Daphnia hyalina, LEYDIG, 1860

DAPHNIA CF. HYALINA LEYDIG, 1860 View in CoL

( FIGS 6 View Figure 6 , 7 View Figure 7 , TABLE 3)

Diagnosis

Adult male: Dorsal margin almost straight, not elevated above head ( Fig. 6H View Figure 6 ). Posterior head margin straight, with a low step-like prominence in proximal half of margin ( Fig. 6I View Figure 6 ). Postero-ventral head angle rounded. Ventral margin of head slightly convex; anterior-most extremity not occupied with optic vesicle. Eye is relatively small. Labrum with a very large distal labral plate. Valve with antero-ventral portion having numerous setae submarginally on inner face of valve ( Fig. 6J View Figure 6 ). Postero-ventral portion of valve with small marginal denticles ( Fig. 6K, L View Figure 6 ). Small mounds on first and third segment, and larger mound on second segment ( Fig. 7A, B View Figure 7 ). Postabdomen with long and remarkably concave pre-anal margin, its distal portion with paired teeth strongly increasing in size distally ( Fig. 7C, D View Figure 7 ); gonopore opens laterally, without a genital papilla ( Fig. 7A View Figure 7 ). On outer surface of postabdominal claws, pectens consist of setules only ( Fig. 7E View Figure 7 ). Antenna I with a small antennular seta located at a small distance from distal end of antenna I body; male seta (flagellum) distally on antenna body without a post-aesthetasc process, this seta somewhat longer than longest aesthetasc ( Fig. 6M View Figure 6 ). Limb I with ODL smallest seta relatively long, largest seta as in other species ( Fig. 7F, G View Figure 7 ); IDL with a relatively short copulatory hook with bent tip ( Fig. 7F, G View Figure 7 ) and two setae of different size; endite 3 with setae 2 and 2′ equally long, setae 3 and 4 as in other taxa. Limb II with anterior seta 1 armed by few short, robust spinules ( Fig. 7H View Figure 7 ). Limb V exopod with setae 2 and 1 subequal in size ( Fig. 7I View Figure 7 ). Size 0.8–1.1 mm.

Type locality

Schliersee ( Germany) and Bodensee (bordered by Germany, Austria and Switzerland).

Type material

Lost.

Material examined here

Many parthenogenetic, ephippial females and males from Sckamützelsee, Brandenburg, Germany, collected on 10 November 2004 by M. A. Belyaeva, AAK M-0468 .

Comments

The examined population contained the females that could be identified as D. cf. hyalina based on morphological traits ( Fig. 6A–G View Figure 6 ). Petrusek et al. (2008) concluded that such morphotypes appeared several times in the evolution of D. longispina sensu stricto, and in D. hyalina and D. rosea , which are junior synonyms of D. longispina sensu stricto. This conclusion was based on the genetic analyses of specimens from type localities of D. longispina (from the region O. F. Müller’s work) and D. hyalina from Lake Constance (including subfossil dormant egg bank from pre-industrial age sediments, to get as close as possible to the material that was the basis of Leydig’s 1860 description). In a subsequent paper ( Thielsch et al., 2009), 13 polymorphic microsatellite loci for populations representing various phenotypes of D. longispina were analysed, and no evidence that hyalina -like pelagic forms show divergence from other phenotypes was found.

Giessler, Mader & Schwenk (1999) first concluded that ‘there are marked morphological differences between typical hyalina and rosea morphotypes’, but Petrusek et al. (2008) reported ‘gradual changes towards hyalina - or rosea -like morphology’ and the presence of intermediate forms. In reality, such differences concern the external shape of the females, which is extremely variable in the D. longispina complex and cannot be regarded as a source of diagnostic features. Fine details, such as limb morphology or male-specific characters, need to be re-examined for an adequate conclusion ( Kotov, 2015). Hyalina -like forms have geographical clades within the D. longispina complex ( Ishida & Taylor, 2007a), which can also have the same diagnostic morphological traits (but not in the female general shape). In general, there are distinct geographical mitochondrial clades within D. longispina sensu Petrusek et al. (2008) (see also Ventura et al., 2014). However, tests of species boundaries between D. longispina sensu stricto and hyalina- like morphotypes with microsatellite markers failed to find evidence of barriers to gene flow ( Thielsch et al., 2009).