Corynocera Zetterstedt

Description

Introduction

Small to medium-sized larvae, to 7 mm long.

Dorsal Head

Not described.

Antenna

Antenna with 5 segments, placed on a tall pedestal lacking any basal tooth or spur. Antennal ratio > 1. Ring organ basal on 1st antennal segment. Seta strongly developed. Lauterborn organs small, on long stems projecting beyond antennal apex, opposite on apex of cylindical 2nd segment. Apical 3 segments short. Antennal blade usually as long as 2nd segment, accessory blade very short. Style short.

Labrum

SI seta comb-like, fused at bases, SII on large pedestal, finely serrate on each side, SIII short, simple, SIV not discernible. Labral lamellae well developed. Pecten epipharyngis 3 distally toothed scales. Premandible with 5 teeth, brush strong; seta premandibularis simple.

Mandible

Mandible without distinct tooth, bluntly rounded and sclerotised distally, with rounded lobe on inner side (ambigua group) or with very unusual arrangement of teeth as follows: dorsal tooth almost as long as apical tooth, 2 additional teeth dorsally and very large toothed lobe overlying the 3 inner teeth (oliveri group). In badly worn specimens of oliveri group the mandible comes to resemble that described for the ambigua group - which may be to some extent also an effect of wear. Seta subdentalis very long, curved, reaching to apex of mandible. Seta interna of 4 plumose branches. Pecten mandibularis an arc of short strong lamellae.

Mentum

Mentum with three median teeth clearly divided from lateral teeth; in ambigua group the 3 median teeth are about equal in height, with only 1-2 pairs of lateral teeth, lying dorsal to outer median tooth; in oliveri group the central median tooth is slightly higher than outer pair, with 4 pairs of lateral teeth. Ventromental plates very close together medially, about 1.7 x (ambigua group) or 1.1x (oliveri group) width of mentum.

Body

Without tubules. Claws of posterior parapod simple.

Notes

Taxonomic Notes

A very characteristic genus, with two distinct types of larva. In both types the central 3 teeth of the mentum form a distinct clearly delineated group.

Hirvenoja (1961a) showed the subfossil species Dryadotanytarsus edentulus to be synonymous with C. ambigua. Corynocera duffi, described from a lake deposit in New Zealand, is said to have 7 mental teeth but clearly also belongs to the ambigua group. The extent to which the appearance of the mandible of C. ambigua is influenced by wear is not clear.

Ecological Notes

Larvae of Corynocera inhabit mud in beds of cold lakes and ponds.

Holarctic distribution, otherwise recorded only from New Zealand as a subfossil species. Corynocera ambigua occurs in both Palaearctic and Nearctic regions, whereas C. oliveri is known only from the Palaearctic. There is at least one undescribed species.

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