Pinnixa plectrophoros Glassell, 1935

Salgado-Barragán, Jose, Barragán, Ana K. & Berrian, James E., 2018, Redescription of the poorly known pea crab, Pinnixa plectrophoros Glassell, 1935 (Decapoda: Pinnotheridae), from the Gulf of California, Zootaxa 4382 (3), pp. 565-572 : 566-571

Pinnixa plectrophoros Glassell, 1935

( Figs. 1–4 )

Pinnixa plectophoros Glassell, 1935b: 102 .

Material examined. Holotype, male (CW= 6.0 mm; CL= 2.0 mm) ( SDNHM 3894 ) Puerto Peñasco , Sonora, México, coll. May 1, 1935.

Other material: 4 males (1 damaged) (CW= 5.8–6.1 mm; CL= 1.9–2.1 mm), 2 ovigerous females (CW= 7.0 mm, 7.1 mm; CL= 2.1 mm) (ICML-EMU 10 575) Bahía Santa María-La Reforma, Sinaloa, Mexico, La Garrapata Island (25° 9'13.20"N, 108°15'24.75"W), 0–0.3 m at low tide, fine sand; taken from burrows of Callichirus aff. major and Neotrypaea sp., coll. Jan 24, 2014; 1 ovigerous female (CW= 6.8 mm; CL= 2.3 mm) (ICML-EMU 10576) SE lagoon (24°44'46.27"N, 107°59'40.71"W), 0.2 m at low tide, sandy mud, taken from burrow of Neotrypaea sp., coll. Jan 18, 2015.

Description. Carapace oblong, about three times as wide as long, CW/CL ratio 2.8–3.1 in males, 3.0– 3.4 in females, nearly flat except toward margins where it slopes gradually downward at lateral angles, abruptly to posterior margin; anterolateral margin feebly indicated by minute granules; orbits, eyes, sub-hepatic regions visible in dorsal view; front not projecting, slightly bilobed, with median sulcus; two transverse lunate pits at cardiac region, one pit in line with those on mesobranchial region; other regions poorly defined, without dorsal granules; orbits small, completely filled by eyes ( Figs. 2 , 3A ).

Fourth thoracic sternite with anterior, lateral notches, anterior notch deeper ( Fig. 4C ).

Third maxilliped ( Fig. 4A, B ) ischium-merus subrectangular, mesial and lateral margins slightly convex; carpus narrower than ischium-merus, longer than propodus, slightly longer than dactylus; propodus short, inserted subdistally on ventral margin of carpus, mesial margin (when plicated) rounded; dactylus spatulate, inner margin concave, outer margin convex, distal end rounded; when propodus, dactylus flexed, long plumose setae located on mesial side of all articles ( Fig. 4A ); one marginal row of setae on ischium-merus, carpus with sub-oval double-row pattern of plumose setae ( Fig. 4B ), outer margin of ischium-merus carpus with pappose setae. Exopod with median protuberance in outer margin, surrounded by pappose setae; flagellum robust, subtriangular, not segmented, ending in few short setae.

Chelipeds weak, subtle ( Fig. 3B, C ) subequal, similar in both sexes; setose, marginally and submarginally covered with dense, long pappose setae; merus longer than carpus, widened mesially; carpus smooth, with pubescent margins; palm longer than dactylus; chelae weak, margins subparallel, compressed, dorsal margin of palm slightly convex, with 2–6 small spines (5 in holotype), ventral margin nearly straight, fixed finger in line with lower margin of hand, dactyl curved, with 3–5 small spines on dorsal margin (4 in holotype), cutting edges of both movable, fixed fingers nearly straight, subparallel, microscopically denticulate.

First walking leg ( Fig. 3D ) slender, margins with sparse, long setae; ischium without spines; merus long, about 2.7 times as long as wide, as long as carpus and propodus combined, margins subparallel, smooth; carpus longer than propodus; posteroventral margin of propodus straight, with a row of spinules distally, dorsal margin convex; dactylus long, lanceolate, longer than propodus, dorsal margin with two nonaligned blunt spines subproximally, distal one smaller and one row of small spinules along anterior and posterior side each.

Second walking leg ( Fig. 1C , 3E ) similar but larger than first; ischium with ventral small spine; ventral margin of propodus straight subdivided in two crests, with a row of spinules each on subdistal portion on anterior side and distal on posterior side; dactylus long, lanceolate, longer than propodus, dorsal margin with two nonaligned tubercles subproximally, distal one smaller and one row of short spinules along anterior and posterior sides each.

Third walking leg ( Fig. 1D , 3F, G ) stoutest; with short spine on ventral margin of coxa; ischium with 1 or 2 strong spines (2 in holotype) and granules along anteroventral margin; merus about 2 times as long as wide, larger than carpus and propodus combined, with large distalward curving spine (spur) on subdistal posterior margin, a small blunt spine at base of concave margin of spur, ventrodistal margin with small granules in Santa María-La Reforma specimens, not seen in holotype; propodus ventral margin broadly produced proximally and a strong submedian spine; dactylus triangular, with 2 or 3 blunt spines near base of anterior side, one row of short simple setae on anterior and posterior side each.

Fourth walking leg ( Fig.4 , E) smallest, slight, distal end not reaching distal margin of merus of third leg, margins covered with long setae; ventral margin of ischium with 2 or 3 strong, blunt spines; merus about 1.7 times as long as wide, posterior ventral margin proximally irregular with blunt spine, anterior ventral margin tuberculated; propodus subquadrate; dactylus triangular, with subdistal row of short spinules near anterior flexor margin and row of short simple setae on posterior side.

Male pleon ( Fig. 1B , 4C, F ), first somite proximally widened, lateral margins oblique, straight; second somite distally widened; margin between second, third somites fringed with short setae; third somite basally wider; somites 4–6 fused, somites becoming narrower from fourth somite to base of fifth and then wider at distal end of sixth somite; telson wider than sixth somite, distally rounded; pleon and telson margins fringed with plumose setae, longer at base of telson. Male first gonopod ( Fig. 4G ) curved outward, tapering, external margin with long simple setae and mesial margin with shorter distal setae. Male second gonopod not observed in any of the male specimens.

Ovigerous female pleon and telson ( Fig. 4H ) subpentagonal, fringed with setae; all somites free; first somite narrowest, 0.8 times as long as second somite; margin between first and second somites fringed with short setae; somites 2, 3 widening distally; second somite slightly broader than first somite; third somite about 1.5 times as long as second; fourth segment the widest, subrectangular, lateral margins convex; somites 5, 6 narrowed, almost as long as fourth; telson triangular, distally rounded.

Color in life. ( Fig. 2 ). Light brown on frontal, hepatic, branchial, gastric and cardiac regions of carapace with lighter or creamy white irregular patches between branchial and the median regions; posterior and posterolateral marginal edges creamy white. Chelipeds diffuse, from creamy white along to brown on dorsal margin of carpus and manus; fingers creamy white or uncolored. Walking legs with similar pattern to chelae, with distal margin obscurer brown followed by a white marginal band, tips of dactyls dark brown. Setae light brown or creamy white.

Habitat. The holotype was recorded as a “commensal in the sand tube of a species of annelid worm ( Clymenella )” ( Glassell, 1935b: 102). The Sinaloa specimens, on the other hand, were collected in sand and muddy sand, associated with burrows of callianassid crustaceans.

Distribution. Gulf of California; Puerto Peñasco, Sonora (the type locality) and Bahía Santa María-La Reforma, Sinaloa, Mexico.

Remarks. Although the male holotype of P. plectrophoros is desiccated ( Fig. 1 ), all the morphological characteristics mentioned by Glassell (1935b: 102) can be easily observed. Other features not mentioned by Glassell could also be seen in both the holotype and the specimens from Sinaloa; among these, the third maxilliped, male gonopod and female abdomen are described for first time. The fourth thoracic somite has notches in the anterior and lateral zone. The chelipeds are similar in both sexes, with small dorsal spines in the propodus and dactyl. The first and second walking legs have the propodus with two rows of ventrodistal spinules and the dactylus with lateral rows of spinules; in addition, the ischium of the second walking leg bears a small ventral spine. The third walking leg may have 1 or 2 spines on the ischium, a small spine at the base of the merus spur, and the dactylus may have 2 or 3 ventral spines. On the other hand, Glassell (1935b) mentioned that the male pleon has the third to sixth somites fused, whereas we could observe that, in the holotype and in the Sinaloa specimens, the fusion involves only somites 4–6. Finally, we could observe that in the Sinaloa specimens, females had a slightly larger CW/CL ratio than males, but there were no other significant morphological differences between sexes. Except for the first male pleopod, all the morphological features described herein were observed in the holotype. Two main variations were observed in the specimens from Sinaloa; the number of spines on the dorsal margin of chelae varied from 2 to 6 spines on the propodus and 3 to 5 on the dactylus. The large outward curving spine and a small accessory spine on ventral margin of the merus of the third walking leg was absent in the left leg of one female, and in the damaged male was replaced by a bifid large spine. In addition, the condition of the accessory spine near the spur varied in some specimens—it was absent in one female, and there were three small spines (instead of one) in the right leg of one male; also, it was located at the base of the spur in most of the specimens but it was located laterally in two females.

This work describes several morphological features of the species that were not mentioned by Glassell in the original description. Glassell (1935b: 102) pointed out that P. plectrophoros is allied to P. retinens ( Rathbun, 1918) , although he did not mention why he considered both species to be allies. Both species have weak chelae and their third walking leg bears ventral spines, although those of P. retinens are acute and have a large, strong spine on the ischium while P. plectrophoros has blunt spines and bears a large, curved spine on the merus. On the other hand, the carapace of P. plectrophoros is much wider than that of P. retinens , and it has an hourglass-shaped pleon with fused segments while P. retinens has a triangular (tapering) pleon with all segments free. Due to the width of its carapace, P. plectrophoros resembles P. tubicola Holmes, 1894 . However, the latter has strong chelae, the walking legs have no spines, and the males possess a triangular abdomen with unfused segments. On the other hand, among the species of Indopinnixa , Pinnixa and Laminapinnixa which have the pleon showing some degree of somite fusion, as mentioned by Naruse & Maenosono (2012), Salgado-Barragán (2015), and McDermott (2016), none of them reach a CW/CL ratio as in P. plectrophoros , nor have the merus of the third walking leg with a large ventral spur. A detailed description of species, with photographs or illustrations is essential for the identification of organisms, especially when the access to reference material is difficult. Fortunately, in this case, the original description of the overall body shape and appendages of the holotype of P. plectrophoros was complete enough to know that we have a record of the species outside its known distribution limits. The second record of P. plectrophoros , in Sinaloa, represents an extension of about 850 km south of the type locality.

Figures

FIGURE 1. Pinnixa plectrophoros, 1935, Glassell Male holotype (SDNHM 3894), Puerto Peñasco, Sonora, México, A, anterodorsal view; B, ventral view; C, propodus and dactyl of second walking leg, arrows point the subproximal tubercles; D, third walking leg, arrows point spur on ventral side of merus and spine and granules in propodus and dactylus.

FIGURE 2. Pinnixa plectrophoros, 1935, Glassell Male from Bahía Santa María–La Reforma (ICML-EMU 10575), color in life.(Scale bar = 1 mm).

FIGURE 3. Pinnixa plectrophoros, 1935, Glassell Male from Bahía Santa María–La Reforma, Sinaloa (ICML-EMU 10575); A, Carapace, dorsal view; B–C, left cheliped, setae omitted in C; D, right first walking leg, posterior view; E, right second walking leg, posterior view; F–G, right third walking leg, F, posterior view; G, anterior view.(Scale bar = 1 mm).

FIGURE 4. Pinnixa plectrophoros Glassell, 1935, A–G, male from Bahía Santa María–La Reforma (ICML-EMU 10575). A– B, third maxilliped, A, external view, B, internal view, exopod and setae omitted but marking the line of points where the long plumose setae emerge; C, sternite, abdomen and telson; D–E fourth walking leg, D, posterior side, E, anterior side; F, male abdomen and telson; G,left gonopod; H, abdomen of female from Bahía Santa María—La Reforma,Sinaloa (A–B, G,scale bar = 0. 5 mm; C–F,H, scale bar = 1mm).