Ventojassa beagle, 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 : 1817-1826

Ventojassa beagle sp. nov.

( Figures 6–11 )

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. ♀ 4 mm, 10 November 1999, MACN-In 38440a. PARATYPES, 1 ovig. ♀ 4 mm, 1 November 1999, MACN-In 38441a; 1 ovig. ♀ 3.6 mm, 10 November 1999, MACN-In 38440b. Same location, same colls., 1 November 1999: 1 ovig. ♀ 3.8 mm, MACN-In 38441b; 1 ♂ 3.95 mm, MACN-In 38441c. Same location, same colls., 11 August 1999: 1 ♀ 3.7 mm, MACN-In 38442a; 1 ♂ 3.2 mm, MACN-In 38442b; 3 ovig. ♀♀ 3.6–3.9 mm, 5 ♂♂ 3–3.9 mm, MACN-In 38442c. Same location, same colls., 1 November 1999: 1 ovig. ♀ 3.9 mm, 1 ♂ 3 mm, MACN-In 38441d; 1 ♂ 3.5 mm, MACN-In 38441e. Same location, same colls., 10 November 1999: 1 ♀ 2.85 mm, MACN-In 38440c; 4 ovig. ♀♀ 3.4–3.7 mm, MACN-In 38440d. Same location, same colls., 10 February 2000: 1 ♀ 3 mm, MACN-In 38443a; 1 ♂ 3.3 mm, MACN-In 38443b. Same location, same colls., 2 May 2000: 1 ovig. ♀ 4.3 mm, 1 ♀ 2 mm, 2 ♂♂ 3 and 4 mm, MACN-In 38444a; 2 ovig. ♀♀ 3. 90 and 4 mm, 1 ♀ 3, MACN-In 38444b .

Material examined

See Type material specified above.

Diagnosis

Head, lateral cephalic lobes triangular, acute. Eyes far from apex of ocular lobe. A1: slender, slightly shorter than A2: primary flagellum, articles 1–3 with long aesthetascs; accessory flagellum bearing two articles, first elongate, second minute. Mx1: inner plate apically naked. Gn1: propodus shorter than carpus. Female Gn2: much stronger than Gn1; carpus subtriangular, very short, with small posterodistal lobe; propodus stout, subquadrate, palm oblique, somewhat longer than posterior margin, medially convex, finely pectinate, with shallow excavation delimited by two robust setae distally; dactylus fitting on palm corner, inner margin crenellate, with subdistal tooth. Male Gn2: stronger than in female; carpus short, saucer-like, with small anterodistal lobe and larger posterodistal lobe; propodus very robust, almost quadrate, palm oblique, crenellate, subequal in length to posterior margin, defined by rounded process on palmar corner with one robust seta, then with medial excavation, and subdistally with a larger protuberant process sinuous and slightly acute, anterior margin strongly setose subdistally; dactylus falcate, fitting on palmar corner, inner margin with very small setae and notch subdistally. P6 much longer than P5; P7 longer than P6. U3: outer ramus with one wire-like seta on outer margin. T: entire, almost as long as broad, scarcely narrowing distally, with well-developed submarginal cusps, bearing two dorsal robust setae, apex truncate with one very fine seta medially.

Description

Holotype ovigerous female: body length 4 mm. Head slightly longer than wide, somewhat shorter than peraeonites 1 and 2 combined; lateral cephalic lobe triangular, apically acute. Eyes roundish, small, dark red in alcohol, far from apex of ocular lobe.

A2: Slender, setose; peduncular article 5 slightly longer than article 4; flagellum six-articulate, 1.2 times as long as peduncular article 5, with last article ending into one long robust seta.

UL: Subrounded, with shallow excavation anteriorly. Epistome large, sharp, conical, projecting anteriorly.

Md: Incisors three or four-toothed; right lacinia mobilis bifid, left three dentate; right accessory setal row with two robust setae, left with three; molar subconical, ridged, with well developed flake and one plumose seta; palp three-articulate, with article clavate, 3 strongly setose, 0.7 times as long as article 2.

Ll: Bearing large inner lobes; outer lobes with margin entire, mandibular projections short, subrounded.

Mx1: Inner plate short, triangular, apically naked; outer plate with 11 terminal setal teeth; palp, article 2 with four large apical robust setae and four subdistal simple setae.

Mx2: Inner plate shorter than outer, bearing medial plumose setae; both plates apically setose.

Mxp: Inner plate subrectangular, bearing two distal and one subdistal robust seta, oblique setal row with about nine plumose setae; outer plate bearing three apical long robust setae and five or six short, robust setae with intermediate simple setae on medial margin; palp four-articulate, article 2 with posterior margin moderately setose and anterior margin with one apical seta, article 3 bearing one medial and three apical setae on anterior margin, few setae on posterior margin and many subapical facial setae, article 4 short, narrow, with longer apical nail and few simple setae.

Gn1: Coxa small, subrectangular, 1.3 times as long as wide, ventral margin with short setae, posterior margin somewhat excavated; basis elongate, posterior margin with long setae proximally; merus triangular, posterior margin apically setose; carpus, posterior margin heavily setose; propodus slightly shorter than carpus, posterior margin dilated medially, palm oblique, longer than posterior margin, bearing simple setae, anterior margin setose; dactylus elongate, as long as palm, with inner margin crenellate, bearing one small tooth subdistally.

Gn2: Much stronger than Gn1; coxa similar to coxa 1, but somewhat larger and posterior margin straight; basis wider distally, posterior margin with long setae medially; carpus subtriangular, very short, with small posterodistal lobe; propodus stout, subquadrate, palm oblique, somewhat longer than posterior margin, setose, convex medially, finely pectinate, distally with shallow excavation delimited by two robust setae, anterior margin with long setae on distal half; dactylus fitting on palmar corner, inner margin crenellate, with subdistal tooth.

P3 and P4: Similar, short; coxa subrectangular; basis bearing long setae on posterior margin, anterior margin with one and two setae, respectively; merus somewhat expanded distally, with setae on anterodistal and posterodistal corners; carpus rectangular, shorter than merus, with posterodistal and anterodistal corners scarcely setose; propodus about as long as merus, bearing setae on posterior margin and on anterodistal corner; dactylus as long as half length of propodus.

P5: Shorter than P3 and P4, stout; coxa with anterior lobe large, as deep as coxa 4, posterior lobe relatively large; basis expanded, subquadrate, with posterodistal lobe small, rounded, anterior margin with medium-length setae, posterior with very short setae; merus and carpus similar in shape to those of P3 and P4; propodus 1.3 times as long as merus and twice as long as carpus, but narrower, bearing two robust setae near apex on posterior margin, anterodistal corner with long setae; dactylus short, strong.

P6: Much longer than P5; coxa small, with short and rounded lobe; basis subrectangular, expanded proximally, with margins almost naked; merus, carpus and propodus narrow; merus 1.3 times as long as carpus, both articles scarcely setose; propodus 1.8 times as long as carpus, with sparse, short, robust setae and long simple setae on anterior margin, posterior margin with long medial and distal setae; dactylus narrow.

P7: Longer than P6; coxa small, subrounded; basis narrower than on P6, with posterior margin bearing very short setae, somewhat expanded proximally, then margin slightly concave, remaining articles as in preceding appendage, but longer.

Gills attached to coxae 2–6, latter smaller. Oostegites present on coxae 2–5.

Pl1–Pl3: Subequal in length. Pl1: peduncle with two locking spines; outer ramus bearing 10 articles, inner with seven longer articles.

Ep1–Ep3: Naked, posteroventral corners rounded.

U1 and U2: With interramal process well-developed, slightly longer on U1, reaching first third on inner ramus of U1 and first fourth of U2; outer ramus shorter than inner; apex of both rami with unguis. U1: peduncle 1.4 times as long as inner ramus, with two dorsolateral and one apicolateral robust seta, two dorsomedial and one apicomedial robust seta; inner ramus bearing one dorsolateral robust seta medially, two apicolateral and one apicomedial robust seta; outer ramus with robust setae as on inner.

U2: Peduncle almost as long as inner ramus, bearing one apicomedial robust seta, one dorsolateral and one apicolateral robust seta; inner ramus with three dorsolateral and one apicolateral robust setae, one dorsomedial robust seta on distal half and two apicomedial robust setae; outer ramus bearing two dorsolateral robust setae, two apicolateral and one apicomedial robust setae.

U3: Small, peduncle broad, 1.7 times longer than inner ramus, bearing five dorsolateral robust setae, three apical robust setae, and about three fine, wire-like setae; outer ramus slightly shorter than inner, with one very fragile wire-like seta on outer margin, apex with two small lateral setae; inner ramus bearing one robust seta on distal half and one smaller terminal robust seta.

T: Entire, almost as long as broad, scarcely narrowing distally, with welldeveloped submarginal cusps, bearing two dorsal robust setae and two penicillate setae, apex truncate with one very fine seta medially.

Additional observations

Paratype ovigerous female: body length 3.6 mm. Body laterally compressed, smooth. A1 and A2: about as long as first five peraeonites combined.

Paratype ovigerous female: body length 4 mm. A1: slender, setose, slightly shorter than 2; peduncle articles 2 and 3 elongate, almost twice longer than article 1, article 3 bearing one long aesthetasc; primary flagellum with five articles, articles 1–3 with long aesthetascs; accessory flagellum with two articles, first elongate, second minute.

Paratype male: body length 4 mm. Gn2: stronger than in females; basis stout, twice as long as wide, anterior margin naked, posterior with two setae; merus subtriangular, apically setose; carpus short, saucer-like, with small anterodistal lobe bearing one short robust seta and larger posterodistal lobe with many fine setae; propodus very strong, almost quadrate, palm oblique, crenellate, subequal to posterior margin, defined by rounded process on palmar corner with one robust seta, then with medial excavation and subdistally with larger protuberant process sinuous and slightly acute, palm and posterior margin with some setae, anterior margin strongly setose subdistally; dactylus falcate, fitting on palmar corner, inner margin with very small setae and notch subdistally. U3: peduncle bearing two dorsomedial, two apicomedial and two apicolateral robust setae, apically with one fine simple seta; outer ramus with two dorsal robust setae and one medial wire-like seta on outer margin.

Etymology

Named after the Beagle Channel where the species was discovered.

Remarks

According to Vader and Myers (1996) Ventojassa J.L. Barnard, 1970 is composed of the following six species: Ventojassa frequens (Chilton, 1883) from New Zealand, Ventojassa ventosa (J.L. Barnard, 1962) , Ventojassa crenulata Ledoyer, 1979 from Madagascar, Ventojassa dentipalma W. Kim and C.B. Kim, 1991 from Korea, and Ventojassa helenae Vader and Myers, 1996 and Ventojassa zebra Vader and Myers, 1996 , both from south-east Australia. These authors did not consider that Ventojassa georgiana ( Schellenberg, 1931) from Antarctica, sub-Antarctic islands and the southern tip of Argentina belonged to Ventojassa and provisionally transferred the species to Ruffojassa Vader and Myers, 1996 .

Ventojassa beagle can primarily be distinguished from the remaining Ventojassa species mainly by the remarkably different shape of the ocular lobe which is acute, the location of the eyes far from the apex of the ocular lobe apex and the numerous subapical cusps on the lateral margins of the telson.

Additionally, the new species differs principally from V. helenae and V. zebra in the sexual dimorphism of the male second gnathopod and the absence of “stridulating ridges” on the basis of the fifth peraeopod. It can be separated from V. crenulata and V. frequens because in these species the basis of the sixth and seventh peraeopods has a crenellate posterior margin, the accessory flagellum is longer and the telson is triangular with an acute apex. It is basically distinguished from V. ventosa because this latter species has more setose antennae and shorter first and second uropods. It differs from V. dentipalma by the shape of the palm on the male second gnathopod, presenting processes of dissimilar structure.

Ventojassa beagle sp. nov. described from the Beagle Channel would be the first taxon representative of Ventojassa in South America if V. georgiana were removed from this genus.

Figures

Figure 6. Ventojassa beagle sp. nov. Holotype, ovigerous female: (A) head; (B) antenna 2; (C) antenna 2 last article; (D) upper lip; (E) epistome; (F, G) right and left mandibles. Scale bars: a: (A, B) 0.2 mm; b: (C) 0.05 mm; c: (D–G) 0.025 mm.

Figure 7. Ventojassa beagle sp. nov. Holotype, ovigerous female: (A) mandibular palp; (B) lower lip; (C) maxilla 1; (D) maxilla 1 palp; (E) maxilla 2; (F) maxilliped; (G, H) maxilliped inner and outer plates; (I) maxilliped dactylus. Scale bars: a: (A, C, E, G–I), b: (B), c: (D) 0.025 mm; d: (F) 0.05 mm.

Figure 8. Ventojassa beagle sp. nov. Holotype, ovigerous female: (A) gnathopod 1; (B) gnathopod 1 propodus; (C) gnathopod 2; (D) gnathopod 2 propodus; (E, F) peraeopods 3, 4. Scale bars: a: (A, C, E, F) 0.2 mm; b: (B), c: (D) 0.1 mm.

Figure 9. Ventojassa beagle sp. nov. Holotype, ovigerous female: (A–C) peraeopods 5–7; (D) pleopod 1; (E) pleopod 1 locking spines; (F) epimera 1–3; (G) uropod 1. Scale bars: a: (A–D, F) 0.2 mm; b: (E) 0.025 mm; c: (G) 0.05 mm.

Figure 10. Ventojassa beagle sp. nov. Holotype, ovigerous female: (A, B) uropods 2, 3; (C) uropod 3 rami; (D) telson. Paratype, ovigerous female 3.6 mm: (E) lateral view. Paratype, ovigerous female 4 mm: (F) antenna 1; (G) antenna 1 flagellum. Scale bars: a: (A, B, G) 0.05 mm; b: (C), c: (D) 0.025 mm; d: (E) 1 mm; e: (F) 0.2 mm.

Figure 11. Ventojassa beagle sp. nov. Paratype, male 3.95 mm: (A) gnathopod 2; (B) gnathopod 2 palm; (C) uropod 3; (D) uropod 3 outer ramus. Scale bars: a: (A) 0.2 mm; b: (B, C) 0.05 mm; c: (D) 0.025 mm.