Leydigia ( Neoleydigia ) cf . striata Birabén , 1939 ( Crustacea : Cladocera : Chydoridae ) from Colombia and its differentiation from L . ( N . ) cf . ipojucae ( Brehm , 1938 )

This paper concerns the chydorid cladoceran Leydigia (Neoleydigia) cf. striata Birabén, 1939 in plankton samples from Ciénaga El Convento, Colombia. The specimen from Colombia bears the diagnostic features of L (N) cf. striata as redescribed by Kotov and Elías-Gutiérrez (2003), Kotov et al. (2004), and Kotov, (2009). However, this particular specimen shows some subtle differences in the morphology of basal spine of claw, spine-like setules on first and second endopod segments of antenna II, and striation on valve. In the Neotropics, L. (N.) cf. striata Birabén, 1939 most closely resembles L. (N.) cf. ipojucae Brehm, 1938 in the structure of thoracic limb II and postabdominal claw, but can be separated from the latter by differences in setules in lateral fascicles on labrum, postpore distance (PP), shape of postabdomen, preanal margin of the postabdomen, and seta 2 of thoracic limb III.


INTRODUCTION
The genus Leydigia Kurz, 1875 (Cladocera: Chydoridae) has a wide distribution, it is present everywhere with the exception of the Pacific Oceanic Islands and Antarctic (Alonso, 1996;Kotov et al., 2013).This genus has been divided in two subgenera: L. Leydigia (Leydigia) Kurz, 1875 and L. Leydigia (Neoleydigia) Kotov, 2009.The subgenus Leydigia (Neoleydigia) contains 12 species worldwide: Leydigia (N.) acanthocercoides (Fischer, 1854) Birabén, 1939, L. (N.) iberica Kotov and Alonso, 2010, L. (N.) korovchinskyi Kotov and Alonso, 2010, and L. (N) lourdesae Kotov and Fuentes-Reinés, 2014.In the Americas, the majority of records of Leydigia come from Argentina, Brazil, Mexico, Venezuela, Perú and a binocular stereoscopic microscope, and studied under a compound optical microscope in a drop of a glycerol-formaldehyde mixture in toto.A single adult and a single juvenile female were dissected under a stereoscopic microscope for the study of appendages and postabdomen.Images were taken using a Kodak Easy Share C140 digital camera attached to a compound Olympus CX22 microscope.The taxonomic identification of the genus and species recorded herein followed Kotov et al. (2003), Kotov andElías-Gutiérrez (2004), andKotov (2009).These specimens were deposited at the Museo de Colecciones Biológicas at the Universidad del Atlántico (UARC), Colombia.For explanation of the system of seta numeration on the thoracic limbs see Smirnov and Kotov (2010).Description.Parthenogenetic female.General.In lateral view, body subovoid, maximum height in posterior half, height/ length = 0.55 in adult (Fig. 1A), and 0.67 in juvenile.Dorsal margin slightly and regularly convex, postero-dorsal angle rounded, although expressed.Postero-ventral angle broadly rounded; ventral margin regularly convex.In both the adult and juvenile specimens, a coarse large striation and dots on valve were not observed.Eye smaller than ocelus.Head shield wide, covered by fine striation (Fig. 1B, arrow), PP = 0.45, lateral head pore at level of central major pore at distance 0.3 IP from midline (Fig. 1B-C).Labral keel triangular-ovoid, posterior and anterior margin with bunch of setules (Fig. 1D-E).Valves large, subovoid, with numerous setae on ventral margin, small setules between them were seen (Fig. 1A, F).
Thoracic limb I: ODL robust and elongated, bearing a single seta (not illustrated), proximal portion of IDL with short setules, distal portion bearing three long setae, endite 1 with 4 setae, endite 2 with robust setae, endite 3 with one small and two long setae (Fig. 2E-F).
Members of genus Leydigia are truly benthic (Kotov, 2006)   According to Kotov (2009), L. cf.striata can be easily differentiated from acanthocercoides-like species by a whole of characteristics such us: 1) the postabdomen of the female is the most narrowest among all species, 2) setules in marginal membrane are minute, 3) setules in lateral fascicles on labral keel are fine, 4) has preanal margin with relatively high hillocks, 5) has distal scraper of limb II with fully setose proximal segment.These five distinctive traits are characteristic for the specimens from Colombia also.
But I do not regard such differences as signs of a separate status of the Colombian populations.According to Kotov (2009) striation on valve and basal spine are good traits for discriminating the two subgenera of Leydiga.Nevertheless, striation on valve is subject of a significant variability, for example, young female of Leydigia cf.striata has no large-scale striation (Kotov and Elías-Gutiérrez, 2004).
The number of Neotropical species recognized by Kotov et al. (2013) was 4 and it remained unchanged until the recent finding of L. lourdesae from Colombia (Kotov and Fuentes-Reinés et al., 2014).The diversity of the genus in the Neotropics could be underestimated and certainly deserves further investigations.
and in the survey, L. (N.) cf.stirata was found among vegetation (Eichhornia crassipes Mart & Solms).In Ciénaga El Convento, floating aquatic vegetation is abundant, represented by patches of Eichhornia crassipes and Nelumbo nucifera (Gaertn.).This small (surface area of 250 Ha) lagoon system is a shallow water body (depth 0.3-0.8m), whose temperature varies over the seasons in the range of 27.5-30 ºC; pH values during sampling measured 8.6 and conductivity measured 2828 μS.cm-1.