Daphnia (Ctenodaphnia) dadayana Paggi, 1999

Dartnall, Herbert J. G. & Hollwedel, Werner, 2007, A limnological reconnaissance of the Falkland Islands; with particular reference to the waterfleas (Arthropoda: Anomopoda), Journal of Natural History 41 (21 - 24), pp. 1259-1300 : 1270

Daphnia (Ctenodaphnia) dadayana Paggi, 1999

Daphnia dadayana is restricted to non-tropical South America where it is regarded as endemic ( Villalobos 1994), and has not been previously recorded from the Falkland Islands.

Adult female: 2.5–3.25 mm; valves oval with a depression between head and dorsal margin. The latter and posterior half of ventral margin with small denticles, the central third of inner ventral margin with a row of longer setae directed inward and posteriorly. Shell spine short or completely reduced. Head high, anterior rounded, ventral margin straight or slightly concave; rostrum pointed, antennulae do not reach the tip of rostrum; ocellus extremely small. First abdominal process double the length of the second, the former curved anteriorly and covered with setules, the latter curved posteriorly and thinly covered with setules, the third and fourth processes are small protruberances. Postabdomen ( Figure 15 ) long and broad, narrowing distally, dorsal margin slightly concave with 16–19 post-anal denticles, post-abdominal claw stout with two pectens, a proximal one with seven to nine smaller denticles, and a distal one with 9–12 longer denticles ( Figure 16 ).

Juvenile female: ventral margin of valves broadly rounded, the whole length covered with denticles, dorsal margin straight, and denticulate, passing over a dorsally directed shell spine, nearly as long as body. Ventral margin of head equally convex, no rostrum, eye near the margin, ocellus not visible; head bearing a rounded horn directed obliquely backward ( Figure 17 ), as in Daday de Dées’s illustration (1902, Table 12, Figure 9 ) and Paggi’s drawing (1999, p. 32, Figure 45). Villalobos (1994) mentions that some of her juvenile specimens from South America have ‘‘a little helmet’’. A similar horn seems to occur in other species. Rane (1986) describes and illustrates juveniles of Daphnia sarojae Rane with a helmet that is similar to the Falkland D. dadayana , but note that Sharma and Sharma (1990) believe Daphnia sarojae to be a helmeted morphotype of D. lumholtzi .

Figures

Figure 9. Alona cf. guttata, female, post-abdomen. Scale bar: 0.5 mm.

Figure 15. Daphnia (Ctenodaphnia) dadayana, female, post-abdomen.

Figure 16. Daphnia (Ctenodaphnia) dadayana, female, post-abdominal claw.

Figure 17. Daphnia (Ctenodaphnia) dadayana, juvenile, head with horn.