Gammarus desperatus Cole, 1981

Cannizzaro, Andrew G. & Berg, David J., 2024, Molecular phvlogenetic analvses reveal a radiation of freshwater Gammarus (Amphipoda: Gammaridae) in the northern Chihuahuan Desert, Zoological Journal of the Linnean Society 202 (1) : -

Gammarus desperatus Cole, 1981

Gammarus sp. 1 ( Adams et al., 2018)

( Figs 4–10)

Material examined: USNM 1607105 , male, 8.5 mm: Rio Hondo , Chaves Countv, New Mexico (33.3897, –104.4170); collector: McKenna P.A. Burns; 28 September 2018 . USNM 1607106 , female, 4.3 mm: Rio Hondo , Chaves Countv, New Mexico (33.3897, –104.4170); collector: McKenna P.A. Burns; 28 September 2018 . USNM 160710 , topotvpe, male, 14.2 mm: North Spring , Chaves Countv, New Mexico, USA (33.425, –104.488);collectors: Stephen Cole and Tom Cole; 12 October 1978 . USNM 1607108 , Topotvpe , male, 15.1 mm: North Spring, Chaves Countv, New Mexico, USA; collectors: Stephen Cole and Tom Cole; 12 October 1978 .

Type locality: North Spring , Chaves Countv, New Mexico, USA (33.425, –104.488)

Diagnosis: Medium-to-large, brightlv marked species showing characteristicstvpicalofmembersofthe Gammaruspecos complex, as outlined bv Cole (1985). Distinguished from other members of the complex through the combination of the following characteristics: setae present on the posterior margin of antenna 1; antenna 1 flagellum with <35 segments; C-setae on mandibular palps up to 2.5× D-setae in length; B-setae on mandibular palps 20%–50% length of longest A-seta; male gnathopods 1 * 2 with distinctlv concave palmar margins on propodi; coxal plates 1–4 with numerous facial setae; bases of pereopods 1–7 with>12 posterior setae, and dense facial setae; posterior setae on basis of pereopod 7 approximatelv 20%–25% width of segment. Males up to 15 mm in length, females up to 12 mm in length.

Description: Male: 8.5 mm in length. Eves reniform, integumentarv pigment present when alive and in freshlv preserved specimens ( Fig. 4B).

Antennae: Antenna 1 ( Figure 5A): approximatelv 45% bodv length, 1.8× as long as antenna 2; peduncle segment 1 with distal robust seta; primarv flagellum with 24 segments; accessorv flagellum five-segmented. Antenna 2 ( Fig. 5B); peduncle ~1.6× as long as flagellum, segment 4 with four tusss of dorsal setae, three tusss of ventral setae, and five tusss of lateral setae, segment 5 subequal in length to segment 4, armed with four tusss of dorsal setae, four tusss of ventral setae, and five tusss of lateral setae; flagellum with 13 segments, setae length on segments decreasing distallv, calceoli absent.

Mouthparts: Mandibles: right mandible ( Fig. 5C) incisor five-dentate, lacinia mobilis bifurcate, both lobes with numerous protuberances; accessorv setae row with five robust, serrate setae and numerous plumose setae; molar process ovate with simple seta; palp with three segments, penultimate segment 1.2× length of ultimate with six α-setae and seven β-setae, α-setae subequal in length to E-setae; ultimate segment with four A-setae, three B-setae, four C-setae, 23 D-setae, and four E-setae, C-setae 1.8× length of longest D-seta, B-setae 20% length of longest A-seta. Less mandible ( Fig. 5D) incisor four-dentate, lacinia mobilis four-dentate, with five robust serrate and numerous plumose accessorv setae; molar process ovate with plumose seta; palp with three articles, relative segment lengths and setation paưerns as in less mandible. Upper lip ( Fig. 6A): rounded, apical margin of labrum with numerous fine setae. Lower lip ( Fig. 6B): inner lobes indistinct; outer margin of outer lobe sparselv covered in fine setae; inner margin of outer lobe heavilv setose. Maxilla 1 ( Fig. 6C, D): inner plate with 13 plumose marginal setae and numerous fine, pubescent setae covering entire plate; outer plate with 11 apical comb spines, pubescence covering inner margin, decreasing laterallv and proximallv; less palp with two segments, subapical margin of distal segment with four long setae, apical margin with six robust setae; right palp with two segments, subapical margin of distal segment with a long seta, apical margin with four robust setae, broader than those of less palp. Maxilla 2 ( Fig. 6E): both inner and outer plates covered in pubescent setae; outer plate with numerous distal setae; inner plate narrowing slightlv distallv, with numerous apical setae and 10 plumose facial setae. Maxilliped ( Fig. 6F): inner plate shorter than outer plate, apical margin with three naked cuspidate setae, inner margin with six plumose setae, surface of plate covered in fine pubescence; outer plate armed with numerous naked cuspidate setae covering inner margin and numerous setae covering both inner and apical margins; palp second segment with numerous marginal setae, third segment with numerous marginal/ submarginal setae; dactvlus with five inner setae and an outer seta.

Gnathopods: Gnathopod 1 ( Fig. 7A): coxal plate with five anterior setae, two posterior setae, and 12 long facial setae, additional smaller, submarginal setae line apex of plate; basis with numerous long setae inserted along anterior and posterior margins, small patch of pubescence on posterodistal corner; ischium with seven setae and pubescence along posterior margin; merus with anterior seta, patch of setae on anterodistal margin, and three tusss of posterior setae, posterior surface of segment weaklv pubescent; carpus approximatelv 75% length of propodus with two tusss of setae along anterior margin, posterior margin with numerous setae and six submarginal setae directed distallv; propodus 2× as long as broad, with two tusss of anterior setae, seven tusss of inferior medial setae, five anterodistal setae, and five tusss of posterior setae; palm oblique, highlv concave with large robust seta placed along margin and numerous inner/ outer marginal setae; defining angle with eight robust setae, and five long setae; dactvlus with outer seta, inner setae lacking. Gnathopod 2 ( Fig. 7B): coxal plate with six anterior setae, two posterior setae, and 10 long facial setae, additional smaller, submarginal setae line apex of plate; basis with numerous long setae inserted along anterior, and posterior margins, small patch of pubescence on posterodistal corner; ischium with seven setae and pubescence along posterior margin; merus with anterior seta, patch of setae on anterodistal margin, and four tusss of posterior setae, posterior surface of segment weaklv pubescent; carpus approximatelv 70% length of propodus with two tusss of setae along anterior margin, posterior margin with six groups of setae, and four submarginal setae directed distallv; propodus 1.8× as long as broad, with two tusss of anterior setae, six tusss of inferior medial setae, eight anterodistal setae, and six tusss of posterior setae; palm oblique, concave with large robust seta placed along margin and numerous inner/outer marginal setae; defining angle with six robust setae and seven long setae; dactvlus with outer seta, inner seta lacking.

Pereopods: Pereopod 3 ( Fig. 7C): coxal plate with five anterior setae, a posterior seta, and 13 long facial setae, additional smaller, submarginal setae line apex of plate; merus 1.4× as long as carpus, carpus subequal to propodus in length; dactvlus approximatelv 60% length of propodus, with plumose seta on anterior margin, and a seta on posterior margin followed bv thin seta on medial margin. Pereopod 4 ( Fig. 8A): coxal plate with five anterior setae, nine posterior setae, and 24 long facial setae, additional smaller, submarginal setae line apex of plate; merus 1.2× as long as carpus; carpus subequal to propodus in length; dactvlus approximatelv 45% length of propodus, setation as in pereopod 3. Pereopod 5 ( Fig. 8B): coxal plate large, bilobate with distinct anterior and posterior lobes, posterior lobe with five setae on distal corner; basis posterior margin weaklv concave with 14 shallow serrations bearing short setae, posterior face of segment with eight setae, anterior margin with seven robust setae, and 10 long setae on anteroproximal corner, anterodistal corner with tuss of setae paired with robust seta; merus subequal in length to carpus; carpus approximatelv 85% length of propodus; dactvlus approximatelv 40% length of propodus, setation as in pereopods 3–4. Pereopod 6 ( Fig. 8C): coxal plate bilobate, posterior lobe with three setae; basis posterior margin straight with 12 shallow serrations bearing setae, posterodistal corner with three setae and robust seta, posterior face of segment with nine setae, anterior margin with six robust setae, and six long setae on anteroproximal corner, anterodistal corner with tuss of setae paired with robust seta; merus approximatelv 88% length of carpus; carpus subequal in length to propodus; dactvlus approximatelv 40% length of propodus, setation as in pereopods 3–5. Pereopod 7 ( Fig. 8D): coxal plate small, lobes indistinct, with two anterior setae and five posterior setae; basis posterior margin convex proximallv with 17 shallow serrations bearing long setae, longest posterior setae 20% width of segment, posterodistal corner with four setae and three robust setae, posterior face of segment with 20 setae, anterior margin with five robust setae, and three anteroproximal setae, anterodistal corner with two robust setae and two setae; merus subequal in length to carpus; carpus subequal in length to propodus; dactvlus approximatelv 35% length of propodus, setation as in pereopods 3–6.

Gills ( Figs 7B, C, 8A–D): Coxal gills on somites 2–6, somite 7 with pereopod 7 gill.

Pleon: Pleopod 1 ( Fig. 8E): peduncle with 16 inner setae, and four coupling hooks; outer, inner rami with 16 and 20 segments respectivelv. Pleopod 2 ( Fig. 8F): peduncle with six inner/outer setae and three coupling hooks; outer, inner rami with 15 and 18 segments, respectivelv. Pleopod 3 ( Fig. 8G): peduncle with 15 inner and 16 outer setae, and three coupling hooks; outer, inner rami with 16 and 18 segments, respectivelv. Epimera ( Fig. 9A): first epimeron anterior margin with nine setae, ventral margin with four setae, distoposterior corner not produced, posterior margin with five setae; second epimeron anteroventral margin with four setae, ventral margin with three robust setae, posteriormost paired with a seta, three robust setae are inserted faciallv along ventral surface, distoposterior corner weaklv produced, posterior margin with seven setae; third epimeron anterior margin with five setae, ventral margin with seven robust setae, distoposterior corner weaklv produced, posterior margin with four setae.

Urosome: Uronites ( Fig. 9B): weaklv humped dorsallv; dorsomedial surface of first and second uronites with two robust setae and six to seven setae; dorsolateral margins of first and second uronites with a pair of robust setae and four to five setae; third uronite with pair of two robust setae and two to three setae dorsolaterallv. Uropod 1 ( Fig. 9C): peduncle 1.2× inner ramus in length with four outer/inner robust setae and two anteroproximal robust setae; outer ramus subequal in length to inner, with one inner and four outer robust seta(e), five apical robust setae, and one anteroproximal seta; inner ramus with three outer, two inner robust setae, and five apical robust setae.Uropod 2 ( Fig. 9D): peduncle 90% length of outer ramus, with two outer robust setae and three inner robust setae; outer ramus approximatelv 1.2× inner ramus in length, with three outer robust setae, two inner robust setae, and six apical robust setae; inner ramus with two outer robust setae, an inner robust seta, and six apical robust setae. Uropod 3 ( Fig. 9E): elongate, biramous; peduncle approximatelv 30% length of outer ramus with two inner robust setae, an outer robust seta, and three marginal robust setae; outer ramus two-segmented, 1.6× length of inner ramus, first segment approximatelv 7× length of second segment, with six groups of robust setae on outer margin, apical-most paired with both setae and plumose setae, inner margin with two groups of robust setae and row of plumose setae lining most of margin; second segment with apical group of setae; inner ramus one-segmented with plumose setae lining outer margin along with two robust setae, plumose setae absent on apical and inner margins. Telson ( Fig. 9F): cless to base, apices each with three to four robust setae and three to four setae; outer margins with a robust seta and one to two setae; inner margins with two groups of setae, apical-most of right lobe with a robust seta.

Female: USNM 1607106, 4.3 mm in length. Differing from male in several points, including smaller size, gnathopod 2 shape/ setation, pereopod shape/setation, and uropod 3 size/setation. Structures not described below are as in male.

Gnathopods: Gnathopod 2 ( Fig. 10A): coxal plate with four anterior setae, two posterior setae, and three long facial setae; basis with numerous long setae inserted along anterior and posterior margins, small patch of pubescence on posterodistal corner; ischium with four setae and pubescence along posterior margin; merus with anterior seta, patch of setae on anterodistal margin, and two tusss of posterior setae, posterior surface of segment weaklv pubescent; carpus approximatelv 90% length of propodus with two groups of setae along anterior margin, posterior margin with five groups of setae and two groups of submarginal setae directed distallv; propodus 2.6× as long as broad, with three groups of anterior setae, four tusss of inferior medial setae, seven anterodistal setae, and four tusss of posterior setae; palm oblique, straight, lacking robust setae, with numerous inner/outer marginal setae; defining angle with two outer and four inner robust setae; dactvlus with outer seta, inner seta lacking.

Brood plates: Slender, expanding apicallv with medium-length setae, present on somites 2–5.

Pereopods: Pereopod 7 ( Fig. 10B): coxal plate small, lobes indistinct, with one anterior seta and four posterior setae; basis posterior margin convex proximallv with eight shallow serrations bearing long setae decreasing in length distallv, posterodistal corner with two setae and a robust seta, posterior face of segment with nine setae, anterior margin with three robust setae and two groups of setae, anterodistal corner with two robust setae; merus 83% length of carpus; carpus 85% length of propodus; dactvlus approximatelv 42% length of propodus, setation as in male. Uropod 3 ( Fig. 10C): less elongate than in male, biramous; peduncle approximatelv 45% length of outer ramus with one inner and outer robust setae, and six marginal robust setae; outer ramus two-segmented, 2× length of inner ramus, first segment approximatelv 4× length of second segment, with four groups of robust setae on outer margin, inner margin with three robust setae and a row of plumose setae lining most of margin; second segment with apical group of setae; inner ramus one-segmented with plumose setae lining outer margin along with a robust seta, inner margin with apical plumose setae, apical margin with robust setae and slender setae.

Variation: Ŋe species was shown to varv slightlv in several morphological characteristics ( Table 3).

Distribution and ecology: Gammarus desperatus is known from onlv two localities in Chaves Countv, New Mexico: its tvpe localitv, North Spring located on the Roswell Countrv Club and nearbv Rio Hondo. Ŋe Rio Hondo population was examined bv Adams et al. (2018) where it was identified as an undescribed Gammarus species, while populations from Biưer Lake National Wildlife Refuge were designated as Gammarus desperatus . Molecular and morphological analvses performed here indicate the inverse ( Figs 2, 3). Ŋese results greatlv circumscribe the range of the species. As evidenced bv its specific epithet, the status of Gammarus desperatus at its tvpe localitv was precarious at the time of its description; propheticallv, G. desperatus was shortlv revealed to be extirpated from North Spring, thought then to onlv survive within Biưer Lake National Wildlife Refuge ( Seidel et al. 2009). With the species’ circumscription, it now solelv occurs in a section of the Rio Hondo, located within the south tract of Biưer Lake National Wildlife Refuge ( Fig. 1). Given the open habitat of the Rio Hondo, the species has onlv been recorded within vegetation along the banks of the river.