Coronatella, Dybowski & Grochowski, 1894

DAMME, KAY VAN, SINEV, ARTEM YU & DUMONT, HENRI J., 2011, Separation of Anthalona gen. n. from Alona Baird, 1843 (Branchiopoda: Cladocera: Anomopoda): morphology and evolution of scraping stenothermic alonines, Zootaxa 2875 (1), pp. 1-64 : 57-58

Similarity with Coronatella

Coronatella and Anthalona gen. n. are similar enough for earlier authors to regard A. verrucosa as a member of Coronatella rectangula- group (e.g., Daday 1910, Jenkin 1934; A. rectangula -group). Also the presence of tubercles in both, has lead to confusion (e.g., Johnson 1956b). Important similarities include ( Van Damme & Dumont 2008b): 1) five pairs of limbs with reductions, typical for the Coronatella- branch (IDL with two setae, reduction of anterior setae in P1, exIII with six setae, no gnV); 2) specialized setal armature (IDL on P1); 3) The A. monacantha group (to be removed from Alona ) has all characters of Coronatella , but some peculiarities of Anthalona (strong armature IDL on P1, denticle on labrum) as well, hence seems intermediate; 4) In general dimensions of body and postabdomen, Coronatella and Anthalona gen. n. look nearly identical.

Coronatella and Anthalona seem both natural assemblages with a separate evolution. The head pore configuration is distinct and stable in each genus (two + cosmaria in Anthalona versus three + no lateral pores in Coronatella ). The phylogenetic importance of head pores in the Aloninae may be overrated, but the difference is significant in that the typical head pore type arose only once in an ancestral Anthalona , maybe even from the Karualona type. It gave rise to a subtle diversity of head pore arrangements in Anthalona . The same can be said for postabdomen armature (lateral spines thicker and basal spine shorter in Anthalona ) and other specific characters ( Fig. 29 ). In the antennae of Coronatella and Anthalona , strong changes and specialisations have occurred independently, suggesting important plasticity in these traits (e.g., C. holdeni and A. acuta ). The limb characters shared by both Coronatella and Anthalona gen. n. are mainly reductions. As a general trend in the evolution of these microcrustaceans (reduction of setae), such reductions may either have arisen independently or stem from a common ancestor.

Similarity in morphological form may be a result of a reversal, close common ancestry, parallel evolution or convergence. Homoplasy may occur under similar adaptive pressures or by evolutionary constraints (constraints to structural solutions; e.g., Wake 1991). The similarities in body size and postabdomen between Coronatella and Anthalona may result from such constraints, although details on their feeding and ecology are yet to be investigated. Reductions on limbs in Coronatella and Anthalona may also be correlated with miniaturization; both are among the smaller Aloninae genera. In the Alona guttata- group for example, which belongs to an entirely different lineage (of six-limbed Alona ), reductions seem correlated with a decrease in body size. In any case, Anthalona and Coronatella are examples of the typical general small, successful Alona body shape. However, closer examination shows that comparative body shapes of Anthalona species are not so similar ( Figs 27–28 ).

Coronatella and Anthalona gen. n. do not necessarily share a close common ancestor. Evolutionary pressures under similar conditions and/or constraints in the Aloninae “Bauplan” may have lead to homoplasy in external and internal characters, with body shape, postabdomen, even limbs, similar. It results in a small model, successful in littoral environments. An independent test to see whether Coronatella and Anthalona share a close common ancestor is by molecular analysis (Van Damme & Dumont, unpubl.), not included in this study. It is this general small “ Alona ” body shape that caused many of our historical taxonomical problems in the lump genus (Van Damme et al., 2010)

Figures

FIGURE 27. Neotropical species of Anthalona gen. n. A. Anthalona verrucosa verrucosa (Sars, 1901), Lençóis Maranhenses, NE–Brazil, from culture (without tubercles on valves), Leg. K. Van Damme. B. Anthalona verrucosa verrucosa (Sars, 1901), Lençóis Maranhenses, NE-Brazil, from sample, same population as in A but with tubercles on valves, Leg. K. Van Damme. C. Anthalona verrucosa ssp. (Sars, 1901) from Fra Bartelomeo de las Casas, Guatemala, Leg. H.J. Dumont. D. Anthalona verru-

FIGURE 28. Asian and African species of Anthalona gen. n., compared to Anthalona verrucosa (Sars, 1901). A. Anthalona verrucosa verrucosa (Sars, 1901), Lençóis Maranhenses, NE-Brazil, from culture, Leg. K. Van Damme. B. Anthalona obtusa n. sp., Borneo, Palangka Raya University Campus, Leg. H.J. Dumont. C. Anthalona harti harti n. ssp., Maun, Okavango Delta, Botswana, Leg. H.J. Dumont. D. Anthalona harti occidentalis n. ssp., Lake Télé, Mali, Leg. H.J. Dumont. E. Anthalona simplex n. sp. from Katanga, DR Congo, Leg. K. Martens. F. Anthalona mediterranea from Wadi Shawqah, Sharjah, UAE, raised from culture, Leg. K. Van Damme.

FIGURE 29. Phylogenetic relationships and evolution in Anthalona gen. n. Parsimony analysis based on 14 morphological characters with Karualona as outgroup. The trees illustrate the hypothesis of a basal position of A. simplex n. sp. and A. brandorffi in Anthalona gen. n. Evolution of four characters plotted next to the tree. A. 50% Majority-rule consensus tree of 4598 trees with bootstrap values at nodes. The separate position of A. simplex n. sp. has high support. B. Strict consensus tree from six most parsimonious trees obtained by heuristic search, with values plotted from the 50% majority rule tree of these six (tree itself not shown). Evolution in the genus shows an increase of specialization/complexity of four synapomorphies, illustrated at the right (pores, IDL armature, sixth scraper of P2 and labral keel). The most primitive condition is found in A. simplex n. sp. Head pores in the genus show an increase of complexity in the lateral cosmaria (from simple unconstricted to involuted and constricted). Limb modifications for scraping, increase in specialization, from fine and similar setules in the basal taxa to strongly modified spines towards the crown taxa. Finally, denticles on the labral keel are absent in A. simplex n. sp. and A. brandorffi and appear in the genus together with stronger specialized scraping mechanisms. Their basal position within the genus is therefore confirmed by more than one character.