Microlysias rectangulatus, Heo & Hendrycks & Kim, 2020

Microlysias rectangulatus sp. nov.

(Korean Name: Ne-mo-deo-deum-i-gin-pal-yeop-sae-u, new)

( Figs. 2–6 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Type material. Holotype, adult male, 7.6 mm, cat no. DKU-099, Gajin-port , Gajin-ri , Jugwang-myeon , Goseonggun, Gangwon-do, Korea, 38° 22′05″N, 128° 30′45″E, 02 February 2008, collected by Y.H. Kim. GoogleMaps Paratypes, 1 adult female, 8.6 mm, cat no. DKU-100, data same as holotype (dissected) GoogleMaps , 2 ♂, 10 ♀, CMNC 2020-0001 , data same as holotype and the remaining paratypes ( 8 ♂, 50 ♀, DKUAMP202001 ) in the collection of the corresponding author GoogleMaps .

Etymology. The species name is from the Latin quadratus (square, four-cornered), referring to the expanded subrectangular peduncular article 5 of male antenna 2.

Description. Holotype adult male.

Body ( Fig. 3A View FIGURE 3 ) dorsally smooth; head ( Fig. 4A View FIGURE 4 ), lateral cephalic lobe subacute, triangular apically; eyes large, ovoid, black; epimeron 1 posterior margin smooth and convex; epimeron 2, posteroventral corner right angled, posterior margin minutely serrated; epimeron 3 posteroventral corner subquadrate, posterior margin minutely and irregularly serrated; urosomite 1 with dorsal depression and mid-dorsal carina, posterolateral margin minutely serrated ( Fig. 4B View FIGURE 4 ).

Antenna 1 ( Fig. 4A, C View FIGURE 4 ) stout, length 0.34 x antenna 2; peduncular article 1 much longer than peduncular articles 2–3, with a row of 7 simple setae dorsally; length ratio of peduncular articles 1–3=1.00: 0.20: 0.17; flagellum 12- articulate, calceoli absent, subequal in length to peduncle, with 2-field callynophore; accessory flagellum 5-articulate, article 1 rather elongate, shorter than other articles combined.

Antenna 2 ( Fig. 4A, D View FIGURE 4 ) elongate; peduncular articles 1–4 rather short; peduncular article 5, subquadrate, length 1.45 x width, broadening ventrodistally; flagellum 51-articulate, first article elongated, calceoli absent.

Epistome ( Fig. 4A View FIGURE 4 ) roundly produced, projecting above upper lip.

Lower lip ( Fig. 4E View FIGURE 4 ), inner lobes indistinct; outer lobe pubescent medially; mandibular lobes narrow.

Left mandible ( Fig. 4F View FIGURE 4 ), incisor simple, smooth; lacinia mobilis simple, slender; accessory setal row with 3 spines and patch of setules; molar slightly elongate, narrow and forms a setose ridge; palp 3-articulate, attached strongly proximal to molar; article 1 unarmed, very long, length 0.98 x article 3; article 2 longest, with 10 A2-setae; article 3 weakly falcate, length 0.64 x article 2, with 1 A3-seta, 14 D3-setae, and 2 E3-setae.

Right mandible ( Fig. 4G View FIGURE 4 ), incisor smooth and without tooth; lacinia mobilis absent; accessory spine row with 5 spines; the other morphological characters generally similar to left mandible.

Maxilla 1 ( Fig. 4H View FIGURE 4 ), inner plate slender, subrectangular, with 2 pectinate setae apically and setules on outer margin, lacking apical spine; outer plate with 11 dentate spine-teeth; palp biarticulate, proximal article short, distal article not expanded, with 1 slender and 4 blunt apical spines.

Maxilla 2 ( Fig. 4I View FIGURE 4 ), inner plate slender, slightly shorter than outer, with 14 apical setae, medial margin with pubescence; outer plate 1.08 x longer than inner one, with pectinate and simple setae distally.

Maxilliped ( Fig. 4J View FIGURE 4 ), inner plate rectangular, with 2 pectinate setae medially, apical margin with 2 unequal simple setae and 3 blunt spines; outer plate subovate, exceeding distal end of article 2 of palp, with 10 spines medially and 4 simple setae on inner margin; palp 4-articulate, article 1 slightly shorter than article 2, with 2 simple setae on inner margin, 1 simple seta laterodistally; article 2 with 11 simple setae on inner margin, 1 simple seta laterodistally; article 3 with simple setae on inner and distal margins; article 4 falcate, shorter than article 3.

Gnathopod 1 ( Fig. 5A View FIGURE 5 ) subchelate; coxa large, broadly rounded anterodistally and expanded, width 0.69 x length; basis subrectangular, with 15 simple setae anteriorly; ischium with 5 simple setae posteriorly; merus with pubescence posteriorly and simple setae posterodistally; carpus subtriangular, shorter than propodus, with short ventral lobe, with 2 clusters of simple setae distally; propodus rectangular, slightly narrowing distally, length 2 x width, slightly concave posteriorly, length 1.44 x carpus; palm short, serrulate, transverse, defined by 1 stout spine posterodistally; dactylus falcate, fitting palm.

Gnathopod 2 ( Fig. 5B View FIGURE 5 ), coxa subrectangular, gradually widening distally, width 0.43 x length; basis slender, elongate, with 1 simple seta posterodistally; ischium elongate, with 6 simple setae on posterior margin, subequal in length to carpus; merus length 0.73 x ischium, with patch of setules posteriorly and 3 simple setae posterodistally; carpus pubescent posteriorly, with clusters of simple setae anteriorly and medially, length 0.54 x basis, posterior margin slightly convex; propodus short, length 2.10 x width, subquadrate, minutely chelate, oblique anterodistally, with 7 long pectinate setae, length 0.50 x carpus, palm obtuse with 1 simple setule; dactylus small, acute, fitting palm.

Pereopod 3 ( Fig. 5C View FIGURE 5 ), coxa similar to that of gnathopod 2 but slightly more curved, width 0.42 x length; basis subrectangular, with 3 simple setae posterodistally; ischium short, length 0.31 x basis, with 8 simple setae posteriorly; merus length 1.50 x carpus, produced anterodistally, with long simple setae posteriorly; propodus subrectangular, slightly longer than carpus, with a row of 7 spines posteriorly; dactylus falcate, length 0.43 x propodus.

Pereopod 4 similar to pereopod 3 except coxa ( Fig. 5D View FIGURE 5 ) broadened, posterior margin excavate, posterodistal lobe produced, truncate, corner rounded.

Pereopod 5 ( Fig. 5E View FIGURE 5 ), coxa large, rounded quadrate, bilobate, width 1.12 x length; basis subcircular, length 0.98 x width, posteriorly expanded, margin weakly serrate, posteroventral lobe broadly rounded, width subequal to length, with a row of spines along anterior margin; merus expanded posteriorly, anterior margin with 5 simple setae and 3 spines, posterior margin with 5 simple setae; carpus length 0.41 x merus, anterior margin with 6 spines, posterior margin with 2 spines distally; propodus rectangular, length 1.75 x carpus, anterior margin with 5 spines; dactylus falcate, length 0.43 x propodus.

Pereopod 6 ( Fig. 5F View FIGURE 5 ), coxa slightly larger than coxa 7, bilobate, anterior lobe small, posterior lobe roundly produced ventrally; basis narrowly subovate, with a row of spines on distal half of anterior margin, posterior margin weakly serrate, posteroventral lobe narrowly rounded; merus expanded posteriorly, anterior margin with 4 long simple setae and 5 small spines, posterior margin with 2 spines and 2 simple setae; carpus length 0.86 x merus, anterior margin with 3 spines and 4 spines distally, posterior margin with 2 spines distally; propodus rectangular, length 1.33 x carpus, anterior margin with 3 clusters of 2 spines; dactylus falcate, length 0.42 x propodus.

Pereopod 7 ( Fig. 5G View FIGURE 5 ) similar to pereopod 6, but coxa subtriangular; basis much broader than that of pereopod 6, posterior margin broadly expanded, merus expanded.

Uropod 1 ( Fig. 6A View FIGURE 6 ), peduncle subrectangular, length 1.33 x outer ramus, with row of spines on dorsolateral and dorsomedial margins, and 2 apicolateral spines dorsodistally; rami lanceolate; outer ramus subequal in length to inner one, dorsolateral margin with 3 spines; inner ramus with 3 dorsolateral and 1 medial spines.

Uropod 2 ( Fig. 6B View FIGURE 6 ), peduncle slightly longer than outer ramus, with 3 dorsolateral and 2 medial spines; rami lanceolate; outer ramus slightly longer than inner one, with 3 dorsolateral spines; inner ramus with a row of 6 dorsolateral spines.

Uropod 3 ( Fig. 6C View FIGURE 6 ) stout, peduncle short, slightly shorter than outer ramus, with 2 groups of 3 laterodistal spines, medial margin with 4 simple setae and 3 spines; outer ramus biarticulate, length 1.16 x inner ramus, proximal article with 7 long medial plumose setae and 1 spine along inner margin, outer margin with 3 spines; distal article short, length 0.22 x proximal one; inner ramus not reaching base of distal article of outer ramus, outer margin with 8 long plumose setae, inner margin with 2 spines and 1 plumose seta.

Telson ( Fig. 6D View FIGURE 6 ) longer than broad, length 1.55 x width, cleft 62% of its length, each lobe with a pair of simple or bifid setae and 2 spines dorsolaterally, 1 spine and 1 seta apically.

Paratype, adult female.

Body ( Fig. 3B View FIGURE 3 ) about 8.6 mm long; head ( Fig. 6E View FIGURE 6 ) similar to that of male; coxa 1 less expanded anteriorly than that of male; urosomite 1 with moderate dorsal elevation and microserrate distal margin.

Antenna 1 ( Fig. 6G View FIGURE 6 ) stout, similar to that of male; peduncular article 1 with 5 penicillate setae ventrally; flagellum 11-articulate.

Antenna 2 ( Fig. 6H View FIGURE 6 ) callynophore slightly smaller, slender, much shorter than male, peduncular articles 3–5 narrow and elongate, article 5 without expansion and more setose than in male; flagellum 11-articulate, article 1 not elongated as in male.

Uropod 3 ( Fig. 6I View FIGURE 6 ) similar to that of male, rami less setose and inner ramus shorter.

Depth range. 60–100 m

Remarks. The genus Microlysias Stebbing, 1918 is similar to the genera Orchomene Boeck, 1871 and Lysianella G.O. Sars, 1882 in having the following characteristics: 1) mouthparts forming quadrate bundle; 2) coxa 1 large and visible, not tapering; 3) gnathopod 1 short, strongly subchelate; 4) gnathopod 2 minutely chelate; and 5) uropod 3, outer ramus 2-articulate ( Barnard & Karaman, 1991). However, Microlysias is easily distinguished from those two genera by having a swollen peduncular article 5 of male antenna 2 ( Barnard & Karaman, 1991; Lowry & Kilgallen, 2014) and an elongated article 1 of the mandibular palp. The mandibular molar of the genus Orchomenella is button-shaped (truncated cylinder) and armed with denticles and cusps but without pubescence, the article 1 of the mandibular palp is short and the outer plate of the maxilliped has 2 strong apical spines ( Barnard & Karaman, 1991). These characteristics are distinctly different from the genus Microlysias . Among the species of Orchomenella , O. japonica Gurjanova, 1962 is similar to Microlysias species in possessing a swollen peduncular article 5 of antenna 2 in male. However, O. japonica is distinguished from species of Microlysias by a combination of the following features ( Microlysias species characters in parentheses): 1) molar button-shaped ( vs. elongate and forms a setose ridge); 2) mandibular palp with very short article 1 ( vs. elongated article 1). These characters exclude O. japonica from Microlysias and therefore it should remain in the genus Orchomenella .

Microlysias rectangulatus sp. nov. is similar to M. xenokeras Stebbing, 1918 , M. soela Lowry & Kilgallen, 2014 , M. triangulus sp. nov. (this paper) and Orchomenella japonica Gurjanova, 1962 . However, M. rectangulatus differs from those species in the following characters: 1) eyes ovate and smaller ( vs. irregularly subrectangular, very large, covering most of head in M. soela , reniform in O. japonica ); 2) antenna 2, peduncular article 5 subrectangular, length 1.45 x width ( vs. length=width in M. xenokeras and length 0.95 x width in M. soela ); 3) mandibular palp, article 1 very long, length 0.98 x article 3 ( vs. short, length 0.23 x article 3 in O. japonica , 0.61 x article 3 in M. triangulus , 0.70 x article 3 in M. xenokeras and 0.60 x article 3 in M. soela ); 4) gnathopod 2, propodus subovate, length 2.1 x width ( vs. slender, length 2.90 x width in M. xenokeras , 2.50 x width in M. soela and 2.43 x width in M. triangulus ); 5) epimeron 2–3 and urosome 1, posterior margin microserrate ( vs. smooth in all the other species); and 6) pereopod 7, merus expanded ( vs. not expanded in all the other species).

The feeding behavior of Microlysias had been unknown, however we discovered the new species scavenging on flat fish caught in the net ( Fig. 2 View FIGURE 2 ). This discovery leads us to report M. rectangulatus as a carnivorous and likely opportunistic, scavenging species.

Distribution. Korea (Goseong-gun).