Eogammarus tiuschovi Derzhavin, 1927

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 : 1136-1143

Eogammarus tiuschovi Derzhavin, 1927

[Japanese name: Ryûkotsu togeo yokoebi, new]

( Figures 33–36 ) Carinogammarus tiuschovi Derzhavin 1927, p 6 –8, Plate 3. Anisogammarus (Eogammarus) tiuschovi: Schellenberg 1937, p 274 ; Gurjanova 1951, p 778–

780, Figure 543; Kurenkov and Mednikov 1959, p 83, Figure 4 ; Tzvetkova 1972, p 214; Tzvetkova 1975, p 114–118, Figure 43. Eogammarus tiuschovi: Bousfield 1979, p 314 . Material examined

Japan. 3 „, 11.8–13.9 mm, 2♀, 9.3 mm, 10.5 mm, ovigerous, Lake Yudo (42 ° 369360N, 143 ° 329300E), Toyokoro Town , Nakagawa County, Hokkaido, 16 August 2002, collected by K. Tomikawa. 1 „, 9.0 mm, 2♀, 6.9 mm, 8.0 mm, Notsuke Bay (43 ° 359300N, 145 ° 139370E), Nakashibetsu Town, Shibetsu County, Hokkaido, 28 May 2002, collected by K. Wada. 1 „, 9.6 mm, 2♀, 8.4 mm, 8.6 mm, Lake Kuccharo (45 ° 079460N, 142 ° 199150E), Hamatonbetsu Town , Esashi County , Hokkaido, 12 July 2002, collected by K. Wada. Four juveniles, 6.6–7.9 mm, Lake Pashikuru (42 ° 559220N, 144 ° 009020E), Onbetsu Town , Shiranuka County, Hokkaido, 11 June 2002, collected by K. Tomikawa. Russia. One juvenile, 5.2 mm, Lake Busse (46 ° 329390N, 143 ° 229300E), north of Aniva Bay , Sakhalin Island , 19 July 2002, collected by J. Toft. „, 9.8 mm, ♀, 5.2 mm, ovigerous, Chayvo estuary (52 ° 219200N, 143 ° 069590E), east of Chayvo Bay, Sakhalin Island, 28 July 2002, collected by J. Toft. 2 „, 10.6 mm, 11.0 mm, ♀, 8.0 mm, Mereya River (46 ° 379410N, 142 ° 539390E), east of Korsakov, Sakhalin Island , 7 August 2002, collected by J. Toft.

Description of male (13.6 mm from Lake Yudo)

Antenna 1 ( Figure 33B ): peduncular articles 1:2: 3 in ratio of 1.0:0.7:0.4; article 1 with slender posterodistal seta in place of robust seta, posterior margin with four pairs of short setae and four short setae; article 2 posterior margin with three pairs of short setae; article 3 posterior margin bare; accessory flagellum five-articulate; primary flagellum 30-articulate, each article with one short aesthetasc ( Figure 33C ). Antenna 2 ( Figure 33D ): peduncular article 1 with slender setae; articles 4: 5 in ratio of 1.0:0.9, posterior margins of articles 4 and 5 with three clusters of short setae; flagellum 14-articulate, with cup-calceoli ( Figure 33E ).

Pleon ( Figures 33A , 35F–H ): carinate, dorsal margin of pleonites 1–3 ( Figure 35F–H ) with minute setae.

Mandible ( Figure 33H–J ): palp article 2 with four inner and two outer marginal and 19 inner submarginal setae; article 3 length 0.8× article 2 length, with two clusters of A-setae and two A-setae. Maxilla 1 ( Figure 33K ): inner plate with 14 plumose setae medially; palp article 1 with two setae on outer margin; article 2 with five setae on outer margin, seven stout and eight slender setae apically. Maxilla 2 ( Figure 33L ): inner plate with 13 facial setae. Maxilliped ( Figure 33M ): 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 slender and robust setae.

Gnathopod 1 ( Figure 34A ): anterior margin of propodus with two clusters of setae; palmar margin ( Figure 34B ) lined with one robust outer simple seta, 11 inner and three outer robust, striated peg setae. Gnathopod 2 ( Figure 34C ): anterior margin of propodus with cluster of setae, palmar margin ( Figure 34D ) lined with seven inner and six outer robust, striated peg setae and three stiff outer pectinate setae.

Pereopod 3 ( Figure 34E ): merus, carpus, and propodus in ratio of 1.0:0.6:0.9. Pereopod 4 ( Figure 34F ): merus, carpus, and propodus in ratio of 1.0:0.9:1.2. Pereopod 6 ( Figure 34H ): posterior margin of basis with short setae. Pereopod 7 ( Figure 34I ): posterior margin of basis with short stiff setae, longest seta 0.6× width of ischium, posterodistal part with robust seta.

Epimera 1–3 ( Figure 35I–K ): with setose anterior margins. Epimeron 1 ( Figure 35I ): with setose ventral margin, posterior margin with 10 setae. Epimeron 2 ( Figure 35J ): ventral margin with seven robust and one short setae, submargin with two robust setae, posterior margin with six setae. Epimeron 3 ( Figure 35K ): ventral margin with seven robust and two tiny setae, posterior margin with three setae.

Uropod 1 ( Figure 35C ): inner and outer ramus length 0.8× peduncle length, latter with robust marginal setae and short seta; inner ramus with three inner marginal robust setae; outer ramus with one outer and two inner marginal robust setae. Uropod 2 ( Figure 35D ): inner ramus length 1.0×, outer ramus length 0.8× peduncle length, latter with robust marginal setae; inner ramus with two robust inner marginal setae; outer ramus with robust outer marginal seta. Uropod 3 ( Figure 35E ): inner ramus length 0.3× outer ramus length; outer margin of outer ramus with three clusters of robust setae and a single robust seta and a few simple and plumose setae, inner margin with two clusters of robust setae and few simple and numerous plumose setae; terminal article of outer ramus length 0.2× proximal article length. Telson ( Figure 35O ): length 1.1× width; apical robust setae longer than apical slender setae; cleft 71%.

Description of female (10.5 mm from Lake Yudo)

Antenna 1 ( Figure 36A ): peduncular articles 1:2: 3 in ratio of 1.0:0.7:0.3, article 1 posterior margin with three pairs of short setae and three short setae, article 2 posterior margin with two pairs of setae and one seta, article 3 posterior margin with cluster of setae; accessory flagellum five-articulate; primary flagellum 29-articulate, each article with one aesthetasc. Antenna 2 ( Figure 36B ): peduncular articles 4 and 5 about equal in length, posterior margin of both articles with two clusters of setae, respectively; flagellum 12-articulate, lacking cupcalceoli.

Gnathopod 1 ( Figure 36C ): palmar margin of propodus ( Figure 36D ) with nine robust simple setae on inner part. Gnathopod 2 ( Figure 36E ): palmar margin of propodus ( Figure 36F ) with six robust simple setae on inner margin and six stiff pectinate setae on outer distal part.

Pereopod 6 ( Figure 36I ): posterior margin of basis with short setae. Pereopod 7 ( Figure 36J ): posterodistal margin of basis with stiff setae, longest seta 0.6× width of ischium.

Uropod 3 ( Figure 36K ): inner ramus length 0.3× outer ramus length; outer margin of outer ramus with three clusters of robust setae and a few simple and plumose setae, inner margin with cluster of robust setae and a few simple setae and 10 plumose setae; terminal article of outer ramus length 0.2× proximal article length.

Variation

The number of clusters of setae on peduncular articles of both antennae 1 and 2 varies from two to four.

Remarks

Eogammarus tiuschovi is readily distinguishable from its congeners by the presence of dorsally carinate pleonites. Eogammarus tiuschovi is similar to E. possjeticus , but is distinguished from the latter by the four characters mentioned in the remarks of E. possjeticus (see Table I). Eogammarus tiuschovi is also similar to E. kygi , but is distinguished from the latter by the following features ( E. kygi in parentheses): (1) on antenna 1, a slender seta is present posterodistally on peduncular article 1 (robust seta); (2) on antenna 2, the calceolus is about 0.25× as wide as the article (greater than 0.25× as wide); (3) calceoli are absent on female antenna 2 (present); (4) on male pereopod 6, the longest seta on the posterior margin of the basis is shorter than half the ischium width (longer); (5) on the telson, the robust apical setae are longer than the slender apical setae (shorter); and (6) the telson is longer than wide (shorter) (see Table I).

Distribution

Sea of Okhotsku coast of Russia, Primorskiy (Sea of Japan coast of Russia), Kamchatka, Kuril Islands, Sakhalin, Hokkaido.

Habitat

Brackish lakes, estuaries.

Figures

Figure 4. Eogammarus kygi (Derzhavin, 1923), Naibetsu River, Chitose, Japan, female, 12.5 mm. (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) brood plate of gnathopod 2; (M) uropod 3. Scale bars: 0.1 mm.

Figure 33. Eogammarus tiuschovi (Derzhavin, 1927), Lake Yudo, Toyokoro, Japan, male, 13.6 mm. (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) palp of right mandible; (J) incisor and lacinia mobilis of left mandible; (K) maxilla 1 (robust apical setae on outer plate are shown enlarged); (L) maxilla 2; (M) maxilliped. Scale bars: 0.1 mm unless indicated otherwise.

Figure 34. Eogammarus tiuschovi (Derzhavin, 1927), Lake Yudo, Toyokoro, Japan, male, 13.6 mm. (A) Gnathopod 1; (B) dactylus and palm of gnathopod 1 (slender setae on palm are omitted); (C) gnathopod 2; (D) dactylus and palm of gnathopod 2 (slender setae on palm are omitted); (E, F) pereopods 3 and 4; (G–I) coxa– ischium of pereopods 5–7. Scale bars: 0.1 mm.

Figure 35. Eogammarus tiuschovi (Derzhavin, 1927), Lake Yudo, Toyokoro, Japan, male, 13.6 mm. (A) Pleopod 1 (some plumose setae on rami are omitted); (B) retinacula of pleopod 1; (C–E) uropods 1–3; (F–H) dorsal margins of pleonites; (I–K) epimeral plates 1–3; (L–N) dorsal margins of urosomites 1–3; (O) telson (dorsal view). Scale bars: 0.1 mm.

Figure 36. Eogammarus tiuschovi (Derzhavin, 1927), Lake Yudo, Toyokoro, Japan, male, 10.5 mm. (A) Antenna 1; (B) antenna 2; (C) gnathopod 1; (D) dactylus and palm of gnathopod 1 (slender setae on palm are omitted); (E) gnathopod 2; (F) dactylus and palm of gnathopod 2 (slender setae on palm are omitted); (G) brood plate of gnathopod 2; (H–J) coxa–ischium of pereopods 5–7; (K) uropod 3. Scale bars: 0.1 mm.