Tiron Lilljeborg 1865

Tiron Lilljeborg, 1865

New diagnosis. Tironin synopiids with interantennal head lobe triangular, acutely pointed or bluntly rounded. Mandible with palp, elongate palp article 2 straight. Coxal plates 1–3 of subsimilar length and shape, about as long as depth of corresponding pereonite, anterior and posterior margins nearly parallel, apex broadly rounded, 4 slightly shorter than 3, moderately tapering to rounded apex; coxal plates 5 and 6 posterolobate, together as broad as first 4 plates combined, coxal plate 7 short, much wider than deep, rounded, broadest in posterior part. Gnathopods 1 and 2 with straight basis, carpus slender, elongate, dactylus with unguis slightly curved, about half as long as propodus; gnathopod 1 propodus with row of short stout, pectinate setae on posterior margin, gnathopod 2 propodus posterior margin with scattered slender setae. Pereopods 3–7 of normal shape, carpus and propodus elongate, dactylus with unguis short curved, dactylus with anterior curved robust seta in opposition to the unguis (pre-stubby, Fig. 1). Uropod 3 outer ramus of single article.

Type species. Lysianassa spinifera Stimpson, 1853.

Component species: Tiron antarcticus K.H. Barnard, 1932.– Jazdzewski, 1990; T. biocellatus J.L. Barnard, 1962, (also J.L. Barnard 1972); T. lilljeborgi sp. nov.; T. canadense sp. nov.; T. sagamiense sp. nov.; T. spiniferus (Stimpson, 1853). Unconfirmed species: T. cf. antarcticus, Lörz & Coleman (2013).

Distribution. Arctic, North Atlantic, Japan, Eastern Pacific, Australia, Antarctica.

Key to species of Tiron

1. Pleonites 1–3 with crenulation along posterior lateral margins................................................. 2

- Pleonites 1–3 with row of acute spines in upper part of posterior lateral margins.................................... 3

2. Telson with 6–7 robust setae dorsally in row on each lobe; crenulation on upper part of posterior pleonite margin.................................................................................... T. a ntarcticus K.H. Barnard,1932

- Telson with 2–3 robust setae dorsally on each lobe; crenulation on entire posterior margin........... T. sagamiense sp. nov.

3. Gnathopod 1 carpus dorsal length 5–6 times greatest depth; gnathopod 2 carpus slender, deepest just in front of merus, dorsal length 7 times greatest depth..................................................... T. spiniferus (Stimpson, 1853)

- Gnathopod 1 carpus dorsal length 3–4 times greatest depth; gnathopod 2 carpus deepest in middle, dorsal length 3+ times greatest depth............................................................................................ 4

4. Telson lobes without robust setae................................................ T. biocellatus J.L. Barnard, 1962

- Telson lobes with 2–3 robust setae........................................................................ 5

5. Urosomites and pleonites dorsally with many small simple setae; telson reaching 2/3 along uropod 3 outer ramus............................................................................................. T. lilljeborgi sp. nov.

- Urosomites and pleonites dorsally naked except single tiny setae between pleonite lateral teeth; telson reaching apex of uropod 3 rami.............................................................................. T. canadense sp. nov.