Ovalona, Van Damme & Dumont, 2008

Damme, Kay Van & Dumont, Henri J., 2008, Further division of Alona Baird, 1843: separation and position of Coronatella Dybowski & Grochowski and Ovalona gen. n. (Crustacea: Cladocera), Zootaxa 1960 (1), pp. 1-44 : 36-37

Allocation of A. weinecki Studer and A. meridionalis Sinev to Ovalona gen. n.

We have earlier considered A. weinecki to be a close relative of A. rectangula as Frey (1988) suggested, perhaps even a member of Coronatella . It has been confused with A. bukobensis sensu Ekman (= Coronatella anemae ) and with A. rectangula (see Frey 1988). We are now convinced that A. weinecki does not belong to Alona sensu stricto (A. quadrangularis- group) and differs more in limb morphology from Coronatella than for example Leberis (Table 2). Females of the latter genus are easier to distinguish because of a peculiar habitus ( Sinev et al. 2005) whereas external differences between A. weinecki and Coronatella are subtler. Frey (1988) listed 19 characters separating A. weinecki from A. rectangula . No doubt that these taxa are related ( Frey 1988; Table 2), but accommodating A. weinecki in Coronatella would simply shift taxa from one polyphyletic genus ( Alona ) to create another ( Coronatella ).

In addition, A. weinecki forms a species complex with A. meridionalis Sinev 2006 . Both are different in limb morphology, postabdomen and head pores and are clearly species in their own right, but share a number of synapomorphies (see also discussion of meridionalis by Sinev 2006). The South African meridionalis can be considered relatively more primitive in retaining three setae, absent in weinecki . These setae are situated on three limbs of meridionalis (P1en1 first seta, P2ex seta and one filter seta P5, see Sinev 2006). Main characters delineating these two species of the weinecki -group (see Table 2) are: 1. body broad in dorsal view (not bilaterally flattened), strongly arched in lateral view, giving the animals an ovoid appearance (also in Leberis and A. dentifera ); posteroventral corner evenly rounded with spinules parallel and close to margin, 2. wedge- shaped ( Sinev 2006) naked labrum (not short and round as in Coronatella ); 3. short, thick antennule with short aesthetascs, 4. well developed, relatively thick first exopod seta on second antenna, 5. P1 with strongly reduced anterior setae on endites, IDL with three and ODL with one seta, 6. ex II seta reduced ( meridionalis ) to absent ( weinecki ), 7. exIII with seven setae, 8. exIV with ventral setae (5-6) not narrowed (as in majority of Aloninae ), 9. exV with first three setae of similar length (instead first longer in most Aloninae ), gnV reduced with 0-1 filter setae, P6 absent; 10. high postabdomen with rounded dorso-distal angle, moderate to long basal spine and small, unmerged marginal denticles.

Within Aloninae , these two species thus markedly differ from the remaining group of Alona’ s closest to A. quadrangularis (Van Damme & Dumont in press) including species of the “ Hexalona -branch” (Table 2), but also from Coronatella . The A. pulchella -group is close in limb morphology to Ovalona gen.n. but differs strongly in postabdomen and habitus. As noted earlier, position of the A. pulchella -group is unclear; it seems to have a quite general limb morphology and can have strong variation in postabdomen and habitus (e.g., A. azorica , A. nuragica ). It is possible that Ovalona is derived from the A. pulchella -group, but this is yet uncertain.

Ovalona gen.n. is externally similar to A. elegans and related species ( A. orellanai , A. salina ). Sinev (2006) noted this similarity for A. meridionalis . The A. elegans -group (See Alonso 1996) also has a relatively ovoid body, relatively short antennules and aesthetascs, similar broad postabdomen with deep preanal corner and with small marginal denticles (in contrast for example to Coronatella , which has long marginal denticles) and second antenna with well developed endopod seta. However, Ovalona (Table 2) has three setae on the IDL (third strongly reduced in A. elegans ), lacks a soft setae on P2 (one long extra seta basally of first scraper in A. elegans , a primitive character!), seven setae on exIII (six in A. elegans ) and 0-1 setae in gnathobase V (two in A. elegans ). Whether these represent generic differences is left undecided here, although the shape and armature (small marginal denticles) of the postabdomen, main limb features and habitus definitely argue for a removal of A. elegans -group from Alona sensu stricto and placement much nearer to Coronatella (Table 2).

Morphological boundaries are tricky here: the A. elegans -group seems somehow intermediate in morphology between Ovalona and Coronatella (Table 2). In external morphology (postabdomen, ovoid habitus), it looks like Ovalona , but it has similar limb reductions (e.g., P1, exIII with six setae) to Coronatella besides separate characters considered as primitive for alonines (e.g., the extra soft seta on P2). We did not study male morphology in detail, but comparison of male postabdomen shape ( rectangula and weinecki in Frey 1988; rectangula and elegans in Alonso 1996; as Alona ) show relatively little difference. Similarity between A. elegans and A. rectangula was also recognized by Smirnov (1971), who listed A. elegans as one of seven rectangula subspecies, and by Dumont et al. (1979) who suggested that both might form hybrids.

So, we have no doubt that these are closely related, but leave the position of the A. elegans -group as undecided here. Several species of this complex ( A. orellanai , A. salina , A. striolata ) need re-evaluation. Removal from Alona and future allocation, maybe to Coronatella or even yet another taxon should be well argumented. Finally, the cave-dwelling Alona hercegovinae -group (e.g., Brancelj 1990) also seems close to Ovalona and the A. elegans -group in postabdomen, habitus and limb morphology, but shows autapomorphies and has likely undergone a separate evolution; detailed limb morphology is under study (Sinev & Van Damme unpubl.).