Eogammarus itotomikoae, Tomikawa & Morino & Toft & Mawatari, 2006

Tomikawa, Ko, Morino, Hiroshi, Toft, Jason & Mawatari, Shunsuke F., 2006, A revision of Eogammarus Birstein, 1933 (Crustacea, Amphipoda, Anisogammaridae), with a description of a new species, Journal of Natural History (J. Nat. Hist.) 40 (17 - 18), pp. 1083-1148 : 1100-1108

Eogammarus itotomikoae sp. nov.

[Japanese name: Ito togeo yokoebi, new]

( Figures 9–13 )

Etymology

The new species is named in honour of Dr Tomiko Ito who has contributed much to the study of this species.

Material examined

Holotype: mature „, 18.9 mm, slide mount, NSMT-Cr 16678, Masuhoro River mouth (45 ° 259590N, 141 ° 519540E), Wakkanai City, Hokkaido, 16 October 2000, collected by M. Nakajima and T. Ito. Paratypes: immature ♀, 14.1 mm, slide mount, NSMT-Cr 16679; „, 19.8 mm, slide mount, NSMT-Cr 16680; „, 18.5 mm, ethanol, NSMT-Cr. 16681; ♀, 15.1 mm, slide mount, NSMT-Cr 16682; collection data same as holotype. Paratype: „, 16.2 mm, slide mount, NSMT-Cr 16683, middle reaches of Masuhoro River (45 ° 209400N, 141 ° 509440E), Wakkanai City, Hokkaido, 6 July 2002, collected by K. Tomikawa. Paratypes: „, 20.4 mm, slide mount, NSMT-Cr 16684; „, 20.0 mm, slide mount, NSMT- Cr 16685; Atsuta River (43 ° 239400N, 141 ° 269210E), Atsuta Village , Atsuta County, Hokkaido, 1 November 2001, collected by T. Ito and M. Nakajima .

Description of male

Holotype, NSMT-Cr 16678.

Head ( Figure 9A ): about as long as deep; eye medium, subreniform. Antenna 1 ( Figure 9B ): peduncular articles 1:2:3 with length ratio of 1.0:0.8:0.3; article 1 with robust seta posterodistally, posterior margin with two pairs and four clusters of setae and a single seta; article 2 posterior margin with five clusters of setae; article 3 posterior margin with pair of setae; accessory flagellum eight-articulate; primary flagellum 22-articulate, each article with two short aesthetascs ( Figure 9C ). Antenna 2 ( Figure 9D ): peduncular article 1 with apical setae; articles 4 and 5 about equal in length; article 4 posterior margin with four clusters of setae and a single seta, article 5 posterior margin with five clusters of setae and a single seta; flagellum 20-articlate, with cup-calceoli ( Figure 9E ).

Pleon: smooth. Coxae: lower and posteroproximal margins of coxae 1–3 ( Figure 10A, D, G ) with short setae, inner face weakly setose; posterodistal corner of coxa 3 with stout seta; lower margin of coxa 4 ( Figure 10H ) with short setae, posterior margin excavated, inner face weakly setose; coxae 5 and 6 ( Figures 10I , 11A ) equilobate, posterior lobe with long, stiff setae; ventral margin of coxa 7 ( Figure 11B ) shallowly concave, posterior margin setose.

Mandible ( Figure 9H, I ): palp article 2 with 21 marginal and 30 submarginal setae; palp article 3 length 0.9× article 2 length, with four clusters of A-setae, cluster of B-setae, and a single B-seta. Maxilla 1 ( Figure 9J ): inner plate with 22 plumose setae medially; palp article 1 with three setae on outer margin, article 2 with six setae on outer margin and seven stout and 11 slender setae apically. Maxilla 2 ( Figure 9K ): inner plate with 22 facial setae. Maxilliped ( Figure 9L–N ): inner plate with three apical and three medial bent, stout setae; outer plate beyond middle of palp article 2; outer distal corner of palp article 2 with cluster of setae.

Gnathopod 1 ( Figure 10A ): basis with setose anterior and posterior margins, with medial setae; anterior margin of propodus with four clusters of setae and a single seta, palmar margin ( Figure 10C ) lined with 13 inner and nine outer robust, striated peg setae; dactylus ( Figure 10B ) with posterior accessory blade longer than nail. Gnathopod 2 ( Figure 10D ): basis with setose anterior and posterior margins, with medial setae; propodus, anterior margin with four clusters of setae, palmar margin ( Figure 10F ) lined with eight inner and seven outer robust, striated peg setae and two inner and two outer stiff pectinate setae; dactylus ( Figure 10E ) with posterior accessory blade longer than nail.

Pereopods 3–4 ( Figure 10G, H ): basis with setose anterior and posterior margins; merus, carpus, and propodus length ratio 1.0:0.9:0.9 for pereopod 3, 1.0:0.9:1.0 for pereopod 4. Pereopod 5 ( Figure 10I ): basis posteroproximally expanded, with setose anteroproximal and posterior margins, stiff setose anterodistal margin, inner face with setae. Pereopod 6 ( Figure 11A ): basis with setose anteroproximal and posterior margins, stiff setose anterodistal margin, inner face with setae, longest posteromarginal seta 0.4× width of ischium. Pereopod 7 ( Figure 11B ): basis posteriorly expanded, with setose anteroproximal and posterior margins, stiff setose anterodistal margin, inner face with numerous setae, longest posteromarginal seta 1.3× width of ischium.

Pleopods ( Figure 11O ): retinacula paired ( Figure 11P ). Epimeron 1 ( Figure 11R ): with setose anteroventral margin, posterior margin with three setae, posterodistal corner with seta. Epimeron 2 ( Figure 11S ): with setose anteroventral margin, ventral submargin with five slender and three spine-like setae, posterior margin with four setae, posterodistal corner with seta. Epimeron 3 ( Figure 11T ): with setose anteroventral margin, ventral margin with three spine-like setae, posterior margin and posterodistal corner each with seta.

Uropod 1 ( Figure 12A ): inner ramus length 0.8×, outer ramus length 0.7× peduncle length; peduncle with robust marginal setae and robust basofacial seta; inner ramus with two robust inner marginal setae; outer ramus with one inner and one outer robust marginal setae. Uropod 2 ( Figure 12B ): inner ramus length 0.9×, outer ramus length 0.7× peduncle length; peduncle with robust marginal setae; inner ramus with two robust inner marginal setae and a slender outer marginal seta; outer ramus with a robust outer marginal seta. Uropod 3 ( Figure 12C ): inner ramus length 0.2× outer ramus length, with lateral plumose setae and stiff lateral setae; outer margin of outer ramus with six clusters of robust setae, a short robust seta, a few simple and plumose setae; inner margin with four clusters of robust setae, a few simple setae and numerous plumose setae; terminal article length 0.1× proximal article length. Telson ( Figure 12D ): length 0.9× width, with robust apical and distolateral setae, slender apical setae, and apical and distolateral penicillate setae; robust apical setae longer than slender setae; cleft 68%.

Description of female (immature)

Paratype, NSMT-Cr 16679.

Antenna 1 ( Figure 13A ): peduncular articles 1:2: 3 in ratio of 1:0.8:0.4; article 1 posterior margin with four pairs and cluster of setae and a single seta; article 2 posterior margin with two pairs and two clusters of setae; article 3 posterior margin with pair of setae; accessory flagellum seven-articulate; primary flagellum 33-articulate, each article with two short aesthetascs. Antenna 2 ( Figure 13B ): peduncular articles 4: 5 in ratio of 1:0.9, posterior margins of articles 4 and 5 each with four clusters of setae; flagellum 15-articulate, with cup-calceoli.

Gnathopod 1 ( Figure 13C ): palmar margin of propodus ( Figure 13E ) with 13 simple robust setae on inner distal part; dactylus ( Figure 13D ) with posterior accessory blade shorter than nail. Gnathopod 2 ( Figure 13F ): palmar margin of propodus ( Figure 13H ) with four simple and four robust pectinate setae on inner distal part, one simple and four robust pectinate setae on outer margin; dactylus ( Figure 13G ) with posterior accessory blade shorter than nail.

Pereopods 5–7 ( Figure 13I–K ): basis more expanded posteriorly than those of male. Pereopod 6 ( Figure 13J ): longest posteromarginal seta of basis 0.3× width of ischium. Pereopod 7 ( Figure 13K ): longest posteromarginal seta of basis 1.1× width of ischium.

Uropod 3 ( Figure 13L ): inner ramus length 0.2× outer ramus length; outer margin of outer ramus with five clusters of robust setae, a few simple and plumose setae; inner margin with four clusters of robust setae, a few simple and numerous plumose setae; terminal article of outer ramus length 0.1× proximal article length.

Variation

The number of clusters of setae on peduncular articles of both antennae 1 and 2 varies from four to six. The number of clusters of robust setae on the outer margin of the ramus of uropod 3 varies from five to six.

Remarks

Eogammarus itotomikoae sp. nov. is distinguished from its congeners by the presence of two aesthetascs on each flagellar article of antenna 1. Eogammarus itotomikoae is distinguishable from E. barbatus , the most similar species by the following characters ( E. barbatus in parentheses): (1) the longest seta on the posterior margin of the basis in male pereopod 6 is shorter than half of the ischium width (longer); (2) robust setae are present on the ventral margins of epimera 2 and 3 (lacking); and (3) the telson is shorter than wide (longer or equal) (see Table I).

Distribution

The new species was found in the Masuhoro and Atsuta Rivers in northern Hokkaido. Habitat

Rivers, river mouths.

Figures

Figure 9. Eogammarus itotomikoae sp. nov., Masuhoro River, Wakkanai, Japan, holotype, male, 18.9 mm, NSMT- Cr. 16678. (A) Habitus (lateral view); (B) antenna 1; (C) flagellar article of antenna 1 (some setae are omitted); (D) antenna 2; (E) flagellar article of antenna 2 (some setae are omitted); (F) upper lip; (G) lower lip; (H) right mandible; (I) incisor and lacinia mobilis of left mandible; (J) maxilla 1 (robust apical setae on outer plate are shown enlarged); (K) maxilla 2; (L) palp of maxilliped; (M) inner plate of maxilliped; (N) outer plate of maxilliped. Scale bars: 0.1 mm unless indicated otherwise.

Figure 10. Eogammarus itotomikoae sp. nov., Masuhoro River, Wakkanai, Japan, holotype, male, 18.9 mm, NSMT-Cr. 16678. (A) Gnathopod 1; (B) dactylus of gnathopod 1; (C) palm of gnathopod 1 (slender setae are omitted); (D) gnathopod 2; (E) dactylus of gnathopod 2; (F) palm of gnathopod 2 (slender setae are omitted); (G) pereopod 3; (H) pereopod 4; (I) coxa–ischium of pereopod 5. Scale bars: 0.1 mm.

Figure 11. Eogammarus itotomikoae sp. nov., Masuhoro River, Wakkanai, Japan, holotype, male, 18.9 mm, NSMT-Cr. 16678. (A, B) Coxa–ischium of pereopods 6 and 7; (C–H) coxal gills of pereopods 2–7; (I–K) dorsal margins of pleonites 1–3; (L–N) dorsal margins of urosomites 1–3; (O) pleopod 1 (plumose setae on rami are omitted); (P) retinacula (coupling spines) of pleopod 1; (Q) clothespin seta; (R–T) epimeral plates 1–3. Scale bars: 0.1 mm unless indicated otherwise.

Figure 12. Eogammarus itotomikoae sp. nov., Masuhoro River, Wakkanai, Japan, holotype, male, 18.9 mm, NSMT-Cr. 16678. (A–C) Uropods 1–3; (D) telson (dorsal view). Scale bars: 0.1 mm.

Figure 13. Eogammarus itotomikoae sp. nov., Masuhoro River, Wakkanai, Japan, paratype, female, 14.1 mm, NSMT-Cr. 16679. (A) Antenna 1; (B) antenna 2; (C) gnathopod 1; (D) dactylus of gnathopod 1; (E) palm of gnathopod 1 (slender setae are omitted); (F) gnathopod 2; (G) dactylus of gnathopod 2; (H) palm of gnathopod 2 (slender setae are omitted); (I–K) coxa–ischium of pereopods 5–7; (L) uropod 3. Scale bars: 0.1 mm.