Megamoera aequidentatum, Labay, Vjacheslav S., 2013

Labay, Vjacheslav S., 2013, Review of amphipods of the Melita group (Amphipoda: Melitidae) from the costal waters of Sakhalin Island (Far East of Russia). I. Genera Megamoera Bate, 1862 and Armatomelita gen. nov., Zootaxa 3700 (1), pp. 65-112 : 94-99

Megamoera aequidentatum sp. nov.

Figures 23–26 , 34 d

Diagnosis. Pleon segment 1 dorsally with posterior row of 6 equal denticles; pleon segment 2 dorsally with posterior row of 10 equal denticles; pleon segment 3 with posterior row of 8 equal denticles. Urosome segment 1 with central tooth and with 2 lateral teeth on each side; urosome 2 with 2 pairs of short teeth and single thin seta among them (not strong cuspidate seta). Telson lobes, proximal subapical notch more on outer margin. Anterior head lobe shallow, lower margin without prominent accessory process. Maxilla 1, palp segment 1 with 2 lateral setae. Maxilla 2, inner plate, facial setae developed, submarginal in position. Uropod 3, proximal segment of outer ramus slender, with 4 clusters of marginal cuspidate setae at each margin.

Type material. Holotype female, 15 mm, X 37867 Cr 1433, Aniva Bay (Sea of Okhotsk) (46° 37' 16.91" N, 142° 53' 49.20" E, 10 m), gravel, M.G. Rogotnev & P.V. Polupanov, October 2010.

Type locality. Aniva Bay (Sea of Okhotsk) (46° 37' 16.91" N, 142° 53' 49.20" E, 10 m)

Description. Female (15 mm). Medium size species. Vital body color is light-brown. Pereon segments smooth dorsally, without teeth or humps ( Fig. 23 a, b, 34d). Pleon segment 1 dorsally with posterior row of 6 equal denticles, and with single simple thin setae among denticles; pleon segment 2 dorsally with posterior row of 10 equal denticles, and with single simple thin setae among them; pleon segment 3 with posterior row of 8 equal denticles and with thin simple setae in intervals. Urosome segment 1 with central tooth and 2 lateral teeth on each side, with long thin simple setae in between; urosome 2 with 2 pairs of short teeth and single thin setae among them (not strong cuspidate seta).

Head: slightly shorter than pereonites 1 and 2 together with an indistinct rostrum; eyes medium oval, anterior head lobe shallow, inferior margin without prominent lobe; inferior antennal sinus a short notch.

Antenna 1: ( Fig. 23 c) 60% of body length, slender; flagellum equal to peduncle length, 26–27 articles, few very thin and short setae scattered along flagellum; peduncle article 1 double width but shorter length to article 2, article 3 1/3 of article 2 length; accessory flagellum 6-articulate.

Antenna 2: ( Fig. 23 d) flagellum almost 0.45 times as long as peduncle, 10–11 articles, bundle of thin setae on each article; peduncle articles 5 shorter than article 4, articles 1 + 2 + 3 shorter than article 5, article 2 with processes on the upper-distal corner, articles 2 with protruding lobe reaching the middle of next article, articles 3 with short protruding lobe, articles 4 and 5 with numerous tufts of thin setae spaced evenly along the article.

Mouthparts.

Labrum: ( Fig. 23 e) rounded, frontal margin slightly concave medially, densely covered by minute setae.

Mandible: ( Fig. 24 a, b) incisor crenulate and stretching in a rounded tip; raker setae stout serrate, numerous (8+), shorter then incisor; molar cylindrical triturative, chewing plate striate; palp 3-articulate, palp segments 2 and 3 subequal, 1st article short with protruding lobe.

Labium: typical for genus; inner lobes small, but well defined, rounded; outer lobes semi-square at distal margin.

Maxilla 1: ( Fig. 24 c) inner plate subtriangular, lined with a row of plumose setae; outer plate elongate, apically with 2 rows of 9 two-end strong setae; palp 2-articulate, article 2 2.5 times as long as article 1, article 2 apically with two rows of 6–7 simple setae each.

Maxilla 2: ( Fig. 24 d) inner plate slightly shorter than outer plate, inner plate with numerous facial setae, closely submarginal, tip covered with numerous simple setae; outer plate with same numerous simple setae, but only on the tip.

Maxilliped: ( Fig. 24 e) compact; inner plates large, fully cleft, distal margin with a row of numerous cuspidate setae, inner margin with long plumose setae; outer plates reaching of distal margin of palp article 2, inner margin lined with a row of short stout teethlike setae longer toward the apex, smoothly into the apical row of long thin plumose setae; palp 4-articulate, the percentage of total length of the articles of the palp are 15% (article 1), 40% (article 2), 25% (article 3), 20% (article 4), tip of article 3 bilobed with a row of long simple setae along apical impression; article 4 slender, inner margin with a two lines of serrate setae.

Pereopod 1: ( Fig. 24 f, g) coxa expanded distally, rounded down, with rare long setae along lower margin; basis straight, with row of rare short and long simple setae along anterior margin and with numerous setae along posterior margin; merus subrectangular, with a cushion of short setae along distal half of posterior margin, distal margin with a row of long simple setae; carpus long, 1.3 times as long as propodus, 5 oblique rows of long serrate setae along posterior margin, with a row of long serrate setae along anterior and posterior parts of distal margin, and with a cushion of short setae along anterior-distal row of long setae; propodus rectangular, with 6 groups of long serrate setae along posterior margin, with 4 tufts of various length simple setae along anterior margin and with a dense bunch of long simple setae at the antero-distal corner, palm slightly oblique and minutely serrate with a row of short thin simple setae and rare long setae along palmar margin; dactylus as long as palm, slightly curved, with a row of spines along inner margin, with long nail.

Pereopod 2: ( Fig. 24 h) coxa long, longer than coxa 1, rounded, with a few long setae at the postero-distal corner; basis straight, as long as coxa, with a rare row of long simple setae along posterior margin and with numerous long setae along distal half of anterior margin; merus subrectangular with acute protrusion at the posterior distal corner, and with a few long setae along posteror margin; carpus triangular, 2.6 times shorter than propodus, with 3 tufts of long setae along posterior margin; propodus subrectangular, slightly broadened distally, palm oblique, substraight, with small posterodistal tooth, posterior margin with 10 tufts of serrate setae, palm with small simple cuspidate setae, and with a row of long setae near posterodistal tooth; dactylus as long as palm, curved to the inside of propodus, inner margin with a rare row of short simple setae, outer margin rarely setose, tip of dactylus with nail.

Pereopod 3: ( Fig. 25 a) coxa similar size as coxa 2, long, slightly narrowed distally, lower margin rounded, with two long setae near posterodistal denticle; basis long, linear in a distal half and curved in a proximal half, with few minutely setae along anterior margin (few long simple setae presented in proximal part) and with rare simple setae of various long along posterior margin; merus long with 3 cuspidate setae along anterior margin and with a single cuspidate setae at the anterior distal corner, posterior margin with 4 bunches of simple setae and with single bunch at the posterodistal corner; carpus 5/6 as long as merus, with 5 bunches of cuspidate setae along posterior margin and with a single tuft in the middle of anterior margin; propodus linear, slightly narrow and as long as carpus, with 6 bunches of cuspidate setae including posterodistal bunch along posterior margin; dactylus medium (1/2 of propodus), with nail.

Pereopod 4: ( Fig. 25 b) coxa as long as coxa 3, width subequal to long, broaded and rounded distally, posteriorly slightly excavated, lower margin oblique; basis long, linear in a distal half and curved in a proximal half, with few minutely setae along anterior margin and with rare row of long simple setae in the proximal part of posterior margin and with rare short simple setae along distal part of posterior margin; merus long with 2 cuspidate setae along anterior margin and with a single cuspidate setae at the anterior distal corner, posterior margin with 2 simple setae and with single bunch at posterodistal corner; carpus 2/3 as long as merus, with 5 bunches of cuspidate setae along posterior margin and with a single cuspidate seta in the middle of anterior margin; propodus linear, slightly narrow and slightly longer than carpus, with 7 bunches of cuspidate setae including posterodistal bunch along posterior margin; dactylus medium (1/2 of propodus), with nail.

Pereopod 5: ( Fig. 25 c, d) coxa with rounded front margin, obtuse triangular hind margin and with anterior lobe pulled back and down, posterior distal corner with single cuspidate seta; basis expanded, with posterior wing and produced down posterior distal lobe, slightly narrowed distally, width 0.62 times length, posterior distal corner rounded, hind margin crenulated, anterior margin with small cuspidate setae; merus broaded medially, with two cuspidate setae along posterior and anterior margins each, and with a single cuspidate seta at the posterior distal and anterior distal corners each; carpus 0.7 as long as merus, with single tuft of cuspidate setae at the anterior margin and with a single clusters of cuspidate setae at the anterior and posterior distal corners each; propodus linear, more narrow and 1.5 times as long as carpus, with 2 bunches of cuspidate setae along anterior margin; dactylus small (1/4 of propodus), with nail.

Pereopod 6: ( Fig. 25 e) coxa with quadrate hind margin and with oblique rounded front lobe, anterior part of which with a rare row of 10 small cuspidate setae, posterior distal corner with single cuspidate seta; basis expanded, with posterior wing, rounded posteriorly, width 0.6 as long, posterior distal corner rounded, hind margin crenulated, front margin with small cuspidate setae; merus expanded medially, with two single cuspidate simple setae along anterior margin and with tree single cuspidate setae along posterior margin, and with single tuft of cuspidate setae at anterior and posterior distal corners each.

Pereopod 7: ( Fig. 25 f) coxa small, without distinct anterior lobe and with rounded posterior lobe, oblique front margin with 8 minutely simple setae, hind margin with 4 small setae; leg unknown.

Coxal gills 2–6. Coxal gill 6 slightly smaller than gill 5.

Epimeral plates: ( Fig. 25 g, h, i) plate 1 rounded quadrate with 1 diagonal ridge, distal corner rectangular with minutely acuminate denticle, posterior margin slightly convex with 2 notches; plate 2 rectangular, with oblique crest, hind corner with minutely acuminate denticle, posterior margin substraight, ventral margin with a row of 7 small cuspidate setae; plate 3 hind corner produced, acute, posterior margin concave, with 3 notches, ventral margin with a row of 8 small cuspidate setae.

Pleopods: ( Fig. 25 j–o) normal, no sexual dimorphism; peduncle of pleopods 1 and 2 with two specific toothed coupling spines on the inner corner each, pleopod 3 with single toothed coupling spine and with single cuspidate setae; coupling basis of inner ramus with 3–6 of specific stout two-pointed plumose setae along inner margin: pleopod 1 (6), pleopod 2 (4), pleopod 3 (3).

Uropod 1: ( Fig. 26 a) peduncle with strong and curved interramal spur; rami subequal in length, subequal to peduncle length; peduncle and rami with tiny simple setae along outer edge, both rami with few tiny cuspidate setae at tip.

Uropod 2: ( Fig. 26 b) peduncle shorter than outer ramus (0.8 ramus length); inner ramus shorter than outer, with numerous simple cuspidate setae along outer margin each; uropod 2 shorter than uropod 1.

Uropod 3: ( Fig. 26 c) peduncle subequal to peduncle of uropod 1, with single cuspidate simple seta at the posterior margin and with a crown of simple cuspidate setae at the apex; elongate 2-articulate outer ramus (6 length of inner ramus), with 4 tufts of small cuspidate setae along anterior margin, and with 4 tufts of longer cuspidate setae along posterior margin of article 1, article 2 minutely, 2 times longer than crowning setae; inner ramous short and ovoid with two cuspidate setaed subapically.

Telson: ( Fig. 26 d) fully cleft; lobes diverging distally; proximal notch positioned laterally; lateral, apical and subapical simple cuspidate setae long, lobes with 2–3 short cuspidate setae at the medial margin and with single lateral cuspidate seta each.

Sexual dimorphism: unknown.

Etymology: Species name aequidentatum is based on Latin words aequalis (equal) and dentatum (denticled), which is explained by similarity in dorsal denticles size of pleon and urosome segments.

Ecology: M. aequidentatum was found only in a type locality at the depth 10 m on the gravel bottom. Female with eggs in marsupium was found in October.

Distribution: Only type locality. Aniva Bay, Okhotsk Sea (Sakhalin Island).

Remarks: Only a single specimen of the new species is known, but the set of characteristics allows easily to separate this species from the other. Megamoera aequidentatum sp. nov. is most similar to M. subtener (Stimpson, 1864) , M. rafiae Jarret & Bousfield, 1996 and M. bowmani Jarret & Bousfield, 1996 by dorsal sculpture. Megamoera aequidentatum differs from M. subtener in absence of subacute processes on the low margin of anterior head lobe, in the increasing of number of dorsal denticles from pleon segment 1 to pleon segment 3, in absence of produced central tooth in dorsal sculpture of pleon and urosome segments, in absence of strong cuspidate setae among of lateral teeth of dorsal sculpture of urosome 2 segment (only thin simple setae). It differs from M. rafiae in absence of subacute processes on the low margin of anterior head lobe, in the number of denticles of dorsal sculpture of pleon segments 1–2, in the number of dorsal teeth of urosome segment 1 (5, not 3), in the shape and armament of telson. The absence of subacute processes on the low margin of anterior head lobe, the number of dorsal denticles of pleon segments 1–3, in the number of dorsal teeth of urosome segment 1 (5, not 3), in the shape and armament of telson Megamoera aequidentatum distinguishes M. aequidentatum from M. bowmani .

Figures

FIGURE 23. Megamoera aequidentata sp. nov., holotype, female: a—lateral view, b—carination of abdominal segments, cantenna 1, d—antenna 2, e—upper lip; scale: a, b— 5 mm; c, d— 1 mm; e— 0.1 mm.

FIGURE 24. Megamoera aequidentata sp. nov., holotype, female: a—right mandible, b—left mandible, c—maxilla 1, dmaxilla 2, e—maxilliped, f—pereopod 1, g—dactylus and palmar margin of pereopod 1, h—pereopod 2; scale: a, b, e— 0.2 mm; c, d, g— 0.1 mm; f, h— 1 mm.

FIGURE 25. Megamoera aequidentata sp. nov., holotype, female: a—pereopod 3, b—pereopod 4, c—coxa 5, d—pereopod 5, e—pereopod 6, f—coxa 7, g—epimer 1, h—epimer 2, i—epimer 3, j—pleopod 2, k—coupling spines of pleopod 2, lcoupling spines of pleopod 3, m – o—coupling setae of pleopods 1 – 3; scale: a, b, d, e, g – j— 1 mm; c, f, k – o— 0.1 mm.

FIGURE 26. Megamoera aequidentata sp. nov., holotype, female: a—uropod 1, b—uropod 2, c—uropod 3, d—telson: a – c— 1 mm; d— 0.1 mm.

FIGURE 34. Dorsal carination of new species of genera Megamoera and Armatomelita: a— Megamoera similidentata sp. nov., holotype, male, b— Megamoera striata sp. nov., holotype, male, c— Megamoera falsomikulitschae sp. nov., paratype, female, d— Megamoera aequidentata sp. nov., holotype, female, e— Armatomelita tshayensis sp. nov., holotype, male; scale: a, b— 2 mm, c, d, e— 1 mm.