T46 Advances in the Fossil Record of Insects and Terrestrial Arthropods

Sunday, 27 October 2002
1:00 PM - 3:45 PM

A MINUTE FUNGUS BEETLE LARVA (COLEOPTERA: CORYLOPHIDAE) FROM DOMINICAN AMBER: A STRIKING EXAMPLE OF MORPHOLOGICAL CONVERGENCE

Paper number: T46-7
Program: Technical Sessions
Time: 2:30 PM – 2:45 PM

Authors

Abstract

Corylophids are cosmopolitan, tiny (1-3 mm long), soil-dwelling insects that feed on spores as larvae and as beetles. Both their inter- and intrafamilial phylogenetic relationships are unclear. All known corylophid larvae have paired abdominal glandular orifices opening dorsally or dorsolaterally. Of the 35 to 40 described genera, larvae are known for only about a third of them. No fossil larval corylophid has ever been described or photographed even though a substantial number of references, mostly unidentified adults, exist in Baltic and Dominican amber.

We describe and illustrate the first fossil larval corylophid and highlight its striking resemblance to other onisciform insect larvae. Larva characteristics are as follows: broadly ovate, strongly flattened, 2.3 mm long, 1.6 mm wide, and unicolorous dark brown dorsally. All surfaces are heavily sclerotized with notal surfaces ornamented with six thoracic and nine abdominal lobes (8-9 not fused). All lobes distinctly separated, lacking gills, A9 tergum simple, and lacking urogomphi. The head prognathous subparalellepipedal, short, wider than long, concealed from above by broadly rounded first pronotal lobe; with relatively long, well-developed antennae, probably bearing three segments (second about 50-60% total length), ending in, at least, 3-4 setae, and the apicalmost the strongest and longest; antennae slightly longer than thorax (ratio 11:9); antennae much longer than head width (ratio 5:3); apical fourth of antennae visible from above under anterior pronotal lobe. All legs are well-developed, moderately separated, articulated at base, with simple tarsungulus (leg 3 with 5 segments), basal portion of thoracic lobes maculated of dark brown and yellow. Head plus thorax is about half the length of larva. Thoracic and abdominal lateral lobes bear about ten strong, and well-separated slightly clavate-ornamented setae of various lengths.

The extreme onisciform morphology is common to a wide variety of immature terrestrial and aquatic insects, including: Termitaphididae (Heteroptera), Coccoidea (Homoptera), Psephenidae, Discolomidae, some hispine Chrysomelidae (Coleoptera), and the Platypezidae (Diptera). Although there are significant differences in their bauplane, this phenomenon represents a striking example of convergence.