Heterophoxus despard, 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 : 1874-1883

Heterophoxus despard sp. nov.

( Figures 31–34 )

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. ♀ 6.2 mm, 10 November 1999, MACN-In 38704. PARATYPE, 1 ovig. ♀ 6.9 mm, 10 February 2000, MACN-In 38705 .

Material examined

See Type material as specified above.

Diagnosis

A2: article 4 remarkably longer than 5, subrectangular, bearing posteroproximal rounded lobe. P6: basis somewhat excavated posteriorly. P7: basis reaching about middle of merus, posterior margin cut into long acute teeth, posterodistal angle subacute; merus robust, unlobed, subrectangular, somewhat expanded anteriorly. Ep3: posteroventral corner with long tooth. U3: inner ramus about half length of outer ramus article 1, bearing one long terminal seta.

Description

Holotype ovigerous female: body length 6.3 mm. Head 0.2 times total body length, greatest width 0.7 times length; rostrum unconstricted, broad, exceeding apex of article 1 on A1. Eyes medium, narrow, subovate, brownish-red in alcohol.

A1: Peduncle article 1 large, 1.4 times as long as wide, ventral margin with five subdistal brush setae, one penicillate seta among them and two distal simple setae, dorsal apex bearing one plumose seta; article 2 short, 0.4 times as long as article 1, 0.4 times its width, with four ventral long plumose setae on distal corner, three subapical facial setae on posterior margin, and two short setae on distal margin; article 3 half length of article 2 and half of its width, bearing one short and one long seta on posterior margin, four subapical short setae on distal margin and one short seta on dorsal apex; primary flagellum as long as peduncular articles 1–3 combined, with eight articles, articles 4–7 each with one aesthetasc; accessory flagellum with five articles, about half the length of primary flagellum.

A2: Longer than A1, almost reaching end of peraeonite 1; peduncular article 1 with ensiform process; article 3 bearing one ventral medium seta with plumes and one short brush seta on dorsal corner; article 4 large, posterior margin with proximal rounded lobe, bearing three minute setae, medially somewhat excavated, distally rounded, with eight mixed plumose, brush and robust setae, one of them very long, subapical surface with two short setae towards distal margin, six long and large setae, mixed with smaller simple setae, dorsal margin bearing one proximal seta; article 5 broad proximally, narrowing towards apex, 0.6 times as long as article 4, about half its width, posterior margin bearing long and medium setae with some plumes, dorsal corner with short setae; flagellum slightly shorter than peduncle, with nine articles.

UL: Subrounded, apically excavated; epistome not produced.

Md: Incisor strongly toothed; lacinia mobilis flagellate, bifid, with small cusps; accessory setal row with seven serrate robust setae, bearing intermediate small plumose setae; molar feeble with three apical robust setae finely serrate.

LL: With small inner lobes, mandibular processes short.

Mx1: Inner plate well developed, with two apical plumose setae; outer plate with nine terminal setal teeth moderately cuspidate; palp biarticulate, article 2 bearing five apical robust setae and two apicofacial simple setae.

Mx2: Both plates extending subequally; inner plate broader than outer, bearing apical and medial plumose setae; outer plate with apical setae and two small lateral medial setae.

Mxp: Inner plate small, apex rounded, bearing one short, thick robust seta and five long plumose setae; outer plate reaching nearly to middle of palp article 2, with eight medial robust setae, about two simple setae among them and three longer apical setae; palp four-articulate, article 2 with medial margin moderately setose, all setae medium-length except two apical setae, one twice as long and one very small, article 3 apically subrounded, scarcely setose, bearing three lateral setae, apicofacial and medial setae, article 4 subrectangular, with three terminal simple setae of different length.

Gn1 and Gn2: Subchelate, similar in size and shape, except coxae. Coxa 1 expanded ventrally, anterior margin straight, posterior margin somewhat convex, both margins divergent, ventral margin convex, covered with plumose setae.

Gn2: Coxa rectangular, ventral margin straight, covered with plumose setae; basis bearing abundant plumose setae along posterior margin; ischium, merus and carpus setose on posterior margin; carpus short, subrectangular, posterior margin straight; propodus subovate, length about twice its width, 2.2 times as long as carpus, palm oblique, palmar hump large, bearing one robust seta; dactylus reaching palmar angle.

P3: Coxa rectangular, longer than coxa 2, ventral margin covered with long plumose setae; basis, posterior margin with long simple setae on distal half and plumose setae on distal corner; ischium, posterior corner setose; merus almost as long as basis, expanded anteriorly, anterodistal corner with six setae, posterior margin with many plumose setae and few simple setae situated distally, subapical face bearing four setae; carpus subrectangular, narrowing at apex, 0.5 times as long as merus, posterior margin bearing many long and few short setae, one thicker robust seta distally, exceeding half length of dactylus, surface of article with five medial setae; propodus narrow, rectangular, 1.2 times as long as carpus, posterior margin bearing six long setae on distal half; dactylus slightly longer than half length of propodus.

P4: Stouter than preceding appendage; coxa large, strongly expanded posteriorly, posterodorsal corner broad, rounded, posterodorsal margin somewhat excavated above; remaining articles as in P3; merus bearing five setae on anterior corner and three subapical setae; carpus with six facial setae; propodus bearing six long setae distally and five facial short setae.

P5: Coxa greatly expanded posteriorly, ventral margin with plumose setae; basis slender, rectangular, anterior margin with medium-length simple setae, anterior corner with one short simple seta and two long plumose setae, posterior margin almost naked; merus broad distally, 1.4 times as long as wide, half length of basis, anterior margin with one long plumose seta and short robust setae, posterior margin bearing plumose setae on distal half, distal margin with short robust setae; carpus rectangular, 1.7 times as long as wide, slightly longer than merus, posterior margin with plumose setae, anterior margin bearing long simple and plumose setae, distal margin with short robust setae; propodus subrectangular, 2.2 times as long as wide, 0.8 times as long as carpus, posterior margin bearing long plumose setae, anterior margin with simple setae, both margins with few short robust setae; dactylus spiniform.

P6: Much longer than other peraeopods; coxa small, posterior margin lined with fine hairs; basis narrowing distally, posterior margin somewhat excavated, with plumose setae and fine hairs distally, anterior margin profusely setose, with plumose and robust setae; merus 2.8 times as long as wide, about half length of basis, anterior and posterior margins with few plumose and short robust setae; carpus 3.7 times as long as wide, 1.1 times as long as merus, anterior and posterior margins with few short robust setae; propodus narrow, 1.2 times as long as carpus, bearing long setae along anterior margin and medially on posterior margin; dactylus slender, spiniform.

P7: Shorter; coxa small, ventral margin with fine hairs and one short seta; basis strongly expanded posteriorly, produced distally, reaching about middle of merus, posterior margin cut into 14 acute teeth, with one plumose seta between each tooth, anterior margin bearing short, sparse setae, anterodistal corner with two long plumose setae; ischium large, slightly wider than long, bearing two short robust and two long plumose setae on anterior margin; merus subrectangular, somewhat expanded anteriorly, 1.4 times longer than ischium, 1.5 times as long as wide, anterior margin with short robust and long plumose setae, posterodistal corner with two small setae; carpus narrow, 0.7 times as long as merus, anterior margin with four long setae, posterodistal corner with one short and one long seta; propodus narrower than preceding article, subequal in length, bearing one long medial seta on anterior margin, one long seta on anterodistal corner and two setae on posterodistal corner; dactylus slender, elongate, as long as propodus.

Gills on coxae 2–6. Oostegites long, thin and setose, on coxae 2–5.

Pl1–Pl3: Subequal in length. Pl3: outer ramus with 14 articles, inner with eight. Ep1: posteroventral corner rounded, posterior margin almost straight, anteroventral corner with three short plumose setae. Ep2: posteroventral corner produced, acute, posterior margin convex, ventral margin bearing nine mediun-length plumose setae medially. Ep3: large, posteroventral corner produced into acute upward tooth, posterior margin almost straight, ventral margin sinuous, with five medium-length plumose setae proximally and five long plumose setae medially.

U1: Exceeding U2; peduncle somewhat longer than outer ramus, with one short apicolateral robust seta, one shorter dorsolateral robust seta subapically, and six dorsomedial robust setae, two distalmost setae largest; inner ramus slightly longer than outer, bearing two dorsolateral robust setae proximally and one small seta distally; outer ramus with three dorsolateral longer robust setae medially.

U2: Exceeding U3; peduncle slightly longer than outer ramus, with three long dorsolateral robust setae, one shorter apicolateral robust seta and four long dorsomedial robust setae; inner ramus slightly longer than outer, with three dorsolateral robust setae and one apical small seta; outer ramus bearing two longer proximal dorsolateral robust setae. U1 and U2: peduncular apicolateral corners with fine hairs.

U3: Peduncle short, thick, bearing row of six apicoventral robust setae; outer ramus two-articulate, article 1 1.2 times as long as peduncle, bearing one short lateral robust seta on distal half, one apicolateral and one apicomedial robust seta, article 2 short, 0.2 times as long as article 1, with two long apical setae; inner ramus about half length of outer ramus article 1, bearing one long terminal seta.

T: Short, broad, split about three-quarters its length, lobes diverging, broadly rounded apically, each bearing one apical robust seta, one smaller lateral seta and two penicillate setae above.

Additional observations

Paratype ovigerous female: body length 6.9 mm.

Md: Palp slender, article 2 bearing four short setae along posterior margin and two long distal setae; article 3 slightly longer than article 2, bearing eight setae on oblique apex and three on posterior margin distally.

Gn1: Shape of coxa as in holotype; following articles as in Gn2 of holotype.

Etymology

Named for Isla Despard located in the Beagle Channel, where the specimens were collected.

Remarks

The genus Heterophoxus Shoemaker 1925 comprises twelve known species ( Ren and Huang 1991; Jarret and Bousfield 1994). J.L. Barnard (1960) provided a diagnosis and a key to four of these species. The present contribution is based on Barnard’s criteria for the characterization of the genus and discrimination of the species by considering primarily the morphological characters used in his key. Additionally, other subtle characters and their combinations were taken into account to establish the relationships among the species.

Heterophoxus despard shares a long tooth on the posteroventral angle of the third epimeron with other species of the genus, such as Heterophoxus oculatus (Holmes, 1908) , Heterophoxus ophthalmicus (Schellenberg, 1925) , Heterophoxus trichosus K.H. Barnard, 1932 , Heterophoxus pellusidus Ren, 1991 , Heterophoxus conlanae Jarret and Bousfield, 1994 and Heterophoxus ellisi Jarret and Bousfield, 1994 ; the remaining species are characterized by a small tooth as in Heterophoxus videns K.H. Barnard, 1930 , or by a notch above the rounded posteroventral angle as in Heterophoxus cephalodens Griffiths, 1975 and Heterophoxus opus Griffiths, 1975 .

The new species has the basis of the seventh peraeopod reaching to the middle of the merus, in common with, e.g. H. oculatus , Heterophoxus affinis (Holmes, 1908) and H. trichosus , whereas in H. ophthalmicus and H. pellusidus the basis of the seventh peraeopod extends to the tip of the merus. Heterophoxus despard , however, is distinguished from H. trichosus by the unlobed merus of the seventh peraeopod, and also by the straight posterodistal margin of the basis of the seventh peraeopod, which is somewhat concave in the latter species.

Additionally, the new species resembles H. oculatus in the merus, but they differ from each other in the following morphological attributes: apparently, the new species has a longer head and less acute lower antennal corner. In the new species article 4 of the second antenna is remarkably longer than article 5, is subrectangular and bears a rounded lobe on the proximal posterior margin, whereas in H. oculatus it is slightly longer than article 5 and has a straight posterior margin expanded distally. In the new species the mandibles have an accessory row of setal teeth with less robust setae, and articles 2 and 3 of the palp bear a different number of setae. In the new species the inner plate of the second maxilla is broader than the outer one, whereas H. oculatus has subequal plates. In the new species, the outer plate of the maxilliped has fewer setae on the lateral margin and the inner plate is shorter. Both species differ in the shape of the basis of the sixth peraeopod; it is narrower distally and has a straighter posterior margin in H. oculatus , whereas the new species has a somewhat excavated posterior margin. In the new species, the posteroventral corner of the second epimeron is sharp and slightly produced, whereas in H. oculatus it is rounded and the ventral margin is less setose. In H. despard the third epimeron has posteroventral margin almost straight above tooth and forming a right angle versus posteroventral margin convex and oblique. Both species differ in the number of setae of the first and second uropods. In H. despard the third uropod is remarkably different; the inner ramus is about half the length of the outer ramus article 1 with one apical seta, whereas in H. oculatus the inner ramus is about two-thirds as long as the outer one with two apical and two subapical long setae, and the outer ramus articles 1 and 2 are remarkably more setose.

Females of H. oculatus described and illustrated by J.L. Barnard (1960) were used for comparing species.

Heterophoxus videns is widespread throughout the Antarctic and sub-Antarctic areas, reaching subtropical latitudes. In South America its distribution is widened from the southern tip of the continent to Valparaiso, Chile, to Buenos Aires province, Argentina and to São Paulo, Brazil. The remaining taxa occur in North America (Pacific coast), South Africa (Atlantic coast) and in Antarctica. Although H. trichosus has been reported from the Beagle Channel by López Gappa et al. (2006), the identity of the species is still to be confirmed.

The new species H. despard from the Beagle Channel is the first species of the genus inhabiting holdfasts of M. pyrifera .

Figures

Figure 31. Heterophoxus despard sp. nov. Holotype, ovigerous female:(A) lateral view; (B) head; (C, D) antennae 1, 2; (E) upper lip; (F, G) right and left mandibles; (H, I) maxillae 1, 2; (J) lower lip. Scale bars: a: (A) 1 mm; b: (B) 0.2 mm; c: (C, D), d: (E, H–J) 0.1 mm; e: (F, G) 0.025 mm.

Figure 32. Heterophoxus despard sp. nov. Holotype, ovigerous female: (A) maxilliped; (B, C) maxilliped inner and outer plates; (D) gnathopod 2; (E) peraeopod 3; (F) peraeopod 3 propodus; (G) peraeopod 4. Scale bars: a: (A–C, F) 0.1 mm; b: (D, E, G) 0.2 mm.

Figure 33. Heterophoxus despard sp. nov. Holotype, ovigerous female: (A–C) peraeopods 5–7; (D) pleopod 3; (E) epimera 1–3. Scale bars: a: (A, C, D), b: (B), c: (E) 0.2 mm.

Figure 34. Heterophoxus despard sp. nov. Holotype, ovigerous female: (A–C) uropods 1–3; (D) telson. Paratype, ovigerous female 6.9 mm: (E) mandibular palp; (F) gnathopod 1. Scale bars: a: (A–E) 0.1 mm; b: (F) 0.2 mm.