Photis posterolobus, Jung, Tae Won, Coleman, Charles Oliver & Yoon, Seong Myeong, 2019

Jung, Tae Won, Coleman, Charles Oliver & Yoon, Seong Myeong, 2019, Taxonomic study on the photid amphipods (Senticaudata, Corophiida, Photoidea, Photidae) from Korean waters, with descriptions of a new genus and seven new species, ZooKeys 886, pp. 1-59 : 1

Photis posterolobus sp. nov. Figs 18 , 19 , 20

Etymology.

The composite epithet of the specific name, posterolobus, is a combination of the Latin words posterus and lobus, referring to the presence of a posterior lobe produced distally on the ischium of male gnathopod 2.

Material examined.

Holotype: ♂ (4.8 mm), NIBRIV0000753909. Geomeunyeo, Jeju-do Island, South Korea (33°14'23"N, 126°34'59"E), 24 Dec 2012, grab sampler (about 24 m depth), by Prof. HY Soh.

Diagnosis.

Male gnathopod 1 palmar margin weakly sinuated. Male gnathopod 2 basis lateral border forming a well-developed sac-like lobe; ischium posterior margin with lateral lobe acutely produced distally; merus rectangular, stout, half as long as basis, with transparent lobe distally; carpus anterior margin irregular, carpal lobe well developed; propodus stout, as long as basis, posterior margin with one elongate process half as long as anterior margin, palmar margin oblique, 0.7 × as long as anterior margin, with two spines (proximal larger than distal), without defining seta. Stridulated ridges only present on gnathopod 2 basis and coxae 3 and 4 in males (unclear in females).

Description.

Holotype male. Head ( Fig. 18A ) as long as pereonites 1 and 2 combined; lateral cephalic lobe rounded; eye circular, moderate in size; located in the middle of lateral lobe; antennal sinus deep.

Antenna 1 ( Fig. 18B ) 0.4 × as long as body; peduncle 1st article stout, 0.7 × as long as head; 2nd article slender, 1.4 × as long as 1st article; 3rd article 0.7 × as long as 2nd article; accessory flagellum absent; flagellum 0.8 × as long as peduncle 1 st– 3rd articles combined, composed of ten articles (terminal article rudimentary).

Antenna 2 ( Fig. 18C ) peduncle 3th article exceeding end of lateral cephalic lobe; 4th and 5th articles as long as 2nd article; flagellum 0.6 × as long as peduncle 3 rd– 5th articles combined, composed of more than six articles.

Upper lip ( Fig. 18D ) convex anteriorly, with notch in the middle, covered with minute setae.

Mandibles ( Fig. 18E, F ) with 5-dentate incisor, 4-dentate lacinia mobilis, and four raker setae on left mandible; with 1/2 and 5-dentate incisor, minutely dentate lacinia mobilis, and three raker setae on right mandible; molar well developed, triturative, with seven setae along the distal margin of right mandible; palp asymmetrical, composed of three articles, 3rd article distally rounded, 0.7 × as long as 2nd article, with setae extending along most of posteriodistal margin.

Maxilliped ( Fig. 19A ) inner lobe subrectangular, weakly expanded distally, with three nodular setae apically and one medial nodular seta subdistally; outer lobe exceeding half of palp 2nd article, lined with nine robust setae along apex to medial margin; palp composed of four articles, 3rd article slightly expanded distally, 0.4 × as long as 2nd article, 4th article 0.8 × as long as 3rd article, with elongate seta apically (1.2 × as long as 4th article).

Maxilla 1 ( Fig. 19B ) inner lobe small, covered with minute setae; outer lobe with ten dentate robust setae on apical margin; palp biarticulated, distal article curved, with five setae on apical margin.

Maxilla 2 ( Fig. 19C ) inner lobe with an oblique row of plumose setae on surface; outer lobe longer and slightly dilated distally than inner lobe.

Gnathopod 1 ( Fig. 19D ) coxa 0.7 × as wide as long, evenly rounded anterioventrally, slightly expanded anteriorly; basis as long as coxa, anterior margin lateral border forming weak lobe distally, with five elongate setae subproximally, posterior margin convex, with five elongate setae at the middle; carpus subtrapezoidal, 0.8 × as long as basis, half as wide as long, posterior lobe blunt; propodus as long and wide as carpus, rounded anteriorly, with minute serrations irregularly along palm and posterior margin, palm 0.8 × as long as posterior margin, weakly bisinuate, defined by one robust seta medially; dactylus 0.7 × as long as propodus, exceeding palm, inner margin serrated, with three teeth.

Gnathopod 2 ( Fig. 19E, F ) stout, coxa subrectangular, 0.8 × as wide as long, produced anterioventrally; basis anterior margin lateral border forming well-developed lobe distally (sac-like lobe reaching middle of carpus) bearing oblique stridulated ridges on surface; ischium anterior lobe small, posterior margin lateral border forming lobe produced distally; merus rectangular, half as long as basis, with transparent lobe distally; carpus anterior margin irregular, carpal lobe well developed; propodus stout, as long as basis, posterior margin with one elongate process half as long as anterior margin, palmar margin oblique, 0.7 × as long as anterior margin, with two spines (proximal larger than distal), without defining seta; dactylus 0.7 × as long as propodus, with two teeth on inner margin.

Pereopod 3 ( Fig. 20A, B ) coxa produced anterioventrally, as long as wide, with stridulated ridges on medial surface and short stridulated ridges near the posterioventral corner on lateral surface submarginally; basis 0.3 × as wide as long, posterior margin expanded; merus 0.6 × as long as basis, anterior margin expanded distally, with two plumose setae submarginally, distal corner weakly produced; carpus half as long as merus, evenly rounded anteriorly; propodus slender, diminished distally, 0.6 × as long as basis; dactylus half as long as propodus.

Pereopod 4 coxa ( Fig. 20C ) not widened distally, as long as that of pereopod 3, with stridulated ridges along anterioventral corner oblique.

Pereopod 5 ( Fig. 20 D–F ) coxa bilobed, large, anterior lobe subovoid, expanded ventrally, posterior lobe small, expanded backwards; basis subovoid, broad, more expanded proximally, 0.8 × as long as wide; merus subrectangular, slightly convex anteriorly, half as long as basis, 0.4 × as wide as long; carpus 0.8 × as long as merus; propodus 1.1 × as long as carpus, with a pair of distal locking setae unequal in length (longer seta 0.8 × as long as dactylus), with a group of four setae (longest seta half as long as propodus) at anteriodistal corner; dactylus half as long as propodus, armed with one accessory cusp on outer margin.

Pereopod 6 ( Fig. 20G ) 1.1 × as long as pereopod 5; coxa bilobed, anterior lobe small, posterior lobe dilated posterioventrally; basis subovoid, 0.8 × as wide as long, anterior margin convex, posterior margin slightly dilated proximally; merus 0.6 × as long as basis, 0.3 × as wide as long; carpus 0.8 × as long as merus; propodus 1.2 × as long as carpus, with a pair of distal locking setae unequal in length (longer seta 0.6 × as long as dactylus), with a group of five setae (longest seta 0.8 × as long as propodus) at anteriodistal corner; dactylus half as long as propodus, without accessory cusp on outer margin.

Pereopod 7 ( Fig. 20 H–I ) 1.3 × as long as pereopod 6; coxa unilobed, produced posteriorly; basis subovoid, 0.8 × as wide as that of pereopod 6, 0.6 × as wide as long, anterior margin rather convex, posterior margin with one blunt extension proximally; merus rectangular, 0.7 × as long as basis; 0.2 × as wide as long; carpus 0.8 × as long as merus; propodus 1.5 × as long as carpus, with a pair of distal locking setae unequal in length (smaller than those of pereopods 5 and 6), with a group of more than seven setae at posteriodistal corner; dactylus 0.4 × as long as propodus, armed with one accessory cusp on outer margin.

Epimeron 1 slightly extended anterioventrally. Epimera 2 and 3 each posterioventral corner produced backwards, but not acute ( Fig. 18G ).

Uropod 1 ( Fig. 20J ) peduncle without distoventral spine, with four robust setae on both dorsolateral and dorsomedial margins; inner ramus 0.8 × as long as peduncle, with one subapical seta only; outer ramus 0.9 × as long as inner ramus, with three dorsolateral setae and one subapical seta.

Uropod 2 ( Fig. 20K ) 0.8 × as long as uropod 1; peduncle 0.7 × as long as that of uropod 1; inner ramus 1.1 × as long as peduncle, with two dorsal robust setae and one subapical seta; outer ramus 0.9 × as long as inner ramus, with two dorsal robust setae and one subapical seta.

Uropod 3 ( Fig. 20L ) 0.8 × as long as uropod 2; peduncle 0.8 × as long as that of uropod 2; outer ramus biarticulated, 0.9 × as long as peduncle, last article vestigial, with two elongate setae subapically; inner ramus scale-like, 0.4 × as long as outer ramus.

Telson ( Fig. 20M ) subtriangular in dorsal view, with a pair of simple setae, a pair of sensory setae, and one nodular robust seta on each side.

Remarks.

Photis posterolobus sp. nov. is closely related to nine Photis species [ P. bronca sp. nov.; P. fischmanni Gurjanova, 1951; P. guerrai Tato & Moreira, 2017; P. hawaiensis JL Barnard, 1955; P. kapapa JL Barnard, 1970; P. lecroyae Ortiz, Varela & Lalana, 2011; P. longicaudata (Spence Bate & Westwood, 1863); P. sarae Souza-Filho & Serejo, 2010; and P. tenuicornis GO Sars, 1882] in bearing a very well-developed sac-like lobe anteriodistally on the basis of male gnathopod 2. However, Photis posterolobus sp. nov. can be distinguished from above species by the presence of a posterior lobe produced distally in the ischium of male gnathopod 2 that is absent in the above species ( Bate and Westwood 1863; Sars 1883; Gurjanova 1951, 1955; Barnard 1955, 1970; Ren 2006; Souza-Filho and Serejo 2010; Tato and Moreira 2017).

Figures

Figure 18. Photis posterolobus sp. nov., holotype, NIBRIV 0000753909, male, 4.8 mm, Geomeunyeo, Jeju-do, South Korea. A habitus B antenna 1 C antenna 2 D upper lip E left mandible F right mandible G pleonal epimera. Scale bars: 0.05 mm (D), 0.1 mm (E, F), 0.2 mm (B, C, G), 0.5 mm (A).

Figure 19. Photis posterolobus sp. nov., holotype, NIBRIV 0000753909, male, 4.8 mm, Geomeunyeo, Jeju-do, South Korea. A maxilliped B maxilla 1 C maxilla 2 D gnathopod 1 E gnathopod 2 F gill of gnathopod 2. Scale bars: 0.05 mm (A-C), 0.1 mm (D-F).

Figure 20. Photis posterolobus sp. nov., holotype, NIBRIV 0000753909, male, 4.8 mm, Geomeunyeo, Jeju-do, South Korea. A coxa 3 B pereopod 3 C coxa 4 D coxa 5 E pereopod 5 F gill of pereopod 5 G pereopod 6 H coxa 7 I pereopod 7 J uropod 1 K uropod 2 L uropod 3 M telson. Scale bars: 0.1 mm.