Gammarus acerbatus, Cannizzaro & Berg, 2024

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 acerbatus sp. nov. Cannizzaro and Berg

Gammarus desperatus ( Adams et al., 2018)

( Figs 4, 11–16)

Zoobank registration: urn:lsid:zoobank.org:act:5BD13043-4C59-49F7-960B-8214607B6C0D .

Material examined: USNM 1607109 , holotvpe male, 12.8 mm: Sago Spring , Biưer Lake National Wildlife Refuge, Chaves Countv, NM, USA (33.478125, –104.419763); collector: Brian K. Lang, date unknown . USNM 1607110 , allotvpe female, 8.1 mm: Sago Spring , Biưer Lake National Wildlife Refuge, Chaves Countv, NM, USA; collector: Brian K. Lang, date unknown . USNM 1607112 , paratvpe males N = 3, Sago Spring , Biưer Lake National Wildlife Refuge, Chaves Countv, NM, USA; collector: Brian K. Lang, date unknown . USNM 1607111 , paratvpe female, 9.0 mm: Sago Spring , Biưer Lake National Wildlife Refuge, Chaves Countv, NM, USA; collector: Brian K. Lang, date unknown . USNM 1607113 , paratvpe females N = 2, Sago Spring , Biưer Lake National Wildlife Refuge, Chaves Countv, NM, USA; collector: Brian K. Lang, date unknown . USNM 1607114 , paratvpe males N = 3, Unit 6 ditch at ‘ Beaver Dam’, Biưer Lake National Wildlife Refuge, Chaves Countv, NM, USA (33.4459, –104.4044); collector: Brain K. Lang, 2005 (precise date unknown) . USNM 1607115 , paratvpe females N = 2, Unit 6 ditch at ‘ Beaver Dam’, Biưer Lake National Wildlife Refuge, Chaves Countv, NM, USA; collector: Brain K. Lang, 2005 (precise date unknown) .

Type locality: Sago Spring , Biưer Lake National Wildlife Refuge , Chaves Countv, New Mexico, USA (33.478125, –104.419763)

Diagnosis: Large, brightlv marked species showing characteristics tvpical of members of the Gammarus pecos 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 3× D-setae in length; B-setae on mandibular palps up to 60% length of longest A-seta; male gnathopods 1 * 2 with straight or slightlv 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 35%–40% width of segment. Males up to 14 mm in length, females up to 9 mm in length.

Description: Male ( Figs 11–15): 12.8 mm in length. Eves reniform, integumentarv pigment present when alive and in freshlv preserved specimens ( Fig. 4D).

Antennae: Antenna 1 ( Fig. 11A): approximatelv 45% bodv length, 1.2× as long as antenna 2; peduncle segment 1 with distal robust seta; primarv flagellum with 26 segments; accessorv flagellum four-segmented. Antenna 2 ( Fig. 11B): peduncle approximatelv 1.4× as long as flagellum, segment 4 with four tusss of dorsal setae, four tusss of ventral setae, and four tusss of lateral setae, segment 5 subequal in length to segment 4, armed with five tusss of dorsal setae, five tusss of ventral setae, and four tusss of lateral setae; flagellum with 12 segments, setae length on segments decreasing distallv, calceoli absent.

Mouthparts: Mandibles: less mandible ( Fig. 5C) incisor five-dentate, lacinia mobilis four-dentate, accessorv setal row with six robust, serrate setae and numerous plumose setae; molar process ovate, lacking seta; palp with three segments, penultimate segment 1.1× length of ultimate with six α-setae and eight β-setae, α-setae subequal in length to E-setae; ultimate segment with five A-setae, five B-setae, three C-setae, 22 D-setae, and five E-setae, C-setae 3× length of longest D-seta, B-setae 60% length of longest A-seta. Right mandible ( Fig. 5D): incisor five-dentate, lacinia mobilis bifurcate, both lobes with numerous protuberances; accessorv setal row with six robust, serrate setae and numerous plumose setae; molar process ovate, lacking seta; palp with three articles, relative segment lengths and setation paưerns as in less mandible. Upper lip ( Fig. 12A): rounded, apical margin of labrum with numerous fine setae. Lower lip ( Fig. 12B): inner lobes indistinct; outer margin of outer lobes sparselv covered in fine setae; inner margin of outer lobes heavilv setose. Maxilla 1 ( Fig. 11C, D): inner plate with 16 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 three long setae, apical margin with eight robust setae; right palp with two segments, subapical margin of distal segment with a long seta, apical margin with five robust setae, broader than those of less palp. Maxilla 2 ( Fig. 12E): 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. 12F): inner plate shorter than outer plate, apical margin with three naked cuspidate setae, inner margin with nine 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 numerus marginal/ submarginal setae; dactvlus with four inner setae and an outer seta.

Gnathopods: Gnathopod 1 ( Fig. 13A): coxal plate with four anterior setae, a posterior seta, and nine 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 eight setae and pubescence along posterior margin; merus with anterior seta, a large patch of setae on anterodistal margin, and a tuss of posterior setae, posterior surface of segment weaklv pubescent; carpus approximatelv 75% length of propodus with one tuss of setae along anterior margin, posterior margin with numerous setae and seven submarginal setae directed distallv; propodus approximatelv 2.3× as long as broad, with two tusss of anterior setae, six tusss of inferior medial setae, nine anterodistal setae, and four tusss of posterior setae; palm oblique, weaklv concave, with large robust seta placed along margin and numerous inner/outer marginal setae; defining angle with nine robust setae and three long setae; dactvlus with outer seta, inner setae lacking. Gnathopod 2 ( Fig. 13B): coxal plate with three 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 three 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 2.0× as long as broad, with two tusss of anterior setae, seven tusss of inferior medial setae, 10 anterodistal setae, and six tusss of posterior setae; palm oblique, weaklv concave with large robust setae placed along margin and numerous inner/outer marginal setae; defining angle with eight robust setae and seven long setae; dactvlus with outer seta, inner setae lacking.

Pereopods: Pereopod 3 ( Fig. 13C): coxal plate with five anterior setae, three posterior setae, and 10 long facial setae, additional smaller, submarginal setae line apex of plate; merus 1.4× as long as carpus, carpus 80% propodus in length; dactvlus approximatelv 50% length of propodus, with plumose seta on anterior margin, and a seta on posterior margin followed bv a thin seta on medial margin. Pereopod 4 ( Fig. 14A): coxal plate with two anterior setae, five posterior setae, and 10 long facial setae, additional smaller, submarginal setae line apex of plate; merus 1.4× as long as carpus; carpus 70% length of propodus; dactvlus approximatelv 50% length of propodus, setation as in pereopod 3. Pereopod 5 ( Fig. 14B): coxal plate large, bilobate with distinct anterior and posterior lobes, posterior lobe with four setae on distal corner; basis posterior margin straight with 13 shallow serrations bearing short setae, posterior face of segment with four setae, anterior margin with four robust setae, and seven long setae on anteroproximal corner, anterodistal corner with tuss of setae paired with robust seta; merus approximatelv 80% length of carpus; carpus subequal in length to propodus; dactvlus approximatelv 38% length of propodus, setation as in pereopods 3–4. Pereopod 6 ( Fig. 14C): coxal plate bilobate, posterior lobe with five long setae; basis posterior margin weaklv convex with 10 shallow serrations bearing long setae, posterodistal corner with four setae and robust seta, posterior face of segment with 14 setae, anterior margin with five robust setae, and 10 long setae on anteroproximal corner, anterodistal corner with tuss of setae paired with robust setae; merus approximatelv 75% length of carpus; carpus subequal in length to propodus; dactvlus approximatelv 50% length of propodus, setation as in pereopods 3–5. Pereopod 7 ( Fig. 14C): coxal plate small, lobes indistinct, with seven posterior setae; basis posterior margin weaklv convex, with 19 shallow serrations bearing long setae, longest posterior setae 40% width of segment, posterodistal corner with five setae and two robust setae, posterior face of segment with 21 setae subequal in length to marginal setae, anterior margin with five robust setae and four anteroproximal setae, anterodistal corner with tuss of setae paired with robust setae; merus subequal in length to carpus; carpus subequal in length to propodus; dactvlus approximatelv 42% length of propodus, setation as in pereopods 3–6.

Gills ( Figs 13B, C, 14A–D): Coxal gills on somites 2–6, somite 7 with pereopod 7 gill.

Pleon: Pleopod 1 ( Fig. 14E): peduncle with seven inner setae, 14 outer setae, and four coupling hooks; outer, inner rami with 16 and 21 segments, respectivelv. Pleopod 2 ( Fig. 14F): peduncle with five inner and 10 outer setae, and five coupling hooks; outer, inner rami with 16 and 18 segments, respectivelv. Pleopod 3 ( Fig. 14G): peduncle with three inner and 14 outer setae, and four coupling hooks; outer, inner rami with 15 and 16 segments, respectivelv. Epimera ( Fig. 15A): first epimeron anterior margin with 14 setae, ventral margin with two setae, distoposterior corner not produced, posterior margin with four setae; second epimeron anterior margin with 10 setae, ventral margin with four robust setae; three robust setae inserted faciallv along the ventral surface, distoposterior corner weaklv produced, posterior margin with five setae; third epimeron anterior margin with 11 setae, ventral margin with four robust setae, distoposterior corner weaklv produced, posterior margin with four setae.

Urosome: Uronites ( Fig. 15B): weaklv humped dorsallv; dorsomedial surface of first and second uronites with a robust seta and four to five setae; dorsolateral margins of first and second uronites with a pair of robust setae and two to three setae; third uronite with three robust setae and five setae dorsolaterallv. Uropod 1 ( Fig. 15C): peduncle 1.2× inner ramus in length with three outer robust setae, six inner robust setae, and two anteroproximal robust setae; outer ramus subequal in length to inner, with two inner robust setae, 3 outer robust setae, five apical robust setae, and one anteroproximal seta; inner ramus with three outer robust setae, two inner robust setae, and five apical robust setae. Uropod 2 ( Fig. 15C): peduncle subequal in length to outer ramus, with four outer robust setae and three inner robust setae; outer ramus approximatelv 1.2× inner ramus in length, with three outer robust setae, an inner robust seta, and six apical robust setae; inner ramus with an inner/outer robust seta, and five apical robust setae. Uropod 3 ( Fig. 15E): elongate, biramous; peduncle approximatelv 40% length of outer ramus with two inner robust setae, an outer robust setae, and four marginal robust setae; outer ramus two-segmented, 1.2× length of inner ramus, first segment approximatelv 9× length of second segment, with four groups of robust setae on outer margin paired with setae and/or plumose setae, inner margin with three 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 margin. Telson ( Fig. 15F): cless to base, apices each with two to three robust setae and four to six setae; outer margins with a robust seta and two to six setae; inner margins with three to five setae and a robust seta.

Female: USNM 1607110, 8.1 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. 16A): coxal plate with one anterior seta, four posterior setae, and six 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 85% 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× as long as broad, with three groups of anterior setae, five tusss of inferior medial setae, seven anterodistal setae, and four tusss of posterior setae; palm oblique, slightlv concave, lacking robust setae, with numerous inner/outer marginal setae; defining angle with two outer and two inner robust setae; dactvlus with outer setae, inner setae lacking.

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

Pereopods: Pereopod 7 ( Fig. 16B): coxal plate small, lobes indistinct, with six posterior setae; basis posterior margin convex proximallv with nine shallow serrations bearing long setae decreasing in length distallv, posterodistal corner with three setae, posterior face of segment with 14 setae, anterior margin with two robust setae and 3 setae, anterodistal corner with two robust setae and two setae; merus subequal in length to carpus; carpus 83% length of propodus; dactvlus approximatelv 43% length of propodus, setation as in male. Uropod 3 ( Fig. 16C): less elongate than in male, biramous; peduncle approximatelv 40% length of outer ramus with three outer, two inner robust setae, and three marginal robust setae; outer ramus two-segmented, 1.6× length of inner ramus, first segment approximatelv 3.3× length of second segment, with three groups of robust setae on outer margin, inner margin with apical robust seta 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, inner margin with apical plumose setae, apical margin with two robust setae and slender setae.

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

Etymology: Ŋe specific epithet acerbatus , derived from the word ‘acerbate’ (to embiưer) is given in reference to the species occurrence within Biưer Lake National Wildlife Refuge.

Distribution and ecology: Gammarus acerbatus sp. nov. is currentlv known onlv from the main tract of Biưer Lake National Wildlife Refuge in Chaves Countv, New Mexico. Here it has been recorded from six localities spanning a significant portion of the refuge ( Fig. 1). Within BLWNR, individuals of G. acerbatus have been associated with vegetation in sinkholes, springs, and the edges of marshes, and are known to co-occur both with an undescribed species of Hyalella and with Gammarus cf. lacustris . Ŋe laưer occurrence has onlv been noted in a single location, Hunter Marsh, towards the south end of the refuge and recent collection aưempts have failed to vield either Gammarus species.