Hyalella lacandonis, Marrón-Becerra & Hermoso-Salazar, 2023

Marrón-Becerra, Aurora & Hermoso-Salazar, Margarita, 2023, Description of three new species of Hyalella Smith, 1874 (Crustacea: Amphipoda) from Southeast Mexico, Zootaxa 5323 (1), pp. 71-93 : 81-86

Hyalella lacandonis n.sp.

Figures 5–7

Etymology. The name is derived from the Lacandona tropical rainforest where it was found.

Material examined: Holotype male, size 6.96 mm (head size 0.66 mm) ( CNCR 36166 ), from lake Península , Montebello Lakes, Chiapas, Mexico (16°7’27”N, 91°44’6”W), 1387 m asl, 12 April 2013. Collectors: C. Orozco. Paratype female total body length 5.3 mm (head size 0.53 mm) ( CNCR 36167 ) . Paratypes (n= 4 males, n= 10 females): males mean size 6.1 ± 0.5 mm, males head mean size 0.5 ± 0.08 mm (n=5), females mean size 5.3 ± 0.5 mm, females head mean size 0.44 ± 0.08 mm (n=10) (males and females paratypes CNCR 36168 , permanent slides CNCR 36169 , and SEM preparations CNCR 36170 ), locality same as holotype .

Type locality: Lake Península , Montebello lakes, Chiapas, Mexico (16°7’27”N, 91°44’6”W).

Habitat: Freshwater epigean.

Diagnosis: Pleonites 1 and 2 with minute dorsoposterior carina. Coxa 4 excavated posteriorly. Eyes pigmented, black. Antenna 1 shorter than antenna 2 without accessory flagellum. Antenna 2 less than one-half of body length. Maxilla 1 palp short, reaching less than half of the length between the base of palp and tip of setae of outer plate, with one short stout distal seta; inner plate slender with four strong pappose distal setae. Maxilla 2 inner plate with two strong pappose setae on inner margin. Gnathopod 1, propodus hammer-shaped, palm with a transverse slope, inner face with three pappose setae in a row, comb scales on distoposterior and distoanterior border. Gnathopod 2, basis hind margin with two setae. Uropod 1 without curved setae. Uropod 3, peduncle and ramus subequal in length, ramus shorter, styliform. Telson slightly longer than wide, distal margin rounded with two long simple setae widely separated.

Description of male (holotype, CNCR 36166). Size 6.96 mm (head size 0.66 mm). Body, tergites of pleon 1 and 2 with minute dorsoposterior carina ( Figs. 5A–B ). Epimeral plates 1–3 slightly acuminate. Coxae 1–3 ( Fig. 5A ) subequal in shape, subrectangular, longer than wide; coxa 1 shorter than coxae 2–3. Coxa 4 wider than coxae 1–3 with deep posterior excavation; coxae 1–4 slightly overlapping anterior coxa, distal margin rounded with small setae widely separated, acumination absent. Coxae 5–7 reduced, shorter than coxae 1–4, bilobate except coxa 7, lobe of basis overlapping posterior lobe of coxa, except coxa 7; coxa 5 with two subequal lobes, anterior lobe slightly shorter than posterior, overlapping anterior and posterior coxae; coxa 6 with two unequal lobes, anterior lobe reduced; coxa 7 with one single lobe, anterior lobe absent.

Head typically gammaridean ( Fig. 5A ), with smooth surface, total length less than the combined length of the first two pereonites, reaching half of second pereonite; rostrum absent. Eyes pigmented, medium, rounded, and black, located between the insertions of antennae 1 and 2.

Antenna 1 ( Figs. 5 A-C) less than half the body length, shorter than antenna 2 (80% length of antenna 2), but longer than peduncle of antenna 2, almost reaching to fourth pereonite; peduncle longer than head, almost reaching half of first pereonite, article 1 and 2 subequal in length, article 1 wider than articles 2–3, article 2 longer and wider than article 3, article 3 shorter and thinner than articles 1–2 (proportions 1.5:1.4:1), article 1 almost at half of ventral surface with three cuspidate setae and one cluster with two cuspidate setae at distal end; flagellum with 11 articles reduced gradually toward distal portion, flagellum longer than peduncle; articles 4–10 with aesthetascs, articles 4–5 with one aesthetasc, 6–8 with one pair, and 9–10 with one aesthetasc. Accessory flagellum absent.

Antenna 2 ( Figs. 5A, D ) almost 1.3 times longer than antenna 1, longer than one-third the body length, but shorter than half of the total body length, almost reaching one-half of the fourth pereonite; peduncle reaching the second pereonite, peduncle articles gradually increasing in length and decreasing in width, article 3 shorter but wider than 4 and 5, article 4 longer than article 3, article 5 longer than article 4 (almost 1.3 times); flagellum with 11 articles, slightly longer than peduncle (almost 1.2 times); flagellum without aesthetascs.

Mouthparts: upper lip ( Fig. 5E ) distal margin rounded and numerous setules present, being longer and more distant towards lateral end, without bifid setae.

Lower lip ( Fig. 5F ) subquadrate, outer lobes without notches or excavations; mandibular projection of outer lobes widely rounded; without inner lobes.

Left and right mandibles ( Figs. 5G–H ) without palp, asymmetric. Incisor with six teeth present. Left lacinia mobilis similar to incisor process, with five teeth; setal row on left mandible with three main pappose setae plus accessory setae. Right lacinia mobilis more reduced than left, with two pairs of asymmetric L-shaped teeth, fused at the base, proximal pair shorter to distal, inner margin denticulate; near lacinia mobilis base with setules on inner margin; setal row on right mandible with two main pappose setae plus accessory setae and with setules near molar process. Molar process large, cylindrical, and triturative; left mandible, molar lateral view almost rectangular and right mandible molar angled 60°; both molar with accessory pappose setae.

Maxilla 1 ( Fig. 5I ), palp short, vestigial, uni-articulated, longer than wide, distally pointed with one short stout distal seta, reaching less than half of palp length, setules present; palp length almost reaching more than half of distance between base of palp and base of seta on outer plate, but less than half distance between base of palp and tip of seta on outer plate ( Fig. 5I ); inner plate slender, shorter than outer plate, with four pappose distal setae; outer plate with nine distal stout serrate setae and with setules.

Maxilla 2 ( Fig. 5J ), plates subequal in length, width, and shape; inner plate shorter and slender, with two pappose setae on mid-distal margin, and with three long serrulate setae on distal margin; outer and inner plates with large simple distal setae (type A2) and few setules on both distal surfaces and margins.

Maxilliped ( Fig. 5K ), inner plate shorter than outer plate; distal margin slightly convex, almost flat, in both plates; inner plate distal margin with three cuspidate setae of equal size and with plumose setae, inner margin with several pappose setae; outer plate, inner and distal margins with numerous simple setae. Palp composed of four articles subequal in maximum length; first article with two simple setae at inner distal end and one seta at outer distal end; second article with numerous simple setae on inner margin and three at outer distal end; third article with several setae on distal margin, distal end on outer margin with five simple setae and comb scales, inner margin with at least eight setae and six at distal end; fourth article unguiform, longer than nail, with comb scales, inner margin with three setae near distal half, outer margin with two setae near nail base; nail almost two-thirds of fourth article in length, with serration on distal half.

Gnathopod 1 ( Fig. 6A ) subchelate, propodus hammer-shaped, shorter than gnathopod 2. Basis elongated, maximum length 3 times longer than maximum width; posterior margin with one medial seta, posterior distal end with one cluster of two setae. Ischium short, subquadrate, longer than wide, length as long as maximum width of basis and slightly shorter maximum length of merus; distal posterior end with one cluster of three setae. Merus longer than wide, almost at midway of the posterior margin with comb scales; almost at distal margin with 5–6 setae. Carpus longer than wide, longer and wider than propodus; with strong, short, and wide posterior lobe, forming one scoop-like structure open to inside; inner surface of lobe with 1–2 serrate setae, external surface on distal half of lobe, near margin, with comb scales and serrate setae, anterior distal end with four setae. Propodus maximum length almost 1.4 times longer than wide; inner surface near distal margin with three serrate setae in one row; anterior distal end with two clusters of approximately four setae; distal half of anterior and posterior surfaces with comb scales; palm transverse, posterior distal end with one robust seta and cup for dactyl. Dactyl claw-like; nail present; anterior surface near proximal third with one plumose seta, with comb scales on anterior surface.

Gnathopod 2 ( Fig. 6B ) subchelate. Basis elongate, almost 3.4 times longer than wide; posterior margin with two long and slender setae. Ischium short, subquadrate, shorter than merus. Merus short; distal end of posterior margin with 4–5 simple setae; distal half of posterior inner and outer surfaces with comb scales. Carpus shorter than propodus, length shorter than merus maximum length, slightly exceeds 1.5 times width of merus; anterodistal end with two setae; posterior lobe scoop-like, elongate, almost 1.5 times width of merus, with several submarginal pappose setae and comb scales. Propodus robust, subrectangular (ovate), length 1.5 times maximum wide; palm slightly oblique shorter than posterior margin; slope slightly irregular, with few long simple setae, several short and medium setae; distal margin of palm without truncated process near insertion of dactyl and with one wide posterior excavation at base; palm posterior distal end with two strong setae, comb scales, and cup for dactyl; cup for dactyl as long as length between cup and truncated process. Dactyl claw-like, congruent with palm, occupying less than half of cup of dactyl, without comb scales; outer margin proximal third with one plumose seta; inner margin slightly crenulated with separated setules.

Pereopods 3–7 ( Figs. 6C–G ) simple, gradually longer posteriorly. Pereopod 5 shorter than 4 and 6.

Pereopod 3 ( Fig. 6C ), basis elongate; posterior margin with one medial simple seta; anterodistal and posterodistal ends with simple seta. Ischium subquadrate; posterodistal end with one pair of setae. Merus longer than ischium (almost 2 times the maximum length); anterior margin with three robust setae; posterior margin with four clusters of slender simple setae (three clusters of two setae plus one single separated seta); anterodistal and posterodistal ends with one cluster of four slender setae, anterodistal end with one robust seta. Carpus shorter and slenderer than merus; posterior margin with 2–3 stout setae plus accessory seta; posterodistal end with at least three slender setae, slender than ones from posterior margin; anterodistal end with at least three setae. Propodus longer than anterior margin of merus, slenderer than carpus; posterior margin with eight stout setae plus accessory seta; anterodistal end with three simple setae. Dactyl claw-like, length almost half of propodus; nail present; first proximal third of anterior margin with one plumose seta; anterior and posterior margins with one simple seta near base of nail.

Pereopod 4 ( Fig. 6D ) similar in shape to pereopod 3 but slightly longer; coxa 4 wider than coxa 3 with posterior excavation; basis posterior margin with one simple seta; propodus posterior margin with seven setae.

Pereopods 5–7 ( Figs. 6E–G ) similar in shape; basis posterior lobe rounded and denticulated. Pereopod 7 ( Fig. 6G ) with basis lobe widely expanded posteriorly, overreaching ischium distal margin; wider than lobes of pereopods 5 and 6; basis lobe, width almost 1.5 times as width as basis (measured at cleft between basis and basis lobe); posterior margin with 11 serrations, each with one setule, and with two stout setae on distal margin; anterior margin with five stout setae and two at distal end. Dactyl length less than half of propodus.

Pleopods 1–3 ( Fig. 7A ) not modified, biramous, elongated, rami multi-annulated, with numerous plumose setae; pleopod 1, inner margin of peduncle at distal end with two short retinacula (coupling hooks).

Uropod 1 ( Fig. 7B ) longer than uropod 2 ( Fig. 7C ); peduncle longer than rami, proximal half of dorsal margin with 2–3 dorsal setae, inner and outer distal ends with one seta; rami subequal, inner ramus slightly longer, with 3–4 dorsal and distal setae, outer ramus with three dorsal and distal setae; male without curved seta on inner ramus.

Uropod 2 ( Fig. 7C ) longer than peduncle of uropod 1; peduncle shorter than rami, with two dorsal setae on distal half and one at distal end; rami subequal, inner ramus slightly longer with four dorsal and distal setae, outer ramus with three dorsal and three distal setae.

Uropod 3 ( Fig. 7D ) similar length than peduncle of uropod 2; peduncle subrectangular, wider than ramus with three robust distal setae of variable length; inner ramus absent, outer ramus uniarticulate, slender, shorter than peduncle, 2 times the length of the larger seta of peduncle, basal width near 3 times as wide as apex of ramus, with four slender apical setae and one connate seta.

Telson ( Fig. 7E ) entire, subquadrate, longer than wide, distal margin rounded with two long simple setae widely separated; dorsal surface with two clusters of three plumose setae near middle distal portion, near margin, symmetrically distributed.

Coxal gills sac-like, present on segments 2–6. Sternal gills tubular, present on segments 3–7.

Female (paratype, CNCR 36167). Size 5.3 mm (head size 0.53 mm). Similar to male. Antenna 1, flagellum with 13 articles. Antenna 2, flagellum with 13 articles. Gnathopod 1 ( Fig. 6H ), carpus with 3–4 setae on inner face lobe; propodus with a row of 4–5 setae on inner face. Gnathopod 2 ( Fig. 6I ) smaller than male gnathopod 2, parachelated; palm reverse oblique, basis posterior margin with 2–3 setae, propodus slightly longer than twice maximum width; outer face with four setae in one row and two medium setae near palm; anterior and posterior distal half surface with comb scales. Pereonite 2 with one anterior excavation or notch for amplexus. Pereopod 7 lobe with 18 serrations and setules, with four stout setae on distal margin. Oostegites subtriangular, with curled setae on margins, almost reaching one-half of the length of merus. With 12 eggs.

Figures

FIGURE 5. Hyalella lacandonis n. sp. lateral habitus, (A) male holotype 6.96 mm (CNCR 36166), dotted lines show the dorsal carina on pleonites 1–2. Scale bar: 1 mm (B) SEM image, male paratype 5.7 mm (CNCR 36170), dorsal view, showing the minute carinae on pleonites 1–2. Scale bar: 300 µm. Male holotype 6.96 mm (CNCR 36166): (C) Antenna 1, (D) antenna 2, (E) upper lip, (F) lower lip, (G) left mandible, (H) right mandible, (I) left maxilla 1, (J) left maxilla 2, (K) maxilliped. Scale bars: 100 µm.

FIGURE 6. Hyalella lacandonis n. sp. male holotype 6.96 mm (CNCR 36166), (A) inner face of male gnathopod 1, (B) inner face of male gnathopod 2, (C) pereopod 3, (D) pereopod 4, (E) pereopod 5, (F) pereopod 6, (G) pereopod 7. Female paratype 5.3 mm (CNCR 36167), (H) inner face of female gnathopod 1, (I) inner face of female gnathopod 2. Scale bars: 100 µm.

FIGURE 7. Hyalella lacandonis n. sp. male holotype 6.9 mm (CNCR 36166), (A) pleopod 1, (B) uropod 1, (C) uropod 2, (D) uropod 3, (E) telson. Scale bars: 100 µm.