Tironinae Stebbing, 1906

Just, Jean, 2022, Tirons of the world: a review of ‘ tironid’ amphipods, description of new genera and species, and establishment of a new subfamily Tironinae Stebbing, 1906 stat. nov. (Crustacea, Synopiidae), Zootaxa 5139 (1), pp. 1-89 : 7

Tironinae Stebbing, 1906 stat. nov. (new subfamily)

Tironidae Stebbing 1906 (syn. of Synopiidae Dana, 1853 by J.L. Barnard 1964).

Diagnosis. Synopiidae with accessory eyes*. Gnathopods 1 and 2 simple with slender, long carpus and propodus. Pereopods 3–7 short, dactylus/unguis short, stubby ( Fig. 1a ), or pre-stubby ( Fig. 1b ) with short, hooked claw and curved counter-seta on dactylus. Uropod 3 longer than uropods 1 and 2, at least as long as elongate, fully split telson.

* Synopia Dana, 1852 and Telsosynopia Karaman, 1986 also have accessory eyes, but otherwise differ in all the diagnostic characters of the Tironinae .

Type genus: Tiron Lilljeborg, 1865

Component genera: Glandulotiron gen. nov., Metatiron Rabindranath, 1972 , Minitiron gen. nov., Pseudotiron Chevreux, 1895 , Tiron Lilljeborg, 1865 , Tironella gen. nov.

Additional characters of the Tironinae . Habitus. The head short to slightly forward projecting, evenly downward curved or rounded angularly curved, with downward pointing acute or blunt rostrum. Eyes and accessory lenses are occasionally reported as absent. In many species of the present study eyes and accessory lenses are clearly scattered, retracted, and fading. In some specimens, especially smaller ones, visual elements cannot be seen at all. Where lack of visual elements has been reported only a single specimen was described. It is often difficult to ascertain the number of accessory lenses, even in specimens undoubtedly of the same species. I agree with Jazdzewski (1990, p. 118) that this character should be avoided in keys due to the uncertainty involved. However, there is little reason to believe that there are truly blind Tironinae , and the data given in descriptions and illustrations below are from particularly well-preserved adult or nearly adult specimens.

Gills are simple sacks. Oostegites on pereonites 2–7 are long narrow straps with few long marginal setae.

Ornamentations are present in most, if not all, tironins in the form of crenulation or small spines or denticles posterodorsally and some way down the sides on the posterior margin of some pereonites and pleonites. Difficulties in interpretation due to allometric and sexual differences make these character problematic in the identification of similar species and is therefore not used consistently in keys or in descriptions below. A large dorsoposterior spine is ubiquitous on urosomites 1 and 2 and often on 3.

Setae. Species of tironins are adorned with a wide variety of pectinate and moderately plumose setae on most appendages. For example, the long dorsal setae on uropod 3 inner ramus are finely plumose, but for ease of clarity they, and other similar setae, are generally illustrated as simple setae. Exceptions are the stout, pectinate setae on the posterior margin of gnathopod 1 propodus and occasionally on gnathopod 2; the unusually dense plumosity of Glandulotiron griffithsi sp. nov. setae on the posterior margin of merus and carpus of gnathopod 2; the anterior margins of the basis, ischium and merus of pereopods 5 and 7 in some species, and penicillate setae on the antennae. Robust setae on maxilla 1, gnathopods, pereopods, uropods and telson are important for identification, and are therefore clearly illustrated.

Uropod 3 peduncle is at most as long as urosomite 3, rami exceed the length of uropods 1 and 2 and the telson. The telson is elongate, split nearly to base, with robust setae dorsally (with the possible exception of Pseudotiron coas ).

Figures

FIGURE 1. Representative habitus illustrations of tironin genera. Tiron spiniferus (from Sars, 1895 pl. 140, ♀ 8 mm); Pseudotiron miratus sp. nov. (this paper, ♀, 4.5 mm); Tironella pervicax comb. nov. (from J.L. Barnard, 1967 fig. 84, ♂ 4.7 mm); Glandulotiron pilocaputis sp. nov. (this paper, ♀, 6.3 mm); Metatiron tropakis (from J.L. Barnard, 1967 fig. 45, ♀, 4.9 mm); Minitiron bellairsi comb. nov. (from Just, 1981 fig. 1, ♀ 2.4 mm). a and b, dactylus and unguis of pereopods 3–7: a, stubby; b, pre-stubby.