Metharpinia grandirama, 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 : 2533-2545

Metharpinia grandirama n. sp.

(figures 8–15)

Material examined

H  : W, 6.2 mm, MACN No. 34793, Buenos Aires: El Rincón, 39 ° 05 ∞ 36 ◊ S, 61 ° 20 ∞ 11 ◊ W (Sta. 3), 9.5 m depth, 78% medium sand, 3 November 1993. P    : Buenos Aires: El Rincón, same data, one mature W partially dissected, 5.2 mm , MACN No. 34794. 39 ° 49 ∞ 58 ◊ S, 61 ° 35 ∞ 02 ◊ W (Sta. 28), 21 m depth, 55% fine sand, 2 November 1993, one X (with oostegites) dissected, 8 mm , MACN No. 34795. 39 ° 40 ∞ 07 ◊ S, 61 ° 35 ∞ 05 ◊ W (Sta. 25), 19 m depth, 67% fine sand, 2 November 1993, one X (with oostegites), 5.4 mm , MACN No. 34796. 39 ° 59 ∞ 53 ◊ S, 61 ° 40 ∞ 09 ◊ W (Sta. 31), 20 m depth, 67% fine sand, 2 November 1993, one immature W, 5.9 mm , MACN No. 34797. 40 ° 09 ∞ 56 ◊ S, 61 ° 40 ∞ 01 ◊ W (Sta. 33), 23 m depth, 63% medium sand, 2 November 1993, one X (with oostegites), 6.5 mm , MACN No. 34798. Collectors and donors: D. Roccatagliata and M. Torres Jordá .

Description

Holotype, mature male (body length 6.2 mm) (figure 8a). Head about 16% of total body length, greatest width about 57% of length, rostrum constricted, narrow, elongate, reaching almost middle of article 2 on antenna 1 (figure 8b). Eyes large, suboval, with light orange pigment in alcohol, sexually dimorphic. Antennae 1 and 2 sexually dimorphic. Antenna 1, peduncle article 1 about 1.1 times as long as wide, about twice as wide as article 2, ventral margin lined with many plumose setules, produced dorsal apex with one long seta; article 2 slightly longer than article 1, with ventral crescent of about seven setae placed proximally; primary flagellum with 11 articles, about 0.9 times as long as peduncle, bearing one calceolus each on articles 1–4 and one aesthetasc each on articles 5–11; accessory flagellum with nine articles, last article shorter, bearing one aesthetasc (figure 8c). Antenna 2, peduncle article 1 without any especial process; article 3 with one setule; articles 3 and 4 with dorsal margins bearing brushes of sensory fine setae; article 4, facial spine formula: 1-2-6-6, ventral margin ornamented with about four plumose setules proximally and with medium to long setae situated along margin, one ventrodistal medium spine; article 5 about 0.9 times as long as article 4, facial spine formula: 3, dorsal margin bearing four to five groups of male setae and one calceolus distally, ventral margin with three long setae and three plumose setules, two ventrodistal medium spines set subfacially; flagellum elongate, longer than total body length, with 30 articles, flagellar formula of calceoli: 2, 3, 4, 6 ...16, 19, 20, 28 (figure 8d).

Upper lip, epistome rounded (figure 8e). Mandibles with weak palpar hump; right incisor with three teeth poorly developed, left incisor with two weak teeth and hump; right lacinia mobilis bifid, distal branch shorter than proximal, left lacinia mobilis with three teeth, middle tooth shorter, rounded tooth minutely denticulate; right rakers 12, left rakers 14 plus one small spine placed between left lacinia mobilis and spine row, proximal four to five raker spines of both sides smaller; molars composed of bulbous plaques, with six primary spines plus one disjunct spine (figure 8f, g); palp, article 1 short, article 2 with one short inner apical seta and three other short and long inner setae, article 3 about 1.1 times as long as article 2, oblique apex with about nine spines, basofacial formula: 0-3 (figure 9a). Lower lip, each outer lobe with one cone (figure 9b). Maxilla 1, inner plate large, pyriform, bearing one long apical seta, one shorter apicomedial seta, two apicolateral similar setae, all setae plumose; outer plate with 11 apical spines, outer spine enlarged; palp, article 2 marginally bearing two apicomedial pectinate spines, two apicomedial setae, and three submarginal setae (figure 9c). Maxilla 2, inner plate shorter than outer, with three medial setae; outer plate broader than inner, bearing three apicolateral setae (figure 9d). Maxilliped, inner plate with two thick apical spines, two apicofacial setae, four medial setae, all setae plumose (figure 9e); outer plate with five masticatory medial spines, one apicolateral seta, three medial setae (figure 9f); palp, articles 1 and 2 with one lateral seta each, medial margin of article 2 moderately setose, article 3 with one lateral seta, a few facial and marginal setae, article 4 slender, elongate, bearing apical short nail, about 15% of article 4 length, almost fully fused and partially immersed, with one setule.

Coxa 1 scarcely expanded apically, anterior margin convex, posterior somewhat concave. Coxa 4, anterior and posterior margins divergent, posterior margin oblique, almost straight, posterodorsal corner rounded, posterodorsal margin short, width/ length ratio: 69:70. Coxae 1–4, main ventral setae: 12-17-13-0, posterior setae of coxa 4: 21. Coxae 1–3, marginal setae confined to posteroventral half, posteriormost seta shorter. Gnathopods similar, subequal in length; width ratios of articles 5 and 6 of both pairs of gnathopods: 21:21 and 27:28, length ratios: 55:49 and 45:44. Gnathopod 1, article 5 elongate, ovate, posterior margin rounded-flat, long (figure 9g). Gnathopod 2, article 5 elongate but shorter than in first pair, ovate, posterior margin rounded, shorter than in gnathopod 1 (figure 9i). Gnathopods 1 and 2, anterior margin of article 6 weakly setose, palms oblique, palmar humps large, ornamented with small setule (figure 9g –j).

Peraeopods 3 (figure 10a, b) and 4 (figure 10c–e) similar (except in coxae), the latter appendage longer, especially article 5, article 4 of peraeopod 3 broader. Peraeopods 3 and 4, facial setal formula on article 4: 6 and 6, on article 5: 6 and 6; main spine on article 5 extending 72% and 80% of article 6; article 5 with one proximoposterior spine, but proximal edge naked for long distance; spine formula of article 6: 4 + 6 plus large mid-distal spine, some spines long, somewhat thick; dactyla with inner acclivity sharp, produced as tooth, emergent setule short, midfacial plumose setule present. Coxae 5–7, posteroventral setal formula: 9-12-10, mostly short, especially those of coxa 7. Peraeopod 5 (figure 11a, b), articles 4 and 5 broad. Peraeopod 6 (figure 11c, d), article 4 broad and 5 of medium width. Peraeopods 5 and 6, facial spine rows dense to moderately developed; dactyla with small inner acclivity, mid-facial plumose setule placed proximad. Peraeopods 5–7, facial ridge formula of article 2: 0-1-1; width ratios of articles 2, 4, 5, 6 of peraeopod 5: 59:63:53:26, of peraeopod 6: 95:74:46:16, of peraeopod 7: 83:22:16:9; length ratios of peraeopod 5: 99:56:50:40, of peraeopod 6: 118:76:65:81, of peraeopod 7: 106:30:22:34. Peraeopod 7 (figure 12a), article 2 extending to apex of article 4, posterior margin with about eight small serrations; article 5, pair of copulating spines straight, elongate, weakly pectinate, exceeding apex of article 6; medial apex of article 6 finely combed, bearing about three digital processes (difficult to distinguish individually, even with great magnification); dactylus without inner acclivity, with mid-facial plumose setule set proximally (figure 12b).

Gills on coxae 2–7, that of coxa 7 smaller. Pleopods ordinary, peduncles powerful, that of pleopod 3 remarkable shorter (figure 12c), each bearing a pair of locking spines (figure 12d).

Epimera 1 and 2 somewhat damaged. Epimeron 3 broadened, posteroventral corner rounded, posterior margin convex, serrate, setose, bearing five setae and one proximal setule, anteroventral corner rounded-quadrate, anterior face with four submarginal plumose setae, ventral margin naked, ventral face with two spines situated vertically on posterior part (figure 12e).

Urosomite 1 with ventral brush of setae and lateral setule at base of uropod 1, articulation line incomplete but long. Urosomite 3 produced upwards into a dorsal pointed process, hook-like, on each side. Uropod 1 (figure 12f), peduncle without basofacial setae, medially with four spines: two proximal long and slender, third subapical short, fourth apical-most long and thick, laterally bearing three short marginal spines, similar in size; inner and outer rami with one and three dorsal spines, respectively. Uropod 2 (figure 12g), peduncle with five dorsal spines: proximal-most small, next three spines much longer, apical spine huge; inner ramus naked, outer ramus with three dorsal spines. Uropods 1 and 2, peduncle apical corners with weak comb; outer rami bearing two subapical nails and inner rami one, both rami without apical nails. Uropod 3 sexually dimorphic (figure 13a), peduncle with four ventrolateral spines, dorsally bearing one lateral spine, medially with one small spine and setule; rami subequal in length; outer ramus, medial margin of article 1 profusely plumose setose, lateral margin with two acclivities, spine formula: 2-2-2, setal formula: 0-0-1; article 2 short, 0.14, apex bearing two long plumose setae; inner ramus, medial and lateral margins plumose setose, apex with two long plumose setae. Telson somewhat elongate and thick, length/width ratio: 106:82, almost fully cleft, each apex wide, rounded, lateral acclivity shallow, bearing lateral plumose setule, spine next medial shorter than setule, each lobe with dorsolateral cluster of five long setae placed subapically and two mid-lateral plumose setules of different length, larger member long (figure 13b).

Additional observations

Paratype, mature male (body length 5.2 mm). Epimeron 1, posteroventral corner rounded, posterior margin convex, serrate, with five setae of medium length and one proximal setule, ventral margin bearing 10 long plumose setae decreasing in length towards anterior margin (figure 13c). Epimeron 2, posteroventral corner rounded, posterior margin convex, serrate, setose, with about six medium setae (some broken) and proximal setule, anteroventral corner quadrate, anterior face bearing four submarginal setae, ventral face with six long plumose setae (figure 13d).

Paratype, female with oostegites (body length 8 mm). Eyes small, rounded, light orange in alcohol (figure 13e). Antenna 1, peduncle article 1 about 1.4 times as long as wide, about 1.8 times as wide as article 2, ventral margin with fewer plumose setules than in male, unproduced dorsal apex with one long seta; article 2 longer than article 1, with ventral crescent of five setae placed proximally, two subapical plumose setules and two medium setae; primary flagellum with 12 articles, about 0.7 times as long as peduncle, bearing one aesthetasc each on articles 6–11; accessory flagellum bearing 11 articles (figure 13f). Antenna 2, article 4 facial spine formula: 1-3-6-6, dorsal margin with weak notch bearing two short spines and one long seta, ventral margin ornamented with several plumose setules and long setae; article 5 about 0.8 times as long as article 4, facial spine formula: 4, dorsal margin naked, apically with three small setules, ventral margin with about three plumose setules and three long setae, three ventrodistal medium to short spines set subfacially; flagellum with 14 articles, about 1.15 times as long as articles 4 and 5 of peduncle combined (figure 13g).

Mandibles, left lacinia mobilis with four defined teeth; right rakers 13, left rakers 15 (figure 14a, b). Maxilla 2, outer plate with two apicolateral setae. Maxilliped, inner plate bearing two apicofacial setae and two apicomedial setae, all setae plumose; outer plate with six medial spines; palp, article 2 with four lateral setae, article 3 with two lateral setae (figure 14c).

Coxa 1, expanded apically, anterior margin almost straight. Coxae 1–4, main ventral setae: 18-17-15-0, posterior setae of coxa 4: 17 (figure 14d–g).

Peraeopods 3 and 4 subequal; facial setal formula on article 4: 5 and 5, on article 5: 5 and 5; spine formula of article 6: 5 + 6 and 5 + 7 (or 6 + 6) plus mid-distal spine (figure 15a). Peraeopod 6, dactylus without inner acclivity.

Oostegites long (incompletely developed), slender, smooth, attached to coxae 2–5.

Epimeron 1, posteroventral corner rounded, posterior margin convex, serrate, setose, with seven long setae (some broken) and one proximal setule, anterior face bearing six medium setae, ventral margin with six plumose setae increasing in length posteriorly (figure 15b). Epimeron 2, posteroventral corner rounded, posterior margin convex, serrate, setose, bearing about seven long setae (some broken), anterior angle subquadrate, ventral margin with seven plumose setae longer posteriorly (figure 15c). Epimeron 3, posteroventral corner rounded, somewhat protuberant, posterior margin straight, serrate, setose, with five long setae and one proximal setule, anteroventral corner rounded-quadrate, anterior face with two short setae, ventral margin naked, ventral face bearing three spines set in an oblique line on posterior half (figure 15d).

Uropod 1, peduncle with five lateral spines, proximal-most smaller, apical-most longer; inner and outer rami with two and four dorsal spines, respectively (figure 15e). Uropod 2, peduncle with seven dorsal spines, distal-most huge (figure 15f). Uropods 1 and 2, peduncle apical corners apparently without comb. Uropod 3, peduncle bearing four ventral spines, dorsally with one lateral spine, one medial spine and setule; rami unequal in length, inner extending 94% on article 1 of outer ramus, apex carrying two setae, medial and lateral margins naked; article 2 of outer ramus 0.34, bearing two long apical setae (broken), medial margin of article 1 naked, lateral margin with two acclivities, spine formula: 2-2-2, no setae present (figure 15g).

Etymology The specific name refers to the great size of the inner ramus of uropod 2.

Relationships

Although Metharpinia and Microphoxus seem to have features without strong morphological discontinuity, both genera are kept until phylogenetic analysis can solve the systematic position of these taxa.

Metharpinia dentiurosoma n. sp. and Metharpinia grandirama n. sp. share the dorsal hook on urosomite 3 with both species of Microphoxus . The new taxa are described as species of Metharpinia in spite of the dorsal hook mentioned above, because they share many other morphological characters that fit them better in this taxon than in Microphoxus . Primarily, these characters are as follows: antenna 1, article 2 with ventral setae placed proximally (widely spread and more distally in Microphoxus ); maxilliped with dactylar nail partially fused and immersed (articulate in Microphoxus species examined); gnathopods 1 and 2, palms oblique and article 6 or propodus poorly setose anteriorly (palms transverse and propodus heavily setose anteriorly in Microphoxus ); peraeopods 3 and 4, article 6 with facial spine formulae composed of thick spines and dactyla with inner acclivity sharp, produced as tooth (spines thin and dactylar acclivity not seen in any member of Microphoxus ).

Metharpinia dentiurosoma can be separated from Metharpinia grandirama by the facial spine formula on article 4 of antenna 2; the posteroventral corner of epimeron 3 strongly produced as a tooth; the uropods 1 and 2 with numerous spines on peduncles and outer rami, and the apical and dorsolateral armaments of telson. Metharpinia grandirama is identified by the article 5 of peraeopods 3 and 4 with proximoposterior spine; coxa 4 with long posterior setae; posteroventral corner of epimeron 3 rounded; the uropods 1 and 2 distinct, shorter and larger, especially uropod 2, with their peduncles and outer rami much less spinose, a character that seems to fit better with Microphoxus species , and inner ramus of uropod 3 longer.

The new species described here are distinguished from all other species of Metharpinia by the huge dorsal hook on urosomite 3.

Ecological notes

Metharpinia dentiurosoma was found inhabiting gravel to fine sand with a depth distribution fluctuating between 14 and 21 m. Metharpinia grandirama was recorded in medium sand at a depth range of 9–23 m and in fine sand from 19 to 21 m.