Ganigamoera, Sidorov, Dmitry A., 2010

Sidorov, Dmitry A., 2010, A new subgenus of eusirid amphipod (Crustacea: Amphipoda: Eusiridae) from subterranean waters and springs of the Eastern Sikhote-Alin Mountain Ridge, with comments on the morphology of sternal humps, genital papillae and pleopods, Zootaxa 2518, pp. 1-31 : 24-25

Remarks on Ganigamoera subgen. nov. morphology

Certain aspects of the morphology of Ganigamoera subgen. nov. are not normally attributed to the genus Paramoera . For example, sternal humps (blisters) have never before been observed for members of the genus. The sternal humps represent a soft evagination on the ventral margins of pereonites 2–7 and appear similar to the sternal tenuitegillate margins permeable for dissolved oxygen as described by Hrabĕ (1948) for Synurella ambulans . The humps were confirmed for several taxa of stygobiont amphipods such as Sternophysingidae , Pseudocrangonyctidae and the hubbsi group of Stygobromus ( Holsinger, 1974, 1992; Tomikawa et al. 2008). The sister genus of Paramoera , Sternomoera , is very morphologically similar and only differs from Paramoera by possessing sternal gills (sternobranchiate processes). Sternomoera dwells exclusively in fast moving freshwater streams and currently includes four species. Three of them ( S. japonica (Tattersall, 1922) , S. yezoensis ( Ueno, 1933) , S. rhyaca Kuribayashi, Mawatari & Ishimaru, 1996 ) are known from the Japanese archipelago and S. moneronensis Labay, 1997 is known from Moneron island ( Kuribayashi et al. 1996; Labay 1997). As revealed by Kikuchi et al. (1993) and exemplified by S. yezoensis , the sterna with sternal gills functions as a transporting as well as respiratory organs ( Kikuchi & Matsumasa 1997). It is possible that the humps (pulvinate sternal epithelium) are a “stygobiont modification” to help the new species inhabit subterranean and spring (seeps) biotopes instead of the fast-moving epigean streams where Sternomoera dwells.

The other interesting feature is the presence of blunt processes ( Figs 27, 28 , 32 , 68, 69 , 73 ) located on the inner face of the first articles of outer rami of pleopods 1–3 for both sexes. Similar features were indicated by M. Ueno (1971, 1971b) for R. relicta and A. kawasawai , and by Jaume & Christenson (2001) for Metacrangonyx dominicanus Jaume & Christenson, 2001 . The only species of Sternomoera as well as majority species of Paramoera have sexually dimorphic outer rami of pleopod 2. The analogous transformation (terminal setae very short and surrounded by strong longer setae) was also seen for pleopod 2 of P. (G.) myslenkovi sp. nov. ( Fig. 32 ) males and was especially developed ( Fig. 73 ) in P. (G.) tiunovi sp. nov. This shape more resembles P. koysama than the two other described forms (see Kuribayashi et al. 1994; Kuribayashi & Kyono 1995).

Finding genital papillae ( Fig. 75 ) on the ventral surface of pereonite 7 for both new species raises the possibility that structures like this exist for other species in the Paramoera-Sternomoera complex. Moreover, the presence of genital papillae is also reported for S. rhyaca in the paper about the catadromous migration of this species ( Kuribayashi et al. 2006, p. 765). The genital papilla is very similar to the sternal gill, but it differs from it by exhibiting vas deferens and a minute aperture on the tip. The genital papillae are accompanied by a small sensory seta at their base. Males with spermatophores emerging from apertures were sometimes seen in our samples. After investigating the samples of S. moneronensis at my disposal, I have concluded that confusion exists when identifying these characteristics. In S. moneronensis males, the genital papillae on pereonite 7 were erroneously identified as a pair of lateral sternal gills. It is obvious that the previously described species require a requalification of the sternal gill character arrangement.

Figures

FIGURES 23 – 29. Paramoera (G.) myslenkovi sp. nov., female, holotype: (23) uropod 1; (24) uropod 2; (25) uropod 3; (26) telson; (27) pleopod 2; (28) first articles of pleopod 2 rami; (29) epimera 1 – 3. Scale bars 0.2 mm.

FIGURES 32 – 33. Paramoera (G.) myslenkovi sp. nov., male, paratype (5.0 mm): (32) pleopod 2; (33) telson. Scale bars 0.2 mm.

FIGURES 65 – 69. Paramoera (G.) tiunovi sp. nov., female, holotype: (68) pleopod 2; (69) first articles of pleopod 2 rami. Female, paratype (7.2 mm): (65) head; (66) rostral point; (67) urosome. Scale bars 0.2 mm.

FIGURES 72 – 75. Paramoera (G.) tiunovi sp. nov., male, paratype (6.0 mm): (72) antenna 2; (73) pleopod 2; (74) telson; (75) ventral surface of pereonite 7. Scale bars 0.2 mm. Abbreviations: g. p., genital papillae; s. s., sensory seta; cox., coxa of pereopod 7; c. g., coxal gill; pr 7, basis of pereopod 7.