The larval head morphology of Xyela sp. (Xyelidae, Hymenoptera) and its phylogenetic implications

Abstract

Larval head structures of Xyela sp. are described in detail. The characters are compared to conditions found in larvae of other groups of Hymenoptera and Endopterygota. Like other symphytan larvae the immature stages of Xyelidae are mainly characterized by presumably plesiomorphic features of the head. The head sutures are well developed and all parts of the tentorium are present. The labrum is free and a complete set of labral muscles is present. The maxillae are in a retracted position. In contrast to other hymenopteran larvae Xyela possesses a clypeofrontal suture, a comparatively long antenna and three well-developed antennal muscles. Apomorphic features of Xyela are the absence of muscles associated with the salivarium and the complete absence of Musculus craniocardinalis. A clade comprising Orussidae and Apocrita is supported by the unsegmented maxillary and labial palps and the absence of the lacinia. Six potential autapomorphies for the Hymenoptera were revealed: (1) the caudal tentorial apodeme, (2) the bifurcated tendon of Musculus craniomandibularus internus, (3) the lateral lobe of the cardo, (4) the origin of M. tentoriohypopharyngalis from the posterior head capsule, (5) the exceptionally strong prepharyngo-pharyngeal longitudinal muscle and (6) the longitudinal muscle of the silk press. The maxillolabial complex, the vestigial M. craniocardinalis and a distinctly developed labio-hypopharyngeal lobe bearing the opening of the salivary duct are potential synapomorphies of Hymenoptera and Mecopterida. The globular, orthognathous head capsule, the modified compound eyes, the occipital furrow and the X-shaped tentorium are features with unclear polarity shared by Hymenoptera and Mecoptera.

The larval head of Nevrorthidae and the phylogeny of Neuroptera (Insecta)

“…It is absent in other groups of Neuroptera including Nevrorthidae (Rousset, 1966) and in other lineages of Endopterygota (e.g. Röber, 1942; Kramer, 1955; Beutel & Ge, 2008; Beutel, Krogmann & Vilhelmsen, 2008). The much smaller structure in Berothidae (MacLeod, 1964: fig.…”

“…Beutel, 1993; Beutel & Molenda, 1997; Beutel & Hörnschemeyer, 2002a, b), and also in other lineages of endopterygote insects (e.g. Crampton, 1921; Hasenfuss & Kristensen, 2003; Beutel et al. , 2008).…”

“…36). M. verticopharyngalis is composed of one moderately sized bundle (e.g., Trachypachus ) or reduced in most groups of Coleoptera, and of several thin parallel bundles in Xyela (Beutel et al. , 2008).…”

“…M. craniolacinialis is undivided in Nevrorthus and in larvae of other groups of Endopterygota (e.g. Das, 1937; Röber, 1942; Beutel & Ge, 2008; Beutel et al. , 2008).…”

Goodbye Halteria? The thoracic morphology of Endopterygota (Insecta) and its phylogenetic implications

“…This comprises characters of larvae (e.g. Beutel and Friedrich, 2008; Beutel and Ge, 2008; Beutel et al., 2008c, 2010), the adult head (Beutel and Vilhelmsen, 2007; Beutel and Baum, 2008; Beutel et al., 2008a), the postabdomen (Hünefeld, 2009), and some developmental features (see ). The results of a considerable number of hitherto unpublished diploma theses were also included in the data set.…”