Tanytarsus van der Wulp

Description

Introduction

Small to large-sized larvae, to 9 mm long.

Dorsal Head

SI simple, bifid or plumose.

Antenna

Antenna with 5 segments on a tall pedestal with or without basal tooth or spur. Antennal ratio > 1. Ring organ basal on 1st antennal segment. Seta variably well-developed. Lauterborn organs variably sized on short to long stems inserted opposite on apex of elongate 2nd segment; stems may be annulate in several Nearctic species. Subsequent segments shorter than 2nd. Antennal blade usually no longer than 2nd segment, accessory blade short. Style on apex of 2nd segment, shorter than segment 3.

Labrum

SI seta comb-like, fused at bases, SII on large pedestal, plumose, perhaps sometimes plume reduced, SIII short, simple, SIVa present. Labral lamellae well developed. Pecten epipharyngis 3 distally serrate scales. Premandible with 3-5 teeth, brush strong.

Mandible

Mandible with 1-2 dorsal teeth apical tooth and 2-3 pointed inner teeth. Seta subdentalis long, curved, not reaching tip of apical tooth. Seta interna of 4 plumose branches. Pecten mandibularis well developed with many branched lamellae.

Mentum

Mentum with rounded or laterally notched median tooth, 5 pair of laterals, regularly decreasing in size laterally. Ventromental plates close together medially, subequal in width to mentum, with fine striae.

Body

Without tubules. Claws of posterior parapod few, arranged in horse-shoe shape, simple or with inner teeth.

Notes

Taxonomic Notes

Until recently Nimbocera Reiss was treated as a distinct genus: in the larval stage this was based on a distinctive annulate stem (pedicel) to the Lauterborn organs. The finding that such a feature occurred also in larvae otherwise clearly belonging to Tanytarsus has led to the formal synonymy of Nimbocera with Tanytarsus (Sanseverino et al., 2010) and this is accepted here.

Based on the adult morphology Reiss and Fittkau (1971a) divided the genus into a number of species groups. Unfortunately there is insufficient reared material available to determine whether these groups have any validity for the larvae. A notable exception is the triangularis group, treated as a valid genus, Virgatanytarsus, of doubtful validity. A number of other larvae, mostly not with certainty associated with an adult, show distinctive features. Whether these characters have any supra-specific value is, at present, impossible to say. The following types of larvae have been examined:
(a) Antennal pedestal with very long tapered spur distally. Includes T. brundini. Hofmann (1971a) ascribed this character to the chinyensis group as a whole, to which T. brundini belongs. Larvae of other groups examined have only a short projection or none at all.
(b) Segment 2 of antenna very long, annulate. Larvae such as this were described from Peru by Roback (1966a). Similar larvae also occur in southern Nearctic (Steiner, pers. comm.).
(c) Mandible with 2 dorsal teeth and additional tooth on dorsal surface. According to Hofmann (1971b) this characterizes larvae of the lugens group.
(d) SIII plumose. Includes pallidicornis group.

Considerable difficulty has been experienced in the past in distinguishing larvae of Tanytarsus from those of Micropsectra. Despite the variation within Tanytarsus, all larvae which could be definitely ascribed to this genus through association with adults, including several Neotropical species, are similar in 2 important respects:
(1) Premandible with more than 2 teeth (always bifid in Micropsectra);
(2) Posterior parapods with rather few claws, all of them simple arranged in a single series in the form of a horse-shoe. In Micropsectra the claws are usually very numerous, many of them small, arranged in the shape of a horse-shoe made up of several irregular rows.

Ecological Notes

Tanytarsus is a eurytopic genus, occurring in all types of freshwater, with some marine and at least 1 terrestrial species.

The distribution is worldwide, with at least 85 named Holarctic species, the vast majority unknown as larvae.

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