Tvetenia calvescens

Author: (Edwards, 1929)

Exuviae 2.1-3.5mm long (m=3.0mm, n=30).
Cephalothorax: Thoracic horn 250-495µm long (m=378µm, n=28), broadest at base, tapered to apex, more strongly tapered over the basal half (053f.jpg); length base 0.20-0.38x length horn (m=0.26, n=28); ThR (base) 1.2-2.5 (m=1.7, n=27). Thorax smooth. Pearl row consisting of a single row of tubercles (053g.jpg).
Abdomen: Hook rows on tergites broken medially (053h.jpg); hooks III 3/2-6/6, IV 2/2-5/5, V 0/0-4/5 (n=29). Abdominal segments II-V dorsally nearly covered with small points except for the adhesion marks; VI-VIII progressively less extensively armed (no anterior transverse band of strong points). Sternites IV-VII with a transverse pair of toothed humps postero-medially. Similar toothed humps are also present on tergites III-VII; on tergite II there is a posterior row or narrow band of teeth which is usually broken medially, and on tergite VIII there is a continuous band of points posteriorly. Segment VIII with all lateral setae very thin, short, inconspicuous.
Anal segment: Anal lobes without fringe. Anal macrosetae conspicuous, an additional fourth seta internally, well-separated from the other three.
(Linked adult male: Langton and Pinder, 2003a)

Species keys out at Page 711: Orthocladiinae 123 Tvetenia of the Text Key.

Holarctic species: widespread in Europe.
(For more information see module IdentifyIt – file: Orthocladiinae).

Ecological notes
Running water.