Hyalella (Hyalella) meraspinosa, Baldinger, 2004

Baldinger, AJ, 2004, A new species of Hyalella (Crustacea: Amphipoda: Hyalellidae) from Ash Springs, Lincoln County, Nevada, USA, with a key to the species of the genus in North America and the Caribbean region, Journal of Natural History 38 (9), pp. 1087-1096 : 1088-1093

Hyalella (Hyalella) meraspinosa new species

(figures 1–6)

Diagnosis. Pereon lacking dorsal mucronations or spines. Antenna 1 and 2 subequal in length. Maxilla 1, palp vestigial. The propodus of gnathopod 2 in males is much larger than in females. Anterior margins of the merus of pereopods 3 and 4 lined with bifurcate spines. Basis of pereopod 7 posterior lobe not expanded. Uropod 3, ramus vestigial with two to four apical spines. Telson quadrate with two short submarginal spines.

Description of male. Length 5.4 mm. Body lacking dorsal mucronations or spines. Eyes normal. Head cuboidal, equal to pereonites 1 and 2 in length. Coxae 1–4 with distomarginal setae, coxa 4 enlarged and subquadrate, coxa 5 with distinct anterior and posterior lobes, coxae 6–7 reduced and with posterior lobes. Sternal gills small, present on pereonites 3–7.

Antenna 1, 40% of total body length, peduncular ratio 1:1:1, flagellum 12-articulate; accessory flagellum absent. Antenna 2 subequal in length to antenna 1, 50% of body length, article 4 of peduncle 70% the length of article 5, flagellum 14-articulate.

Upper lip rounded, anterior margin with fine setae. Mandibles lacking palp; left incisor and lacinia mobilis with four teeth, spine row with three plumose setae, molar normal, lacking accessory plumose seta. Right incisor with six teeth, lacinia mobilis with two teeth, spine row with two setae, molar normal, with accessory plumose seta. Lower lip large, lacking inner lobes; outer lobes subovate, anterior and inner margins setose. Maxilla 1, inner plate narrow with two terminal plumose setae, inner margin finely setose; outer plate with nine strong apical serrate and comb-like spines; palp vestigial. Maxilla 2, plates subequal in width; apical margins of inner and outer plates setose. Maxilliped, right inner plate subrectangular with three strong apical teeth, apical and inner margin setose; outer plate ovate, apical and inner margin setose; palp 4-articulate, articles 2–4 longer than wide, inner margin of article 2 setose, article 3 with rather long distal setae, dactylus triangular with strong distal spine. Left half of maxilliped similar to right, but inner plate with two apical teeth.

Gnathopod 1, basis elongate, posterior lobe of carpus with seven marginal setae; propodus rectangular, palm and hind margin equal in length, palm transverse with marginal and submarginal setae; hind margin and palm demarcated by two bifurcate spines. Gnathopod 2, basis elongate; propodus robust and much larger than that of gnathopod 1, palm oblique with marginal and submarginal slender spines and a lobe near hinge of dactylus; hind margin and palm demarcated by a bifurcate spine. Pereopods 3 and 4 similar in shape and size, anterior margins of the merus lined with bifurcate spines. Pereopod 5 approximately 80% length of pereopod 6. Pereopod 7 slightly larger than pereopod 6. Pereopods 5–7 bases expanded posteriorly, stronger in pereopod 7. Basis of pereopod 7, weakly expanded and longer than wide.

Pleopods 1–3 long and slender, peduncles with one to two coupling hooks, rami with plumose setae. Uropod 1, outer margin of peduncle with three to four spines, inner margin with one to two spines; inner ramus with two marginal spines and five apical spines; outer ramus with three to four marginal and four apical spines. Uropod 2, 58% length of uropod 1, outer margin of peduncle with two to three marginal spines, inner margin with one marginal spine; inner ramus with two marginal and five apical spines; outer ramus with three marginal and four apical spines. Uropod 3, inner margin of peduncle with one to two spines, outer margin with one marginal and three distomarginal spines; ramus vestigial with two to four apical spines. Telson quadrate with two distal submarginal bifurcate spines.

Female. All features same as male except as noted. Gnathopod 1, resembling male; propodus, hind margin and palm demarcated by a single bifurcate spine. Gnathopod 2, similar to gnathopod 1, merus with expanded posterior lobe, setose; propodus, hind margin and palm demarcated by distinct lobe bearing two bifurcate spines. Gnathopod 2 and pereopods 3–5 with oostegites. Uropod 2, both inner and outer margin of peduncle each with two marginal spines; rami each with two marginal and four to five apical spines.

Etymology. The specific epithet meraspinosa refers to the presence of spines on the anterior margins of the merus of pereopods 3 and 4.

Material examined. Male holotype, 3.6 mm, MCZ 46000, Nevada, Lincoln County, Ash Springs ; collector: William D. Shepard, 5 April 1998 . Allotype, 3.4 mm, MCZ 46001, same data as holotype. Male paratype, 5.4 mm, MCZ 46002, same data as holotype. Female paratype, 3.4 mm (ovigerous with five eggs), MCZ 46003, same data as holotype. Male paratype, 3.5 mm, MCZ 46004, same date as holotype. Paratypes (25 males and 15 females) MCZ 46005, same data as holotype. Paratypes (25 males and 12 females), YPM 24292, Nevada, Lincoln County, Ash Springs ; collector: William D. Shepard, 5 April 1998 . Paratypes (25 males and 12 females), CASIZ 162724 , Nevada, Lincoln County, Ash Springs ; collector: William D. Shepard, 5 April 1998 . Ten specimens, MCZ 46006, Nevada, Lincoln County, Ash Springs ; collector: William D. Shepard, 5 April 1998 . Thirty-one specimens, MCZ 46007, Nevada, Lincoln County, Ash Springs , second spring above big pool; collector: William D. Shepard, 5 April 1998 . Thirteen specimens, MCZ 46008, Nevada, Lincoln County, Ash Springs , fourth spring above big pool; collector: William D. Shepard, 5 April 1998 . Ninety-two specimens, YPM 24293, Nevada, Lincoln County, Ash Springs , first spring above big pool; collector: William D. Shepard, 5 April 1998 . Fifty specimens, CASIZ 162725 , Nevada, Lincoln County, Ash Springs , third spring above big pool; collector: William D. Shepard, 5 April 1998 .

Remarks. Hyalella (Hyalella) meraspinosa is morphologically similar to Hyalella (Hyalella) sandra Baldinger, Shepard and Threloff, 2000 , and Hyalella (Hyalella) longicornis Bousfield, 1996 . The most significant differences are: antenna 2 is approximately twice the length of antenna 1 in both H. (H.) sandra and H. (H.) longicornis , but subequal in length in H. (H.) meraspinosa ; the anterior margins of the merus of pereopods 3 and 4 are lined with bifurcate spines in H. (H.) meraspinosa , while these spines are absent in both H. (H.) sandra and H. (H.) longicornis ; the posterior lobe on the basis of pereopod 7 is distinctly expanded in both H. (H.) sandra and H. (H.) longicornis and weakly expanded in H. (H.) meraspinosa ; the ramus of uropod 3 is vestigial with two to three apical spines in H. (H.) meraspinosa , robust with seven apical spines in H. (H.) sandra , and slender with apical setae in H. (H.) longicornis ; the telson is quadrate with two spines in H. (H.) meraspinosa , rounded with two spines in H. (H.) sandra , and broadly rounded with two long setae in H. (H.) longicornis . These differences and others are shown in table 1.