Simocephalus (Echinocaudus) exspinosus ( De Geer, 1778 )

Sinev, Artem Y., Dadykin, Ivan A., Umi, Wahidah A. D. & Yusoff, Fatimah M., 2025, New data on Cladocera (Crustacea: Branchiopoda) of Peninsular Malaysia, Zootaxa 5604 (3), pp. 255-284 : 257

Simocephalus (Echinocaudus) exspinosus ( De Geer, 1778) s. lato

Figs. 1A–E

De Geer 1778: 457 ( Monoculus ); Flössner 1972: 184–187, Fig. 87; Orlova-Bienkowskaja 2001: 76–78, Figs. 94–99, Pl. 33–34; Hudec 2010: 160–161, Fig. 32J–M; Rogers et al. 2019: 679, Figs. 16.2.18; Korovchinsky et al. 2021b: 163, Figs. 48, 9–10.

Material examined. Numerous parthenogenetic females from a pond in Permai Lake, Ipoh, Perak (4.47728° N, 101.0492° E), 28.01.2018.

This is the first record for Peninsular Malaysia. Studied specimens have typical general morphology ( Fig. 1A ) and morphology of postabdomen ( Fig. 1B ), with the outer side of the postabdominal claw bearing a pecten of spines near the base ( Figs. 1C–D ). Studied specimens have clusters of darkly pigmented hypodermal cells on the valves ( Figs. 1A, E ), but such pigmentation was not recorded in populations from temperate regions. The species was recorded in the Sarawak State, East Malaysia by Spandl (1925). In South-East Asia, it was recorded in Thailand ( Sanoamuang 1998; Maiphae et al. 2008), Vietnam ( Sinev & Korovchinsky 2013, as S. congener (Koch, 1841)) and Indonesia ( Korovchinsky 2013). According to Orlova-Bienkowskaja (2001), S. expinosus has a cosmopolitan distribution, as well as its sibling-species, S. congener . These two taxa differ only in the morphology of the postabdominal claw: S. congener has a pecten of 20–25 thin spines on the outer side instead of 8–12 large spines in S. expinosus . In our materials, we found specimens with intermediate number of spines (15–18), which was also observed in populations from Vietnam ( Sinev & Korovchinsky 2013) and Central China ( Dadykin et al. 2023). Thus, we consider S. congener as possible synonym of S. expinosus , despite this should be tested using molecular methods. For detailed description, see Orlova-Bienkowskaja (2001).

Figures

FIGURE 1. Simocephalus (Echinocaudus) exspinosus (De Geer, 1778) from pond at Permai Lake, Ipoh, Perak, Malaysia, parthenogenetic female. A, lateral view. B, postabdomen, С, postabdominal claw from outer side. D, basal portion of postabdominal claw from outer side. E, group of pigmented hypoderm cells on valves. Simocephalus (Simocephalus) mixtus Sars, 1903 pond at the Permai Lake, Ipoh, Perak, Malaysia, F, lateral view. G, head. H, posteroventral angle of valves. I, postabdomen. J, basal portion of postabdominal claw from outer side.