Astylosternus occidentalis, Parker, 1931

Schweiger, Susan, Rödel, Mark-Oliver, Hammel, Jörg. U. & Müller, Hendrik, 2024, Don’t go with the flow: cranial adaptations of stream tadpoles in the Afrobatrachian family Arthroleptidae, Zoological Journal of the Linnean Society 202, pp. 1-17 : 5-7

Astylosternus occidentalis

The tadpole was robust with a long, muscular tail and low dorsal and ventral fins (Fig. 1). The oral disc showed lateral papillae on the anterior lip; the posterior lip consisted of 2–3 rows of rounded-triangular papillae (see Griesbaum et al. 2019 for a detailed description; Fig. 3B).

The cornua trabeculae were about one-third of the length of the chondrocranium and were partially fused (Fig. 4B). The palatoquadrate was dorsally connected to the neurocranium via a broad commissura quadratoorbitalis (Fig. 4B), and anteromedially by a broad commissura quadratocranialis (Fig. 6B). The processus muscularis was flattened, larger, and more heavily chondrified in comparison to L. parkeri (Fig. 5B). Ventrolaterally, the palatoquadrate bore a processus ventralis, which was not seen in the tadpole of L. parkeri (Fig. 5B). The cartilago labialis superior was formed as a single massive element and not separated as in L. parkeri (Fig. 6B). The cartilago labialis inferior is a paired element of the upper jaw and is v-shaped (Fig. 6B). Posteriorly, it articulates with the cartilago meckeli. For a detailed description of the complete cranial skeleton see Supporting Information (Fig. S2, Table S2 ).

The ceratohyale was massive compared to L. parkeri . A basibranchiale was present in all four species and was connected to the ceratohyale and the planum hyobranchiale. The basihyale and the pars reuniens were absent (Fig. 7B). The planum hyobranchiale was anterolaterally connected to the ceratohyale via the processus anterior branchialis (Fig. 7B). Posteriorly, the planum hyobranchiale formed a narrow and tapering processus posterior. The branchial basket consisted of four separated ceratobranchialia that were fused medially to the planum hyobranchiale (Fig. 7B).

The large m. orbitohyoideus originated on the mediolateral part of the ceratohyale and inserted on the ventromedial process of the palatoquadrate (Fig. 8B). For a complete description of the cranial musculature see Supporting Information (File S1, Fig. S6; Table 2 ).