Microlysias rectangulatus, Heo & Hendrycks & Kim, 2020

Heo, Jun-Haeng, Hendrycks, Ed A. & Kim, Young-Hyo, 2020, Two new species of the genus Microlysias (Crustacea, Amphipoda, Tryphosidae) from Korean Waters, Zootaxa 4759 (4), pp. 543-556 : 544-550

publication ID	https://doi.org/ 10.11646/zootaxa.4759.4.5
publication LSID	lsid:zoobank.org:pub:B22B175F-D98F-459E-9BE0-E9779AD7A3F3
DOI	https://doi.org/10.5281/zenodo.3810563
persistent identifier	https://treatment.plazi.org/id/03E3D535-DD57-3A6A-FF18-53DAEE70FAC6
treatment provided by	Plazi
scientific name	Microlysias rectangulatus
status	sp. nov.

Treatment

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).