Pseudotiron miratus, 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 : 72-73

Pseudotiron miratus sp. nov.

( Figs 41–42 )

Type fixation. Holotype, ♀.—Here designated.

Etymology. The epithet miratus is Latin for ‘astonished’ indicating the surprising find of this species in NW Australia.

Material examined. Holotype, ovigerous ♀, 4.5mm. Western Australia, Northwest Shelf, between Dampier and Port Hedland, 19°56.54’S, 117°52.48’E, 44 m, S-M grab, RV Soela, CSIRO Div. of Fisheries , 25 June 1983, stn NWA 156, WAM C76568

Paratype. Western Australia, Northwest Shelf, between Dampier and Port Hedland, 19°04.48’S, 118°50.42’E, 84 m, S-M grab, RV Soela, CSIRO Div. of Fisheries , 29 June 1983, stn NWA 171, NMV J73778 (1 tiny specimen) .

Description. Head with blunt anterior projection, dorsal and anterior margins straight, rostrum apex rounded with tiny setules. Interantennal head margin vertical, lower corner broadly rounded. Eyes and assessory eyes present (lenses reduced to lump in holotype).

Pleonites 1 and 2 with very fine irregular serration on lower half of posterior margin. Urosomites 1–3 with small dorsodistal spine.

Mouthparts. Maxilla 1 palp apex with 4 finely denticulate peg-like setae and 1 lateral and 1 medial more slender seta, outer plate with 9 sharply pointed spine-setae. Mouthparts otherwise normal.

Antenna 1 as long as pereonite 1–7 combined along dorsum, sparsely setose, peduncle article 2 about half length of 1, article 3 about 1/3 longer than article 2, flagellum about 1.25 length of peduncle, with 14 articles, accessory flagellum of 2 articles. Antenna 2 as long as pereonites 1–7 and half of pleonite 1 combined along dorsum, peduncular article 4 the longest with dense row of setae on anterior margin, flagellum of 14 articles; antennae otherwise sparsely setose.

Coxal plate 1 distally widening, anterior margin with blunt mid-anterior projection, plate 2 longer than 1, nearly rectangular with weak mid-anterior concavity. plate 3 strongly pelagont, posterior projection broadly rounded, with short plate 4 about as long as broad, anteriorly and distally rounded, posterior margin with weak concavity, plate 7 about twice as long as greatest depth, slightly posterolobate.

Gnathopod 1 basis length about 6 times width, 1.2 length of carpus, anterior margin with long and medium setae, posterior margin with a couple of medium setae, ischium with posterodistal tuft of setae, merus with some long setae in posterior distal half, carpus about 5 times longer than greatest width, posterior margin with row many setae of varying length, dorsal margin with 1 long setae in middle and 1 in distal corner, propodus 0.6 length of carpus with 3 stout, pectinate setae and some simple setae on posterior margin, dactylus and unguis of equal length, combined nearly half as long as carpus. Gnathopod 2 basis length 8.0 times width, 1.2 length of carpus, anterior margin with spaced row of about 6 long setae, posterior margin with 4 long setae in proximal half, ischium with small posterior tuft of setae, merus with row of setae in distal third, carpus about 10 times longer than wide, posterior margin with spaced row of medium length setae, propodus long and slender, 2/3 the length of carpus, posterior margin with spaced row of about 6 short, stiff setae, dactylus and unguis of subequal length, combined about half length of carpus.

Pereopods 3–6 dactylus about as long as broad, nearly fully stubby, dactylus of 7 conical, about twice as long as broad. Pereopods 3–4 basis about 2.5 times longer than wide, about as long as ischium and merus combined, all articles with few short robust setae. Pereopod 5 shorter than 6 and 7, basis pear shaped broadest in distal half, merus and carpus with few short robust setae. Pereopod 6 basis ovoid, posterior margin with slight bulge in middle, anterior margin with a few long setae distally, merus posterior margin with single robust seta in middle and 1 long and 1 short in distal corner, anterior margin with 2 short robust setae in middle and 2 of unequal size in distal corner, carpus posterior margin with single robust seta in middle and group of 3 in distal corner, anterior margin with 4 pairs of unequal robust setae, propodus anterior margin with 2 robust setae distally, posterior distal corner with 3 unequally long robust setae. Pereopod 7 (especially propodus) longer than pereopods 5 and 6, basis anterior margin shorter than pereopod 6 basis, 1.4 times wider than anterior margin length, posterior margin forming broadly rounded lobe with tiny setules curving smoothly unto slightly projecting distal lobe, anterior margin with a few long setae distally, medial surface with row of several long setae, merus posterior margin with 1 long simple seta and 1 robust seta in middle and 1 short and 1 long robust setae in distal corner, carpus posterior margin with 1 small and 1 long robust seta on distal corner, anterior margin with robust setae; propodus anterior margin with 3 robust setae, posterior distal corner with 3 unequally long robust setae, dactylus about twice length of unguis, unguis and opposing seta of equal length.

Uropod 1 peduncle dorsolateral margin with 3 small robust setae, dorsomedial margin with 4 long robust setae, rami slender, inner ramus 0.8 length of peduncle with 3 robust setae dorsodistally and strong terminal robust seta in hollow, outer ramus 0.9 length of inner ramus, naked except for strong terminal robust seta in hollow. Uropod 2 peduncle half as long as 1, reaching as far as distal corner of urosomite 3, outer ramus about half as long as inner, naked, peduncle and inner ramus with 1 dorsal robust seta each. Uropod 3 peduncle about 0.6 as long as outer ramus, dorsodistal corner with group of 3 slender robust setae, outer ramus basal article dorsolateral margin with 3 robust setae, dorsomedial margin with 3 or more robust setae, dorsodistal corner with 2 larger robust setae, short second article acutely pointed, with 3 robust setae of markedly different length, inner ramus as long as outer ramus basal article, with dorsal row of long setae in proximal half, apex with at least 1 long and 1 short robust setae.

Telson. Length about 4 times greatest depth in lateral view, reaching to middle of uropod 3 rami, dorsal view length 3 times greatest width, each lobe with 1 mid-point and 1 distal robust setae, apices with group of 4 slender robust setae of varying length.

Rows of elongate glands present in uropod peduncles, adjacent parts of urosomites, and telson.

Size. Largest ♀, 4.5 mm. ♂ not known.

Distribution. NW Australia; 44– 84 m.

Remarks. Pseudotiron miratus differs from P. bouvieri in the shape of the head, and in the truncate posterior projection of coxal plate 3 of the latter. Pseudotiron miratus shares with P. golens the angularly projecting head, but the uropods of the latter are much shorter than in P. miratus , and the dactyli of pereopods 3–7 are distinctly elongate pre-stubby. Pseudotiron coas differs from the other 3 species in its rectangular, non-pelagont coxal plate 3, and in having hardly any setae on pereopods and uropods.

Urosomal glands, as found in Pseudotiron miratus , have not been reported in the other 3 species in the genus. If it can be shown that these glands are absent in the type species Pseudotiron bouvieri Chevreux, 1895 , a new genus will be required for Pseudotiron miratus .

Figures

FIGURE 41. Pseudotiron miratus sp. nov. Holotype., ♀. dlv, head lateral view; ep2, epimeral plate 2 lower posterior margin; gl us, urosome (part) with glands indicated; mx1, maxilla 1; tel, telson; us, urosome. Habitus scalebar: 1 mm.

FIGURE 42. Pseudotiron miratus sp. nov. Holotype, ♀. gp1–gp2, gnathopod 1 and 2; p3, p5–7, pereopods 3 and 5–7; (all same scale).