Aora parda, 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 : 1803-1813

Aora parda sp. nov.

( Figures 1–5 )

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, mature ♂ 7 mm, 10 November 1999, MACN-In 38431a. PARATYPES, 1 mature ♂ 7 mm, 1 November 1999, MACN-In 38432a; 1 immature ♂ 5.85 mm, 10 November 1999; MACN-In 38431b; 1 ovig. ♀ 8 mm, 29 May 2000, MACN-In 38433a. Same location, same colls., 27 May 1999: 1 ♂ 7 mm, MACN-In 38434a; 1 ♂ 6 mm, MACN-In 38434b. Same location, same colls., 5 August 1999: 1 ovig. ♀ 7 mm, MACN-In 38435a; 1 ovig. ♀ 8.1 mm, MACN-In 38435b. Same location, same colls., 11 August 1999: 1 ovig. ♀ 8.3 mm, MACN-In 38436a; 4 ovig. ♀♀ 6.7–7 mm, MACN-In 38436b. Same location, same colls., 1 November 1999: 1 ovig. ♀ 8 mm, MACN-In 38432b; 1 ovig. ♀ 7.2 mm, 1 ♂ 7.2 mm, MACN-In 38432c; 1 ♀ 4.6 mm, 1 sex indet. 6.2 mm, MACN-In 38432d. Same location, same colls., 10 November 1999; 1 ovig. ♀ 9 mm, 1 ♀ 6 mm, 1 ♂ 6.9 mm, MACN-In 38431c; 1 ovig. ♀ 9.5 mm, 1 ♂ 6 mm, MACN-In 38431d. Same location, same colls., 10 February 2000: 1 ♂ 6 mm, MACN-In 38437a; 1 ovig. ♀ 6.3 mm, 2 ♂♂ 5.95 and 6 mm, MACN-In 38437b; 2 ♀♀ 4.7 and 6 mm, MACN-In 38437c. Same location, same colls., 14 February 2000: 1 ♀ 5.6 mm, MACN-In 38438. Same location, same colls., 2 May 2000: 2 ovig. ♀♀ 7 mm, 5 ♀♀ 5–7.6 mm, MACN-In 38439a; 1 ovig. ♀ 7 mm, 1 ♀ 4.5 mm, 1 sex indet. 3 mm, MACN-In 38439b. Same location, same colls., 29 May 2000: 1 ♀ 5 mm, MACN-In 38433b; 1 ♀ 5 mm, 1 ♂ 6.7 mm, MACN-In 38433c .

Material examined

See Type material specified above.

Diagnosis

Male peraeonites 2–4: with ventral, anteriorly rounded sternal processes; male peraeonites 5 and 6 with flat ridge-like processes. Male Gn1 merochelate: coxa with anteroventral corner produced, rounded; basis stout, anterior margin straight, posterior convex; ischium 0.4 times as long as basis; merus subtriangular, elongate, reaching apex of carpus, strongly diverging from it distally, posterior margin straight; carpus subequal in length to basis, expanded distally; propodus about same length as carpus, subrectangular, posterior margin straight, palm somewhat excavate; dactylus about twice as long as palm, slightly swollen medially, with posterior margin crenellate. Male Gn2 subchelate: ischium and merus short; carpus 0.9 times as long as basis; propodus 0.8 times as long as carpus, 0.5 times as wide as long, palm oblique, slightly convex, palmar angle rounded, defined by one robust seta; dactylus almost as long as palm, slightly swollen medially, posterior margin with small crenellations, bearing minute setae distally. Female Gn 1: carpus subtriangular, 0.9 times as long as basis; propodus subrectangular, slightly shorter than basis, posterior margin straight, palm oblique, palmar corner defined by one robust seta; dactylus somewhat longer than palm, posterior margin bearing denticles and small setae. Maximum length of specimens: 7.2 mm for males and 9.5 mm for females.

Description

Holotype male: body length 7 mm. Colour whitish in alcohol.

Head somewhat shorter than peraeonites 1 and 2 combined; lateral cephalic lobes broadly produced, rounded; posteroventral angle weakly acute. Eyes medium-sized, oval, dark red. A1 and 2 missing.

UL: Broad, ventral margin convex, setose.

Md: Incisors well developed, broad, with six teeth; right lacinia mobilis narrow, with three teeth, left broad, with five teeth; accessory setal row with seven robust setae bearing cusped distally, with intermediate and distal plumose setae; molar prominent, margins with long teeth and surface covered by small denticles, bearing one long plumose seta at its base, on distal corner; palp, articles 1–3 ratio 8: 40: 52, article 2 with posterior medium-length setae, distal surface with medium and long setae, article 3, posterior margin somewhat excavate, bearing long setae and dense row of short setae, apex with two long setae, anterior margin with dense row of short setae and few long setae located medially, all setae pectinate.

LL: Outer plates well developed, separated, bearing three or four robust setae distally, inner margins finely setose, mandibular processes long and acute; inner lobes proportionally smaller, with distal minute setae.

Mx1: Inner plate small, with one long, terminal, plumose seta; outer plate bearing 10 terminal robust setae with one to two cusps, except one smooth outermost seta; palp biarticulate, article 2 with eight distal robust setae and oblique row of seven long simple setae.

Mx2: Inner plate shorter and broader than outer, with mediofacial row of setae, margin and apex with plumose and simple setae; outer plate with three subapical plumose setae on outer margin, many distal setae and two subdistal plumose setae on inner margin.

Mxp: Inner plate subrectangular, short, broad, with three terminal conical setal teeth and oblique row of 12 long, plumose setae; outer plate bearing three long simple setae on apex, 12 setal teeth on inner margin and facial slender setae medially; palp four-articulate, article 1 with one apical seta, article 2 setose on proximal and distal parts of posterior margin, article 3 bearing setae on distal half of posterior margin, distal surface and outer corner; dactylus very long, shorter than article 3, with two fine setae on apex and long terminal unguis.

Gn1: Merochelate; coxa with anteroventral corner produced, rounded, bearing one small seta; basis stout, anterior margin straight, posterior convex, both with few sparse minute setae; ischium stout, 0.4 times as long as basis; merus subtriangular, elongate, reaching apex of carpus, strongly diverging from it distally, posterior margin straight, with setae medially; carpus subequal in length to basis, expanded distally, posterior margin bearing bundles of setae on distal half; propodus about same length as carpus, subrectangular, posterior margin straight, with groups of simple setae and one subdistal robust seta, palm somewhat excavate, crenellate, moderately setose; dactylus about twice as long as palm, slightly swollen medially, posterior margin with notches, bearing minute setae, distal half with longer setae.

Gn2: Subchelate, smaller than Gn1; coxa subquadrate, ventral margin with very short setae; basis stout, 2.9 times as long as wide, anterior margin with very short setae, spaced at regular intervals, posterior margin convex, with few short setae medially, one long seta proximally and one medium-length seta on distal corner; ischium and merus short; carpus 0.9 times as long as basis, posterior margin setose, anterior margin with few setae; propodus 0.8 times as long as carpus, 0.5 times as wide as long, with setae on both posterior and anterior margins, especially on former, palm oblique, slightly convex, with setae, palmar angle rounded, defined by one robust seta; dactylus almost as long as palm, slightly swollen medially, posterior margin with small crenellations, bearing minute setae, distal half with longer setae.

P3 and P4: Similar in shape and size: coxa subquadrate, ventral margin with very short setae; basis slender, anterior and posterior margins with short setae and one long seta proximally on posterior margin; merus 0.7 times as long as carpus, wider distally, scarcely setose; carpus subrectangular, 0.9 times as long as basis, moderately setose; propodus slender, as long as merus, with few sparse setae along posterior margin; dactylus narrow, 0.5 times as long as propodus.

P5: Coxa with deep anterior lobe; basis 1.9 times as long as wide, anterior margin with short robust setae, posterior straight, with short setae; merus expanded, distally, margins with few setae, distal corners rounded, bearing longer setae; carpus subrectangular, anterodistal corner setose, posterodistal corner with robust setae; propodus slender, 0.7 times as long as merus and carpus combined, anterior margin with few setae, posterior with robust setae, distalmost larger, posterodistal corner bearing many long setae; dactylus 0.5 times as long as propodus.

P6: Much longer than P5; coxa small, slightly bilobate; basis subrectangular, somewhat expanded medially, anterior margin with short robust setae, posterior margin with short setae; merus subrectangular, elongate, 0.9 times as long as basis, slightly expanded distally, both margins moderately setose; carpus 0.7 times as long as merus; propodus subequal in length to merus, anterior margin with groups of medium-length setae, anterodistal corner with longer setae, posterior margin bearing robust setae; dactylus 0.3 times as long as propodus.

P7: Coxa small, subrounded; remainder articles similar in shape to those of P6, but much longer and setose.

Peraeonites 2–4: With ventral, anteriorly rounded sternal processes, peraeonites 5 and 6: flat ridge-like processes.

Gills attached to coxae 2–6.

Pl1–Pl3: Subequal in length; peduncle with two locking spines; inner ramus longer than outer. Pl3: both rami composed of 11 articles, articles of inner ramus longer.

Ep1–Ep3: Posteroventral corner weakly produced, notched, with one short seta in notch.

U1: Peduncle slightly longer than rami, with well-developed posteroventral interramal process, 0.4 times as long as outer ramus, bearing one apicolateral robust seta, six dorsolateral robust setae in two rows, three dorsomedial and two apicomedial robust setae; rami subequal in length; outer ramus with three dorsolateral robust setae, apex bearing four robust setae, apicalmost very long, spine-like; inner ramus with three dorsolateral and one dorsomedial robust seta, apex with five robust setae, one of them very long, spiniform.

U2: Peduncle shorter than rami, bearing one dorsomedial, one apicomedial and one dorsolateral robust seta; outer ramus slightly shorter than inner, with three dorsolateral robust setae; inner ramus with five dorsolateral robust setae; apex of both rami as in U1.

U3: Peduncle short, 1.3 times as long as wide; 0.7 times as long as inner ramus, with three subapical robust setae; inner ramus longer than outer, with one dorsolateral, one subapical and one terminal, longer, robust seta; outer ramus biarticulate, article 1 with one subapical robust seta and three distal robust setae, article 2 very small, with three robust setae of different length, apical-most very long.

T: Entire, slightly longer than wide, with four subapical robust setae on each side, outermost longest, about three-quarters as long as T, setae decreasing in length towards innermost seta.

Additional observations

Paratype male: body length 7 mm.

A1: Slender, elongate; peduncular article 1 3.4 times as long as wide, bearing one subdistal robust seta and few simple setae; article 2 long, 1.2 times as long as article 1, setose; article 3 short, 0.3 times as long as article 1; primary flagellum broken at article 31, weakly setiferous, aesthetascs on articles 5 to 30; accessory flagellum with five articles, terminal article small.

A2: Stout, shorter than A1; peduncular article 3 with two distal robust setae and few simple setae; article 5 elongate, slightly longer than article 4, both articles setose; flagellum subequal in length to article 5, with nine articles bearing simple setae, articles 4, 6, 8 and 9 each with two aesthetascs, article 9 spine-like.

Paratype male (body length 5.9 mm): Merus apex acute, extending to threequarters of carpus. Younger males: Gn1 merus of varying length, correlating with specimen size, coxa with anteroventral margin rounded, not produced; basis relatively stouter; carpus somewhat shorter and wider; propodus, palm straight, not excavated; dactylus slightly overlapping palm with inner margin bearing larger denticles.

Paratype ovigerous female: body length 8 mm.

Gn1: Larger than Gn2, except coxa; coxa subquadrate, anteroventral margin rounded; basis stout, 2.7 times as long as wide; merus with posterior margin very setose distally; carpus subtriangular, 0.9 times as long as basis, posterior margin convex, setose; propodus subrectangular, slightly shorter than basis, surface with groups of setae, posterior margin straight, setose, palm oblique, with groups of setae, palmar corner defined by one robust seta; dactylus longer than palm, posterior margin with denticles bearing setae in notches.

Gn2: As in male, but with shorter carpus; propodus, palmar corner with two robust setae; dactylus, posterior margin with denticles more distinct than in holotype male.

Other ovigerous female paratypes with A1 and A2 more slender than in males.

Etymology

Named for its association with M. pyrifera , which is a brown alga and “brown” is translated into Spanish as “ parda ”.

Remarks

Aora Krøyer, 1845 comprises 17 species. In general, they are morphologically very uniform, except for the strongly dimorphic first gnathopod of males. Myers and Moore (1983) provided a key to males of 14 species from all over the world based on the gnathopoda, which are of important diagnostic value. Later on, Hirayama (1984), Appadoo and Myers (2004) and Vader and Krapp (2005) described three other species.

Aora parda is characterized by the remarkable palm on the propodus of the male first gnathopod, which is absent or inconspicuous in the other species.

The new species resembles superficially Aora kergueleni Stebbing, 1888 , and Aora trichobostrychus Stebbing, 1888 both from Kerguelen Island, and Aora karibu Vader and Krapp, 2005 from Malvinas / Falkland Islands, which are the only taxa possessing a distinct palm on the male first gnathopod. However, that of Aora trichobostrychus is poorly developed and convex, instead of well developed and excavated. According to the descriptions and figures of Stebbing (1888) and Vader and Krapp (2005), the four species also share similar mouthparts, antennae and peraeopods, but they differ in the male first and second gnathopods, and shape and setation of uropods and telson. In addition, the eyes of A. trichobostrychus and A. karibu are rounded instead of oval.

A comparison of the illustrations of the known Aora species indicates small differences in the shape and setation of some appendages, presence or absence of ventral sternal structures in males and peduncular process on the first and second uropods.

These species exhibit all possible combinations of shape and setation of appendages; some of the most striking features are the densely setose carpus and propodus of male second gnathopod in Aora mortoni (Haswell, 1879b) from New Zealand and Australia, Aora inflata Griffiths, 1976 from Southern Africa and Aora hebes Myers and Moore, 1983 from Australia. Peculiar “wings” on the basis and ischium, and a triangular process on the anterior margina on the basis of the male first gnathopod have only been observed in Aora typica Krøyer, 1845 from the Southern Hemisphere. An uncommon excavation on the posterodistal margin of the basis of the male fifth and sixth peraeopods is found in Aora gracilis (Bate, 1857) from the North Atlantic and Aora inermis Appadoo and Myers, 2004 from Mauritius, respectively. An unusual curved merus of the male first gnathopod has been described in A. hebes . A strong posterodistal process on the carpus of the male first gnathopod is a characteristic feature of Aora anomala Schellenberg, 1926 from southern Argentina. Aora parda displays male second gnathopod moderately setose; basis and ischium of male first gnathopod with smooth margins; basis of peraeopods with straight margins; straight merus and carpus of male first gnathopod with smooth posterior margin.

According to the descriptions, the ventral sternal processes are rarely found in Aora species. These features are present only in the new species described herein, in Aora mortoni , Aora adpressa Myers and Moore, 1983 from Australia and Aora inermis . Nevertheless, the sternal processes on their peraeonites exhibit different shape and location.

The development of the peduncular interramal process on the first and second uropods is variable among mature specimens of almost all the species. The peduncular process on the second uropod is described as a short, triangular process to a larger, spiniform structure. This configuration is lacking in A. parda , A. trichobostrychus , A. hebes and A. karibu .

Aora parda , which is associated with holdfasts of the kelp M. pyrifera from the Beagle Channel, is the third species recorded in the Magellanic area, together with A. anomala and A. karibu .

Figures

Figure 1. Aora parda sp. nov. Holotype, male: (A) head; (B) upper lip; (C, D) right and left mandibles; (E) mandibular palp; (F) lower lip; (G, H) maxillae 1, 2. Scale bars: a: (A) 0.2 mm; b: (B–H) 0.1 mm.

Figure 2. Aora parda sp. nov. Holotype, male: (A) maxilliped; (B) gnathopod 1; (C, D) gnathopod 1 palm and dactylus; (E) gnathopod 2; (F) gnathopod 2 dactylus; (G, H) peraeopods 3, 4. Scale bars: a: (A) 0.1 mm; b: (B, E, G, H) 0.2 mm; c: (C, D, F) 0.05 mm.

Figure 3. Aora parda sp. nov. Holotype, male: (A–C) peraeopods 5–7; (D) pleopod 1; (E) pleopod 1 locking spines; (F, G) epimera 2, 3. Scale bars: a: (A), b: (B), c: (C), d: (D, F, G) 0.2 mm; e: (E) 0.025 mm.

Figure 4. Aora parda sp. nov. Holotype, male: (A–C) uropods 1–3; (D) telson. Paratype, male 7 mm: (E, F) antennae 1, 2. Paratype, male 5.85 mm: (G) gnathopod 1; (H) gnathopod 1 dactylus. Scale bars: a: (A–C), c: (E–G) 0.2 mm; b: (D), d: (H) 0.05 mm.

Figure 5. Aora parda sp. nov. Paratype, ovigerous female 8 mm: (A) gnathopod 1; (B) gnathopod 1 dactylus; (C) gnathopod 2; (D) gnathopod 2 dactylus. Scale bars: a: (A, C) 0.2 mm; b: (B, D) 0.05 mm.