Sternomoera moneronensis Labay, 1997

Tomikawa, Ko & Sidorov, Dmitry A., 2014, Redescription of Sternomoera moneronensis (Crustacea: Amphipoda: Gammaridea) from Moneron Island, the Russian Far East, Species Diversity 19 (1), pp. 35-41 : 36-41

Sternomoera moneronensis Labay, 1997 ( Figs 2–5 )

Sternomoera moneronensis Labay, 1997: 754–758 , figs 1–3; Sidorov 2006: 168

Material examined. NSMT-Cr 22189, 3 immature females (9.4–11.0 mm), nameless brook, Moneron Island , Russia, 23 August 2001, collector unknown . X37756 /Cr- 1420- FENU, 1 immature male (11.0 mm), upper part of brook N2, Chuprova Bay , Moneron Island, Russia, 15 July 2004, coll . Bogatov . IBSS-18/1sd, 5 immature males (9.0– 11.0 mm) and 13 immature females (5.0– 8.5 mm), data same as for above immature male ( X37756 /Cr-1420- FENU) . 10 immature males (9.0– 11.5 mm) and 2 immature females (8.5 mm), lower part of brook N2, Chuprova Bay , Moneron Island, Russia, 19 July 2004, coll . Bogatov . Eight males and 1 female (all immature), 2 nameless brooks (46°15.568´N, 141°15.074´E), south part of Moneron Island , Russia, 15 July 2004, coll . Makarchenko . 13 juveniles (3.0– 3.5 mm), middle part of nameless brook (46°15.869´N, 141°14.800´E), Chuprova Bay , Moneron Island, Russia, 15 July 2004, coll . Makarchenko . 15 males and 2 females (all immature), nameless brook near “Paletc” rock (46°15.844´N, 141°14.680´E), Chuprova Bay , Moneron Island, Russia, 16 July 2004, coll . Makarchenko . 13 males and 2 females (all immature), “Vodopadny” brook (46°15.497´N, 141°15.254´E), Moneron Island , Russia, 19 July 2004, coll . Makarchenko .

Description. Immature female (11.0mm), NSMT-Cr 22189. Head ( Fig. 2A ) slightly shorter than pereonites 1 and 2 combined, rostrum short, antennal sinus sharply incised, dorso-ventral length of eyes about 45% of that of head. Dorsal margins of body smooth. Epimeral plates 1–3 ( Fig. 4 F–H) with 1, 5, and 4 robust setae along their respective ventral margins, and 10, 11, and 6 short setae on their respective posterior margins.

Antenna 1 ( Fig. 2B ): peduncular articles 1 to 3 in length ratio of 1.0: 0.7: 0.4; peduncular article 1 with 1 single seta and 2 clusters of setae on posterior margin, peduncular articles 2 and 3 respectively with 2 and 1 clusters of setae on posterior margins; accessory flagellum 1-articulate with 4 apical setae; primary flagellum 35-articulate, calceoli absent. Antenna 2 ( Fig. 2C ): shorter than antenna 1; gland cone of peduncular article 2 reaching distal part of article 3, with 6 apical setae; peduncular article 4 slightly longer than article 5; flagellum more than 25-articulate, calceoli absent.

Upper lip ( Fig. 2D ) with fine setae on rounded ventral margin. Lower lip ( Fig. 2E ) with broad outer lobes, inner lobes absent. Mandibles ( Fig. 2F, G ): both left and right incisors 6-dentate; left lacinia mobilis 5-dentate, right one indistinctly bifid and bearing 5 teeth; each accessory setal row consisting of weakly pectinate setae; palp 3-articulate, article 3 with A-, B-, D-, and E-setae. Maxilla 1 ( Fig. 2H, I ): inner plate with many plumose setae on medial margin, inner surface setulose; outer plate subrectangular, with 11 apical robust, serrate setae; palp 2-articulate, exceeding tip of outer plate, article 1 short, without marginal setae, article 2 with 9 robust and 5 slender apical setae and 2 outer marginal setae. Maxilla 2 ( Fig. 2J ) with row of setae on medial margin of inner plate, oblique setal row of inner plate consisting of plumose setae. Maxilliped ( Fig. 3A ): inner plate with 2 nodular and 1 slender robust setae apically; outer plate with both apical and medial setae, including some robust and some plumose setae; palp 4-articulate, article 2 with marginal and sub-marginal rows of setae, article 3 with setae on inner surface.

Gnathopod 1 ( Fig. 3B ): coxa rectangular; basis with setae on anterior and posterior margins; carpus length 1.6 × width; propodus length 1.8 × width, palmar margin of propodus ( Fig. 3C ) almost straight, palmar corner with 3 medial and 4 lateral robust setae; dactylus curved inward, posterior margin serrate. Gnathopod 2 ( Fig. 3D ): coxa rectangular; basis with setae on anterior and posterior margins; carpus length 1.8 × width; propodus length 1.8 × width, palmar margin of propodus ( Fig. 3E ) almost straight, palmar corner with 4 medial and 4 lateral robust setae; dactylus curved inward, posterior margin serrate. Pereopod 3 ( Fig. 3F ): coxa rectangular; anterior and posterior margins of basis with setae; anterior margin of merus and posterior margins of carpus and propodus with robust setae. Pereopod 4 ( Fig. 3G ) similar to pereopod 3 except coxa subrectangular with shallow posterior concavity. Pereopod 5 ( Fig. 3H ): coxa bilobed, ventral margin of posterior lobe with robust seta; anterior margins of basis to propodus and posterior margins of merus to propodus with robust setae. Pereopod 6 ( Fig. 4A ): coxa bilobed, anterior lobe small, ventral margin of posterior lobe with robust seta; articles longer than those of pereopod 5. Pereopod 7 ( Fig. 4B ): coxa semicircular; articles longer than those of pereopod 6.

Coxal gills present on gnathopod 2 and pereopods 3–7; accessory lobe absent. Sternal gills on pereonites 2–7, arranged as follows ( Fig. 4I ): 1–4–4–4–5–3. Oostegites absent.

Pleopods 1–3 ( Fig. 4C ) each with retinacula ( Fig. 4D ), inner basal margin of inner ramus with bifid plumose setae ( Fig. 4E ). Uropod 1 ( Fig. 4J ): peduncle with 2 lateral and 1 medial robust setae along margins, basofacial seta absent; outer ramus length 0.8 × peduncle, lateral margin with 2 robust setae; inner ramus slightly longer than outer, medial margin with 3 robust setae. Uropod 2 ( Fig. 4K ): peduncle with 2 lateral and 2 medial robust setae along margins; outer ramus length 0.8 × peduncle, lateral margin with 2 robust setae; inner ramus length 1.3 × outer, lateral and medial margins with 1 and 3 robust setae, respectively. Uropod 3 ( Fig. 4L ): peduncle with robust setae distally; outer ramus 1-articulate, inner margin with plumose setae; inner ramus 1-articulate, almost as long as outer, outer and inner margins with plumose setae. Telson ( Fig. 4M ) length 1.2 × width, cleft for 70% of length, each lobe with 4 apical setae.

Immature male (11.0 mm), X37756 /Cr-1420-FENU. Similar to female but differing as follows. Gnathopod 1 ( Fig. 5B ): carpus length 1.4 × width; propodus length 1.7 × width, palmar margin of propodus ( Fig. 5C ) slightly convex, palmar corner with 5 medial and 5 lateral robust setae. Gnathopod 2 ( Fig. 5D ): carpus length 1.6 × width; palmar margin of propodus ( Fig. 5E ) straight, palmar corner with 4 medial and 6 lateral robust setae. Sternite of pereonite 7 bearing 2 genital papillae situated lateral to and behind 3 sternal gills.

Remarks. The original description of S. moneronensis was based on three male specimens ( Labay 1997). The type series of S. moneronensis are deposited in the Far East National University in Vladivostok. Unfortunately the type series are in a very bad condition and could not observe (DAS pers. obs.). Compared with the original description, the present new material differs in the following features (features of the original description in parentheses): (1) antennal sinus sharply incised (shallowly rounded), (2) pereonite 7 with three sternal gills (two), and (3) ventral margin of peduncular article 1 of antenna 1 with three bundles of setae (two).

We suspect that the first two discrepancies are due to misobservation or mis-interpretation of characters. Without removing the antenna 2, the edge of the antennal sinus is hard to observe and the anterior margin of peduncular article 1 of antenna 2 may be mistaken for it. In our specimens retaining antenna 2, the antennal sinus indeed appears similar to the figure in the original description. Similar results were found for the related amphipods Relictomoera relicta (Uéno, 1971) and R. tsushimana (Uéno, 1971) . Uéno (1971a, b) described the heads of these two species with unusual sinusoidal anterolateral margins. However, in connection with a redescription of R. tsushimana now in preparation, one of us (KT) examined their type specimens and found that Uéno’s (1971a, b) original descriptions were erroneously described in a similar manner.

The sternal gills of pereonite 7 are often overlooked because the gills are small ( Sidorov 2010). Although we were not able to confirm the situation in type specimens, we found three sternal gills on pereonite 7 of the newly available specimens. We think that Labay (1997) overlooked one sternal gill of pereonite 7 and erroneously described just two sternal gills in the original description.

The number of setal bundles on the ventral margin of peduncular article 1 of antenna 1 is an important diagnostic character for distinguishing S. japonica and S. rhyaca ( Kuribayashi et al. 1996) . The present material shows three bundles, as in S. rhyaca , although the original description shows two, as in S. japonica . To clarify the diagnostic validity of this character in S. moneronensis , intensive study of its variability is needed.

Since our specimens lacked any development of secondary sex characteristic (calceoli in males and oostegites in females), they were judged to be immature. Gnathopods 1 and 2 of mature males show strong sexual dimorphism in S. japonica and S. rhyaca , but only slight dimorphism in S. yezoensis . Immature females are similar to immature males in many respects in S. moneronensis . Nonetheless, the following differences were found in immature individuals that could be sexed through the presence or absence of genital papillae: gnathopods 1 and 2 with more slender carpi, and palmar corners of gnathopods 1 and 2 with fewer robust setae in females. Labay (1997) described his specimens as male but did not mention the presence or absence of genital papillae in the description of S. moneronensis . Therefore the sex of the type specimens is unclear. The proportions of gnathopods 1 and 2 of original description are similar to these of our immature male. On the other hand, the distal corners of the palmar margins, with two medial and two lateral setae on gnathopod 1, and three medial and three lateral robust setae on gnathopod 2, are similar to these of our immature female, although these robust setae were only roughly illustrated in the original description. Examination of mature males and females is needed to clarify the degree of sexual dimorphism of the gnathopods in S. moneronensis .

Figures

Fig. 2. Sternomoera moneronensis Labay, 1997. Immature female (11.0 mm), NSMT-Cr 22189, Moneron Island, Russia. A, head, lateral view; B, peduncular articles 1–3, primary flagellar articles 1–4, and accessory flagellum of antenna 1, medial view; C, peduncular articles 1–5 and flagellar articles 1–3 of antenna 2, medial view; D, upper lip, anterior view; E, lower lip, ventral view; F, right mandible (molar seta broken), medial view; G, incisor and lacinia mobilis of left mandible, medial view; H, maxilla 1, dorsal view; I, apical part of outer plate of maxilla 1, dorsal view; J, maxilla 2, dorsal view.

Fig. 3. Sternomoera moneronensis Labay, 1997. Immature female (11.0 mm), NSMT-Cr 22189, Moneron Island, Russia. A, maxilliped, dorsal view; B, gnathopod 1, medial view; C, palmar margin of propodus and dactylus of gnathopod 1, medial view; D, gnathopod 2, medial view; E, palmar margin of propodus and dactylus of gnathopod 2, medial view; F–H, pereopods 3–5, respectively, lateral views.

Fig. 4. Sternomoera moneronensis Labay, 1997. Immature females (11.0mm, NSMT-Cr 22189, A–H, J–M; 8.5mm, X37756/Cr- 1420-FENU, I), Moneron Island, Russia. A and B, pereopods 6 and 7, respectively, lateral views; C, peduncle and proximal parts of inner and outer rami of pleopod 1, anterior view; D, retinacula on peduncle of pleopod 1, posterior view; E, bifid plumose seta (clothes-pin seta) on inner basal margin of inner ramus of pleopod 1, anterior view; F–H, epimeral plates 1–3, respectively, lateral views; I, sternal gills of pereonites 2–7; J–L, uropods 1–3, respectively, dorsolateral view of uropod 1 and dorsal views of uropods 2 and 3; M, telson, dorsal view.

Fig. 5. Sternomoera moneronensis Labay, 1997. Immature male (11.0 mm), X37756/Cr-1420-FENU, Moneron Island, Russia. A, peduncular articles 1–5 and flagellar articles 1–2 of antenna 2, medial view; B, gnathopod 1, medial view; C, palmar margin of propodus and dactylus of gnathopod 1, medial view; D, gnathopod 2, medial view; E, palmar margin of propodus and dactylus of gnathopod 2, medial view; F, coxa, basis, and ischium of pereopod 7, lateral view; G–I, uropods 1–3, respectively, dorsal views; J, telson, dorsal view.