The head morphology of Clambidae and its implications for the phylogeny of Scirtoidea (Coleoptera: Polyphaga)

Abstract

External and internal structures of the head of adults of Clambus are described and illustrated in detail. The results are compared with structural features found in the clambid genus Calyptomerus, in representatives of other scirtoid families, and also in species of other coleopteran suborders, notably Myxophaga. The results tentatively support the monophyly of Scirtoidea and a close relationship between Clambidae and Eucinetidae is suggested by one shared derived feature of the mandible, a long and slender apical tooth with a serrate edge. The monophyly of Clambidae is very strongly supported and Acalyptomerus is probably the sistergroup of a clade Calyptomerus + Clambinae. Potential scirtoid autapomorphies are the loss of the dorsal tentorial arms, a bulging gula, a strongly transverse labrum, and a ridge separating the mediostipes from the lacinia. However, all these features are homoplasious. The monophyly of Clambidae is supported by modifications of the head capsule which is strongly flattened and broadened, by a deep clypeofrontal incision enabling vertical antennal movements, and a series of antennal features. Synapomorphies of Clambinae + Calyptomerus (Clambidae excluding Acalyptomerus) are the conglobate body form with the ventral side of the head capsule in contact with the mesocoxae, and compound eyes integrated in the contour of the head. The completely subdivided eye is an autapomorphy of Clambus. An entire series of features is shared by Clambidae (or Scirtoidea) and Myxophaga. Most of them are apomorphies that apparently evolved independently in both groups. However, the presence of well‐developed maxillary and labial glands is arguably a retained groundplan feature of Coleoptera, with parallel loss in Archostemata, Adephaga and various groups of Polyphaga. J. Morphol. 277:615–633, 2016. © 2016 Wiley Periodicals, Inc.

The cephalic morphology of the troglobiontic cholevine species Troglocharinus ferreri (Coleoptera, Leiodidae)

“…The middle region of the epipharynx (Figure d), posterad the unsclerotized ventral wall of the labrum, is medially divided by a dense, posteriorly narrowing triangular group of microtrichia (see Anton & Beutel, ; Anton, Yavorskaya, & Beute, : lep [longitudinal epipharyngeal process]); large paired areas with rows of posteriorly oriented microtrichia are present posterolaterad this structure, placed in shallow depressions of the lateral epipharyngeal surface. The largely semimembranous hypopharynx (Figure c) forms a structural and functional unit with the dorsal prementum; lamellae with several dense comb‐like rows of microtrichia extend along its lateral edges, from the anterior to the posterior region (Figure c2,c4); two dense tufts of hairs are present on the anteromesal and posteromesal areas, the anterior one on a distinct elevation (Figure c1,c3; see Anton & Beutel, ; Anton et al, ; lhp [longitudinal hypopharyngeal process]); two strongly developed plate‐like posterolateral apodemes are muscle attachment sites. The posteriormost parts of the epipharynx and hypopharynx are laterally fused, thus forming a short prepharynx anterad the anatomical mouth opening.…”

Cephalic anatomy of Sphaeriusidae and a morphology‐based phylogeny of the suborder Myxophaga (Coleoptera)

“…However, in contrast to the typical condition in Coleoptera, externally recognizable ridges are also missing, even though the clypeofrontal ridge is distinctly developed as internal structure, and gular ridges are also discernible internally. Simplifications of the cephalic skeleton, including an almost complete lack of distinctly developed ridges, have been observed in small beetles of different families, especially in the strongly miniaturized Ptiliidae (Polilov & Beutel, ; Polilov, ; Yavorskaya et al ., ), but also in Corylophidae (Polilov & Beutel, ; Yavorskaya & Polilov, ) and Clambidae (Anton et al ., ). Similar conditions also occur in microinsects belonging to other groups (Polilov, ).…”

“…The feeding apparatus of Sphaerius is similar to that of Lepiceridae (Anton & Beutel, ) in its general configuration, but also to that of polyphagan groups with saprophagous or sporophagous feeding habits, notably in the Scirtoidea (Anton et al ., ) and Staphyliniformia (e.g. Anton & Beutel, ; Antunes‐Carvalho et al ., ; Yavorskaya et al ., ).…”

“…Apparently, the cephalic muscle system is rarely affected by reduction, as investigations of different groups have shown. This includes Ptiliidae (Polilov & Beutel, ; Polilov, ; Yavorskaya et al ., ), Corylophidae (Polilov & Beutel, ; Yavorskaya & Polilov, ), Clambidae (Anton et al ., ), and also groups outside of Coleoptera (Polilov, ). However, the head of the extremely small first instars of Strepsiptera forms a noteworthy exception: only nine cephalic muscles are preserved in the primary larva of Stylops (Knauthe et al ., ).…”

“Noah’s Ark” Project: Interim Results and Outlook for Classic Collection Development

“…Ptiliidae), Psocoptera (fam. Liposcelididae), and Thysanoptera orders, which are comparable in size to unicellulars (about 1 mm), has almost no effect on the anatomy of the most important organs of the head section [101, 102]. The result is of fundamental importance for understanding the mechanisms that ensure conservation of the structure of multicellular animals.…”