Elasmopus mukuinu, Sir & White, 2022

Sir, Sally & White, Kristine N., 2022, Maerid amphipods (Crustacea: Amphipoda) from Okinawa, Japan with description of a new species, Zootaxa 5093 (5), pp. 569-583 : 574-581

Elasmopus mukuinu sp. nov.

( Figs 1C, D, 4–9)

Material examined. Holotype: male, 6.1 mm, 27 April 2012, Kaichu Doro Site 2N, 26° 19’55.70”N, 127° 54’52.50”E, rubble bottom, from sediment wash, 1 m depth, K. N. White and I. Kawamura col., NMST-Cr 29017 ; Paratype: male 5.1 mm, same station data, NMST-Cr 29018 ; Paratype: male 4.7 mm, same station data, NMST-Cr-29225 ; Paratype: female, 4.2 mm, same station data, NMST-Cr 29019 .

Other material examined. 1 specimen, 17 November 2011, Kaichu Doro Site 2N; 1 specimen, 17 November 2011, Kaichu Doro Site 2S; 5 specimens, 17 November 2011, Kaichu Doro Site 3S; 11 specimens, 17 November 2011, Kaichu Doro Site 5N; 12 specimens, 9 specimens, 2 February 2012, Kaichu Doro Site 3N; 2 February 2012, Kaichu Doro Site 3S; 17 specimens, 2 February 2012, Kaichu Doro Site 5N; 16 specimens, 2 February 2012, Kaichu Doro Site 5S, NMST-Cr 29021; 9 specimens, 27 April 2012, Kaichu Doro Site 2N, NMST-Cr 29021; 9 specimens, 27 April 2012, Kaichu Doro Site 3N; 16 specimens, 27 April 2012, Kaichu Doro Site 3S; 14 specimens, 27 April 2012, Kaichu Doro Site 4N; 94 specimens, 27 April 2012, Kaichu Doro Site 5N; 23 specimens, 27 April 2012, Kaichu Doro Site 5S; 4 specimens, 19 July 2012, Kaichu Doro Site 3N; 2 specimens, 19 July 2012, Kaichu Doro Site 3S.

Diagnosis. Gnathopod 2 of male propodus palm medial surface with subrectangular hump near insertion of dactylus, distomedial shelf rounded with dense plumose setae, subpalmar surface with dense tufts of long setae. Pereopod 5 posterior margin convex, almost smooth, without long setae. Pereopod 6 posterior margin concave, serrate, without long setae. Pereopod 7 posterior margin convex, crenulate, without long setae. Epimeron 3 posteroventral margin with notch. Uropod 3 inner ramus length 0.8 x outer ramus length, rami distally truncated.

Description of male (holotype, 6.1 mm).

Head ( Fig. 4C): eyes ovate; lateral cephalic lobe rounded, anteroventral margin with notch, anteroventral corner subquadrate. Antenna 1 ( Fig. 4A): length 2.4 × length of antenna 2; peduncular articles 1–3 length ratio 1.0: 0.9: 0.6; all articles sparsely setose; accessory flagellum 2-articulate, second article minute; ( Fig. 4B) flagellum 19- articulate. Antenna 2 ( Fig. 4A): flagellum 6 articulate, densely setose. Maxilliped ( Fig. 8G): inner plate with dense plumose setae, outer plate reaching half of palp article 2, densely setose, apical margin with plumose setae, palp article 3 apically setose, 0.7 × palp article 2. Lower lip ( Fig. 8F): inner lobes rounded, setose outer lobes with small gape, marginally setose. Maxilla 1 ( Fig. 8C): outer plate with two rows of serrate setae, palp 2 articulate, article 2 with 8 apical plumose setae. Maxilla 2 ( Fig. 8B): inner and outer plates with dense apical setae, inner plate lined with marginal setae. Mandible ( Fig. 8A, D): incisors dentate, left lacinia mobilis weakly dentate, right lacinia mobilis strongly dentate; molars triturative; palp well developed, 3 articulate, article 1 shorter than article 2, article 3 long (about 3 × as long as broad) subequal in length with article 2, moderately falcate. Upper lip ( Fig. 8E): apically rounded, setose.

Pereon ( Fig. 4A): body smooth, covered with sparse setae. Gnathopod 1 ( Fig. 6A, C): subchelate; coxa anterior margin concave, anteroventral corner slightly produced, subquadrate ventral margin with several long and short setae; basis posterior margin with 7 long medial setae; merus without posterodistal tooth; carpus about 1.5 × as long as broad, shorter than propodus, posterior margin densely setose, propodus palm subacute, straight, smooth, densely setose; dactylus apically subacute, symmetrical. Gnathopod 2 ( Fig. 5E–H): subchelate; basis slender, posterior margin with 3 long medial setae; merus with subquadrate distoventral corner; carpus compressed, lobate, length 1.6 × width; propodus expanded with dense medial brushes of setae, palm convex, medial surface with subrectangular hump near insertion of dactylus bearing three marginal spine-setae, distomedial shelf rounded with dense plumose setae, palm reaching 0.6 × length of propodus, subpalmar surface with dense tufts of long setae; dactylus apically subacute, reaching 0.4 × length of propodus. Pereopod 3 ( Fig. 4A): coxa longer than broad, with four long and several short ventral setae; basis posterior margin with 3 long and several short setae. Pereopod 4 ( Fig. 4B): coxa posterior margin concave, with 2 long and several short ventral setae; basis posterior margin with 2 long and a few short setae; propodus with posterior margin with several robust setae. Pereopod 5 ( Fig. 7D): coxa bilobed, posterior lobe with two short setae; basis expanded, posterior margin rounded, almost smooth, without long setae; merus slightly broadened; merus, carpus, propodus with few long slender setae. Pereopod 6 ( Fig. 6B): coxa bilobed, anterior lobe with two setae, posterior lobe with two short setae; basis expanded, posterior margin convex, serrate, without long setae; merus slightly broadened; merus, carpus, propodus with few long slender setae. Pereopod 7 ( Fig. 7C): coxa ventral margin slightly convex, anterior margin with two plumose setae; basis expanded, posterior margin rounded, crenulate, without long setae; merus slightly broadened; merus, carpus, propodus with many long slender setae.

Pleon ( Fig. 4A): Epimera 1–3 smooth, bare; epimeron 3 ( Fig. 5D): posteroventral margin with notch. Uropod 1 ( Fig. 5C): peduncle 1.4 × length of outer ramus, with several facial setae; inner and outer rami subequal in length, each with several robust marginal setae. Uropod 2 ( Fig. 5B): peduncle 1.2 × length of outer ramus with two robust setae; inner and outer rami subequal in length each with several robust marginal setae. Uropod 3 ( Fig. 5A): inner ramus length 0.8 × outer ramus length, outer ramus subequal in length with peduncle; rami distally truncated, with short apical robust setae; Telson missing.

Description of female (paratype, 4.2 mm). Similar in all aspects to male except for the following. Gnathopod 1 ( Fig. 9A, E): coxa with several short setae; basis with 7 long medial setae; propodus palm tapered, moderately setose; dactylus with three small spines. Gnathopod 2 ( Fig. 9B, D): basis posterior margin lacking long medial setae; propodus not expanded, lacking dense medial brushes of setae, palm convex, without hump, distomedial shelf straight with moderately setose, subpalmar surface lacking plumose setae. Telson ( Fig. 9C): length 0.9 × width, moderately cleft (50%), pointed distally, each lobe with 2 robust setae and 2 slender setae.

Etymology. After the Japanese word ‘mukuinu’, meaning ‘shaggy dog’ and referring to the long, thick, and unkempt, plumose setae on the gnathopod 2 propodus (pronounced moo-koo-ee-noo).

Remarks. Elasmopus mukuinu sp. nov. is similar to all species in the E. pectenicrus group as defined by Hughes & Lowry (2011) in having a short mandibular palp article 3, long bunches of setae on male gnathopod 2 propodus, and at least one crenulate posterior margin on pereopod 5–7 bases. The E. pectenicrus group includes Elasmopus brasiliensis ( Dana, 1853) ; E. canarius Krapp-Schickel & Ruffo, 1990 ; E. carteri Hughes & Lowry ; 2011; E. crenulatus Berents, 1983 ; E. leveque Hughes & Lowry, 2011 ; E. nanshaensis Ren, 1998 ; E. otus Hughes & Lowry, 2011 ; E. pectenicrus ( Bate, 1862) ; E. spinibasus Sivaprakasam, 1970 ; and E. yunde Barnard, 1974 ( Hughes & Lowry 2011). The new species differs from all mentioned species in having dense plumose setae covering the distomedial shelf (no plumose setae mentioned in other descriptions) and pereopod 5–7 posterior margins all serrate or crenulate (some or all casteloserrate in others). Of this group, the new species is most similar to E. nanshaensis in having a subrectangular hump on male gnathopod 2 propodus palm, but differs in having a rounded distomedial shelf (subrectangular in E. nanshaensis ) and in having a concave posterior margin on pereopod 6 basis (tapering in E. nanshaensis ). Elasmopus yunde also shares the subrectangular hump and the rounded distomedial shelf on male gnathopod 2 propodus with the new species but differs in having all posterior margins of pereopods 5–7 casteloserrate and a straight posterior margin on pereopod 6 basis. Elasmopus mukuinu sp. nov. shares the concave pereopod 6 basis posterior margin with E. pectenicrus , but E. pectenicrus differs due to the triangular hump on the palm of gnathopod 2 propodus and casteloserrate pereopod 6 basis posterior margin. In addition, Elasmopus mukuinu sp. nov. is similar to Elasmopus souzafilhoi Senna, 2011 in having long plumose setae on gnathopod 2 propodus palm, but the latter species has a casteloserrate posterior margin on pereopod 7 basis.

Distribution. Japan: Okinawa, (present study).