Imbachoculodes namhaensis, Kim & Hendrycks & Lee, 2012

Kim, Young-Hyo, Hendrycks, Ed A. & Lee, Kyung-Sook, 2012, New genera and species of the Synchelidium group (Amphipoda: Oedicerotidae) from Asia-North Pacific, Journal of Natural History 46 (37 - 38), pp. 2349-2376 : 2361-2367

Imbachoculodes namhaensis sp. nov.

(Korean name: Nam-hae-but-eun-nun-yeop-sae-u, new)

( Figures 6–8 )

Type material

Holotype. M ale. Body 3.6 mm (appendages on one slide), NIBRIV0000246430, Suryuk, Tongyeong-si, Korea (34 ◦ 49 ′ 16 ′′ N, 128 ◦ 26 ′ 26 ′′ E), 24 August 2005, collected with light trap on the bottom, depth 5 m, collected by Y.-H. Kim.

Paratype. Adult female, 4.1 mm (appendages on one slide), NIBRIV0000246431, other data same as holotype.

Etymology

The new species is named after the type locality. The Korean name for the Korea Strait is Namhae .

Description

Holotype male. Body ( Figure 6A ) 3.6 mm long. Rostrum ( Figure 6B ) elongate, slightly deflexed, not reaching end of peduncular article 1 of antenna 1, apical margin subacute distally; lateral cephalic lobe subacute; no trace of ommatidia observed.

Antenna 1 ( Figure 6C ) a little shorter than head and pereonites 1–4 combined; length ratio of peduncular articles 1–3 = 1.00: 0.55: 0.28; flagellum nine-articulate, 1.78 times peduncle; flagellum articles 1–4 callynophorate, each with rows of numerous aesthetascs dorsomedially.

Antenna 2 ( Figure 6D ) 0.75 times body length, 3.07 times antenna 1; peduncular articles 1 and 2 ambiguous, short; peduncular article 4 stout, 1.12 times peduncular article 5; flagellum long, 39-articulate.

Upper lip missing.

Lower lip ( Figure 6E ) inner lobes unknown; outer lobes densely pubescent on apical margins, lacking gland cones; mandibular processes strong.

Right mandible ( Figure 6F ) incisor slightly projecting on both sides, teeth obsolescent; lacinia mobilis absent; accessory spine row with five spines; molar small, with two broad barbed spines and three-cuspidate spine, positioned close to end of spine row; palp triarticulate.

Left mandible ( Figure 6G ) similar to right; lacinia mobilis broad, blunt, uneven apically; accessory spine row with four spines; palp triarticulate, article 2 1.15 times article 3, with nine D2 setae, article 3 rounded apically, with 15 D3 setae and one E3 seta.

Maxilla 1 ( Figure 6H ) inner plate elongate, bearing one short apical seta; outer plate with seven spine-teeth; palp biarticulate, distal article 2.43 times proximal one, with seven apical setae.

Maxilla 2 ( Figure 6I ) plates equal in length, weakly setose; apical margin of inner plate and distal and apical margins of outer plate with four and six setae.

Maxilliped ( Figure 6J ) inner plate small, with one conical spine and two submedial setae; outer plate large and very broad, as wide as article 2 of palp, reaching about 0.6 times article 2 of palp, medial margin with 10 stout spines; palp four-articulate, article 2 0.46 times palp, setose on medial margin, article 3 slightly curved inward, dactylus strong, falcate, slightly shorter than article 3.

Gnathopod 1 ( Figure 7A ) subchelate, articles slender; coxa axe-shaped, gradually widened distally, ventral margin weakly setose; basis 0.46 times length of appendage, anterior margin with three setules and two setae, posterior margin with two setae; carpus about 0.5 times propodus, narrow carpal lobe extended slightly beyond palmer corner of propodus and appressed to ventral margin of propodus, with two tiny spines apically; palm of propodus oblique with short and long setules, delimited by one spine; dactylus fitting palm.

Gnathopod 2 ( Figure 7B ) similar to gnathopod 1, but coxa narrowly rectangular and each article slightly longer.

Pereopod 3 ( Figure 7C ) coxa rectangular, similar to coxa 2; basis slightly bent distally, 1.58 times merus, with three long and short setae on both margins; merus gradually expanding distally, setose distally; carpus narrower than merus, with long setae on posterior margin, slightly shorter than propodus; dactylus elongate and falcate, 0.82 times propodus.

Pereopod 4 ( Figure 7D ) similar to pereopod 3, but coxa 4 twice width of coxa 3 and distal inner margin of basis with two long plumose setae.

Pereopod 5 ( Figure 7E ) coxa large, bilobate, midventral margin slightly concave; basis elongate ovate, slightly longer than 0.25 times length of pereopod, anterior margin with six long setae and two plumose setae medially, posterior margin convex with nine short setae and posteromedially with a row of seven plumose setae; merus gradually widened, 1.43 times carpus, anterior margin with nine simple setae, posterior margin with 10 long simple setae and four plumose setae; carpus and propodus subequal in length, narrower than merus; dactylus falcate, 1.10 times propodus, with one penicillate seta proximally.

Pereopod 6 ( Figure 7F ) similar to pereopod 5, but stouter and longer especially the basis; coxa 6 nearly square, 0.62 times coxa 5, anterior margin slightly concave, midventral margin with two setules and one setule anteroventrally; anterior margin of basis with nine simple and nine long plumose setae, posteromedially with a row of 11 plumose setae.

Pereopod 7 ( Figure 8A ) long, 1.72 times pereopod 6; coxa small, ventral margin rounded; basis subtriangular, narrowing distally, lacking posteroventral lobe, anteromedial margin with three and two spines anterodistally, posterior margin with row of 14 long spines and three plumose setae medially; merus as long as basis, with 10 spines anteriorly and two groups of four spines posteriorly; carpus slightly longer than merus and subequal to propodus, with spines facially; propodus 1.39 times dactylus, both with spines and long plumose setae.

Pleopods strong; rami long, subequal, articles with long plumose setae.

Uropod 1 ( Figure 8B ) peduncle rectangular, 1.24 times inner ramus, distal half of dorsolateral margin with seven spines, proximal half of lateral margin with four spines, medial margin with three spines and one distal long spine; outer ramus 0.84 times inner ramus, with three dorsal spines; inner ramus with two dorsal spines, proximal parts of lateral margin of inner ramus and medial margin of outer ramus finely serrate.

Uropod 2 ( Figure 8C ) 0.86 times uropod 1; peduncle subequal to inner ramus, dorsolateral margin with six spines, medial margin with three dorsal spines and one distal spine; inner ramus longer than outer ramus, each with three dorsal spines; lateral margin of inner ramus and medial margin of outer ramus finely serrate.

Uropod 3 ( Figure 8D ) 0.91 times uropod 2; peduncle slightly shorter than rami, with three lateroproximal and three dorsodistal spines; outer ramus subequal in length to inner ramus, medial margin of outer ramus regularly finely serrate, lateral margin of inner ramus irregularly serrate.

Telson ( Figure 8E ) subquadrate, with rounded corners, 1.25 times width, slightly narrowed distally, distal margin with a pair of setae, dorsodistal surface with a pair of penicillate setae.

Paratype female (sexually dimorphic characters). Body ( Figure 8F ) about 4.1 mm long, head ( Figure 8G ) longer than pereonites 1–3 combined; rostrum moderately deflexed, almost reaching end of peduncular article 1 of antenna 1; lateral cephalic lobe subacute.

Antenna 1 ( Figure 8H ) slightly longer than head and pereonites 1–3 combined; length ratio of peduncular articles 1–3 = 1.00: 0.86: 0.62; peduncular article 1 stout; peduncular article 2 setose; flagellum six-articulate, articles more stout and setose than male, 0.71 times peduncle.

Antenna 2 ( Figure 8I ) peduncular article 3 stout, 0.79 times article 4; article 4 0.72 times article 5; flagellum 10-articulate, subequal in length to peduncle.

Right mandible ( Figure 8J ) incisor straight and smooth; lacinia mobilis possibly present as a bifid spine, because it is differentiated from the simple spines of the spine row; accessory spine row with three spines; molar small, with one tricuspidate and two broad spines; palp triarticulate, shorter and much less setose than male, article 2 2.4 times article 3, with one A2 seta and three D2 setae, article 3 narrowing distally, lacking D3 setae, with three apical E3 setae.

Remarks

Imbachoculodes namhaensis sp. nov. is similar to I. longirostratus ( Hirayama, 1987) , distributed in West Kyushu, Japanese waters, I. vietnamensis sp. nov. in Vietnam, South China Sea, and I. angustipes ( Ledoyer, 1983) in the Mediterranean. Imbachoculodes namhaensis is distinguished from I. longirostratus by a combination of the following features ( I. longirostratus characters in parentheses): in female, 1) rostrum subacute distally (vs. acute); 2) peduncular articles of antenna 1 setose (vs. sparsely setose); 3) peduncular article 2 of antenna 1 length 1.38 times article 3 (vs. article 2 0.78 times article 3); 4) outer lobe of lower lip lacking gland cone (vs. with one gland cone); and 5) outer plate of maxilliped reaching about 0.6 times palp article 2 (vs. extending beyond palp article 2). The new species is also easily distinguished from I. vietnamensis sp. nov. by the following characteristics ( I. vietnamensis characters in parentheses): 1) rostrum moderately deflexed (vs. strongly deflexed); 2) head long, wider than deep (vs. as wide as deep); 3) lateral cephalic lobe subacute (vs. rounded); and 4) pereopod 7, basis subtriangular (vs. subovate). The new species also differs from I. angustipes by the following characters: ( I. angustipes characters in parentheses): 1) peduncular article 2 of antenna 1 length 1.38 times article 3 (vs. article 2 length 0.69 times article 3); and 2) pereopod 7 basis narrow, posterior margin straight (vs. wider, bearing posterior lobe).

Distribution

Korea ( Korea Strait).

Figures

Figure 6. Imbachoculodes namhaensis gen. et sp. nov., holotype, male, 3.6 mm: (A) habitus; (B) head; (C) antenna 1; (D) antenna 2; (E) lower lip (only half shown); (F) right mandible; (G) left mandible; (H) maxilla 1; (I) maxilla 2; (J) maxilliped. Scale bars = 0.4 mm (A), 0.2 mm (B–D), 0.05 mm (E–J).

Figure 7. Imbachoculodes namhaensis gen. et sp. nov., holotype, male, 3.6 mm: (A) gnathopod 1; (B) gnathopod 2; (C) pereopod 3; (D) pereopod 4; (E) pereopod 5; (F) pereopod 6. Scale bar = 0.2 mm.

Figure 8. Imbachoculodes namhaensis gen. et sp. nov., holotype, male, 3.6 mm: (A) pereopod 7; (B) uropod 1; (C) uropod 2; (D) uropod 3; (E) telson; Imbachoculodes namhaensis gen. et sp. nov., paratype, female, 4.1 mm: (F) habitus; (G) head; (H) antenna 1; (I) antenna 2; (J) right mandible. Scale bars = 0.4 mm (F), 0.2 mm (A, G), 0.1 mm (B–E, H–J).