articulation ( Figure 1 J). Coxae of fourth pereiopod with elongated, slightly angled boss.

First pleopods symmetrical at base, total length 2.4 mm; terminal elements as described in “Diagnosis” ( Figures 1 B, C, D, E & H).

Description of allotype female. Differs from male holotype in the following: Cephalothorax TCL 8.2 mm and PCL 5.9 mm; maximum width slightly less than maximum height (3.1 and 3.3 mm, respectively). Abdomen length 8.3 mm, slightly wider than cephalothorax (3.2 and 3.1 mm, respectively). Areola 2.9 mm long, 0.8 mm wide. Cephalic portion of cephalothorax 1.8 times longer than areola; areola comprising 36.0% of TCL (40.0% of PCL). Rostrum widest at base (1.3 mm), 2.3 mm long. Antennal scale 2.2 mm long, 0.9 mm at widest point. Right chela total length 4.2 mm, dactyl length 2.1 mm; palm width less than palm length (1.0 and 1.9 mm, respectively); carpus with well-developed large spine at distal margin just mesial to joint with chela. Merus with single well-developed dorsal spine at distal quarter or segment. No hook on ischium of second or third pereiopod. No boss on coxae of fourth pereiopod, width 1.1mm. Annulus ventralis ( Figure 1 L) as described in “Diagnosis,” width 1.1mm.

Description of the morphotype male, form II. Differs from male holotype in the following: Cephalothorax TCL 9.2 mm and PCL 6.6 mm; maximum width slightly more than maximum height (4.1 and 4.0 mm, respectively). Abdomen length 11.2 mm, slightly narrower than cephalothorax (3.9 and 4.1 mm, respectively). Areola 3.9 mm long, 0.9 mm wide. Cephalic portion of cephalothorax 1.4 times longer than areola; areola comprising 42.3% of TCL (59.4% of PCL). Rostrum widest at base (1.5 mm), 2.7 mm long. Right chela total length 6.0 mm, dactyl length 2.7 mm; palm width subequal to palm length (2.6 and 2.7 mm, respectively). Merus with single well-developed dorsal spine at distal quarter of segment. Opposable margin of dactyl with 10 round tubercles. Hook on ischium of second and third pereiopod small, rounded and not bifid. Gonopod length 1.7 mm ( Figures 1 F & G).

Color. ( Figures 2 & 3 ). There are two distinctly different color forms for this species and they occur in the same populations. The first color form ( Figures 2 & 3 ) has a pair of wide dark olive green stripes that start anteriorly on the carapace just behind the eyes and extend the length of the body to the telson base. A pair of second much thinner stripes run parallel to the dorsal stripes and are located on the lateral surfaces of the carapace and abdomen. These too originate just behind the eye and extend to the base of the uropods. The base color of the carapace and abdomen is tan. This color, however, does not solidly cover these structures, especially on the abdomen. There are distinct areas where the tan is broken into small tan spots and in between the spots there is a lack of color so the exoskeleton looks clear. The chelipeds have blotches of olive green, while the exoskeleton of the rest of the leg segments are clear. The exoskeleton on the legs is mostly clear except for tan bands at the joints of the legs. The uropods and telson have a transverse arc-shaped dark brown. In addition, the medial lobes of the uropods and distal lobe of the telson have large splotches of dark brown. The uropods and telson also have numerous small white spots, and in between these spots the exoskeleton is translucent. The antennae are yellow to tan.

The second color pattern ( Figure 3 ) lacks the stripes and bands. In these specimens the dorsum of the carapace and abdomen is dark yellow to tan, while the sides are cream colored. The carapace and abdomen throughout are speckled with dark brown to black spots. On the carapace these spots coalesce around the areola and around the mandibular muscle scar. On the abdomen the dark spots coalesce dorsally and dorsolaterally to form larger dark Vshaped splotches. Laterally on the abdomen they coalesce to form dark U-shaped splotches that form an interrupted dark stripe. The telson and uropods have a cream base color with dark splotches throughout. The chelae have large translucent areas mixed with dark splotches. The remaining legs are mostly clear but have darker coalesced spots that may form bands near the joints of the segments. The antennae are dark yellow to tan.

Disposition of primary types. The holotype, allotype, and morphotype are deposited in the Illinois Natural History Survey Crustacean Collection , Champaign, IL as INHS 15497 , INHS 15499 and INHS 15498 , respectively.

Size. The largest specimen in this study was a ♂ I having a TCL of 11.3 mm (PCL 8.0 mm). The largest ♀ had a TCL of 9.5 mm (PCL 7.2 mm). The smallest ♂ I had a TCL of 7.4 mm (PCL 5.6 mm). The TCL for ♂ IIs ranged from 6.6–9.2 mm (in PCL 4.8–6.7 mm) while females ranged in TCL from 7.2–9.5 mm (in PCL 4.8–6.6).

Type locality. A tupelo swamp on Allen Acres, 4.3 mi W of Moundville along Lock 9 Rd., Hale County, Alabama (32.9928N; - 87.7042W).

Range and specimens examined. Cambarellus rotatus is currently known only from 4 tupelo swamp locations in Greene, Hale, and Marengo counties, AL.: USNM 218739 & 218742, 2♂ II, 2♀: Greene County, unnamed slough, 3.7 miles S of Boligee, April 26, 1978, Collector: J.F. Fitzpatrick, Jr. ; INHS 15496 , Paratypes, 1♂ I, 2♂ II: Hale County, Tupelo swamp, 1.8 mi NW of Stewart, along White Rd., June 13, 2014, Collectors: MRK, A.D. Huryn;

INHS 15497 , Holotype, 1♂ I: Hale County, tupelo swamp, 1.8 mi NW of Stewart, along White Rd. , August 29, 2014, Collectors: MRK, A.J. Constantin ; INHS 15499 , Allotype, 1♀: Hale County, tupelo swamp on Allen Acres , 4.3 mi W of Moundville along Lock 9 Rd., June 30, 2015, Collectors: MRK, R.A. Bearden, N. Brooke ; INHS 15498 , Morphotype , 1♂ II: Hale County, tupelo swamp, 1.8 mi NW of Stewart, along White Rd., August 29, 2014, Collectors: MRK, A.J. Constantin ; INHS 15500 , Paratypes, 1♂ I, 2♂ II, 2♀: Hale County, tupelo swamp on Allen Acres , 4.3 mi W of Moundville along Lock 9 Rd., June 30, 2015, Collectors: MRK, R.A. Bearden, N. Brooke ; INHS 15501 , Non-types , 2♂ I, 6♂ II, 1♀, 6 ovigerous ♀: Hale County, tupelo swamp on Allen Acres , 4.3 mi W of Moundville along Lock 9 Rd., June 30, 2015, Collectors: MRK, R.A. Bearden, N. Brooke ; USNM 130924 , Paratype, 1♂ I: Marengo County, small deep creek, 8.9 miles W of Demopolis, April 23, 1970.

Etymology. The species name originates from the Latin word rotatus , meaning rotated, reflecting the mesial rotation or twisting of the gonopods so that the terminal elements oppose each other.

Habitat. Specimens of Cambarellus rotatus have been collected from four different locations along the Black Warrior and Tombigbee rivers. Two populations along the Tombigbee River were identified from historic collections in museum records (USNM 218739, 218742, and 130924) but specific habitat details are not provided with these records. Contemporary sampling documented two populations of Cambarellus rotatus from water tupelo ( Nyssa aquatica ), which dominated floodplain swamps along the Black Warrior River in Hale Co. Alabama. These sample sites represent the only known habitat associations for this species. The soils in these areas are from the Urbo-Mooreville-Una soil unit and are characterized as floodplain soils that are poorly drained and frequently flooded (Soil Survey 2016); holding water most of the year, drying entirely or almost entirely in late-summer to early-autumn. It is unclear to what extent this species might create burrows to escape drying conditions. Individuals collected in August, 2014 were found in a hollowed N. aquatica trunk, which held the only surface water in the area at the time of sampling. While N. aquatica is generally restricted to coastal habitats in Alabama, a disjunct band of N. aquatica can be found in central Alabama. If our limited sampling is indicative of an obligate association with N. aquatica , the range of C. rotatus . may be restricted to this small band of N. aquatica in central Alabama. Alternatively, increased attention on dwarf crayfishes in this region may determine that this species is not restricted to N. aquatica swamps.

Life-history notes. First form males were collected in three sampled months, April, June, and August, while ovigerous females of were only collected in April and June. Peak reproductive activity in Cambarellus shufeldtii and C. puer appears to occur in February/March, but ovigerous females and first form males of both C. shufeldtii and C. puer can be found throughout the year ( Penn 1942, Penn 1950, Black 1966). Given the potential range of reproductive activity and the relatively small sample size in this study, the reproductive phenology of this species remains unclear.

The number of eggs per female and the size of eggs were similar to data available for C. shufeldtii . Average number of eggs per female in C. rotatus was 32 (range = 27–38), compared with 33 eggs /female documented for C. shufeldtii ( Penn 1942) . Eggs from six ovigerous females were measured. Five eggs from each female were subsampled for measurement. The average egg diameter was 0.8 mm (range = 0.8–0.9 mm), compared with an average of 1.0 mm diameter eggs measured for C. shufeldtii ( Penn 1942) .

Crayfish Associates. Species that have been collected in the vicinity of C. rotatus include: Cambarus diogenes , C. ludovicianus , C. polychromatus , Fallicambarus fodiens , Hobbseus prominens , Procambarus acutissimus , P. acutus , P. clarkii , P. lancifer , and P. viaeviridis .

Variation. The greatest amount of variation noted in this species was in the color pattern. As noted in the Color Section above there are two color morphs: a striped morph and a speckled morph. Similar variation has been seen in other Cambarellus species as well as in Faxonella clypeata . In C. rotatus both sexes exhibit both color patterns. The reason for or the utility (if any) of, these patterns is unknown.

Relationships. The subgenus Pandicambarus, including the newly described species, has eight nominal species. These can broadly be divided into two groups based on the shape of the mesial process. Three species ( C. ninae , C. puer , and C. texanus ) have elongated finger-like mesial processes while the remaining species ( C. blacki , C. diminutus , C. lesliei , C. schmitti , and C. rotatus ) have broad triangle-shaped mesial processes. Based on the similarities in gonopod elements, and width of the areola the new species most closely resembles C. lesliei . In both species ( Figures 4 B & E) the caudal process is long and digitiform, and they have narrower areolae than C. blacki , C. diminutus , or C.schmitti . They differ from each other in a number of significant characters. First, in C. rotatus , pleopods are rotated mesially ( Figure 4 A) so that the terminal elements directly oppose each other, while in C. lesliei they are not rotated and the terminal elements are parallel to each other ( Figure 4 D). Second, because of the twisting in C. rotatus , the sperm groove is distinctly short and C-shaped ( Figure 4 B), while in C. lesliei it is elongated and only slightly curved ( Figure 4 E). Third, the central projection in C. rotatus is longer and not as curved as in C. lesliei ( Figures 4 B & E). Fourth, the zygomatic arch is broadly arched ( Figure 4 C) in C. rotatus ; in C. lesliei it is strongly arched and U-shaped ( Figure 4 F).

Without molecular data it is not clear what the closest relative of C. rotatus is. The mesial twisting of the gonopods so that the elements oppose each other and that the sperm groove is dramatically shortened seem to be unique features for this species. Although morphologically, it most closely resembles C. lesliei , it is uncertain if this is in fact its closest relative. Both species are found in the same drainage basin (Mobile River), however, C. lesliei is known only from lower parts of the Tombigbee and Alabama rivers and south into the Mobile River system while C. rotatus is currently known only from the middle sections of the Tombigbee River and the lower Black Warrior drainages in central Alabama. Based on what we know now they seem to be allopatric.

Common name. The suggested common or vernacular name for this species is Twisted Dwarf Crayfish after the mesial twisting or rotation of the gonopods.

Conservation status. Although extensive collecting has been done in the counties in the vicinity of the known locations for this species, no additional populations have been found. Additional fieldwork needs to be done to better assess the distribution and population sizes of this species and its current status. However, based on the criteria of the American Fisheries Society as outlined by ( Taylor, et al. 2007) and the system developed by The Nature Conservancy/NatureServe ( Master 1990), we propose that this species, because of its apparent narrow range, be considered Vulnerable (V) with a G3 global ranking. The species should rank as Vulnerable by the International Union for the Conservation of Nature (IUCN) under Criteria D.

Figures

FIGURE 1. Cambarellus (Pandicambarus) rotatus, n. sp.: A. lateral view of carapace; B, C, D, and E, respectively, mesial, lateral, caudal, cephalic views of terminal end of left gonopod of ♂ I; F & G, respectively, mesial and lateral view of terminal end of left gonopod of ♂ II; H, mesial view of entire ♂ I gonopod; I, epistome; J, ischial hooks on legs II & III; K, dorsal view of carapace; L, ♀ annulus ventralis; M, antennal scale; N, dorsal view of right chela and carpus of ♂ I. (1 A – E, H, J, K & N of holotype ♂ I; 1 L of allotype ♀; 1 F, G, I & M of morphotype ♂ II).

FIGURE 2. Cambarellus (Pandicambarus) rotatus, n. sp.: Holotype, Hale County, AL, dorsal view.

FIGURE 3. Cambarellus (Pandicambarus) rotatus, n. sp.: Two color morphs, Hale County, AL.

FIGURE 4. Comparison of important morphological structures of Cambarellus rotatus, n. sp. and Cambarellus lesliei. A – C, Cambarellus rotatus, n. sp. respectively, gonopods in situ, ventral view, ♂ I gonopod, mesial view, and epistome; D – F, C. lesliei, respectively, gonopods in situ, ventral view, ♂ I gonopod, mesial view, and epistome. (4 A – C of holotype ♂ I).

Tables

TABLE 1. Measurements (mm) of type specimens of Cambarellus rotatus, new species.

	Holotype	Allotype	Morphotype
Carapace
Height	4.0	3.3	4.0
Width	4.0	3.1	4.1
Total carapace length (TCL)	9.0	8.2	9.2
Postorbital carapace length (PCL)	6.7	5.9	6.6
Areola length	3.7	2.9	3.9
Areola width	0.9	0.8	0.9
Eye diameter	1.2	1.0	1.1
Rostrum
Width	1.5	1.3	1.5
Length	2.2	2.3	2.7
Chela
Length, mesial margin palm	2.9	1.9	2.7
Width, palm	1.3	1.0	2.6
Length, total	5.8	4.2	6.0
Length, dactyl	2.8	2.1	2.7