Periparatanais mergaxilla, Bird, 2019

Bird, Graham J., 2019, Tanaidacea (Crustacea: Peracarida) from the Southern French Polynesia Expedition, 2014. I. Tanaidomorpha, Zootaxa 4548 (1), pp. 1-75 : 35-40

publication ID	https://doi.org/10.11646/zootaxa.4548.1.1
publication LSID	lsid:zoobank.org:pub:4C6DB448-DE0B-41E1-BAB1-4ACAE95F756F
DOI	https://doi.org/10.5281/zenodo.5612820
persistent identifier	https://treatment.plazi.org/id/03B78797-C660-DF30-0BE8-06EEFBD9FDD4
treatment provided by	Plazi
scientific name	Periparatanais mergaxilla
status	sp. nov.

Treatment

Periparatanais mergaxilla n. sp.

( Figs 16–18 View FIGURE 16 View FIGURE 17 View FIGURE 18 )

Diagnosis. Monotypic; see genus diagnosis above.

Etymology. Conjunction of Latin merga ‘two-pronged pitchfork’ and axilla ‘armpit’, alluding to the spinose apophysis on the posterior margin of the coxae of pereopods 4–5, as noun in apposition.

Material examined. Holotype —non-ov. ♀, 1.8 mm, P. 102328, Stn 64-2, Morane, rubble, 19 m, 12 October 2014, coll. A. Berthelsen, A. Reid, S.J. Keable, and C. Bedford.

Paratypes —MORANE: two non-ov. ♀♀ P. 102329, one non-ov. ♀ dissected on two microslides P.102330.001, Stn 64-2.

GAMBIER ISLANDS: one non-ov. ♀ P. 102331, Stn 66-A; two non-ov. ♀♀ MA73585, Stn 66-4.

Description. Holotype non-ovigerous female, 1.8 mm (P. 102328). Habitus ( Fig. 16A–B View FIGURE 16 ) slender, 8.9 times ltb (extended, ca. 6.5 times ltb contracted). Cephalothorax ( Fig. 16A–B, D View FIGURE 16 ) 1.3 times ltb, just longer than pereonites 1–2 combined (contracted), with single anterolateral setae posterior to eyes. Pereon with all pereonites shorter than broad, pereonite-1 shortest, pereonites 2–3 and 6 subequal, pereonites 4–5 subequal, longest; pereonite-1 with four anterodorsal setae, other pereonites with two, pereonites 4–6 with two posterolateral setae. Pleon 1.34 times ltb, about 19% of body length (contracted), pleonites equal in length, with slightly raised sternites. Pleotelson ( Fig. 16C View FIGURE 16 ) shorter than pleonites 4–5 combined, with two posterolateral setae, two posterodistal setae and two PSS, two apical setae, and two deflected ventro-apical setae.

Paratype non-ovigerous female, 2.2 mm (P.102330.001). Antennule ( Fig. 16E View FIGURE 16 ) 0.9 times length of cephalothorax, 4.3 times ltb; article-1 1.3 times longer than articles 2–3 combined, 2.4 times ltb, with one distomesial seta, lateral margin with group of three PSS, a simple seta and at least two PSS and distal group of one simple seta and three PSS; article-2 shorter than broad, with lateral and mesial single setae; article-3 five times length of article-2, 4.5 times ltb, with apical spur, without distinct cap-like segment, with five simple setae, one aesthetasc and one PSS. Antenna ( Fig. 16F View FIGURE 16 ) article-1 shorter than broad, naked; article-2 slightly inflated, with ventral ridge, 1.2 times ltb, twice length of article-3, with dorsodistal seta, distolateral seta, and small ventral seta; article-3 just longer than broad, with acute dorsodistal fused spine; article-4 just shorter than article-2, 2.7 times ltb, with one simple seta and three PSS; article-5 half length of article-4, 2.4 times ltb, with distal seta; article-6 caplike, with one short and four long setae .

Mouthparts. Labrum ( Fig. 17A View FIGURE 17 ) distally setulate, hood-like. Mandibles robust, right incisor not observed; left mandible ( Fig. 17B View FIGURE 17 ) distally setulate, incisor weakly crenate, lacinia broad, weakly flared and distally crenate, molar cylindrical with rosette of apical spines. Labium not observed. Maxillule ( Fig. 17C View FIGURE 17 ) with at least eight terminal spines, three of which are larger than others and weakly hooked. Maxilla not observed.

Maxillipeds ( Fig. 17D–E View FIGURE 17 ) typical paratanaidin, basis with seta about length of endite. Endites with distomedial tubercles longer than broad, incisor-like, medial seta length of endite. Palp article-1 as long as broad, naked; article-2 lateral seta short, mesial margin with two unequal simple setae, and pectinate seta; article-3 with mesial apophysis bearing three serrulate setae, with one inner (oral) small simple seta; article-4 with proximomesial setules, one small superior seta and five distal serrulate setae. Epignath not observed.

Cheliped ( Figs 16D View FIGURE 16 ; 17F–G View FIGURE 17 ) with coxal sclerite extending to posterior margin of cephalothorax ( Fig. 16D View FIGURE 16 ); basis 1.4 times ltb, posterior lobe length of anterior mass, latter with dorsodistal seta; merus typical, with ventrodistal seta; carpus 1.8 times ltb, with two dorsal and two ventral setae. Chela just longer than, but narrower than carpus, propodus 2.1 times ltb, palm 1.9 times longer than fixed finger; palm with two ventrodistal setae, slender spine near articulation with dactylus, and one dorsomesial pectinate spine ( Fig. 17G View FIGURE 17 ); fixed finger with tricuspid incisive margin and three setae, middle longest, terminal spine narrow; dactylus strong, with one flat spine on incisive margin and proximomesial spine.

Pereopod-1 ( Fig. 18A View FIGURE 18 ) coxa with seta on slight apophysis; basis arcuate, 3.5 times ltb, with superoproximal seta; ischium with small seta; merus twice length of broad, with two small inferodistal setae; carpus 0.9 times length of merus, 1.8 times ltb, with two superodistal setae and two small inferodistal setae; propodus 1.6 times longer than carpus, 3.4 times ltb, with one superodistal seta and one inferodistal seta; dactylus about one third length of unguis, with accessory seta; unguis together with dactylus 0.8 times length of propodus.

Pereopod-2 ( Fig. 18B View FIGURE 18 ) coxa with seta; basis broader than pereopod-1, 2.6 times ltb, with superoproximal seta; ischium with seta; merus short, length of broad, with inferodistal spine and seta (mesial); carpus 1.3 times longer than merus, 1.2 times ltb, with superodistal crotchet, and two unequal inferodistal crotchets; propodus length of merus and carpus combined, 2.3 times ltb, with two unequal superodistal setae and one inferodistal seta; dactylus with accessory seta, 0.4 times length of unguis; unguis together with dactylus about 0.9 times length of propodus.

Pereopod-3 ( Fig. 18C View FIGURE 18 ) like pereopod-2 but slightly shorter overall; propodus with one superodistal seta.

Pereopod-4 ( Fig. 18D View FIGURE 18 ) coxa broad with posterior apophysis (see genus diagnosis); basis broader than in pereopods 2–3, 1.6 times ltb, with longitudinal groove on superodistal margin, inferior margin with two PSS; ischium with two unequal setae; merus sub-geniculate, longer than broad, with two unequal inferodistal crotchets, and spinulate inferior margin; carpus about length of merus, 1.1 times ltb, distally wider, with superodistal seta, three unequal distal crotchets, inferior margin with paired spinulate ridges; propodus just longer than carpus, 1.9 times ltb, widest at midlength with superior PSS, with superodistal slender spine and two highly unequal inferodistal crotchets; dactylus and unguis claw-like, unguis half length of dactylus, together 0.6 times length of propodus.

Pereopod-5 ( Fig. 18E–F View FIGURE 18 ) like pereopod-4 but basis with one inferodistal PSS.

Pereopod-6 ( Figure 18G–H View FIGURE 18 ) as pereopods 4–5, including coxa ( Fig. 18H View FIGURE 18 ) but basis naked; propodus without superior PSS and with one thick and two slender superodistal spines.

Pleopod ( Fig. 18I View FIGURE 18 ) peduncle just longer than broad; rami unequal in length and proportion; endopod 2.5 times ltb, with distomesial seta, proximolateral plumose seta separated by gap from fringe of seven distolateral plumose setae, distalmost whip-like; exopod longer and wider than endopod, 2.3 times longer than broad, with proximal plumose seta, and distal fringe of 13 lateral plumose setae.

Uropod ( Fig. 16G View FIGURE 16 ) just shorter than pleotelson, peduncle 1.1 times ltb; endopod two-segmented, 1.3 times longer than peduncle, segment-1 about as long as segment-2, with distal seta and two PSS, segment-2 with four setae and one PSS; exopod one-segmented, half length of peduncle, 0.7 times length of endopod segment-1, with subdistal seta and two apical setae.

Intraspecific variation. Body length 1.3–2.2 mm (n=6).

Distribution and habitat. Taravai (Gambier Islands) and Morane; 10–19 m, from (coral?) rubble.

Remarks. This paratanaid is easily distinguished from the other known paratanaidin from French Polynesia (see below) by its antennule configuration and the spinose coxa of pereopods 4–6.