Metatiron Rabindranath, 1972

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 : 76

Metatiron Rabindranath, 1972

( Fig. 1 ; Fig. 43 a, b )

Metatiron Rabindranath, 1972, p. 84 , fig. 1.

Type species. Pseudotiron brevidactylus Pillai, 1957 .—Original designation.

Component taxa. Metatiron bonaeriensis Alonso de Pina, 1998 ; M. brevidactylus ( Pillai, 1957) ; M. triocellatus ( Goeke, 1982) ; M. tropakis (J.L. Barnard, 1972) .

New diagnosis. Tironid Synopiidae without mandible palp. Cephalon in lateral view forming an even curve (occasionally slightly angular in males) terminating in a downward pointing short, acute rostrum. Interantennal head lobes triangular pointed or bluntly rounded. Maxilla 1 outer plate apex broad with two rows of pointed, generally denticulate spine-setae ( Fig. 43b ). Coxal plates 1 and 2 of subsimilar length and shape, plate 3 the largest, expanded in middle, posterior margin tapering from middle to blunt apex, plate 4 the shortest, anterior and distal margins broadly rounded, posterior margins straight to shallow concave comma-shape, plates 5 and 6 posterolobate, together, wider than plates 1–4; coxal plate 7 short, much wider than deep. Gnathopod 1 basis nearly straight ( Fig. 43a ), carpus nearly as long as basis. Pereopods 3–7 merus, carpus and propodus short, with stubby dactylus/unguis. Urosomites 1 and 2, or all 3, with posterior dorsal spine. Uropod 3 outer ramus of single article.

Distribution. Travancore SW India, Eastern America (Virginia to Florida), Caribbean Sea ( Venezuela), Golf of Mexico, SW Atlantic ( Brazil to Argentina), Eastern Pacific (California to Peru).

Key to species of Metatiron

1. Telson with small simple dorsal setae on each lobe........................................................... 2

- Telson with strong robust setae in row on each lobe.......................................................... 3

2. Pereopod 7 basis round, broader than long; uropod 3 peduncle about half as long as outer ramus, outer ramus with 7 robust setae dorsally...................................................................... M. brevidactylus ( Pillai, 1957)

- Pereopod 7 basis broadly rounded, as broad as long; uropod 3 peduncle about 9/10 length of outer ramus, outer ramus with 4 (5) robust setae dorsally......................................................... M. triocellatus ( Goeke, 1982)

3. Gnathopod 1 basis with row of long plumose setae on anterior margin; uropod 3 peduncle about half as long as outer ramus, outer ramus with about 8 dorsal robust setae; telson lobes with dorsal row of 7 8 small robust setae........................................................................................... M. bonaerensis Alonso de Pina, 1998

- Gnathopod 1 basis with simple setae of varying length on anterior margin; uropod 3 peduncle about 2/3 length of outer ramus, outer ramus with about 15 robust dorsal setae; telson lobes with dorsal row of about 8 long robust setae............................................................................................ M. tropakis (J.L. Barnard, 1972)

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.