Gammarus , FABRICIUS 1775
Creators: name: Walters, Ashley D.
name: Cannizzaro, Andrew G.
name: Trujillo, Daniel A.
name: Berg, David J.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Tanaidacea
Gammaridae
Gammarus

description: GENUS GAMMARUS, FABRICIUS, 1775   
 GAMMARUS LACUSTRIS SARS, 1863 CRYPTIC SPECIES COMPLEX   
 Composition: Gammarus lacustris Sars, 1863, s.l.; Gammarus colei s p. nov., Gammarus langi sp. nov., Gammarus malpaisensis sp. nov. and Gammarus percalacustris sp. nov.   
 Diagnosis   
 Large-sized, lightly marked species distinguished from other freshwater Nearctic members of the genus Gammarus by subreniform/circular eyes; lack of C-setae on ultimate segments of mandibular palps; long B-setae on ultimate segments of mandibular palps, inserted in two rows; short posterior setae on bases of pereopods 5–7; epimeral plates 2 and 3 with distinctly produced distoposterior corners; plumose setae on apical segment of outer ramus of uropod 3; and presence of calceoli on second antennae of males.   
 Description   
 Male (Figs 4–9): 13 mm. Eye subreniform to circular in shape, interantennal lobe narrow with gently rounded upper and lower lobes.   
 Antennae: Antenna 1 (Fig. 5B): approximately 30% of body length, 85% the length of antenna 2; peduncle of first segment lacking posterodistal robust setae, short (some plumose) setae arise from both posterior and anterior margins, longer smooth setae arise distally; second segment with two groups of posterior setae, a single lateral setal group, and numerous distal setae; third segment similar to second in regards to setation; primary flagellum with 18 segments, aesthetascs absent; accessory flagellum with two segments. Antenna 2 (Fig. 5C): peduncle approximately 2.1 times longer than flagellum; fourth segment with two groups of anterior setae, three groups of lateral setae and two groups of posterior setae; fifth segment with three groups of anterior setae, four groups of lateral setae and five groups of posterior setae; flagellum with ten segments, calceoli present on anterior margins of most segments.   
 Mouthparts: Mandibles (Fig. 5D–E): left mandible incisor five-dentate, lacinia mobilis four-dentate, with 20 robust and plumose accessory setae; molar process lachrymiform, with a single plumose seta. Right mandible incisor four-dentate, lacinia mobilis bifurcate, proximal lobe with four dentations, distal lobe with six dentations; accessory setae row with 18 robust and plumose setae; molar process similar to left mandible. Palp three-segmented, antepenultimate segment unarmed; penultimate segment with four α- setae, shorter in length than E-setae, six long β- setae and indistinct γ- setae; ultimate segment with straight to concave posterior margin, 16 D-setae, five E-setae and three long A-setae, set in a single row on face of outer surface of segment, longest reaching tip of segment; inner surface armed with two rows of two to five long B-setae, subequal to or longer than A-setae, 66% length of E-setae; C-setae absent. Upper lip (Fig. 6A): rounded, apical margin of labrum covered with numerous fine setae. Lower lip (Fig. 6B): inner lobes vestigial, numerous fine setae are placed along apical and inner margins, with distinct break on apex of shoulders; face of lip covered in pubescence. Maxilla 1 (Fig. 6C, D): inner plate with 21 plumose marginal setae and numerous fine, pubescent setae covering the entirety of the plate; outer plate with up to 12 apical comb-spines, entire plate covered with pubescence; palp two-segmented, both segments lacking pubescence; apical segment of right palp with seven spine-teeth, accompanied by a more elongate tooth paired with a slender plumose seta and a single anterior seta; left palp with 15 marginal and submarginal setae. Maxilla 2 (Fig. 6E): both plates covered with pubescence; outer plate broad with up to 25 apical setae; inner plate narrowing distally, with 30 apical setae and 38 plumose facial setae. Maxilliped (Figs. 6F): inner plate shorter than outer plate, with four apical spine-teeth and eight plumose marginal setae, surface of plate covered in pubescence; outer plate with 30 apical setae paired with a row of 20 submarginal robust setae, surface of plate covered in pubescence similar to inner plate; palp four-segmented, second segment with numerous setae on inner margin and two groups of setae on outer margin; third segment setaceous with three large groups of smooth/plumose setae on outer margin and a single group of setae on inner margin; dactylus with six setae on inner margin, at base of nail.   
 Gnathopods: Gnathopod 1 (Fig. 7A): slightly larger than gnathopod 2; coxal plate with one posteroventral seta, two anteroventral seta, a facial seta and a subapical row of short setae; basis with multiple long setae on both anterior and posterior margins, posteroventral corner with two to three broad rastellate setae paired with a tuft of long smooth setae; ischium with a tuft of long posteroventral setae along with a group of two short posterior setae; merus with pubescence covering posterior surface and multiple long, smooth setae lining posterodistal margin; carpus approximately 60% length of propodus, with three groups of anterior setae, a group of facial setae and a group of rastellate distolateral setae, posterior margin armed with multiple groups of rastellate setae and a distal group of smooth setae; propodus 1.6 times longer than broad, narrowing distally, with one anterior seta, four groups of one to six superior medial seta(e), four groups of one to four inferior medial seta(e) and four groups of posterior setae, each paired with two short robust setae; palm straight, with a single, large, robust seta and multiple setae on both inner and outer margins; defining angle with row of four robust setae, decreasing in size laterally; dactylus with single seta on outer margin. Gnathopod 2 (Fig. 7B): coxal plate with one posteroventral seta, three anteroventral setae, two facial setae and a subapical row of short setae; basis with multiple long setae on both anterior and posterior margins, posteroventral corner with three to four rastellate setae paired with a tuft of smooth setae; ischium with single tuft of posteroventral setae; merus with pubescence covering posterior surface, multiple long posterodistal setae and three anterolateral setae; carpus 70% length of propodus, with two groups of anterior setae, one group of facial setae and a single group of distolateral setae, posterior margin armed with multiple groups of rastellate setae and a distal group of smooth setae; propodus subrectangular, 1.6 times longer than broad, with three groups of four to eight superior medial setae, six groups of two to six inferior medial setae and six groups of rastellate posterior setae; palm slightly convex, with a single, large, robust seta and multiple setae on both inner and outer margins; defining angle with six robust setae; dactylus with single seta on outer margin.   
 Pereopods: Pereopod 3 (Fig. 7C): coxal plate with three anteroventral setae, one posteroventral seta, one facial seta and a submarginal row of short setae; basis posterior setae slightly longer than anterior setae, anterodistal corner with single robust seta; merus longer than carpus; carpus subequal to propodus in length; anterodistal corner of carpus and posterior margins of both carpus and propodus with robust setae paired with smooth setae; dactylus approximately 40% length of propodus, with a single plumose seta on outer margin, a stout seta on distal corner of inner margin followed by a thin seta on distolateral margin. Pereopod 4 (Fig. 7D): coxal plate broad, with excavation along posterodorsal margin, armed with three anteroventral setae, six posterior setae and a submarginal row of short setae; basis posterior setae longer than anterior setae; merus longer than carpus; carpus subequal to propodus in length; anterodistal corner of carpus and posterior margins of both carpus and propodus with robust setae paired with smooth setae; dactylus approximately 40% length of propodus, setation similar to pereopod 3. Pereopod 5 (Fig. 8A): coxal plate large, bilobate, with a single seta on apical margin of anterior lobe and two setae on posterior lobe; basis posterior margin straight with twn weak serrations, anterior margin with five split-tipped robust setae, two to three groups of anteroproximal setae and a robust seta and setal group on anterodistal corner, segment covered with short facial setae, typically placed near posterior margin; carpus slightly longer than propodus; dactylus approximately 40% length of propodus, with a single plumose seta on outer margin, a stout seta on distal corner of inner margin and a thin seta on distolateral margin. Pereopod 6 (Fig. 8B): coxal plate bilobate, with a single seta on apical margin of posterior lobe; basis posterior margin straight to slightly concave with 11 weak serrations, anterior margin with six split-tipped robust setae, two to three groups of anteroproximal setae and a robust setal group paired with a single seta on anterodistal corner, segment with facial setae inserted parallel to posterior margin; carpus 1.3 times longer than propodus; dactylus approximately 35% length of propodus, setation similar to pereopod 5. Pereopod 7 (Fig. 8C): coxal plate reduced, lobes indistinct, with six posterior setae; basis posterior margin convex with 12 weak serrations, anterior margin with five split-tipped robust setae, two to three groups of anteroproximal setae and a robust setal group on anterodistal corner, segment with six long facial setae and a row of shorter facial setae parallel to posterior margin; carpus slightly longer than propodus; dactylus approximately 45% length of propodus, setation similar to pereopods 5 and 6.   
 Gills (Figs 7B–D, 8A–C): Simple and laminate in shape, decreasing in size posteriorly; coxal gills present on somites 2–6, pereopod 7 gill present on seventh somite; sternal gills absent.   
 Pleon (Fig. 5A): Dorsodistal corners of somites 1–3 with two to nine setae, lacking spines. Pleopods (Fig. 8D–F): pleopod 1 peduncle with four coupling spines; outer and inner rami with 17 and 19 segments, respectively; first segment of inner ramus with ‘clothes-pin’ robust setae. Pleopod 2 peduncle most setose of the three, with four coupling spines; outer and inner rami with 16 and 19 segments, respectively. Pleopod 3 peduncle with five coupling spines; outer and inner rami with 17 and 19 segments, respectively. Epimeron 1 (Fig. 9B): rounded ventrally; anterior margin with 20 long setae, reaching anteroventral corner, with some inserted submarginally; ventral margin unarmed; posterior margin with weak notch on posteroventral corner and two short setae. Epimeron 2 (Fig. 9B): anterior margin oblique, lacking setae; ventral margin with two robust setae and two long, smooth setae inserted submarginally or facially; posteroventral corner distinctly produced, posterior margin with two short setae. Epimeron 3 (Fig. 9B): anterior margin transverse, lacking setae; ventral margin with two robust setae and two long setae inserted submarginally; posteroventral corner distinctly produced, posterior margin with two short setae.   
 Urosome (Fig. 9A): Somites not distinctly humped dorsally; somites 1 and 2 with three clusters of one to two robust setae and two to four smooth setae; somite 3 with two clusters of robust setae and smooth setae. Uropod 1 (Fig. 9C): peduncle 1.3 times length of inner ramus, with four robust setae on both outer and inner margins; outer ramus 95% length of inner ramus, with one robust seta on inner and outer margins and five apical robust setae; inner ramus lacking robust setae on inner margin, with up to two robust setae on outer margin and five apical robust setae. Uropod 2 (Figs 9D, 11A, 12A, 13A): peduncle subequal in length to inner ramus with three robust setae on both inner and outer margins; outer ramus 70% length of inner ramus, with a single outer robust seta and six apical robust setae; inner ramus lacking robust setae on inner margin, with two robust setae on outer margin and six apical robust setae. Uropod 3 (Figs. 9E): outer ramus 2.6 times longer than peduncle; peduncle with two robust setae, two smooth setae on inner margin and eight robust setae on apex of outer margin; inner ramus 75% length of outer ramus, inner margin with four groups of robust setae among plumose and smooth setae, outer margin with a single robust seta on apical corner; distal segment 15% length of proximal segment, armed with a plumose seta and small number of smooth setae; outer ramus with single group of robust setae placed toward proximal corner of outer margin, both inner and outer margins with multiple plumose setae and a small number of smooth setae; distal segment reduced, 5% of length of proximal segment, armed with plumose/smooth setae and an apical robust seta. Telson (Fig. 9F): cleft to base, apices armed with one to three robust setae and five to six smooth setae on each lobe; outer margins of lobes with two groups of plumose setae or a robust seta.   
 Female (Fig. 10A–C): Morphologically similar to male, differing in the following features: smaller body length (6.8 mm); lacking calceoli on the flagella of antenna 2; less robust more elongate gnathopods, especially gnathopod 2, which shows a carpus approximately 85% length of propodus and propodus 2.2 times longer than broad; gnathopods 1 and 2 with robust setae on defining angles but lacking large robust setae on palmar margin; pereopods 5–7 with bases less elongate and more convex posteriorly; uropod 3 reduced, outer ramus two times longer than peduncle, inner ramus 63% length of outer ramus, both rami with a reduced number of setae; brood lamellae broad, decreasing in size distally.   
 Remarks   
 Using molecular evidence (see Diagnoses for GenBank accession numbers associated with each species), four morphologically cryptic species from the Gammarus lacustris lineage are shown to occur in the northern Chihuahuan Desert of New Mexico, USA. Along with genetic distinction, each species is geographically isolated with no other known Gammarus inhabiting the same or adjacent spring systems.   
 Individual members of the Gammarus lacustris species complex exhibit subtle differences in antennal/uropod characteristics, with a broad level of overlap between component species (Table 3; Fig. 14). The G. lacustris species complex can be easily distinguished from other Chihuahuan Desert Gammarus of the G. pecos species complex by the lack (Fig. 1). Sequences under GenBank accession numbers MH499560 – MH499567 for cytochrome c oxidase subunit 1 (COI), MH509570 – MH509577 for mitochondrial 16S and MH509707 – MH509708 for nuclear 28S.   
 Type locality: Leonora Curtin Wetland Preserve, Santa Fe County, New Mexico, USA (35.565 18, –106.102 57; Fig. 1).   
 Distribution and ecology: Gammarus langi is currently known only from its type locality, Leonora Curtin Wetland Preserve in Santa Fe County, New Mexico. It is a 35-acre protected ciénega, fed by Ciénega Creek, a tributary of the Santa Fe River which drains into the Rio Grande.   
 of distinct markings on the carapace, lack of C-setae on mandibular palps, long B-setae on mandibular palps, short posterior setae on bases of pereopods 5–7; epimeral plates 2 and 3 with distinctly produced distoposterior corners; plumose setae on apical segment of outer ramus of uropod 3; and presence of calceoli on second antennae of males. These characters are also present in the circumpolar freshwater species G. lacustris sensu lato (Sars, 1863; Bousfield, 1958).   
 GAMMARUS LANGI WALTERS, CANNIZZARO &
description: Published as part of Walters, Ashley D., Cannizzaro, Andrew G., Trujillo, Daniel A. & Berg, David J., 2021, Addressing the Linnean shortfall in a cryptic species complex, pp. 277-305 in Zoological Journal of the Linnean Society 192 on pages 286-298