Minitiron orpheus, 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 : 79-82

Minitiron orpheus sp. nov.

( Figs 44–45 )

Type fixation. Holotype, ♀.—Here designated.

Etymology. This species is named after the type locality Orpheus Island in northeastern Queensland.

Material examined. Holotype, ovigerous ♀, 3.6 mm. Australia, Queensland, Orpheus Island, north of Fantome Island , 18°37’S, 146°30’E, 3 m, sand, J.D. Thomas, 14 February 1989, stn JDT/OPH-11, AM P103554 .

Paratypes. Same data as holotype, AM P105644 (24 ♀♀, 1♂ subadult) . Australia, Queensland, Orpheus Island, north of Fantome Island , 18°37’S, 146°30’E, 3 m, sand, J.D. Thomas, 14 February 1989, stn JDT/OPH-11, NHMD 917119 (5 specimens) . Australia, Queensland, Orpheus Island, past reef flat at Northeast Point , 18°37’S, 146°30’E, 8 m, sand, J.D. Thomas, 15 February 1989, stn JDT/OPH-13, AM P103555 (1 subadult ♂, 2.5 mm, illustrated, 1 ♀) .

Description (female). Head deeper than long, evenly down curved. Rostrum acute, apex pointed. Interantennal lobes wide angled, bluntly pointed. Eyes and accessory eyes present. Pleonites with small double-spine in posterodorsal corner followed laterally by a few small crenations. Urosomites 1 and 2 with large dorsal spine, urosomite 3 without spine, dorsodistally with 1 robust seta on each side.

Mouthparts. Lower lip with proximal half of lateral lobes much expanded in lateral view partly covering maxilla 1 (observed, not illustrated; see Minitiron bellairsi ( Just, 1981, fig. 1)). Maxilla 1 palp article 2 reaching nearly to tips of outer plate long spine setae, apex with 4 short, pointed setae, inner plate broad at base, tapering to pointed apex with tuft of small setae, mid-medial margin a low convex bulge with 3 long simple setae and tiny marginal setules. Maxilla 2 plates of subequal length, both with apical long simple setae, inner plate the broader, with submarginal oblique row of long setae. Mandible molar in ventral view obliquely truncate, acute pointed, grinding surface with many small denticles. Maxilliped palp sparsely setose, outer plate apex rounded with 3 blunt, curved setae, (inner plate not observed).

Antennae 1 about 0.6 length of antenna 2, as long as pereonites 1–5 combined along dorsum, peduncle article 1 twice length of 2, article 3 about 1.2 length of 2, flagellum 1.2 length of peduncle, with 7 articles, some articles with single long aestetasc, accessory flagellum with 3 articles, as long as flagellar articles 1 and 2 combined. Antenna 2 as long as pereonite 1–6 combined along dorsum, peduncle articles 4 and 5 of equal length, with many short setae on anterior margin, flagellum as long as peduncle articles 5 and 4 combined, with 7+ articles, most articles with short, forward pointing robust seta. Antennae generally sparsely setose.

Coxal plates 1–3 of equal length, plate 2 tapering to rounded apex, plate 3 broader than plate 2, apically blunt, distal margin oblique forming rounded corner with short posterior margin, plate 4 half as long as plate 3, nearly rectangular with rounded distal corners; all plates with small apical setae.

Gnathopod 1, expanded distal half of curved basis with a few long setae along anterior margin, posterior margin with a couple of long setae and a few tiny setae in distal corner, carpus about 3/5 length of basis, posterior margin with scattered simple setae of differing length and a few strong pectinate robust setae distally, propodus half as long as carpus with 5 small peg-like robust setae on posterior margin, dactylus about 0.3 length of propodus, unguis short, nearly straight. Gnathopod 2 basis straight, widening distally with a few small setae on anterior margin, apical corners with single long seta, merus covering 1/3 of carpus posterior margin; carpus 0.8 length of basis, broadest in middle, posterior margin with 5-6 long setae and 3 short robust setae on mid-margin, propodus 0.4 length of carpus, with a few simple setae on both margins and 1–2 short, peg-like setae on posterior margin, dactylus about 0.3 length of propodus, unguis less than half length of dactylus.

Pereopods 3–4 basis slender, as long as succeeding 3 articles combined, with a few distal setae; remaining articles with few small setae distally.

Pereopods 5 basis narrowly oval, slightly widening distally, with broadly rounded, shallow posterodistal lobe, margins with few tiny setules, merus posterior margin with 1 midposterior and 1 distal slender robust seta, anterior margin with 1 small and 3 slender robust setae. Pereopod 6 basis ovoid with broad, shallow posterodistal lobe, posterior margin with a few small setae, anterior margin with a few long and short setae, merus with 1 midposterior and 1 distoposterior seta, anterior margin with a few short and 2 long slender robust setae, carpus with 1 or 2 posterodistal robust seta, anterior margin with 2 mid-margin groups of 1 short and 1 longer robust setae, and distal group of 4 robust setae, propodus with 1 robust seta in anterior corner and group of 3 robust setae of different length in posterior corner. Pereopod 7 basis with broadly rounded posterior proximal lobe, posterior margin convex, smooth with a few tiny setae, curving into broad shallow distal lobe, anterior distal corner with a short and a longer setae, medial surface with row of about 3 long setae, merus posterior margin with 1 simple seta and 3 slender robust setae in distal half, anterior margin with 3 tiny and single longer robust setae, carpus about 4 times longer than broad, longer and more slender than in pereopod 6, posterior margin with 3 setae of different length and 1 short and 1 long seta in distal corner, anterior margin with 3 robust setae, propodus with 1 anterodistal robust seta and 4 posterodistal robust setae of different length.

Uropods 1 and 2 peduncles both reaching to the middle of uropod 3 peduncle. Uropod 1, peduncle with 2 short dorsolateral and 2 long dorsomedial robust setae, rami of equal length, 0.7 length of peduncle, outer ramus distally with 3 small robust setae, inner ramus with 2 long dorsal robust setae, apically with 1 long and 1 short robust seta and curved, hook-like seta (damaged on outer ramus). Uropod 2 peduncle with 4 robust setae dorsally, inner ramus with two robust setae dorsally and apex similar to uropod 1 (outer ramus apex damaged). Uropod 3 peduncle 3/4 length of outer ramus, dorsally with 2 robust setae, outer ramus dorsally with 6 upright robust setae, ventrolaterally with row of about 9 small robust setae, concavely truncate apex with 1 long, 1 short and 2 small robust seta, inner ramus nearly as long as outer ramus, dorsally with long plumose setae and 2 robust setae distally, apex as in outer ramus.

Telson length close to twice greatest width in dorsal view, reaching about 3/4 along uropod 3 outer ramus, lobes with 3 long, upright robust setae dorsally, apices laterally pointed, with short robust seta medially.

Male. Generally as female but differing in the following points: interantennal lobes more broadly rounded, antenna 1 as long as pereonites 1–6 combined, peduncular articles 2 and 3 broader than long, combined shorter than article 1, flagellum twice as long as peduncle, article 1 as long as peduncle articles 1 and 2 combined, accessory flagellum of 4 articles as long as flagellum article 1. Antenna 2 as long as pereonite 1–7 and pleonite 1–2 combined, flagellum of 10 very slender articles. Urosomite 3 with short distal tooth but no robust setae. Uropod 3 outer ramus with fewer robust setae dorsally and laterally.

Size. Largest ♀, 4.4 mm. Largest ♂, 2.5 mm.

Distribution. Australia, north-east Queensland, Orpheus Island; 3– 8 m.

Figures

FIGURE 44. Minitiron orpheus gen. et sp. nov. Holotype, ♀, except M, ♂, paratype, 2.5 mmm. ceph, head with antennae; md, mandible; mx1, maxilla 1; mx2, maxilla 2; mxp, maxilliped; tel, telson; up1 and up3, uropods 1 and 3 (ir, inner ramus, or, outer ramus), ur, urosome. Habitus scale bar, 1 mm.

FIGURE 45. Minitiron orpheus gen. et sp. nov. Holotype, ♀; gp1, gp2, gnathopods 1 and 2; p3, p5–7, pereopods 3 and 5–7.