Eur. J. Entomol. 101: 293–311, 2004 ISSN 1210-5759 Larval morphology of three species of Hygrobiidae (Coleoptera: Adephaga: Dytiscoidea) with phylogenetic considerations YVES ALARIE1, ROLF G. BEUTEL2 and CHRIS H.S. WATTS3 1Department of Biology, Laurentian University, Ramsey Lake Road, Sudbury, ON, Canada; e-mail:
[email protected] 2Institut für Spezielle Zoologie und Evolutionsbiologie, FSN Jena, Germany; e-mail:
[email protected] 3South Australian Museum, North Terrace, Adelaide, SA 5000, Australia; e-mail:
[email protected] Key words. Hygrobiidae, Hydradephaga, larvae, morphology, phylogeny, chaetotaxy Abstract. A provisional larval groundplan of the family Hygrobiidae is provided through descriptions of internal and external fea- tures of three of six extant species, Hygrobia hermanni (Fabricius, 1775), H. wattsi Hendrich 2001 and H. australasiae (Clark, 1862) and phylogenetic interpretations. Hygrobiidae larvae are morphologically differing dramatically from all other known Adephaga by 20 autapomorphies. Structures involved with feeding, i.e., mouthparts, prepharynx and foregut are highly modified as a result of a specialisation on small tubificid worms and chironomid larvae. A placement of Hygrobiidae within Dytiscoidea is well supported by the reduced condition of the terminal abdominal segments, and the presence of 10 ancestral setae on femur and a clade comprising Hygrobiidae, Amphizoidae, and Dytiscidae by the presence of thin and elongate caudal tentorial arms, a very strong musculus verti- copharyngalis and a longitudinally divided adductor tendon of the mandible. A highly modified foregut, reduced terminal spiracles VIII and the presence of tubular gills are features which distinguish hygrobiid larvae from those of other groups of Dytiscoidea (i.e, Amphizoidae, Noteridae, Dytiscidae).