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).