Palaemonetes mexicanus

Palaemonetes mexicanus

DISPOSITION OF TYPES.—Male holotype, USNM 152393, and one male and one female paratype, USNM 152394; one male and one female paratype, Instituto de Biología de la Universidad Nacional Autónoma de México; one male and one female paratype, Rijksmuseum van Natuurlijke Historie, Leiden, The Netherlands.

TYPE-LOCALITY.—Small river 15 road miles (24 km) west of Ciudad Valles, San Luis Potosí, Mexico.

DESCRIPTION.—Rostrum (Figure 3a) high; upturned at end; extending to anterior margin of scaphocerite; dorsal margin with six to seven teeth, usually six, one of which is placed behind orbit; ventral margin with one or two teeth, usually two. Antennal spine sharp and distinct. Branchiostegal spine placed on anterior margin of carapace a short distance below branchiostegal groove.

Abdomen normal; pleura of fifth somite forming right angle; pleura of fourth somite rounded; sixth somite 1.5 times as long as fifth. Telson (Figure 3b) equal in length to sixth somite; anterior pair of dorsal spines located one-fourth of telson length from posterior margin; posterior pair on or near posterior margin. Posterior margin of telson with sharp median point flanked by two pair of spines and one pair of plumose setae; mesial pair of spines elongate and extending much beyond median point; lateral pair of spines extending to or slightly overreaching median point of telson.

Eyes (Figure 3a) well developed; cornea globular and well pigmented.

Stylocertie (Figure 3e) sharp and extending one-third length of basal segment of antennular peduncle; anterolateral spine strong, slightly overreaching anterior margin of segment; lateral antennular flagellum with rami fused for 14 to 24 articles; free portion of shorter ramus consisting of four to six articles.

Scaphocerite (Figure 3d) about three times as long as wide, lateral margin slightly concave, blade well overreaching lateral tooth.

Mouthparts (Figure 3f-k) typical.

First pereiopod (Figure 3l) extending to distal margin of third segment of antennular peduncle; palm and finger bearing numerous setae distally; carpus twice as long as chela and 1.3 times as long as merus. Second periopod (Figure 3m) overreaching scaphocerite by length of dactyl; carpus 1.6 times as long as chela; chela and merus equal in length. Third pereiopod (Figure 3n) extending to midregion of third segment of antennular peduncle; propodus 1.7 times as long as carpus; merus twice as long as carpus. Fourth pereiopod overreaching anterior margin of third segment of antennular peduncle by length of dactyl; fifth pereiopod overreaching anterior margin of scaphocerite by length of dactyl.

Appendix masculina (Figure 3c) of male with five apical spines. Eggs of gravid females few and large: 1.3 mm to 1.6 mm in length. Lateral ramus of uropod with or without movable spine between fixed distolateral tooth and margin of blade.

SIZE.—Male with carapace length to 6 mm (including rostrum, to 11 mm); females, to 11 mm (including rostrum, to 18 mm).

VARIATION.—The movable exopod spine on lateral ramus of the uropod is quite variable; both movable spines may be present, both may be absent, or only a left or right one may be present.

RANGE.—This species is known only from a small spring-fed river in the Sierra Madre Orientals, 15 road miles (24 km) west of Ciudad Valles, San Luis Potosf, Mexíco.