(Figs 1; 4S)
Lysianassa spinifera Stimpson, 1853.
Tiron acanthurus Lilljeborg, 1865.—G.O. Sars 1895 p. 399, Pl.140; Gurjanova 1951, p.591, fig. 397.
Tiron spiniferum (Stimpson).—Stephensen 1938, p. 231, 1944, p. 76; Shoemaker 1955, p. 38; Lincoln 1979, p. 400, figs 188a, 190.
Tiron spiniferus (Stimpson).—Jazdzewski 1990, p. 114, nomenclatural correction of epithet.
Type material: unknown.
Distribution. North Atlantic, E and W north to Svalbard and NW Greenland.
Remarks. As stated above under tironin characters, eyes and accessory lenses in particular are often retracted, scattered or totally faded. Stimpson (1853) described Lysianassa spinifera from the entrance to Fundy Bay, Nova Scotia, but made no comments on eyes. Since Sars (1895) there has been doubts about the accessory eyes of the type species. Sars (p. 398), in describing Tiron wrote “Eyes...; below them on each side, a minute accessory eye.” and on T. acanthurus (p. 400, = T. spiniferus) he stated “... accessory eyes very small,...”, and his illustrations (pl. 140) show an accessory eye of presumably one lens, or possibly 2–3 tightly aggregated tiny lenses. Lincoln (1979, p. 400 and fig. 188a) wrote “eyes..., also with pair of small accessory eyes”, and the illustration shows a full habitus with the position of accessory eyes rendered as a single circle, similar to his circular marking of the main eye.
Tiron spiniferus is the only representative of the genus reported from across the boreal North Atlantic, from New England and the low-arctic of West Greenland to Northern Norway and southern Scandinavian waters. Specimens from a large collection from southern West Greenland (the closest location to the type locality) and from the Skagerrak between Denmark and Norway in the eastern Atlantic have been examined. In both areas there are specimens with reasonably well-preserved visible eyes. Such specimens invariably have 2 somewhat segregated accessory lenses (Fig. 4S). Accessory eyes of 2 lenses have thus been confirmed in 4 of the 6 species of Tiron (T. spiniferus, T. biocellata, T. lilljeborgi sp. nov., T. canadense sp. nov.), while accessory lenses have as yet not been observed in T. antarcticus, and T. sagamiense sp. nov.