Metharpinia iado, ALONSO DE PINA, 2003

ALONSO DE PINA, GLORIA M., 2003, A new species of Phoxocephalidae and some other records of sand-burrowing Amphipoda (Crustacea) from Argentina, Journal of Natural History 37 (9), pp. 1029-1057 : 1031-1045

Metharpinia iado n. sp.

( figures 1–9 )

Material examined The material examined is detailed in table 1.

Description

Allotype, ovigerous female. Body length ca 7 mm. Head about 16% of total body length, greatest width about 53% of length, rostrum constricted, narrow, spatulate, elongate, extending beyond middle of antenna 1 article 2. Eyes medium, rounded, light brown in alcohol ( figure 1a, b ). Antenna 1, peduncle article 1 about 1.3 times as long as wide, about 1.9 times as wide as article 2, ventral margin with eight plumose setules, unproduced dorsal apex with one setule and one long seta; article 2 about 0.7 times as long as article 1, bearing ventral crescent of eight setae widely spread proximally, one apicolateral plumose setule and two short and medium setae; primary flagellum with 10 articles, about 0.6 times as long as peduncle, bearing one short aesthetasc each on articles 5, 6, 8 and 9; accessory flagellum with nine articles ( figure 1c ). Antenna 2, peduncle article 1 without any special process; article 3 with two setae; article 4, dorsal margin without notch, bearing bundle of one spine and six long setae proximally, five apicolateral medium setae, ventral margin with about eight groups of three to four long to medium and short setae, one long ventrodistal spine; facial spine formula: 1-3-6-5; article 5 about 0.7 times as long as article 4, facial spine formula: 5, dorsal margin naked, bearing about four small setae medially, one apical setule and two medium apicolateral setae, ventral margin with seven sets of one to two long to medium and short setae, three ventrodistal long to medium spines placed subfacially; flagellum with 12 articles, about as long as articles 4 and 5 of peduncle combined ( figure 1d ).

Mandibles with weak palpar hump; right and left incisors with three teeth; right lacinia mobilis simple or apparently bifid, so deeply divided that distal longer member assumes appearance of raker spine, left lacinia mobilis with four strong teeth; right and left rakers 13, three of these proximal rakers smaller than rest; molars composed of bulbous plaques, without plume, bearing five primarily stout spines plus one thin spine strongly disjunct ( figure 1e, f ); palp, article 1 short, naked, article 2 with one short inner apical seta and six other short and long inner setae, and two outer setae, article 3 about 1.3 times as long as article 2, oblique apex with 12 spine-setae, basofacial formula: 0-2 ( figure 1g ). Lower lip, each outer lobe with cone ( figure 2a ). Maxilla 1, inner plate large, broad, bearing one medium apical plumose seta, one similar apicomedial plumose seta, two short apicolateral setae; outer plate with 11 spines, one spine especially thickened; palp biarticulate, article 2 with two apical spines, one thin, other larger and pectinate, two medial setae and three submarginal setae ( figure 2b ). Maxilla 2, plates extending almost subequally; outer plate broader than inner, with three short apicolateral setae; inner plate with three medial plumose setae ( figure 2c ). Maxilliped, inner plate with one large thick apical spine, four apicofacial plumose setae, four medial plumose setae; outer plate with six medial spines and three medial setae; palp, article 1 with two apicolateral setae, article 2 with six lateral setae, medial margin moderately setose, article 3 with four lateral setae, group of apical setae, and many facial setae, article 4 thin, almost as long as article 3, with medium apical nail almost fully fused and partially immersed, bearing one accessory setule ( figure 2d ).

Coxae 1–3 moderately expanded apically, anterior margin almost straight, main ventral setae: 18-15-14. Coxa 4 large, subquadrate, anterior and posterior margins almost parallel, posterior margin almost straight, posterodorsal corner sharp-rounded, posterodorsal margin short, weakly concave, main ventral and posterior setae: 20; width/length ratio 100:123. Gnathopods 1 and 2 small, similar; gnathopod 2 slightly larger than 1; width ratios of articles 5 and 6 of gnathopods 1 and 2, 25:29 and 25:29; length ratios, 59:53 and 56:50. Gnathopod 1, article 5 elongate, ovate, posterior margin rounded-flat, long. Gnathopod 2, article 5 elongate, ovate, posterior margin rounded, shorter. Gnathopods 1 and 2, article 6 ovatorectangular, moderately setose anteriorly, palms oblique, palmar humps large, ornamented with setule ( figure 2e–h ).

Peraeopod 4 slightly stouter than peraeopod 3, especially on articles 4 and 5. Peraeopods 3 and 4, facial setal formula on article 4: 7 and 7, almost parallel to apex, on article 5: 7 and 6; main spine of article 5 extending along 78% and 75% of article 6; article 5 with one proximoposterior spine on each peraeopod, but proximal edge naked for long distance; spine formula of article 6: 7 + 12, plus long middistal spine, some spines especially long; acclivity on inner margin of dactyla sharp, produced as tooth, midfacial plumose setule short ( figure 3a–e ). Coxae 5–7, posteroventral setule-seta formula: 6 (only these are seen, some other setae broken) -20-11. Peraeopods 5 ( figure 4a, b ) and 6 ( figure 4c ), articles 4 and 5 broad, facial spine rows dense; dactyla with inner acclivity produced as sharp tooth. Peraeopod 6, right dactylus short and broad ( figure 4d ), left dactylus ordinary, long and thin ( figure 4e ). Peraeopods 5–7, article 2 facial ridge formula: 0-1-1; width ratios of articles 2, 4, 5, 6 of peraeopod 5, 65:81:61:25; of peraeopod 6, 120:89:50:20; of peraeopod 7, 120:31:22:11; length ratios of peraeopod 5, 114:53:55:56; of peraeopod 6, 130:84:65:88; of peraeopod 7, 136:40:35:45. Peraeopod 7 ( figure 4f ), article 2 almost reaching apex of article 5, posterior margin with eight small serrations, medial apex of article 6 combed, bearing about five digital processes (comb and processes difficult to see, even with the greatest magnification) ( figure 4g ).

Fully developed oostegites elongate, slender, marginally setose, on coxae 2–5. Gills attached to coxae 2–7, those of coxae 6 and 7 very small.

Epimeron 1, posteroventral corner produced, rounded, posterior margin straight below, then convex, serrate, setose, with 14 setae and small setule proximally, anteroventral corner subquadrate, anterior face and margin with five long to medium plumose setae, posteroventral face with two long plumose setae set horizontally above margin ( figure 5a ). Epimeron 2, posteroventral corner rounded, posterior margin straight below, weakly convex above, serrate, setose, bearing 15 long to medium setae and small setule proximally, anteroventral corner quadrate, anterior face with three medium plumose setae, ventral face with nine long plumose setae ( figure 5b ). Epimeron 3, posteroventral corner rounded, posterior margin evenly convex, serrate, setose, with 17 long to medium setae and setule proximally, anteroventral corner rounded-quadrate, anterior face with three medium setae widely spread, ventral margin and face bearing 14 long to medium setae, placed on posterior half ( figure 5c ). Pleopods 1–3 slightly different in length ( figure 5d–f ); peduncle with two locking spines ( figure 5g ); pleopods 1 and 2, outer and inner rami with 19 and 13 articles; pleopod 3 outer ramus with 17 articles and inner ramus with 13.

Urosomite 1 with ventral brush of long setae, articulation line incomplete. Urosomite 3 not produced dorsally, scarcely protuberant. Uropod 1, peduncle without basofacial setae, medially with four marginal spines, distal-most enlarged, laterally with one apical spine as large as the latter; inner and outer rami with one and six dorsal spines, respectively ( figure 6a ). Uropod 2, peduncle with eight dorsal spines, distal-most thick and proximal-most thin, medially with two thin spines situated proximally; inner ramus without dorsal spines, outer with six ( figure 6b ). Uropods 1 and 2, peduncular apical corners apparently without comb; outer rami bearing two subapical nails and inner rami one, both rami without apical nails. Uropod 3, peduncle bearing seven ventral spines, dorsally with two lateral spines, one medial spine, one setule and one seta; rami unequal in length, inner ramus as long as article 1 of outer ramus, apex with two setae, medial and lateral margins setose, all setae plumose; article 2 of outer ramus elongate, 0.41, bearing two medium setae, medial margin of article 1 with many plumose setae, lateral margin with three acclivities, spine formula: 4-3-4-3, setal formula: 0 ( figure 6c ). Telson long, exceeding peduncle of uropod 3, length/width ratio 102:58, three-quarters cleft, each apex of medium width, subtruncate, medial apex produced, acclivity weak, bearing one long medial spine, short plumose setule, and three shorter lateral spines, each side with brush of four long setae and mid-lateral pair of plumose setules of different length, longer setule about twice as long as other setule ( figure 6d ).

Holotype, male. Body length ca 8 mm ( figure 6e ). Rostrum narrower than in female. Pigmented eyes larger. Antenna 1, peduncle article 1 with one setule; article 2 with nine ventral setae proximally; primary flagellum with 11 articles, bearing one calceolus each on articles 1–4, short aesthetascs present on articles 4–7, 9, 10; accessory flagellum with 10 articles ( figure 7a ). Antenna 2, peduncle articles 3 and 4 dorsomedially with sensory brushes of setae; article 4, facial spine formula: 3-6-6, dorsal margin with one spine and four setae, ventral margin with several setae less crowded than in female; article 5, dorsal margin with three sets of male setae and one calceolus distally, ventrodistal apex with two thin spines and one setule, ventral margin scarcely setose; flagellum elongate, with 37 articles, formula of calceoli: 2, 4, 6..., 24, 28 ( figure 7b, c ).

Mandibles, right lacinia mobilis bifid, left with five teeth; right and left molars bearing six spines ( figure 6f–i ); palp article 3, basofacial formula: 0-3.

Coxae 1 and 2 with greater number of ventral setae than in allotype. Coxae 4 smaller in relation to coxa 4 of female, anterior and posterior margins somewhat divergent ( figure 7d ). Coxae 5–7, posteroventral setule-seta formula: 13-15-15.

Peraeopods 3 and 4, facial setal formula on article 4: 6 and 6, on article 5: 10 and 8. Peraeopod 6, right and left dactyla ordinary. Peraeopod 7, article 2 narrower than in female.

Epimera 1–3 broadened. Epimeron 1, posterior margin with 12 shorter setae, anterior face bearing seven long plumose setae, posteroventrally with four plumose setae ( figure 8a ). Epimeron 2, posterior margin bearing 14 shorter setae, anterior face and margin with six setae, face with 12 long plumose setae ( figure 8b ). Epimeron 3, posterior margin with 10 setae, anterior face and margin bearing seven setae, ventral face with 10 setae situated towards posterior margin ( figure 8c ).

Urosomite 1 with lateral short setae near base of segment and ventral long setae. Uropod 1, inner ramus with three dorsal spines, outer bearing seven ( figure 8d ). Uropod 2, peduncle with one large apical spine medially; inner ramus bearing two dorsal spines, outer with seven shorter spines ( figure 8e ). Uropod 3, peduncle with six ventral spines; inner ramus elongate, reaching half length on article 2 of outer ramus, medial and lateral margins more setose than in female; outer ramus article 1, lateral margin with two acclivities, spine formula: 3-3-2 ( figure 9a ). Telson elongate, apical spines longer, one lobe with five spines (the other with four as in female), each side bearing bundle of six long setae ( figure 9b ).

Etymology

The specific epithet iado , a noun in apposition, refers to the abbreviations of IADO, which stand for Instituto Argentino de Oceanografía of Bahía Blanca (Buenos Aires province).

Relationships

The new species, Metharpinia iado , is closely related to M. longirostris Schellenberg, 1931 in the general aspect of the body, rostrum, antennae, gnathopods and peraeopods. The description by Schellenberg (1931) of M. longirostris , the unique species of Metharpinia recorded in South America, Valparaíso to Río de La Plata, and the more recent description of the same species by Barnard (1980), based on a female from Schellenberg’s collection in the Swedish Museum, demonstrate that the new species can be separated from it in many character states. Comparisons between the two species are based on Barnard’s description and illustrations (1980), which are detailed and complete, while Schellenberg’s description is vague and his figures lack subtle details useful for species identification. The main morphological attributes that separate the two species are as seen in table 2.

Metharpinia iado shares many characters with the known species of Metharpinia . Its maxillipedal inner plate has one thick apical spine as in M. longirostris and M. floridana ( Shoemaker, 1933) ; epimeron 3 posteroventral corner is rounded, without any projection, as in M. longirostris , M. floridana , M. oripacifica Barnard, 1980 and M. coronadoi Barnard, 1980 ; uropods 1 and 2 outer and inner rami bear two and one subapical nails, respectively, as in M. jonesi (Barnard, 1963) , M. floridana , M. oripacifica , M. coronadoi and M. protuberantis Alonso de Pina, 2001 . Metharpinia jonesi , M. oripacifica , M. coronadoi and M. protuberantis all differ from the new species in having two thick apical teeth on the maxillipedal inner plate; also epimeron 3 posteroventral corner is produced as a tooth in M. jonesi and M. protuberantis . The number of spines and setae on the appendages and telson are variable in all the known species of Metharpinia , this being another attribute which, in combination with other character states, separates the new species from other known Metharpinia species. The spine formula of article 6 on peraeopods 3 and 4 in the new species is a character state not obseved in other known species of the genus.

Metharpinia iado was common in the El Rincón area (Buenos Aires) and in Golfo San José , dwelling in fine sand and with a depth distribution fluctuating between 9 and 22 m.

Figures

FIG. 1. Metharpinia iado n. sp. Allotype, ovig. female: (a) head, lateral view; (b) head, dorsal view; (c, d) antennae 1, 2; (e, f) right and left mandibles; (g) mandibular palp. Scales (µm): A: (a, b); B: (c, d); C: (e, f); D: (g).

FIG. 2. Metharpinia iado n. sp. Allotype, ovig. female: (a) lower lip; (b, c) maxillae 1, 2; (d) maxilliped; (e) gnathopod 1; (f) propodus and dactylus of gnathopod 1; (g) gnathopod 2; (h) propodus and dactylus of gnathopod 2. Scales (µm): A: (a–d); B: (e, g); C: (f, h).

FIG. 3. Metharpinia iado n. sp. Allotype, ovig. female: (a) peraeopod 3; (b) propodus and dactylus of peraeopod 3; (c) coxa 4; (d) peraeopod 4; (e) propodus and dactylus of peraeopod 4. Scales (µm): A: (a, c, d); B: (b, e).

FIG. 4. Metharpinia iado n. sp. Allotype, ovig. female: (a) peraeopod 5; (b) dactylus of peraeopod 5; (c) peraeopod 6; (d, e) right and left dactyla of peraeopod 6; (f) peraeopod 7; (g) dactylus of peraeopod 7. Scales (µm): A: (a, c); B: (b, d, e, g); C: (f).

FIG. 5. Metharpinia iado n. sp. Allotype, ovig. female: (a–c) epimera 1–3; (d–f) pleopods 1–3; (g) locking spines of pleopod 3. Scales (µm): A: (a–c); B: (d–f); C: (g).

FIG. 6. Metharpinia iado n. sp. Allotype, ovig. female: (a–c) uropods 1–3; (d) telson. Holotype, male: (e) lateral view; (f) right mandible; (g) right molar; (h) left mandible; (i) left molar. Scales (µm): A: (a–d); B: (e); C: (f, h); D: (g, i).

FIG. 7. Metharpinia iado n. sp. Holotype, male: (a, b) antennae 1, 2; (c) last two articles of antenna 2; (d) coxa 4. Scales (µm): A: (a–c); B: (d).

FIG. 8. Metharpinia iado n. sp. Holotype, male: (a–c) epimera 1–3; (d, e) uropods 1, 2.

FIG. 9. Metharpinia iado n. sp. Holotype, male: (a) uropod 3; (b) telson.