Eylais extendens (Müller, 1776)

Synonyms: Hydrachna extendens Müller, 1776 (original designation); Eylais undulosa Koenike, 1897; Eylais muelleri Koenike, 1897; Eylais limnophila Piersig, 1899; Eylais soari Piersig, 1899; Eylais similis Thon, 1899; Eylais tenera Thon, 1899; Eylais mosquensis Croneberg, 1899; Eylais unisinuata Croneberg, 1902; Eylais instabilis Halbert, 1903; Eylais similis gibberipons Viets, 1910; Eylais sugambra Koep, 1911; Eylais thienemanni Koenike, 1911; Eylais monofissa Szalay, 1934; Eylais szalayi Husiatinschi, 1939

Type material: Unknown, possibly lost.

Type locality: Denmark (probably surroundings of Copenhagen) or Norway (Müller 1776) .

Geographical distribution: Western Palaearctic (Davids et al. 2006).

Distribution in Portugal: Centre: Beira Litoral, Alcobaça municipality; South: Alentejo, Guadiana River-between Serpa and Beja municipalities (Lundblad 1956; Valdecasas 1988).

Ecological notes: In oligotrophic and euritrophic slow-moving waters and sensitive to high electrolyte concentrations (absent in brackish water) (Davids et al. 2006), present in dead twigs, plants, such as grasses, Alisma spp., Myriophyllum spp. and Scirpus spp. (Lundblad 1956); Larval insects hosts: parasitic of 26 different water beetle species from families Dytiscidae, Haliplidae, Noteridae, Lacophilidae, and Hydrophilidae (Davids et al. 2006) .