Tiron sagamiense, 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 : 16-18

Tiron sagamiense sp. nov.

( Figs 6–7 )

Type fixation. Holotype, sex not determined.—Here designated.

Etymology. This species is named for the Sagami Sea, Japan.

Material examined. Holotype, 6.0 mm. Japan, Sagami Sea , 300 fv, (1 old Danish favn equaling 1.88 m, hence 300 fv. = 564 m), hard bottom, Dr. Th. Mortensen, 29 June 1914, NHMD 916108 . (Unique).

Description. Rostrum strongly down curved, acutely pointed. Frons broadly rounded above epistome. Interantennal lobes rounded (marginal apical setae not observed). Eyes faded.

Pleonites 1–3 with dorsoposterior double-spines and broad crenulation with setae along entire posterior lateral margins.

Mouthparts. Not observed.

Antenna 1–2 (broken in middle of peduncle).

Coxal plate 1 partly broken, apical margin slightly crenulate with setae in indentations; plate 3 nearly rectangular with long setae on apical margin; plates 5–7 normal posterolobate.

Gnathopod 1 basis as long as merus and carpus combined, mid-posterior margin with a few long setae, anterior margin with several long and a few short setae in distal half, carpus broadest close to merus, posterior margin with several groups of long setae, propodus about 3/5 length of carpus, with 4 pairs of unequally long pectinate setae on posterior margin, dactylus with unguis 3/4 length of propodus. Gnathopod 2 basis slightly longer than merus and carpus combined, mid-posterior margin with a few long setae, distal half of anterior margin with about 8 long setae, carpus posterior margin slightly rounded, deepest close to merus, with about 8 clusters of long setae, anterior margin with a few setae, medial face with a number of setae in a row, propodus, half as long as carpus, posterior margin with 5 groups of short pectinate setae and long simple setae, dactylus with unguis about 3/4 length of propodus.

Pereopod 3 basis about 3.5 times longer than wide, as long as ischium, merus and carpus combined, with tuft of long setae distally on anterior margin, ischium to propodus with a few simple setae and short robust setae. Pereopods 5 and 6 basis ovoid, longer than wide, pereopod 5 with posterior distal rounded lobe, pereopod 6 with angular posterodistal corner, anterior and posterior margins with few small simple setae, merus with a few tiny robust setae on anterior margin, posterior margin with single robust seta in middle and 2 at distal corner, carpus with 3 anterior groups of robust setae and 1 at posterodistal corner. Pereopod 7 basis nearly circular, slightly broader than long, medial surface with many scattered small setae, posterior margin with broad crenulations, each indentation with tiny setule, merus with 2 mid-posterior and group of posterodistal robust setae, anterior margin with middle and distal groups of robust setae.

Uropod 1 peduncle reaching as far as peduncle uropod 2 and to middle of uropod 3 peduncle, inner ramus the longer, reaching 2/3 along the middle of outer ramus uropod 3, lateral margin of peduncle with single short robust seta, inner ramus with 2 long dorsal robust setae. Uropod 2 peduncle with a few robust setae, longer on medial than on lateral margin, inner ramus the longer, reaching as far as outer ramus of uropod 1, outer ramus with a few dorsal short robust setae. Uropod 3 peduncle about half as long as outer ramus, rami elongate oval, outer ramus slightly longer than inner ramus, both reaching to apex of telson lobes, both rami with row of long setae, outer ramus with row of about 7 short robust setae on dorsal margin, midlateral row of 5 longer robust setae, and ventrolateral row of 4 short robust setae, inner ramus with 4 dorsal robust setae in distal 1/3 (ventrolateral robust setae not observed).

Telson. Length about 4.7 times greatest lateral depth, reaching to about apex of uropod 3 inner ramus, each lobe with 3 robust setae dorsally (small simple setae not observed).

Size. Unique, 6.0 mm, sex not known.

Distribution. Japan, Sagami Sea, 564 m.

Remarks. The single specimen available is in a poor condition being somewhat squashed, thus preventing illustrations at the same level as the remaining species herein. There are however enough characters to allow newly collected specimens of Tiron to be recognised as belonging to this new species, especially if found on the southeast coast of Japan centering around the Sagami Sea. In this connection it is of interest to draw attention to an excellent colour photo of a specimen listed as Tiron sp. (JAMBIO, see reference). It was collected 19 February 2014 (100 years after Th. Mortensen’s efforts) in the eastern Sagami Bay at 35˚08’N 139˚34.6’E off Miura. Based on the shape of the cephalon and the structure of the urosome it may be a specimen of Tiron sagamiense described above.

Figures

FIGURE 6. Tiron sagamiense sp. nov. Holotype. clv, head lateral view; gp1–gp2, gnathopods 1 and 2; ple 3, pleonite 3 posterior margin; us, urosome.

FIGURE 7. Tiron sagamiense sp. nov. Holotype. p3, pereopod 3, p5–p7, pereopods 5 to 7.