Paraboreochlus Thienemann

Description

Introduction

Small larvae, 5 mm long; conspicuously slender; about 17x longer than broad.

Antenna

Antenna with 5 segments; at least the apical 1/2 of segment 3 annulated. Ring organ situated somewhat below the middle of basal segment. Blade somewhat longer than segment 2; accessory blade short, hardly reaching the middle of the slender segment 2. Lauterborn organs present or absent.

Labrum

Labrum with labral sensillae long and slender; SI and SII on high, somewhat clubbed tubercles, SIII on low tubercles; SIV A again on high tubercles; SIV B developed as a long, slender rod. Numerous apically divided chaetae present in front of SI. Pecten epipharyngis 3 lobed.

Mandible

Mandible with 6 inner teeth.

Mentum

Mentum with 1 protruding median tooth and 7-8 pairs of lateral teeth.

Body

Body with procercus long and slender, hyaline anteriorly, blackish posteriorly; with 7-8 apical setae, one of them several times longer than procercus. Two distinctive long, black setae just before the anal tubules.

Notes

Taxonomic Notes

Larval Paraboreochlus and Boreochlus have bicoloured procerci, hyaline anteriorly, dark from base to apex posteriorly, as in most Boreochlini. A prominent, as opposed to recessed, median mental tooth distinguishes from Trichotanypus, and the few lateral mental teeth (7) from Lasiodiamesa. Paraboreochlus is distinguished from Boreochlus by the unique presence of two long, strong black setae lying dorsal to the anal tubules in Paraboreochlus, and the reduced number of anal setae (5 vs. 8) in Boreochlus.

Ecological Notes

One species of Paraboreochlus is known from Europe (Brundin 1966a) and one from North America. The immature stages of the European species, P. minutissimus, seem to prefer to live amongst mosses in springs and creeks.

In southeastern New York (USA), Shannon et al. (1998) found larvae of Paraboreochlus stahli in two streams, Esopus Creek and Coxing Kill, during a study of hyporheic invertebrates in the Lower Hudson River Basin. All were collected from hyporheic zones of exposed lateral gravel bars. Only two larvae of P. stahli were collected in October from Esopus Creek. By contrast, larvae were present through most of the year at Coxing Kill, but were more abundant in fall and spring samples, and consisted of a mixture of second, third and mature fourth instars. It is concluded that larvae inhabit and grow to maturity in lateral hyporheic zones, which may account for their absence in standard benthic samples from streams. Pupal exuvial evidence suggests that the genus is widespread in USA.

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