Larval head morphology of Hydroscapha natans (Coleoptera, Myxophaga) with reference to miniaturization and the systematic position of Hydroscaphidae |
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Authors: | R G Beutel A Haas |
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Institution: | Institut für Spezielle Zoologie und Evolutionsbiologie, Friedrich-Schiller-Universit?t, Erbertstrasse 1, D-07743 Jena, Germany e-mail: b5bero@rz.uni-jena.de, Fax: +03641-949 142, DE
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Abstract: | The head of third instar larvae of Hydroscapha natans was reconstructed three dimensionally on a computer. This technique allowed a detailed examination and presentation of internal
features of a representative of the ’suborder’ Myxophaga, which is characterized by the very small size of the immature stages
and adults. Larval character states of H. natans were compared with features found in other representatives of the Coleoptera. The monophyly of the Myxophaga (excluding Lepiceridae)
is supported by several autapomorphies of the larval head: a broadened, transverse head, scale-like cuticular surface structures,
round and flattened labral sensilla, short antennae with only two antennomeres, a ligula with papillae, and a broadened tentorial
bridge. A monophylum comprising the Hydroscaphidae and Microsporidae is characterized by a very unusual semientognathous condition
of the mouthparts and an unusual shape and large relative size of the brain. The last common ancestor of the Hydroscaphidae,
Torridincolidae, and Microsporidae was probably living in hygropetric habitats. Several apomorphies have evolved in correlation
with this peculiar life style. The very dense arrangement of muscles and other internal structures, and the unusual shape
and size of the cerebrum have resulted from miniaturization. The overall complexity of the head is not reduced in comparison
to larvae of other representatives of Coleoptera. A negative allometric relationship between body size and the size of the
brain, and a correlation between brain size and the size of neurons was found in several species of Coleoptera examined.
Accepted: 16 December 1997 |
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