Metharpinia dentiurosoma, Alonso De Pina, 2003

Alonso De Pina, Gloria M., 2003, Two new species of Metharpinia Schellenberg (Amphipoda: Phoxocephalidae) from the south-west Atlantic, Journal of Natural History 37, pp. 2521-2545 : 2523-2533

Metharpinia dentiurosoma n. sp.

(figures 1–7)

Material examined

H  : X (with oostegites), 6.3 mm, MACN No. 34790, Buenos Aires: El Rincón, 39 ° 49 ∞ 58 ◊ S, 61 ° 35 ∞ 02 ◊ W (Sta. 28), 21 m depth, 55% fine sand, 2 November 1993. P    : Buenos Aires: El Rincón, same data, one immature W, 6.2 mm , MACN No. 34791, 40 ° 00 ∞ 25 ◊ S, 61 ° 50 ∞ 02 ◊ W (Sta. 30), 14 m depth, 66% gravel, 2 November 1993, one sub-adult W dissected, ca 8 mm , MACN No. 34792. Collectors and donors: D. Roccatagliata and M. Torres Jordá .

Description

Holotype, female with oostegites (body length 6.3 mm). Head (figure 1a, b) about 16% of total body length, greatest width about 60% of length, rostrum constricted, narrow, of medium length, slightly exceeding apex of article 1 on antenna 1. Eyes small, suboval, light orange occluded with dark pigment in alcohol. Antenna 1, peduncle article 1 about 1.3 times as long as wide, about 1.8 times as wide as article 2, ventral margin bearing a few plumose setules, produced dorsal apex with one long seta; article 2 about 0.77 times as long as article 1, with proximal ventral crescent of six setae; primary flagellum with 13 articles, about 0.96 times as long as peduncle, bearing one aesthetasc each on articles 6–9; accessory flagellum with 10 articles (figure 1c). Antenna 2, peduncle article 1 without any special process; article 3 with one setule; article 4 facial spine formula: 1-3-5-4, dorsal margin with notch bearing proximally one long seta and two short spines, apically with two plumose setules and one medium seta, ventral margin with two groups of four to five long to medium and short setae, one ventrodistal long and thick spine set subfacially; article 5 about 0.73 times as long as article 4, facial spine formula: 4, dorsal margin almost naked bearing only one small seta, apically with two plumose setules and two short setae, ventral margin lined with long to medium and short setae on distal half, three ventrodistal medium to short thicker spines placed subfacially; flagellum with 14 articles, about 1.3 times as long as articles 4 and 5 of peduncle combined (figure 1d).

Upper lip ordinary, as in the genus. Mandibles with weak palpar hump; right incisor with three very weak teeth, left incisor with two humps; right lacinia mobilis bifid, distal branch much shorter than proximal, narrow, sharp, proximal branch pointed, left lacinia mobilis with three teeth, one larger and sharp, two others rounded, rest of margin near teeth straight; right and left rakers 14, two proximal very small; molars composed of bulbous plaques, without plume, each molar with six primarily stout spines plus one thin spine strongly disjunct (figure 1e–g); palp, article 1 short, article 2 with one short inner apical seta and seven other short to medium inner setae, article 3 slightly longer than article 2, oblique apex with seven spines/setae, basofacial formula: 0-2 (figure 1h). Lower lip ordinary, as in the genus, each outer lobe with one cone. Maxilla 1, inner plate large, broad, bearing one medium apical seta, one similar apicomedial seta and two short apicolateral setae; outer plate with 11 apical spines, outer spine enlarged; palp, article 2 bearing two apicomedial pectinate spines, one apicomedial seta (broken), and five submarginal setae (figure 1i). Maxilla 2, inner plate shorter than outer, outer broader than inner; outer plate with three apicolateral setae, inner bearing three medial setae with plumosity (figure 1j). Maxilliped, inner plate with two large thick apical spines, two apicofacial setae and four medial setae, all setae plumose; outer plate with four masticatory medial spines, few medial setae and one lateral seta; palp, article 1 with one apicolateral seta, article 2 with three lateral setae, medial margin moderately setose, article 3 with two lateral setae, few facial setae, article 4 elongate, narrow, bearing long apical nail, about 24% of article 4 length, not fully fused and partially immersed, with one accessory setule (figure 2a).

Coxa 1 scarcely expanded apically, anterior and posterior margins straight. Coxa 2 slightly expanded apically, anterior margin convex, posterior straight. Coxa 3 rectangular. Coxa 4 subtriangular, anterior and posterior margins strongly divergent, posterior margin oblique, almost straight, posterodorsal corner rounded-quadrate, posterodorsal margin short, almost straight, width/length ratio: 85:93. Coxae 1–4, main ventral setae: 20-12-10-3 (and posterior setae: 1-1-4-12); posteriormost seta of coxae 1 and 2 shortest, of coxa 3 short; coxa 1, setae ornamenting the whole ventral margin, in coxae 2 and 3 only distributed on half towards posterior margin. Gnathopods 1 and 2 small, similar, second pair longer than first pair; width ratios on articles 5 and 6 of both pairs: 25:36 and 25:35, length ratios: 60:55 and 54:54. Gnathopod 1 (figure 2b, c), article 5 elongate, ovate, posterior margin rounded-flat, long. Gnathopod 2 (figure 2d, e), article 5 elongate but shorter than in gnathopod 1, ovate, posterior margin rounded, expanded, short. Gnathopods 1 and 2, article 6 stout, oval-rectangular shape, poorly setose anteriorly, palms oblique, palmar humps large, ornamented with setule.

Peraeopods 3 (figure 3a, b) and 4 (figure 3c, d) similar (except in coxae) in shape and size; peraeopod 4, article 4 with posterior margin somewhat more setose than on preceding appendage. Peraeopods 3 and 4, facial setal formula on article 4:4 and 6, almost parallel to apex, on article 5:4 and 4; main spine of article 5 extending 78% and 84% of article 6; article 5 without proximoposterior spine, proximal edge naked for long distance; spine formula of article 6: 3 + 4 and 4 + 4 plus mid-distal spine, all spines thick, some spines especially long; dactyla with weak acclivity on inner margin, sharp, produced as tooth, emergent setule short, mid-facial plumose setule long. Coxae 5–7, posteroventral setule/seta formula: 6-17-10, mostly short, especially those of coxa 7. Peraeopod 5 (figure 3e, f), articles 4 and 5 broad; dactylus without acclivity, emergent setule long, immersed. Peraeopod 6 (figure 4a, b), article 4 broad and article 5 medium width; dactylus without acclivity, with short emergent setule immersed and small nail fused. Peraeopods 5 and 6, facial spine rows moderately to scarcely developed. Peraeopods 5–7, article 2 facial ridge formula: 0-1-1; dactyla with mid-facial plumose setule set proximal and posteriorly; width ratios of articles 2, 4, 5, 6 of peraeopod 5: 67:62:46:23, of peraeopod 6: 106:70:41:18, of peraeopod 7: 119:26:20:13, length ratios of peraeopod 5: 108:41:54:57, of peraeopod 6: 126:76:67:60, of peraeopod 7: 152:26:30:34. Peraeopod 7 (figure 4c, d), article 2 extending to apex of article 5, posterior margin with about 12 serrations; article 6, medial apex finely combed, bearing about three digital processes (processes difficult to distinguish individually using the greatest magnification).

Gills attached to coxae 2–7, in coxa 7 very small. Oostegites not completely developed, elongate, slender, smooth, on coxae 2–5. Pleopods 1–3 ordinary, slightly different in length; peduncle with two locking spines.

Epimeron 1 damaged (right); on left side, posteroventral corner produced, posterior margin somewhat convex, setose, with three setae and small setule proximally, anterior margin and face bearing about seven setae, ventral margin with five or six plumose setae. Epimeron 2, posteroventral corner produced, posterior margin convex proximally and straight below, setose, bearing five setae (some broken) and small setule proximally, anteroventral corner quadrate, anterior margin and face naked, ventral margin with three long plumose setae, but some sockets observed probably indicate existence of about three more setae (ventral margin on left side with seven plumose setae) (figure 4e). Epimeron 3, posteroventral corner strongly produced into a large tooth, posterior margin almost straight, serrate, setose, bearing five setae widely spread, all long except proximal-most, near this latter small setule, anteroventral corner rounded-quadrate, anterior face with one medium plumose seta, ventral face bearing oblique row of nine spines extending from ventral posterior face to middle of epimeron, decreasing in length (figure 5a).

Urosomite 1 with ventral brush of setae emerging on to lateral surface, articulation line incomplete but long. Urosomite 3 with large acute hook dorsally on each side. Uropod 1 (figure 5b), peduncle without basofacial setae, medially with four marginal spines, apical-most enlarged, laterally with 10 dorsal smaller spines, apicolateral larger; inner ramus bearing four dorsal spines, outer with seven. Uropod 2 (figure 5c), peduncle with one medium apical spine as long as greatest width of inner ramus, and two smaller marginal spines/setae medially, seven dorsolateral spines, apical-most thick; inner ramus bearing two dorsal spines, outer with five. Uropods 1 and 2, peduncle apicolateral corners coarsley combed; outer rami with two subapical nails and inner with one, both rami without apical nails. Uropod 3 (figure 5d), peduncle bearing five ventral spines, dorsally with one lateral spine, one hooked medial spine, three setules; rami unequal in length, inner ramus extending 70% of article 1 of outer ramus, apex carrying one small seta, medial and lateral margins naked; article 2 of outer ramus elongate, 0.40, bearing two setae of different length (longest broken), medial margin of article 1 with two plumose setae, one apical, other subapically, lateral margin with two acclivities, spine formula: 2-2-3, setal formula: 0. Telson long, thick, length/width ratio: 110:90, almost fully cleft, each apex of medium width, subtruncate, bearing one short lateral and one long medial spines separated by one long plumose setule, each side with two long and medium setae placed subapically, mid-lateral plumose setules distinct, larger member about twice as long as other (figure 5e).

Additional observations

Paratype, subadult male (body length ca 8 mm) (figure 5f). Eyes very large, dark brown pigmented in alcohol (figure 5g). Antenna 1, peduncle article 1 with a few ventral setules, dorsal margin with patch of sensory fine setae set proximally, produced dorsal apex with one long seta and two setules; article 2 with seven ventral setae set proximally, apically bearing six facial setules/setae; primary flagellum with 15 articles bearing one aesthetasc each on articles 6–14 (calceoli not observed); accessory flagellum with 10 articles (figure 6a). Antenna 2, peduncle articles 3 and 4 with dorsomedial margins bearing brushes of sensory fine setae; article 4, facial spine formula: 1-3-5-5, dorsal margin with two short spines inserted in weak notch proximally, ventral margin with many plumose setules proximally, long to medium setae distributed on distal half, one ventrodistal thick medium spine placed subfacially; article 5, facial spine formula: 4, with four dorsal sets of male setae (calceolus not observed), ventral margin with two long setae and three plumose setules, three distal spines: two medium length, one shorter and thicker, this latter set subfacially; flagellum extending to about one-third of total body length, bearing 23 articles (calceoli not observed) (figure 6b).

Mandibles, left lacinia mobilis with five teeth (figure 6c); palp, article 2 with one outer facial seta subdistally, article 3 with oblique apex bearing nine spines/setae, basofacial formula: 1-3. Maxilliped, inner plate with three medial plumose setae; outer plate with six masticatory medial spines; palp, article 2 with four lateral setae, article 3 with three lateral setae.

Coxae 1–4, main ventral setae: 19-13-10-3 (and posterior setae: 1-1-3-12). Peraeopods 3 and 4, facial setal formula on article 4: 5 and 7, on article 5: 5 and 5; article 6, spine formula: 4 + 4 and 5 + 5 plus mid-distal spine; dactyla with more remarkable acclivity than in female. Coxae 5–7, posteroventral setule/seta formula: 11-22-15. Peraeopods 5 and 6, dactyla with inner acclivity and long emergent setule immersed. Peraeopod 7, article 2 extending to middle of article 5; article 5, pair of copulating spines straight, weakly pectinate, as long as article 6; article 6, apex with four digital processes.

Epimeron 1, posterior margin strongly convex proximally and straight below (figure 6d). Epimeron 2, posterior margin somewhat undulate, bearing four setae, anteroventral corner rounded-quadrate, anterior face with two submarginal plumose setae, ventral margin bearing 10 long plumose setae (figure 6e). Epimeron 3, anterior face with eight medium plumose setae, ventral face bearing oblique row of eight spines (figure 7a).

Uropod 1, peduncle with 14 dorsolateral spines; outer ramus with 10 dorsal spines (figure 7b). Uropod 2, outer ramus bearing seven dorsal spines (figure 7c). Uropod 3, peduncle with two setules instead of three as in female; inner ramus exceeding article 1 of outer ramus, medial and lateral margins plumose setose, apex with two plumose setae; article 2 of outer ramus short, 0.26, bearing two medium setae, medial margin of article 1 plumose setose (figure 7d). Telson, each apex with shallow acclivity, bearing two short lateral spines, instead of one as in female (figure 7e).

Etymology The specific name refers to the upward tooth of urosomite 3.