Minitiron, Just, 2022

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 : 78

Minitiron gen. nov.

( Fig. 1 , 43 c, d )

Diagnosis. Tironin Synopiidae without mandible palp. Cephalon in lateral view forming an even curve terminating in a downward pointing short, acute rostrum. Interantennal head lobes triangular, pointed or blunt. Massive squarely bundled mouthparts as deep below head as depth of head. Maxilla 1 outer plate apex narrow, with amassed group of 7–9 distally curved, unequally long spine-setae ( Fig. 43 d ). Coxal plates 1 and 2 of subequal length, plate 3 the largest, posterior margin tapering from middle to blunt apex, plate 4 the shortest, nearly rectangular; coxal plates 5 and 6 posterolobate, together wider than plates 1–4, plate 7 short, much wider than deep. Gnathopod 1 basis strongly forward curved ( Fig. 43 c ), carpus about 3/4 length of basis. Pereopods 3–7 propodus short, with stubby dactylus / unguis. Urosomites 1 and 2, or all 3, with posterior dorsal spine. Uropod 3 outer ramus of single article.

Note regarding eyes. In the Australian material the ocelli of both main and accessory eyes are retracted and faded to become almost invisible, but the circumference of the eye and accessory eye and a central globulose mass on each are often distinctive. This may also be the case in the two Japanese species ( Hirayama 1988) where accessory eyes have not been noted. Eyes and accessory eyes (cf. Minitiron bellairsi , Fig. 1 ) are likely to be present in all Minitiron species.

Etymology. These species generally are the smallest of the tironins, hence the prefix mini- before the group name.

Type species. Minitiron orpheus sp. nov. —Here designated.

Component taxa. Minitiron bellairsi ( Just, 1981) comb. nov.; M. caecus ( Ledoyer, 1979) comb. nov.; M. galeatus ( Hirayama, 1988) comb. nov.; M. orpheus sp. nov.; M. ovatibasis ( Hirayama, 1988) comb. nov.; M. thompsoni ( Walker, 1904) sp. indet.; M. sp. comb. nov. ( Ledoyer 1979, as Metatiron brevidactylus ( Pillai, 1957)) .

Distribution. Northwest Atlantic ( Barbados), Gulf of Mexico (SW Florida), Caribbean Sea ( Belize, Venezuela), Japan, Indian Ocean ( Madagascar, Sri Lanka), Australia.

Remarks. In addition to 5 previously described species here transferred to Minitiron gen. nov., specimens belonging to this shallow water genus have been collected in numerous places in Australia: from NE Queensland along the east, south, and west coasts north to around Dampier, Western Australia; from Auckland Islands, New Zealand, and from several locations in Thailand. A separate study of this apparently quite diverse group is needed. Therefore only one species from eastern Australia is being described here. Collection locations in Australian for material not reported here are shown in Fig. 47 .

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.

FIGURE 43. Principal characters separating Metatiron and Minitiron gen. nov. Upper row, gnathopod 1; lower row, maxilla 1 outer plate. a and b, Metatiron tropakis, original; c and d, Minitiron bellairsi, c from Just 1981; d, from Barnard & Thomas 1989.

FIGURE 47. Distribution of Glandulotiron and Minitiron (Tironinae, Synopiidae) in Australia. A, Adelaide; B, Brisbane; D, Darwin, Da, Dampier; JB, Jervis Bay; L, Lizard Is.; M, Melbourne; Or.Is., Orpheus Island (type locality of Minitiron); P, Perth; PH, Port Hedland; S, Sydney; SB, Shark Bay; T, Townsville. Dots may represent more than one sample. Open circles: undescribed material of Minitiron.