Rheosmittia spec-b

Author: Cranston and Saether, 1986

Diagnosis (in part after Cranston and Saether, 1986a)
Exuviae very small, 1.6mm long (n=1); brown or brownish. (1.7-2.1mm (m=1.9mm, n=10), weakly infuscate).
Cephalothorax: Frontal setae absent; cephalic area smooth, without warts or tubercles. Ocular area with 1 postorbital and 1 vertical seta, when visible, ocular and postorbital setae single and about 40µm long. Thoracic horn absent. Thorax with 1 or 2 median and 1 or 2 lateral antepronotal setae; 3 precorneals in a line with second the longest; dorsocentrals arranged in 2 groups of 2 setae. Precorneal and dorsocentral setae none longer than 45µm long (damaged and/or obscured). Thorax smooth to weakly rugulose; wing sheaths smooth; leg sheath arrangement normal for Orthocladiinae.
Abdomen: Tergite I and sternite(s) I or I-IV and V-VIII or VII-VIII without shagreen. Tergites II-IV or III and IV with caudal, anteriorly directed points. Tergites II-VII (or (VII) with posterior transverse band of posteriorly-directed points and an antero-median area of smaller points which may extend posteriorly to contact posterior band. Median point area weaker on posterior segments and very reduced on tergites VII and/or VIII. Tergites IV-VI without a distinct circular antero-median point patch. Sternites V and VI with posterior transverse rowsof weak, anteriorly directed points. Apophyses absent. Pedes spurii A vestigial on IV of some specimens; pedes spurii B absent. Segment I with 2(?) weak or 5 stronger dorsal setae, 0-2 ventral setae and 1 lateral seta. Segments II-VII with 4 or 5 dorsal setae, 4 or 5 ventral setae and 3 or 4 lateral setae. Segment VIII with 2 or 4 dorsal setae, 1 ventral seta and 2 lateral setae. On tergites II-IV or VI dorsal seta 5 enlarged, dorsal seta 5 on tergite III 32-54µm long, 10-12µm wide apically (058k.jpg), narrower and less deeply split than in Rheosmittia spinicornis. Lateral seta 2 often more strongly developed than remaining lateral setae. Lateral setae 20-32µm long on segment III.
Anal segment: Tergite IX medially with or without shagreen. Anal lobe very reduced with tergite IX postero-laterally expanded into spinose tails; lobe, including tails, 165-180µm (m=172µm) long. Genital sacs of male large, nearly extending to apex of tails. Anal lobes without fringe and macrosetae.

Species keys out at Page 749: Orthocladiinae 161 Rheosmittia of the Text Key.

(For more information see module IdentifyIt – file: Orthocladiinae).

Ecological notes
Northern streams and lakes.