Gammarus pecos ( Cole, 1985 )

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 pecos ( Cole, 1985)

Gammarus sp. 2 ( Adams et al., 2018)

( Figs 4, 17–22)

Zoobank registration: urn:lsid:zoobank.org:act:303A01C8-95F4-4B57-A073-7D274BF729A9 .

Material examined: USNM 1607116 , holotvpe male, 13.7 mm: San Solomon Spring , Reeves Countv , TX, USA (33.478125, –104.419763); collector: Ashlev D. Walters, 1 June 2018 . USNM 1607117 , allotvpe female, 9.6 mm: San Solomon Spring , Reeves Countv , TX, USA; collector: Ashlev D. Walters, 1 June 2018 . USNM 1607118 , paratvpe male, 12.4 mm: San Solomon Spring , Reeves Countv , TX, USA; collector: Ashlev D. Walters, 1 June 2018 . USNM 1607119 , paratvpe males N = 3, San Solomon Spring , Reeves Countv , TX, USA; collector: Ashlev D. Walters, 1 June 2018 . USNM 1607120 , paratvpe females N = 2, San Solomon Spring , Reeves Countv , TX, USA; collector: Ashlev D. Walters, 1 June 2018 . USNM 1607121 , paratvpe males N = 3, East Sandia Spring , Reeves Countv , TX, USA (30.94583, –103.79); collector: unknown, 1 June 2013 . USNM 1607122 , paratvpe females N = 2, East Sandia Spring , Reeves Countv , TX, USA; collector: unknown, 1 June 2013 .

Type locality: San Solomon Spring , Reeves, Texas, 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, with the exception of Gammarus hyalelloides , through the combination of the following characteristics: antenna one flagellum with up to 28 segments; mandibular palp ultimate and penultimate segments subequal; α setae on mandibular palp slightlv as long as E-setae; C-setae on mandibular palps up to 1.5× D-setae in length; B-setae on mandibular palp shorter than longest A-seta; male gnathopods 1 * 2 with weaklv convex palmar margins on propodi; coxal plates 1–4 lacking numerous facial setae; basis of pereopod seven convex posteriorlv, and with dense facial setae; posterior setae on basis of pereopod 7 10%– 20% width of segment; posterior margin of pereopod 7 convex; males up to 15 mm in length, females up to 10 mm in length. Distinguished from the similar G. hyalelloides through the combination of the following characteristics: larger average size (ossen> 8–10 mm in length), A-setae on mandibular palps not reaching past tip of palp segment; C-setae on mandibular palps short, up to 1.5× the length of the D-setae; and male gnathopods 1 * 2 propodi with palms weaklv concave to straight mediallv.

Description: Male ( Figures 16–21): 13.7 mm in length. Eves reniform, integumentarv pigment present when alive and in freshlv preserved specimens ( Figure 4F).

Antennae: Antenna 1 ( Fig. 17A): approximatelv 40% bodv length, 1.2× as long as antenna 2; peduncle segment one with distal robust setae; primarv flagellum damaged in holotvpe, with more than 22 segments; accessorv flagellum five-segmented. Antenna 2 ( Fig. 17B): peduncle approximatelv 2× as long as flagellum, segment 4 with four tusss of dorsal setae, four tusss of ventral setae, and five tusss of lateral setae, segment 5 subequal in length to segment 4, armed with six tusss of dorsal setae, five tusss of ventral setae, and five tusss of lateral setae; flagellum with 10 segments, setae length on segments not decreasing distallv, calceoli absent.

Mouthparts: Mandibles: less mandible ( Fig. 17C) incisor five-dentate, lacinia mobilis five-dentate, accessorv setal row with four robust, serrate setae and numerous plumose setae; molar process ovate, with plumose seta; palp with three segments, penultimate segment 1.2× length of ultimate with six α-setae and four β-setae, α-setae slightlv as long as E-setae; ultimate segment with five A-setae set proximallv in two rows, longest of which not projecting bevond tip of segment, three B-setae, four C-setae, 15 D-setae, and five E-setae, C-setae 1.5× length of longest D-seta, longest B-setae shorter in length than longest A-seta. Right mandible ( Fig. 17D) incisor four-dentate, lacinia mobilis bifurcate, both lobes with numerous protuberances; accessorv setal row with four robust, serrate setae, and numerous plumose setae; molar process ovate, with plumose seta; palp with three articles, relative segment lengths and setation paưerns as in less mandible. Upper lip ( Fig. 18A): rounded, apical margin of labrum with numerous fine setae. Lower lip ( Fig. 18B): inner lobes weak; outer margin of outer lobes sparselv covered in fine setae; inner margin of outer lobes heavilv setose. Maxilla 1 ( Fig. 18C, 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 long seta, apical margin with seven 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. 18E): 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. 18F): 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 six inner setae and two outer setae.

Gnathopods: Gnathopod 1 ( Fig. 19A): coxal plate with three anterior setae, a posterior seta, and a long facial seta, 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 five setae and pubescence along posterior margin; merus with two anterior setae, a large 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 tusss of setae along anterior margin, posterior margin with numerous setae and 10 submarginal setae directed distallv; propodus approximatelv 2× as long as broad, with three tusss of anterior setae, two tusss of inferior medial setae, eight anterodistal setae, and four tusss of posterior setae; palm oblique, weaklv concave mediallv with large robust seta placed along margin and numerous inner/outer marginal setae; defining angle with four robust setae and four long setae; dactvlus with outer seta, inner setae lacking. Gnathopod 2 ( Fig. 19B): coxal plate with three anterior setae, a posterior seta, and two 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 two anterior setae, patch of setae on anterodistal margin, and three tusss of posterior setae, posterior surface of segment weaklv pubescent; carpus approximatelv 60% length of propodus with two tusss of setae along anterior margin, posterior margin with five groups of setae and two tusss of submarginal setae directed distallv; propodus 2.0× as long as broad, with three tusss of anterior setae, 6 tusss of inferior medial setae, eight anterodistal setae, and six tusss of posterior setae; palm oblique, nearlv straight mediallv with large robust setae placed along margin and numerous inner/outer marginal setae; defining angle with five robust setae and three long setae; dactvlus with outer seta, inner setae lacking.

Pereopods: Pereopod 3 ( Fig. 19C): coxal plate with three anterior setae, a posterior seta, and two 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 25% 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. 20A): coxal plate with four anterior setae, three posterior setae, and five long facial setae, additional smaller, submarginal setae line apex of plate; merus subequal to carpus in length; carpus subequal to propodus in length; dactvlus approximatelv 40% length of propodus, setation as in pereopod 3. Pereopod 5 ( Fig. 20B): coxal plate large, bilobate with distinct anterior and posterior lobes, anterior lobe with a distal seta, posterior lobe with four setae on distal corner; basis posterior margin straight with 13 shallow serrations bearing shortsetae, posteriorfaceofsegmentwithfoursetae, anteriorface of segment with an additional four longer setae, anterior margin with four robust setae, and three setae on anteroproximal corner, anterodistal corner with tuss of setae paired with robust seta; merus subequal to carpus in length; carpus subequal in length to propodus; dactvlus approximatelv 38% length of propodus, setation as in pereopods 3–4. Pereopod 6 ( Fig. 20C): coxal plate weaklv bilobate, posterior lobe with two long setae; basis posterior margin weaklv convex with 11 shallow serrations bearing long setae, posterior face of segment with three setae, anterior margin with four robust setae, and three setae on anteroproximal corner, anterodistal corner with tuss of setae paired with three robust setae; merus subequal in length to carpus; carpus subequal in length to propodus; dactvlus approximatelv 30% length of propodus, setation as in pereopods 3–5. Pereopod 7 ( Fig. 20D): coxal plate small, lobes indistinct, with five posterior setae; basis posterior margin convex, with 11 shallow serrations bearing long setae, longest posterior seta 20% width of segment, posterodistal corner with a seta and two robust setae, posterior face of segment with five setae, anterior margin with three robust setae and three anteroproximal setae, anterodistal corner with tuss of setae paired with two robust setae; merus subequal in length to carpus; carpus subequal in length to propodus; dactvlus approximatelv 40% length of propodus, setation as in pereopods 3–6.

Gills ( Figs 19B, C, 20A–D): Coxal gills on somites 2–6, somite 7 with pereopod 7 gill.

Pleon: Pleopod 1 ( Fig. 20E): peduncle with eight inner setae, seven outer setae, and three coupling hooks; outer, inner rami with 19 and 14 segments, respectivelv. Pleopod 2 ( Fig. 20F): peduncle with 12 inner and 10 outer setae, and three coupling hooks; outer, inner rami with 17 and 18 segments, respectivelv. Pleopod 3 ( Fig. 20G): peduncle with 13 inner and three outer setae, outer setae paired with robust seta, and three coupling hooks; outer, inner rami with 14 and 17 segments, respectivelv. Epimera ( Fig. 21A): first epimeron anterior margin with eight setae, ventral margin convex with one seta placed faciallv near distoposterior corner, distoposterior corner weaklv produced, posterior margin with two setae; second epimeron anterior margin with two setae, ventral margin with two robust setae; three robust setae are inserted faciallv along ventral surface, distoposterior corner weaklv produced, posterior margin with three setae; third epimeron anterior margin with two setae, ventral margin with four robust setae, distoposterior corner weaklv produced, posterior margin with three setae.

Urosome: Uronites ( Fig. 21B): weaklv humped dorsallv; dorsomedial surface of first and second uronites with a robust seta and two to three setae; dorsolateral margins of first and second uronites with a pair of one to two robust setae and two to four setae; third uronite with four robust setae and five setae dorsolaterallv. Uropod 1 ( Fig. 21C): peduncle 1.2× inner ramus in length with four outer robust setae, five inner robust setae and an anteroproximal robust seta; outer ramus subequal in length to inner, with three inner robust setae, five apical robust setae, and one anteroproximal seta; inner ramus with two outer robust setae, three inner robust setae, and five apical robust setae. Uropod 2 ( Fig. 15C): peduncle 80% length of outer ramus, with three outer robust setae and two inner robust setae; outer ramus approximatelv 1.1× inner ramus in length, with three outer robust setae, an inner robust seta, and five apical robust setae; inner ramus with two inner/outer robust setae, and five apical robust setae. Uropod 3 ( Fig. 21E): elongate, biramous; peduncle approximatelv 35% length of outer ramus with two inner robust setae, an outer robust seta, and five marginal robust setae; outer ramus two-segmented, 1.4× length of inner ramus, first segment approximatelv 5× length of second segment, with five groups of robust setae on outer margin paired with setae and/or plumose setae, inner margin with one group of marginal 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, apical margin with two robust setae, paired with setae and plumose setae. Telson ( Fig. 21F): cless to base, apices each with one to two robust setae and three to four setae; outer margins with a robust seta and two to four setae; facial surface with no to one robust seta, and two to three setae.

Female: USNM 1607117, 9.6 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. 22A): coxal plate with three anterior setae, one posterior seta, 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 80% length of propodus with two groups of setae along anterior margin, posterior margin with four groups of setae, and two groups of submarginal setae directed distallv; propodus 2.5× as long as broad, with three groups of anterior setae, four tusss of inferior medial setae, six anterodistal setae, and three tusss of posterior setae; palm oblique, weaklv convex, lacking robust setae, with numerous inner/outer marginal setae; defining angle with two outer and two inner robust setae; dactvlus with an outer and inner seta.

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

Pereopods: Pereopod 7 ( Fig. 22B): coxal plate small, lobes indistinct, with four posterior setae; basis posterior margin convex proximallv with seven shallow serrations bearing long setae decreasing in length distallv, posterodistal corner with seta and two robust setae, face of segment with seven setae, anterior margin with two robust setae, anterodistal corner with three robust setae and a seta; merus subequal in length to carpus; carpus subequal in length to propodus; dactvlus approximatelv 43% length of propodus, setation as in male. Uropod 3 ( Fig. 22C): less elongate than in male, biramous; peduncle approximatelv 40% length of outer ramus with one outer/inner robust seta, and six marginal robust setae; outer ramus two-segmented, 1.5× length of inner ramus, first segment approximatelv 5× length of second segment, with three groups of robust setae on outer margin, inner margin with two apical robust setae and row of plumose setae lining distal margin; second segment with apical group of setae; inner ramus one-segmented with plumose setae lining outer margin along with a robust setae, inner margin with apical plumose setae, apical margin with two robust setae, paired with plumose setae and setae.

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

Etymology: Ŋe specific epithet balmorhea , derived from Balmorhea State Park, where the species’ tvpe localitv is located. Ŋe state park’s name references the nearbv citv/lake Balmorhea, whose name is an amalgamation of the citv’s three founders (Ernest D. Balcom, H.R. Morrow, and John/Joe Rhea).

Distributionandecology: Gammarusbalmorhea iscurrentlvknown from three springs (San Solomon Spring, East Sandia Spring, and Giffin Spring) within the Balmorhea Springs complex in Reeves Countv, Texas. San Solomon and Giffin springs are located on or near Balmorhea State Park in the communitv of Tovahvale; East Sandia Spring is located north-east of the other springs near the citv of Balmorhea ( Fig. 1). Ŋe Balmorhea Springs complex has undergone significant modification during its historv, primarilv due to the construction of numerous canal svstems to divert water in the region for agricultural and recreational use; these actions led to habitat modification and reduced spring flow. However, more recentlv, efforts to improve habitat qualitv in the region include the construction of refuge canals and restored ciénegas like that present around San Solmon Spring ( Lewis et al. 2013). Ŋe svstem occupied bv G. balmorhea is also known to be occupied bv the pupfish Cyprinodon elegans Baird and Girard, 1853 , which has been recorded in all three of the aforementioned springs. However, unlike G. balmorhea , C. elegans enjovs a larger distribution throughout the spring complex, also occurring at the headwaters of the complex (Phantom Lake Spring), where it co-occurs with Gammarus hyalelloides ( Lewis et al., 2013) .