Hydrosmittia Ferrington Jr & Saether 2011, gen. n.

Key to known larvae of Hydrosmittia gen. n.

1. Mandible with 4 inner teeth............................................................................. 2

– Mandible with 3 inner teeth.............................................................................. 3

2. Anterior parapods without any longer claws; total length of fourth instar about 6.2 mm; postmentum about 137 µm long......................................................................... Hydrosmittia sp. “ Northwest Territories ”

– Anterior parapods with 20–60 longer claws; total length of fourth instar 2.3–4.6 mm; postmentum 73–79 µm long; Holarctic............................................................................. H. oxoniana (Edwards) (p. 120)

3. Largest of 10–12 claws of posterior parapods 43–78 µm long; anterior parapods each with about 40–60 longer claws; anal seta bifid or 2–3 anal setae.................................................................................. 4

– Largest of 7–11 claws of posterior parapods 15–34 µm long; anterior parapods each with about 25–30 longer claws; anal seta single....................................................................................................... 5

4. Posterior parapods of fourth instar 149–194 µm long, of third instar about 110 µm long; anal seta bifid or 2 anal setae; seta interna present............................................................... H. ruttneri (Strenzke et Thienemann) (p. 129)

– Posterior parapods of fourth instar about 98 µm long; 3 anal setae; seta interna not observed...... H. falsicostata sp. n. (p. 134)

5. Posterior parapods each with 9–11 claws; anal tubules 71–117 µm long, with 1–2 constrictions... H. montana (Strenzke) (p. 118)

– Posterior parapods each with 7–10 claws; anal tubules about 25–65 µm long, without constrictions... H. virgo (Strenzke) (p. 126)