Oradarea surera, Alonso, 2012

Alonso, G. M., 2012, Amphipod crustaceans (Corophiidea and Gammaridea) associated with holdfasts of Macrocystis pyrifera from the Beagle Channel (Argentina) and additional records from the Southwestern Atlantic, Journal of Natural History 46 (29 - 30), pp. 1799-1894 : 1829-1837

Oradarea surera sp. nov.

( Figures 12–16 )

Type material

Argentina; Beagle Channel, northern Isla Despard , 54 ◦ 52 ′ S, 68 ◦ 10 ′ W, 8–12 m depth, colls. D. Aureliano and A. Ferlito, don. G. Lovrich: HOLOTYPE, ovig. ♀ 8 mm, 29 May 2000, MACN-In 38534a. PARATYPES, 1 ♀ 7.1 mm, 19 March 1999, MACN- In 38535; 1 ♀ 5.8 mm, 24 May 1999, MACN-In 38536. Same location, same colls., 27 May 1999: 6 ovig. ♀♀ 7.8–8.5 mm, 1 ♂ 5.7 mm, MACN-In 38537a; 1 ovig. ♀ 8.9 mm, 1 ♀ 7.5 mm, MACN-In 38537b; 1 ♀ 5 mm, 1 sex indet. 3.5 mm, MACN-In 38537c. Same location, same colls., 5 August 1999: 2 ♂♂ 5 and 5.95 mm, MACN-In 38538a; 1 ♀ 7 mm, MACN-In 38538b. Same location, same colls., 11 August 1999: 8 ovig. ♀♀ 5.8–9 mm, 4 ♀♀ 6–7.25 mm, 1 sex indet. 6 mm, 1 ♂ 6.05 mm, MACN-In 38539a; 1 ovig. ♀ 8 mm, MACN-In 38539b; 1 ovig. ♀ 9 mm, MACN-In 38539c; 3 ovig. ♀♀ 8–9 mm, 2 ♀♀ 6 and 7 mm, MACN-In 38539d, Same location, same colls., 1 November 1999: 1 ovig. ♀ 8.05 mm, MACN-In 38540a; 1 ovig. ♀ 8 mm, 1 ♀ 6.25 mm, MACN-In 38540b; 1 ovig. ♀ 7 mm, 1 ♀ 4.9 mm, 1 sex indet. 6.25 mm (damaged), MACN-In 38540c. Same location, same colls., 10 November 1999: 1 ♀ 5.95 mm, MACN-In 38541a; 5 ovig. ♀♀ 7–10.2 mm, 5 ♀♀ 5.3–8 mm, 1 sex indet. 6 mm, 5 ♂♂ 4.5–6 mm, MACN-In 38541b. Same location, same colls., 10 February 2000: 2 ♀♀ 4.9 and 5.15 mm, 1 ♂ 4 mm, MACN-In 38542a; 1 ♀ 4.8 mm, MACN-In 38542b; 1 ovig. ♀ 7.5 mm, MACN-In 38542c; 1 ♀ 6.3 mm, 1 sex indet. 4.8 mm, MACN-In 38542d; 1 ovig. ♀ 7.5 mm, 1 sex indet. 5.15 mm, 2 May 2000, MACN-In 38543. Same location, same colls., 29 May 2000: 3 ♀♀ 5.7–6 mm, 1 ♂ 6 mm, MACN-In 38544a; 2 ovig. ♀♀ 7.8 and 8 mm, 1 ♀ 6.3 mm, 1 ♂ 5.6 mm, MACN-In 38544b; 1 ovig. ♀ 7 mm, MACN-In 38544c .

Material examined

See Type material specified above.

Diagnosis

Head, lateral cephalic lobes rounded, prominent; anteroventral margin acutely produced. Eyes large, subrounded, major diameter 0.48 times height of head. A1 and A2: slender, very long. Gn2: propodus appreciably longer than carpus, slightly expanded distally; palm excavate, palmar angle well defined. P3–P7: rather slender, elongate, P7 longer than P6. Ep3: ventral and posterior margins convex, posteroventral corner with acute tooth, immediately above it margin concave. Peraeonite 7: dorsal edge free from pleonite 1, convex, with one small obtuse tooth. Pleonites 1 and 2: each produced dorsally into one sharp tooth. Integument with long scales on pleosome. T: longer than broad, lateral margins somewhat concave, apex rounded, distinctly crenellate. Specimens medium-sized, up to 10.2 mm.

Description

Holotype ovigerous female: body length 8 mm. Head somewhat shorter than peraeonites 1 and 2 combined, dorsal margin distally convex, rostrum short, slightly downturned; lateral cephalic lobe prominent, rounded; anteroventral margin acutely produced. Eyes large, subrounded, dark red in alcohol, major diameter almost half length of head height.

A1 and A2 slender, elongate.

A1: Peduncle article 1 broad, 1.6 times as long as wide, with few setae distally, anteroventral margin convex; article 2 narrow, slightly shorter than 1; article 3 short, about half length of 2; primary flagellum broken at article 56; article 1 about half length of peduncle article 3; accessory flagellum uni-articulate, about as long as flagellum article 1.

A2: Peduncle article 3 short; article 4 long, with anterior and posterior angles produced; article 5 slender, subequal in length to article 4, both articles bearing simple setae; flagellum broken at article 80.

UL: Entire, with fine setae apically; epistome triangular.

Md: Incisors with six or seven teeth; right lacinia mobilis narrow, four dentate, left wider, six dentate; accessory setal row with eight cuspidate robust setae, numerous fine setae among them; molar stout, columnar, triturating, with strong denticles, bearing one long pappose seta; palp, article 1 short, article 2 elongate, with four subapical setae on posterior margin, article 3 shorter, 0.9 times as long as article 2, bearing nine pappose setae on posterior margin, two strong and two long, slender, robust setae on apex.

LL: Without inner lobes; outer lobes large, apically setose; mandibular processes subrectangular.

Mx1: Inner plate bearing 12 medial plumose setae, apicalmost seta larger; outer plate with 11 cuspidate robust setae, very fine setae among them; palp biarticulate, robust; article 2 with eight apical robust setae.

Mx2: Inner plate with facial row of 13 setae and some medial setae, apex setose; outer plate apically setose and laterally with two setae.

Mxp: Inner plate rectangular, elongate, with three stout terminal robust setae, fine distal simple setae and oblique row of seven plumose setae; outer plate shorter than inner, bearing four apical long setae and eight short, stout, robust setae on medial margin; palp four-articulate; article 2 elongate, with posterior margin setose, anterior margin with one subapical seta and two distal setae; article 3 somewhat shorter than article 2, posterior margin setose distally, anterior margin bearing two medial setae and some distal setae, face with few setae on distal half; dactylus short, subapical surface setose, bearing unguis.

Gn1: Subchelate; coxa subrectangular, slightly expanded anteriorly; basis, posterior margin with few long setae, anterior margin with very short setae; merus with posterior margin setose; carpus shorter than propodus, posterior margin setose, anterior with few long setae; propodus subrectangular, 1.4 times as long as carpus, 2.5 times as long as wide, anterior margin with few setae, posterior margin and face setose, palm somewhat excavated, with three stout robust setae on rounded corner; dactylus as long as palm, posterior margin crenellate, with small setae.

Gn2: Much longer than Gn1, subchelate, rectilinear; coxa narrower, subrectangular, ventral margin with weak notches bearing minute setae; basis, posterior margin with one long and many short setae, anterior margin with setae distally; ischium and merus subequal in length, bearing few posterior setae, especially merus; carpus slender, much longer than on Gn1, with groups of marginal and submarginal setae posteriorly; propodus as thin as and 1.4 times as long as carpus, slightly expanded distally, bearing groups of setae along posterior margin and on surface, palm somewhat excavated, corner rounded, defined by three stout robust setae; dactylus as in Gn1, but shorter.

P3: Coxa subrectangular, larger than coxae 1 and 2, ventral margin with notches; basis, posterior margin with short setae, anterior with long setae; merus with anterodistal corner produced, both margins with few setae; carpus subrectangular, subequal in length to merus, scarcely setose; propodus rectangular, 1.4 times as long as carpus, with few setae on anterior margin and short robust setae along posterior margin; dactylus elongate, bearing two small setae distally.

P4: Coxa larger than coxa 3, with ventral margin convex, bearing notches with small setae, posterior margin excavated; remaining articles as in P3, but basis and propodus shorter and merus longer.

P5: Somewhat longer than P4; coxa bilobate, posterior lobe larger than anterior; basis oval, both margins with small setae; remaining articles as in preceding pairs, but merus stouter and propodus longer.

P6: Longer than P5; coxa smaller, with anterior lobe small and posterior large; basis similar in shape to that of P5, but more elongate; remainder articles as in preceding pairs, but longer.

P7: Longer than P6; coxa small, suboval; remainder articles similar to those of preceding appendage, but basis stouter and longer.

Gills attached to coxae 2–7. Oostegites on coxa 2–5, oostegites 2–4 wide, 5 narrow.

Peraeonite 7: Dorsal edge free from pleonite 1, convex, with one small obtuse tooth. Pleonites 1 and 2: each produced dorsally into one acute tooth.

Pleon: Integument with elongate scales. Pl1–Pl3: subequal in length; peduncle stout, with pair of locking spines. Pl3: outer ramus slightly shorter than inner, bearing 14 and 16 articles respectively. Ep1 and Ep2: posterior margin convex, posteroventral corner acutely produced. Ep3: ventral margin convex; posteroventral corner produced into an acute tooth, immediately above it, posterior margin concave and then rounded.

U1: Peduncle slightly shorter than inner ramus, bearing six medial, one apicomedial, four lateral and one apicolateral robust seta; outer ramus shorter than inner, with three dorsolateral robust setae, apex bearing four robust setae (longest broken); inner ramus 1.6 times as long as outer, bearing three dorsolateral and four dorsomedial robust setae, apex with four short and one long robust seta.

U2: Peduncle 1.3 times as long as outer ramus, with three dorsomedial and one apicolateral robust seta; outer ramus (broken at apex) shorter than inner, with two dorsolateral robust setae, apex, robust setae missing; inner ramus 2.1 times as long as outer, bearing four dorsolateral and five dorsomedial robust setae, one subdistal, and two short and one long apical robust seta.

U3: Peduncle short, broad, produced at insertion of inner ramus, with one small lateral seta; outer ramus shorter than inner, bearing three dorsolateral and three dorsomedial robust setae, apex acute; inner ramus 1.5 times as long as outer, with five dorsolateral and five dorsomedial robust setae, apex bearing broad spiniform structure with hook.

T: Longer than wide, lateral margins slightly concave, apex rounded, noticeably crenellate, most proximal notch bearing one small seta on each side, dorsal surface with two pairs of penicillate setae medially and two pairs of minute setae distributed on distal half.

Additional observations

Paratype females with A1 and A2 reaching end of pleon. Paratype males with A1 and A2 overreaching end of pleon.

Etymology

The specific name, derived from the Spanish word “sur”, is used in Argentina to refer to southern inhabitants.

Remarks

Oradarea Walker, 1903 comprises 15 known species, 13 of which are found in the Antarctic and sub-Antarctic islands, and in the tropical Indo-West Pacific. Oradarea surera sp. nov. is the first species described from the Magellanic area.

Oradarea surera can be primarily separated from all the known species by combination of differences in the lateral cephalic lobes, head anteroventral margin, second gnathopod propodus, dorsal margin of the seventh peraeonite and first and second pleonites, third epimeron and telson.

The new species resembles Oradarea ocellata Thurston, 1974a from Antarctica and Oradarea novaezealandiae (Thomson, 1879) from New Zealand and sub-Antarctic islands, in the presence of an obtuse tooth on the dorsal margin of the seventh peraeonite and first and second pleonites, which are produced dorsally into an acute tooth. It is similar to O. ocellata in possessing a rounded lateral cephalic lobe, a third epimeron with convex ventral margin and sinuous posterior margin, and a telson with convex and crenellate apex. However, the two taxa are distinguished because the new species has larger eyes, more prolonged anteroventral margin of head, second gnathopod propodus with less concave palm, larger pleon teeth, posteroventral corner of third epimeron bearing larger tooth, and more elongate telson. It can be distinguished from O. novaezealandiae because the latter has a more prominent lateral cephalic lobe and head with straight anteroventral margin instead of apically produced. Although in both species the apex of the telson is convex and crenellate, that of O. novaezealandiae has straight lateral sides and apex with apparently weak crenellations versus somewhat excavated sides with strong apical crenellations.

The other two southern species, Oradarea rossi Thurston, 1974a and Oradarea crenelata Alonso de Pina, 1995 from the Antarctic, also possess telson with rounded and crenellate apex, but they are basically distinguished by having body dorsal teeth.

This is the first record of the genus Oradarea using holdfasts of M. pyrifera as habitat.

Figures

Figure 12. Oradarea surera sp. nov. Holotype, ovigerous female: (A) lateral view; (B) head; (C, D) antennae 1, 2; (E) upper lip and epistome; (F, G) right and left mandibles; (H) left lacinia mobilis. Scale bars: a: (A) 3 mm; b: (B), c: (C, D) 0.2 mm; d: (E), e: (F, G) 0.1 mm; f: (H) 0.025 mm.

Figure 13. Oradarea surera sp. nov. Holotype, ovigerous female: (A) mandibular palp; (B) lower lip; (C, D) maxillae 1, 2; (E) maxilliped; (F) gnathopod 1; (G) gnathopod 1 palm. Scale bars: a: (A, C–E), b: (B), d: (G) 0.1 mm; c: (F) 0.2 mm.

Figure 14. Oradarea surera sp. nov. Holotype, ovigerous female: (A) gnathopod 2; (B) gnathopod 2 palm; (C–F) peraeopods 3–6. Scale bars: a: (A, C–F) 0.2 mm; b: (B) 0.1 mm.

Figure 15. Oradarea surera sp. nov. Holotype, ovigerous female: (A) peraeopod 7; (B) pleopod 3; (C) pleopod 3 locking spines; (D) peraeonite 7 and pleonites 1–3. Scale bars: a: (A), b: (B), d: (D) 0.2 mm; c: (C) 0.05 mm.

Figure 16. Oradarea surera sp. nov. Holotype, ovigerous female: (A–C) uropods 1–3; (D) telson. Scale bars: a: (A–C) 0.2 mm; b: (D) 0.1 mm.