Priscomilitaris heike, Tomikawa, Ko, Tanaka, Hayato & Nakano, Takafumi, 2016

Tomikawa, Ko, Tanaka, Hayato & Nakano, Takafumi, 2016, A new species of the rare genus Priscomilitaris from the Seto Inland Sea, Japan (Crustacea, Amphipoda, Priscomilitaridae), ZooKeys 607, pp. 25-35 : 28-32

Taxon classification Animalia Amphipoda Priscomilitaridae

Priscomilitaris heike sp. n. Figures 2, 3, 4, 5

Holotype.

Male (2.3 mm), NSMT-Cr 24368, east of Abashima Island (34°19'30.6"N, 132°56'31.9"E; 14 m deep), Takehara, Hiroshima, Japan, 15 February 2016, collected by H. Tanaka.

Description.

Head (Fig. 2): slightly shorter than pereonites 1 and 2 combined; rostrum short, acute; eyes absent; lateral cephalic lobe acute, ventral margin with 2 minute setae; antennal sinus rounded. Pereon (Fig. 2): pereonite 1 short, 0.6 times as long as pereonite 2; pereonite 5 with strong sternal tooth extending anteroventrally (Fig. 3J). Pleon (Fig. 2): dorsal surfaces of pleonites 1-3 smooth, with pair of minute setae; epimeral plates 1-3 rounded, each with minute seta on ventral submargin. Urosomites 1-3 (Figs 2, 3 K–M): dorsal surfaces with pair of minute setae.

Antenna 1 (Fig. 3A): length 0.4 times as long as body; length ratio of peduncle articles 1-3 1.0: 1.1: 0.8; peduncle article 1 with 1 penicillate and 3 minute setae on anterior margin, and 2 pairs of setae and 2 single setae on posterior margin; peduncle article 2 with 2 setae on medial surface, and 3 pairs and 3 clusters of setae on posterior margin; peduncle article 3 medial and lateral surfaces each with a seta, and 3 pairs and 2 clusters of setae on posterior margin; primary flagellum 6-articulate with long aesthetascs, article 1 long, length 2.1 times as long as article 2, article 6 minute; accessory flagellum absent.

Antenna 2 (Fig. 3B): length 0.9 times as long as antenna 1; length ratio of peduncular articles 3-5 1.0: 1.7: 1.7; article 3 quadrate with 2 single setae and a pair of setae on posterior margin; article 4, anterior margin with 2 short setae and one long seta, posterior margin with 4 single setae and pair of setae; article 5 with 2 short setae on anterior margin, and 4 pairs and 2 clusters of setae on posterior margin; flagellum 5-articulate, article 1 long, length 2.5 times as long as article 2, article 5 minute; calceoli absent.

Upper lip (Fig. 3C): ventral margin concave, with minute setae. Lower lip (Fig. 3D): outer lobes broad, setulose, mandibular lobes narrow; inner lobes distinct. Mandible (Fig. 3E, F): left and right mandibles similar to each other; incisors 5-dentate, lacinia mobilis 4-dentate, accessory setal rows each with 4 blade setae, molar process triturative with a plumose seta; palp 3-articulate, length ratio of article 1-3 1.0: 2.1: 1.3, article 1 bare, article 2 with 4 ventral, 2 dorsal and 2 lateral setae, article 3 with 4 A-, 4 C-, 9 D-, and 2 Esetae. Maxilla 1 (Fig. 3G): inner plate small, subtriangular without setae; outer plate rectangular with 10 weakly serrate or unarmed robust setae; palp 2-articulate, exceeding outer plate, article 1 lacking setae, article 2 with 3 robust and 1 slender setae on apical margin, and 2 slender setae on apical submargin. Maxilla 2 (Fig. 3H): inner and outer plates with apical setae. Maxilliped (Fig. 3I): inner plate rectangular, not reaching half of palp article 1, with 2 robust setae on apical margin; outer plate weakly curved inward, exceeding half of palp article 2, with robust and slender setae; palp 4-articulate, ventral margin of article 2 with setae, medial and lateral surfaces of article 3 with setae, article 4 with long, slender robust setae.

Gnathopod 1 (Fig. 4A, B): smaller than gnathopod 2, coxa ovate, with or without ventral setae; posterior margin of basis with long setae; carpus not lobate, slightly longer than propodus, with weakly pectinate setae on posterior margin; propodus ovate, posterior margin serrate; dactylus long, smooth. Gnathopod 2 (Fig. 4C): coxa semicircular, covering coxa of gnathopod 1, with minute setae on ventral submargin; basis anteroproximally concave, posterior margin with a long seta; carpus not lobate, length 0.9 times as long as propodus; palmar margin of propodus shallowly concave, with acute protuberance; dactylus long, smooth, exceeding palmar margin.

Pereopod 3 (Fig. 4D): coxa semioval with 2 minute setae on ventral margin; anterodistal margin of basis shallowly concave, posterior margin with long seta; length ratio of merus, carpus, propodus and dactylus 1.0: 0.8: 0.9: 0.6; dactylus smooth. Pereopod 4 (Fig. 4E): coxa semioval with 3 minute setae on ventral margin; basis lacking anterodistal concavity, posterior margin with 3 long setae; length ratio of merus, carpus, propodus and dactylus 1.0: 0.8: 0.9: 0.6; dactylus smooth. Pereopod 5 (Fig. 4F, G): coxa bilobate, anterior lobe large with small seta on distal margin, posterior lobe with small seta on posterodistal corner; basis subrectangular, lacking posterodistal lobe; length ratio of merus, carpus, propodus and dactylus 1.0: 1.0: 1.0: 0.4; propodus with long plumose seta on distal margin; dactylus with small accessory tooth. Pereopod 6 (Fig. 4H, I): coxa shallow, bilobate, posterior lobe with small seta on posterodistal corner; basis oval, lacking posterodistal lobe; length ratio of merus, carpus, propodus and dactylus 1.0: 0.8: 1.0: 0.3; distal margin of merus oblique; propodus with long plumose seta on distal margin; dactylus with accessory tooth. Pereopod 7 (Fig. 4J, K): coxa oblong with seta on posterodistal corner; basis ovate, lacking posterodistal lobe; ischium rectangular, length 1.6 times as long as width; length ratio of merus, carpus, propodus and dactylus 1.0: 0.5: 0.7: 0.5; propodus with long plumose seta on distal margin; dactylus smooth.

Coxal gills (Fig. 2): present on gnathopod 2, pereopods 3-6.

Pleopods 1-3 (Fig. 5A, B) each with paired retinacula (Fig. 5B) on inner distal margin of peduncle, bifid plumose setae (clothes-pin setae) on inner basal margin of inner ramus absent; inner and outer rami of pleopods 1-3 consisting of 5 and 6 articles, respectively.

Uropod 1 (Fig. 5C): extending beyond uropod 2; peduncle long, length 1.6 times as long as inner ramus, dorsolateral margin with robust seta and numerus minute setae; inner ramus length 1.1 times as long as outer ramus, inner and outer margins with minute robust setae, apical part with robust seta; inner margin of outer ramus with minute robust setae, outer submargin with seta, apical part with robust seta. Uropod 2 (Fig. 5D): extending beyond uropod 3; peduncle almost as long as inner ramus, distal part of dorsolateral margin with minute robust setae; inner ramus slightly longer than outer ramus, inner distal and outer margins with minute robust setae; outer ramus with minute robust setae on outer and inner distal margins. Uropod 3 (Fig. 5E): extending beyond telson, uniramous; peduncle short, with facial seta and minute robust setae along with distal margin; ramus long, length 2.4 times as long as peduncle, 1-articulate with terminal robust seta. Telson (Fig. 5F): entire, fleshy, length 0.6 times width, with 2 clusters of 6 setae on distal submargin. Female unknown.

Sequences.

Three nucleotide sequences of the holotype, NSMT-Cr 24368, were determined: 28S, LC155260 (1274 bp); H3, LC155261 (328 bp); and COI, LC155259 (658 bp).

Distribution.

This species is known only from the type locality.

Etymology.

After ‘Heike’ (literally 'House of Taira’) that controlled the Seto Inland Sea, the Chugoku region, the Shikoku region as well as the Kyushu region during the Heian Period. The specific name is a Japanese word, not a Latin or Latinized one.

Remarks.

Priscomilitaris heike sp. n. is distinguished from Priscomilitaris tenuis by the following features (features of Priscomilitaris tenuis in parentheses): antennal sinus deep (shallow), flagellar article 1 of antenna 1 length 2.1 (1.3) times as long as article 2, flagellar article 1 of antenna 2 length 2.5 (1.0) times as long as article 2, mandibular palp article 2 longer than article 3 (subequal), outer plate of maxilla 1 with 10 (12) robust setae, epimeral plates rounded (quadrate). This new species differs from Paraphotis sinensis in the following features (features of Paraphotis sinensis in parentheses): antennal sinus deep (shallow), sternal tooth present on pereonite 5 (pereonite 4), flagellar article 1 of antenna 1 length 2.1 (1.4) times as long as article 2, flagellar article 1 of antenna 2 length 2.5 (1.4) times as long as article 2, outer plate of maxilla 1 with 10 (9) robust setae, palmar margin of propodus of gnathopod 2 with protuberance (absent).