Sididae Baird, 1850

Guo, Fei-Fei & Dumont, Henri J., 2014, Relict populations of Diaphanosoma (Cladocera: Ctenopoda) in the Chadian Sahara, with the description of a new species, Zootaxa 3856 (1), pp. 135-142 : 136-138

Family Sididae Baird, 1850

Genus Diaphanosoma Fischer, 1850 Diaphanosoma excisum Sars, 1885 ( Fig 3 )

Material examined. Rather abundant in the plankton of guelta Io at Totous, 19° 26’ 38” N, 17° 31’ 51” E, 15 March 2014. No males seen.

Short description. Total length of adult females 0.81 ± 0.07 mm (SD) (n= 10), qualifying them as rather small-sized. Diagnostic characters as in Figure 3 . The habitus is somewhat striking by the rather uncharacteristic big eye ( Fig. 3 A), although this is not exceptional for the species. The ventral rim of the valves is deeply infolded ( Fig. 3 B), and is posteriorly continued in a small series of irregularly spaced and sized marginal spines ( Fig. 3 C–D). The dorsal spines are single or double ( Fig. 3 C–D, G). The swimming antenna sometimes lacks a spine at the top of the basipodite; the four spines on the top of the segments of the exopodite and endopodite are rather robust ( Fig. 3 F). Postabdomen ( Fig. 3 G) as typical for most species of the genus, adorned by fields and lines of spinules. Sixth trunk limb (P6): exopodite with six setae; of the three apical most ones, the middle one is the longest; endopodite lined by four plumose setae between its apex and a hard chitin hillock (arrowed) that separates them from the two basal setae and the gnathobase ( Fig. 3 H). This chitin hillock has turned out to be constant in shape and position throughout Diaphanosoma : we found it in 35 of the ca 40 described species that we could examine. However, this is not necessarily true of other genera. In Sida , for example, it is transformed into a spiny seta (for figures, see Alonso, 1996).

Figures

FIGURE 3. Diaphanosoma excisum female from Totous. A, Habitus. B, Infolded rim of ventral valve opening. C – D, Adornment of ventral and posterior valve margins. E, Swimming antenna. F, Postabdomen. G, Postero-dorsal spines of valves. H, Sixth trunk limb (P 6).