Alona isabellae Sousa, Elmoor-Loureiro and Santos, 2016

Alona isabellae Sousa, Elmoor-Loureiro and Santos, 2016

Synonymy. See Sousa et al. (2016): 23.

Material examined. 2 adult females, UARC316 M–

UARC 320M.

Remarks. Alona isabellae was originally described by Sousa et al. (2016) based on specimens previously identi ed as Alona intermedia Sars, 1862 in Brazil (see Sousa et al., 2016). Its body is oval ( Fig. 1E), maximum height at middle of body, body height/ length ratio about 0.63 µm, body length = 0.27 mm, average: 0.27 mm (n = 2), head with two major pores connected ( Fig. 1F), postabdomen about 2.6 times as long as wide ( Fig. 2A), with nine lateral fascicles and ten postanal marginal denticles. IDL and ODL of limb I with three and one setae respectively. Limb II with inner portion armed with eight scrapers, rst and second ones di erent in size.

Alona isabellae can be easily separated from other members of the Alona intermedia- group by the peculiarities of the spinule of distalmost fascicles, which is thicker than the others and goes beyond the postabdomen margin and the marginal denticles (arrowed in Fig. 2A, B). Another important diagnostic feature is the labrum with two short and ne spinules on the anterior margin and a cluster of setules on the posterior margin ( Fig. 2C). ese two distinctive characters are present in the Colombian specimens.

e specimens from Colombia have diagnostic features of A. isabellae as described by Sousa et al. (2016). ere are, however, some small di erences in our specimens: (1) proximal and distal denticles of the postabdomen with ne spinules in the populations from Brazil ( Sousa et al., 2016, fig. 7O), while in Colombian populations this structure is only absent in distal denticles ( Fig. 2B, present data); (2) scraper 4 and 5 of limb II di erent in length in specimens from Colombia ( Fig. 2D), while they are of the same size in Brazilian populations ( Sousa et al., 2016, g. 8F). Overall, these di erences are deemed to be intraspeci c variations and thus expand the knowledge on the morphometric variability of this species.

Distribution. Alona isabellae is so far known only from Brazil ( Sousa et al., 2016) and Colombia (present study). Some records of A. intermedia have been recorded from Venezuela, Peru, and Paraguay ( Daday, 1905; Stingelin, 1906; Delachaux, 1918; Rey and Vazquez, 1986), and these reports could correspond to A. isabellae or to a new species; nevertheless, an exhaustive review of these records is required.