Symbiocloeon, Muller-Liebenau & Heard, 1979

Kluge, Nikita J., Vishnevskaya, Maria S. & Palatov, Dmitry M., 2025, Winged stages of Symbiocloeon laoense Palatov 2023 (Ephemeroptera: Baetidae) and systematic position of larvae developing inside mantle cavities of bivalve mollusks, Zootaxa 5728 (2), pp. 287-320 : 308

Position of Symbiocloeon within Baetovectata

Does Symbiocloeon belong to Baetungulata? The taxon Baetungulata Kluge & Novikova 2011 comprises overwhelming majority of Baetovectata; it is characterized by asymmetric larval claw bearing a single row of denticles on its inner side, which represents the inner-anterior row among two initial rows; the second (inner-posterior) row is either absent (in overwhelming majority of Baetungulata), or consists of denticles much smaller than denticles of the inner-anterior row.Among Baetungulata, in Nigrobaetis ( Takobia) maxillaris ( Braasch & Soldán 1983) denticles on claw are completely lost. In taxa other than Baetungulata, either two inner rows of denticles (the inner-anterior and the inner-posterior ones) are equally developed, or both rows are equally reduced or lost.

In all species of Symbiocloeon , claws do not have the single row of denticles characteristic for Baetungulata. Claws of S. heardi and S. madhyasthai lack any denticles, and claws of S. corbiculinum and S. laoense have two symmetric rows of peculiar denticles near the claw apex ( Figs 23–24 ), which are probably not homologous to more proximal denticles of other Baetidae . The modified claw structure of Symbiocloeon does not allow us to determine if they originated from the claws characteristic for Baetungulata, or not.

Baetovectata other than Baetungulata. Among Baetovectata not belonging to Baetungulata (which can be indicated as Baetovectata-non-Baetungulata), the Old World fauna contains only the genus Centroptella Braasch & Soldán 1980 (including subgenera Centroptella , Crassolus Salles et al. 2016 and Chopralla Waltz & McCafferty 1987 ) ( Kluge 2021). Symbiocloeon clearly differs from Centroptella by non-modified patella-tibial suture on larval legs, so it could not originate from Centroptella . All other representatives of Baetovectata-non-Baetungulata are found in New World only and probably have Neotropical origin, while all species of Symbiocloeon are known from the Old World.

We proceed from the assumption that Symbiocloeon belongs to Baetungulata and have lost the primary denticles on claw, similar to Nigrobaetis ( Takobia) maxillaris .

Figures

FIGURES 23–25. Symbiocloeon laoense: larval legs. 23–24, claw; 25, apex of femur, view from anterior side.