Eudiaptomus transylvanicus (Daday, 1891)

Podshivalina, V. N., Sheveleva, N. G., Semenova, A. S. & Mirabdullayev, I. M., 2022, Eudiaptomus transylvanicus and E. vulgaris (Copepoda: Calanoida: Diaptomidae): comparative morphology, distribution and ecology, Zoosystematica Rossica 31 (1), pp. 42-54 : 47-51

Comparison of Eudiaptomus transylvanicus and E. vulgaris

Diagnostic characters. Eudiaptomus transylvanicus was described by Daday (1891), with the main diagnostic features in male right leg 5. Eudiaptomus vulgaris , described by Schmeil (1898), was distinguished from the related diaptomids by the claw on exopod segment 2 of male right leg 5 and by the length of the antennule. In the review of the genus Eudiaptomus, Kiefer (1968) compared the morphological features for all relative species of Eudiaptomus and defined the differences between the species, in the antennule and appendages of leg 5 in males and females.

According to our data, Eudiaptomus transylvanicus and E. vulgaris differ from each other in the features given in Table 2 .

The females of E. transylvanicus examined in our study differ from those of E. vulgaris , E. gracilis , E. siewerthi , E. arnoldi and E. drieschi in having the endopod of leg 5 longer (vs. shorter) than exopod 1 ( Borutzky et al., 1991; Błędzki & Rybak, 2016). The endopod of leg 5 in females of E. graciloides , E. intermedius and E. padanus is equal to or slightly (less than 10% of endopod length) longer than exopod 1, whereas in E. transylvanicus and E. zachariasi it is noticeably (ca. 15% and 20−30% of its length, respectively) longer than exopod 1 ( Borutzky et al., 1991; Błędzki & Rybak, 2016).

The females of E. vulgaris examined in our study differ from those with short endopod of leg 5 ( E. gracilis , E. siewerthi and E. arnoldi ) in having long (ca. 40−50% of endopod length) apical setae on the endopod, and from those of E. drieschi in having short antennule (reaching the tip of the last thoracic segment, vs. long, reaching the tip of caudal ramus) ( Borutzky et al., 1991).

The males of E. transylvanicus examined in our study differ from those of E. intermedius , E. siewerthi and E. padanus in having three processes on the basis of right leg 5 (two well-visible and a small one between them, vs. two in E. intermedius and one in E. siewerthi and E. padanus ) and granulate surface (missing in other species of Eudiaptomus ) near distal process on the basis of right leg 5 ( Kiefer, 1978; Borutzky et al., 1991). The examined males of E. transylvanicus differ from those of E. graciloides and E. arnoldi in the relatively short (about 1.7 times as long as wide vs. twice as long as wide) exopod segment 2 of right leg 5 and from those of E. gracilis and E. zachariasi in having a spine inserted in distal part (instead of the middle) of the lateral margin of this segment ( Borutzky et al., 1991).

The examined males of E. vulgaris have a large hook-shaped lateral process on the basis of left leg 5, as distinct from E. drieschi , in which it is absent, and a large, rounded, well-sclerotised distolateral projection on the coxa of right leg 5, as distinct from E. gracilis , E. graciloides , E. zachariasi , E. arnoldi , E. siewerthi , E. intermedius and E. padanus ( Borutzky et al., 1991) .

Distribution. Eudiaptomus vulgaris is widely distributed in the European ( Borutzky et al., 1991; Błędzki & Rybak, 2016) and Asian ( Borutzky et al., 1991) parts of the Palaearctic and has a continuous range. It is distributed from Spain ( Miracle, 1982) in the west to the Far East of Russia ( Smirnov, 1929), but was not recorded from Slovenia, Bosnia, Lithuania, Moldavia and Scandinavia ( Błędzki & Rybak, 2016). Eudiaptomus transylvanicus is known from most parts of the West Palaearctic: from Bulgaria ( Naidenow, 1994), Romania (temporary waterbodies; Demeter & Marrone, 2009), Slovenia (Lake Bled; Simčič & Brancelj, 2001), Croatia (Lake Vrana; Sket, 1988), Slovakia (Cierny Vah River; Kokavec et al., 2017), Ukraine (temporary and perennial waters with varying salinity; Samchyshyna, 2008), Belarus (ponds and temporary and fishery waterbodies; Solov’yov, 1927), European Russia ( Spanovskaya & Grigorash, 1962; Evdokimov & Ermokhin, 2009; Krylov & Zhgareva, 2016; Kurbatova et al., 2018), Kazakhstan ( Krupa et al., 2012) and from the West Siberian Plain in Asian Russia: the Ob’ River ( Semyonova & Aleksyuk, 2010), its tributary Chulym ( Kukharskaya & Dolgin, 2011), the Vilyuy River ( Ogay & Sokolova, 1972), and the Irtysh River basin ( Klebanovsky, 1986). Thus, the species is rather widespread, but only few records are available from each area.

Bionomics. In the Middle Volga region, we found the populations of E. transylvanicus in shallow perennial water bodies of natural or artificial origin (see Electronic supplementary material), similar to other European populations of this species ( Błędzki & Rybak, 2016). The water bodies inhabited by E. transylvanicus are partially overgrown by macrophytes, and their surface area and depth varies substantially (about 0.8−1.0 m) during the ice-free period due to natural reasons (surface water feeding and high evaporation). According to our data, E. vulgaris in the Middle Volga region occurs in shallow water bodies of various origin, both perennial and temporary, which are similar to those of E. transylvanicus .

Both species prefer warm waters with pH values close to neutral or slightly varying. They appear as a part of the spring plankton at water temperature more than 10 ºC ( Table 1 ). Eudiaptomus transylvanicus occurs in waters with low salinity, while E. vulgaris occurs in both fresh and brackish waters ( Table 1 ).

According to our data, the species occurrence in the potential habitats (shallow permanent and temporary water bodies, pools, ponds, bogs and dystrophic water bodies, according to Błędzki & Rybak, 2016) of the Middle Volga region is about 0.05 (5%) for E. transylvanicus and 0.10 (10%) for E. vulgaris . Thus, E. transylvanicus is relatively rare in the study region, while E. vulgaris is more common but its occurrence is still low. According to our data, the two species do not coexist in the study region, i.e. they were not found in the same water bodies. We could not find published records of both E. transylvanicus and E. vulgaris from the same bodies of water, suggesting that they do not coexist in other regions either.