Baissalarva, Fikáček & Prokin & Yan & Yue & Wang & Ren & Beattie, 2014
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publication ID |
https://doi.org/ 10.1111/zoj.12114 |
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DOI |
https://doi.org/10.5281/zenodo.10274508 |
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persistent identifier |
https://treatment.plazi.org/id/03C287AC-FF88-D67E-FE9A-BBDC40359B39 |
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treatment provided by |
Marcus |
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scientific name |
Baissalarva |
| status |
gen. nov. |
BAISSALARVA View in CoL GEN. NOV.
Type species: Baissalarva hydrobioides sp. nov., by present designation.
Time range: Early Cretaceous.
Diagnosis: Labrum fused with clypeus; labroclypeus with five large teeth with slightly more isolated left lateral-most one ( Figs 3E View Figure 3 , 6B View Figure 6 ); epistomal lobes low, symmetrical ( Fig. 3D–E View Figure 3 ); occipital foramen situated dorsally ( Figs 3E View Figure 3 , 6A View Figure 6 ); mandible with three retinacular teeth ( Figs 3D View Figure 3 , 6C View Figure 6 ); prothorax completely sclerotized dorsally ( Figs 3C, F View Figure 3 , 6A, D View Figure 6 ); meso- and metathorax with large transverse sclerites ( Figs 3C, F View Figure 3 , 6A, D View Figure 6 ); abdominal segments largely membranous, with small dorsal circular sclerites only ( Figs 3C, F View Figure 3 , 6A, D View Figure 6 ); tracheal system with a pair of large tracheal trunks ( Figs 3C, F View Figure 3 , 6A, D View Figure 6 ).
Etymology: The generic name consists of the name of the type locality in which the genus was found (Baissa) and the ending -larva indicating that it represents the larval stage. Feminine.
Family assignment: The combination of dorsally situated occipital foramen of the head (present due to the hyperprognathous head allowing it to hold the prey above the water surface when it is processed preorally) and the anterior margin of the head bearing series of teeth on labroclypeus reliably assigns the fossils to the family Hydrophilidae . The family assignment is also supported by the general habitus, which closely corresponds to those of larvae of extant Hydrophilidae (see, e.g. Fig. 6E–H View Figure 6 ), and by the presence of massive tracheal trunks in the abdomen (an adaptation for breathing atmospheric oxygen in submerged larvae).
Results of phylogenetic analysis: The unconstrained analysis resulted in seven most parsimonious trees 207 steps in length. Their strict consensus tree ( Fig. 4A View Figure 4 ) is largely unresolved, but Baissalarva is still recognized to form a group with all included genera of the Hydrobiusini and the hydrophiline genus Sternolophus based on the nasale with five teeth and the left-most one distinctly separated from the other. In the constrained analysis using the molecules-based backbone tree, a single most parsimonious tree of length 240 steps was found ( Fig. 4B View Figure 4 ). Baissalarva is placed as a sister taxon to the extant representatives of the Hydrobiusini based on characters of the nasale.
Comparison with other genera: The presence of five teeth of labroclypeus with the left one slightly more separated from the others is very characteristic for the modern larvae of the tribe Hydrobiusini and the hydrophiline genus Sternolophus Solier, 1834 (Archangelsky, 1997, 2004; Minoshima & Hayashi, 2011a, b, 2012b). The form of the nasale (i.e. characters 5 and 6) is also responsible for grouping Baissalarva with these taxa in both phylogenetic analyses performed. Comparison of Baissalarva with modern representatives of the Hydrobiusini ( Fig. 6E, G View Figure 6 ) and Sternolophus ( Fig. 6F, H View Figure 6 ) shows that the fossil resembles the hydrobiusine larvae (mandibles wide with wider retinacular teeth, head widely quadratic, anterior margin of the occipital foramen arcuate, cervical sclerites wide, abdominal segments 1–8 with two pairs of isolated sclerites). At the same time, it clearly differs from the larva of Sternolophus , which has long slender mandibles and retinacular teeth, elongate head, triangular anterior margin of the occipital foramen, very narrow cervical sclerites, and mesonotum with both pairs of tergites fused). All these characters are shared by all other genera of the Hydrophilini except Hydrophilus Geoffroy, 1762 . Comparison of the fossils with modern larvae hence corresponds well with the results of our constrained analysis, and we consider Baissalarva as belonging to the tribe Hydrobiusini . Knowledge of the extant larvae of the Hydrobiusini is still rather limited and the fossils lack the generic diagnostic characters (chaetotaxy, detailed morphology of mouthparts and antenna). For this reason we prefer to assign the fossil to a new fossil genus, Baissalarva gen. nov.
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