Sinodiaptomus sarsi ( Rylov, 1923 )

Sinodiaptomus sarsi ( Rylov, 1923) View in CoL

( Figs 1–3)

Material examined. Russia, Chuvash Republic , Atrat Settlm. environs, quarry pond, 54°58′08″N, 046°40′50″E, 24 May 2018, coll. A. Aleksandrov GoogleMaps , May– October 2019, coll. E. Osmelkin, 14 males, 10 females; same locality, ravine pond, 55°01′18″N, 046°47′31″E, 24 May 2018, coll. A. Aleksandrov, 3 males GoogleMaps .

Description. Female. Body ( Fig. 1a) length 2.20–2.35 mm (n = 5) in specimens collected on 24 May 2018, and 19.00–19.50 (n=3) mm in specimens collected on 3 July 2019. Middorsal projection on pediger 5 ( Fig. 2a) acute, triangular and directed posteriorly. Genital compound somite relatively asymmetrical, with weak dilation on left lateral surface ( Fig. 2a). Caudal ramus 1.5 times as long as wide. Antennule extending almost to tip of apical caudal setae ( Fig. 1a). Rostrum with two long curved processes ( Fig. 1b). Cutting margin of mandible with plumose bristle and one ventral tooth ( Fig. 1c). Ventral tooth separated from other teeth by deep diastema ( Fig. 1c′). Central teeth rounded, bicuspidate, with wide base ( Fig. 1c). Dorsal teeth unimucronate, acute, with narrow base bearing one spinule. Maxilla ( Fig. 1d) and maxilliped ( Fig. 1e) with long plumose setae raising capacity for filtration. In leg 5, coxa with distolateral projection nearly as large as endopod ( Fig. 2b); exopod segment 1 square; exopod segment 2 with spine located close to base of segment 3 ( Fig. 2b) and with terminal claw bearing a row of spinules in middle part of lateral and medial margins ( Fig. 2c–d); exopod segment 3 with two apical spines, from which longer spine with spinules ( Fig. 2c–d); endopod two-segmented, with terminal setulae (8–15) and one apical and one subapical spines ( Fig. 2e–f).

Male. Body ( Fig. 1b) length 2.10–2.25 mm (n=8) in specimens collected on 24 May, and 17.50–17.70 mm (n=4) in specimens collected on 3 July. Caudal ramus 1.8 times as long as wide. Left antennule extending to middle of caudal ramus. Right antennule with spiniform projections at segments 10, 11 and 13–16; segment 15 ( Fig. 3a–b) with longer projection than that of segment 14; antepenultimate segment with comb-like process ( Fig. 3c). In right leg 5 ( Fig. 3d), basis with small plate-shaped hyaline process in distal part of medial margin and with wide-based triangular distal process ( Fig. 3e–f, arrowed), apical end of which almost reaching exopod segment 2; exopod segment 2 about 1.4 times as long as wide, with lateral spine inserted at distal one-thirds of lateral margin (spine as long as one-thirds of segment width), and without sclerotised process between spine and distal end in population from the quarry pond (males from the ravine pond with such process); endopod one-segmented. In left

V.N. Podshivalina & N.G. Sheveleva. First record of Sinodiaptomus sarsi leg 5 ( Fig. 3d), basis with small lateral spine and small medial process near distal margin ( Fig. 3g, arrowed); exopod two-segmented, with setulae in middle of segment 1 and in proximal part of segment 2, and with setae in proximal part of segment 2 ( Fig. 3h–i); proximal part of exopod segment 1 wider than its distal part; exopod segment 2 with long spine being slightly curved subapically and transverse terminally, with tiny hairs on anterior surface, with setae at extreme apex ( Fig. 3j), and with overlapping membranous folds in amount of six to nine on distomedial surface ( Fig. 3h–i); endopod two-segmented, apically with setulae locat- ed in semicircle ( Fig. 3 g –h).

Distribution. Rylov (1923) described Sinodiaptomus sarsi based on the material from the vicinity of Harbin, and recorded it from other parts of China, from Khabarovsk Territory and Mongolia. In China and Mongolia, this species was also found by Kiefer (1928), Shen (1956), and Borutzky (1959). Later, it was recorded from Bering Island ( Novichkova & Chertoprud, 2015), Vietnam ( Hai et al., 2008), the Korean Peninsula ( Chang & Kim, 1986; Chang, 2014), Indonesia ( Sari et al., 2014), Philippines ( Lagbas et al., 2017) and Transbaikalia ( Afonina, 2018). A wide disjunction separates the eastern populations of S. sarsi from a group of populations in Kazakhstan ( Krupa et al., 2016), Iran ( Löffler, 1961; Smagowicz, 1976), Azerbaijan ( Weisig, 1931; Ali-Zade, 1939; Kasymov et al., 1972), Eastern Anatolia ( Gündüz, 1998), Ciscaucasia ( Rylov, 1923), and the Carpathian Mountains in Ukraine ( Mykitchak 2016) ( Fig. 4). It is doubtful that this disjunction is natural; most likely it is the result of unevenness in the study of different territories within the continuous range of the species. Also, the western group of populations may be a separate species and deserves additional research with a genetic analysis ( Li et al., 2014). When considering the distribution of Diaptomidae in the Western Palearctic, Marrone et al. (2017) concluded that there was no reliable data on the identity of the Sinodiaptomus species occurring in Turkey and Ukraine, and had opted for its exclusion from the analysis. There may be some reasons for finding a new species outside of East and Central Asia, but according to the morphological characters described above and literature data, it can be concluded that the studied population from the Sura River basin is mostly similar to those from the eastern part of S. sarsi range (in China and Japan).

Bionomics. The population from the Sura Riv- er basin inhabits shallow water bodies ( Fig. 5,) as well as populations from Manchuria ( Rylov, 1923) and Japan ( Ueda & Ohtsuka, 1998). These crustaceans prefer warm waters with pH close to neutral and with low salinity ( Table 1). The quarry pond is totally overgrown with macrophytes, and its surface changes substantially during the summer.

Population features. Individuals of S. sarsi appeared from late May to August, at water temperatures of 19–23°C. In early May (water temperature was about 10°C) they were not found. The population consisted of adult and juvenile specimens. Ovigerous females occurred from May to August. Males prevailed over females in May (50 and 36% of the total abundance, respectively) and August–October (31–100 and 11–33% of the total abundance, respectively) ( Fig. 6). Juvenile specimens were abundant in August (57% of the total abundance). The highest population density was observed in August ( Fig. 6). The largest specimens occurred in May, similarly to the population from Japan ( Ueda & Ohtsuka, 1998), and in October.

Ovigerous females were observed during the main part (May–July) of the vegetation period, and in the population from Manchuria ( Rylov, 1923), they occurred in late July only. The population abundance dynamics was similar to that in the cooler pond of the Kharanorskaya hydroelectric power station in Transbaikalia ( Afonina, 2018).

The most abundant zooplankton species found together with S. sarsi were Mesocyclops leuckarti (Claus, 1857) , Chydorus sphaericus (O.F. Müller, 1776) , Diaphanosoma mongolianum Ueno, 1938 (in summer), Polyphemus pediculus (Linnaeus, 1761) , and Euchlanis dilatata Ehrenberg, 1832 . Frequently encountered zooplankton species are acidophilic rotifers of the genus Lecane Nitzsch, 1827 : L. ungulata (Gosse, 1887) , L. bulla (Gosse, 1851) , L. luna (Müller, 1776) , L. ligona (Dunlop, 1901) , and L. crenata (Harring, 1913) . The quarry pond is inhabited by the crucian carp Carassius carassius (Linnaeus, 1758) .