Megamoera similidentata, 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 : 70-80

publication ID

https://doi.org/ 10.11646/zootaxa.3700.1.3

publication LSID

lsid:zoobank.org:pub:B227BEB7-C44B-47C0-AF15-21B5469B8875

DOI

https://doi.org/10.5281/zenodo.5620492

persistent identifier

https://treatment.plazi.org/id/7B1F87ED-FFF0-2C6B-FF32-FA5D60DC6F29

treatment provided by

Plazi

scientific name

Megamoera similidentata
status

sp. nov.

Megamoera similidentata View in CoL sp. nov.

Figures 1–9 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 , 34 View FIGURE 34 a

Diagnosis. Pleon segments 1–3 with central tooth and 0–3 lateral denticles on each side; pleons 2 and 3 with large central tooth and 3 denticles, first of which is the smallest (may be reduced). Urosome segment 1 with central tooth and 1 lateral denticle; urosome 2 with 2 pairs of short teeth and single cuspidate seta. Telson lobes, proximal subapical notch more on outer margin. Anterior head lobe shallow, lower margin with prominent accessory process. Pereopod 1 (male) broadest distally, palm oblique, sharply angled from posterior margin. Pereopod 2 (male), anterior margin of dactyl strongly setose; palm oblique, convex, with low irregular hinge tooth and stout posterodistal tooth. Maxilla 1, palp segment 1 with 7–8 lateral setae. Maxilla 2, inner plate, facial setae reduced, marginal in position. Uropod 3, proximal segment of outer ramous slender, with 5 clusters of marginal stout simple setae.

Type material. Holotype male, 34 mm, X 37855 View Materials Cr 1421, the north-east shelf of Sakhalin Island, Okhotsk Sea, Far East of Russia (51°42'N 143°53'E, 87 m), silt and sand, M.G. Rogotnev & P.V. Polupanov, 0 9 July 2010. Paratypes: 1 female, 28 mm, X 37856 View Materials Cr 1422; 2 males and 1 female X 37857 View Materials Cr 1423 with same data as holotype; 1 male X 37858 View Materials Cr 1424, the north-east shelf of Sakhalin Island, Okhotsk Sea, Far East of Russia (52°25'N 143°51'E, 101 m), sand, M.G. Rogotnev.

Type locality. The north-east shelf of Sakhalin Island, Okhotsk Sea, Far East of Russia (51°42'N 143°53'E, 85–90 m).

Description. Male (34 mm). Vital body color is grey-olive with an unclear picture of the diffuse bands and spots. Thoracic segments smooth dorsally, without teeth and humps ( Fig. 1 View FIGURE 1 a, b). Pleon segments 1 with centre tooth, without lateral denticles; pleons 2 and 3 with large centre tooth and 3 denticles, first of which is unclear. Urosome segment 1 with central tooth and 1 lateral denticle; urosome 2 with 2 pairs of short teeth and single cuspidate seta.

Head: ( Fig. 1 View FIGURE 1 c) slightly shorter than pereonites 1 and 2 together, with an indistinct rostrum; eyes medium oval, anterior head lobe shallow, inferior margin with prominent lobe; inferior antennal sinus with a short notch.

Antenna 1: ( Fig. 1 View FIGURE 1 d) 60% of body length, slender; flagellum exceeding 1.3 length of peduncle, 48–49 articles, few very thin and short setae scattered along flagellum; peduncle article 1 double width but slightly shorter length to article 2, article 3 0.25 of article 2 length; accessory flagellum 5-articulate.

Antenna 2: ( Fig. 1 View FIGURE 1 e) flagellum almost 1/3 times as long as peduncle, 15–16 articles, with numerous thin setae on each article; peduncle articles 5 shorter than article 4, articles 1 + 2 + 3 shorter than article 5; article 2 with protruding lobe reaching the middle of next article; article 3 with short protruding lobe; article 4 and 5 with numerous evenly spaced tufts of thin setae.

Mouthparts.

Labrum: ( Fig. 1 View FIGURE 1 f) rounded, frontal margin slightly concave medially, densely covered by minute setae.

Mandible: ( Fig. 2 View FIGURE 2 a, b) incisor crenulate and stretching in a rounded tip; raker setae stout subplumose, numerous (14+), shorter then incisor; molar cylindrical triturative, chewing plate striate; palp 3-articulate, palp segments 2 and 3 strongly setose, 1-st article with protruding lobe, the percentage of total length of the articles of the palp 14% (article 1), 36–43% (article 2) and 43–50% (article 3).

Labium: ( Fig. 2 View FIGURE 2 c) inner lobes small but well defined, rounded; outer lobes semi-square at distal margin.

Maxilla 1: ( Fig. 2 View FIGURE 2 d, e) inner plate subtriangular, lined with a row of simple setae; outer plate elongate, 1.3 as long as inner plate, apically with 2 rows of 9 apically bifurcate strong setae; palp 2-articulate, article 2 2.3times as long as article 1, article 2 apically with two rows of 12–13 simple setae each.

Maxilla 2: ( Fig. 2 View FIGURE 2 f) inner plate slightly shorter than outer plate, facial setae of inner plate reduced (16–20), distal, closely submarginal, tip covered with numerous simple setae; outer plate with same numerous of simple setae, but only on the tip, subapically with a rare row of 10–12 setae.

Maxilliped: ( Fig. 3 View FIGURE 3 a) compact; inner plates large, fully cleft, distal margin with a row of 4 teeth, inner and distal margins with long plumose setae; outer plates reaching of ¾ 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 14% (article 1), 44% (article 2), 24% (article 3), 18 (article 4), article 2 with numerouse setae along distal part of inner margine; tip of article 3 bilobed with a row of long simple setae, densely pubescent along apical impression; article 4 inner margin with a line of serrate setae (Watling type IV.1) (Watling 1989).

Pereopod 1: ( Fig. 3 View FIGURE 3 b, c) coxa subrectangular, slightly extended distally; basis straight with a dense row of simple setae along anterior margins and more rare long setae along posterior margin; merus subrectangular, with a 4 tufts of plumose setae along posterior margin and with a cushion of short setae along distal part of posterior margin, distal margin with a row of long simple setae; carpus long, 1,5 times as long as propodus, 12–13 oblique rows of long serrate setae along outer posterior margin, with a row of long setae along anterior and posterior parts of distal margin and tomentose at the anterior-distal corner; propodus suboval, broadest distally, with numerous groups of long serrate setae along outer posterior margin, with 6 tufts of long simple setae and with a dense bunch of long simple setae at the anterior distal corner, palm oblique and minutely serrate with a row of short thin simple setae and rare long setae along palmar margin, sharply angled from posterior margin; dactylus as long as palm, curved, with a row of spines along posterior margin, with nail and with tooth-like protrusion as long as nail above it.

Pereopod 2: ( Fig. 3 View FIGURE 3 d, e) coxa rounded subrectangular, slightly narrowing distally; basis straight, longer than coxa, with a few long simple setae along posterior margin and with numerous long setae along anterior margin; merus subrectangular with long acute protrusion at the posterior distal corner, with a few long setae along posterior margin; carpus triangular, 2 times shorter than propodus; propodus subrectangular, palm oblique, convex, with low irregular hinge tooth and stout postero-distal tooth, inner face of anterior margin lined with several groups of serrate setae, posterior margin with numerous tufts of serrate setae, palm with small simple setae, and with a dense cluster of serrate setae; dactylus as long as oblique part of palm, curved to the inside of propodus, inner margin with a rare row of short simple setae, outer margin strongly setose, tip of dactylus with obtuse nail.

Pereopod 3: ( Fig. 4 View FIGURE 4 a) coxa similar size as coxa 2, suboval; basis long linear with few minutely setae along anterior margin and with rare long simple setae along posterior margin; merus long with 3 strong simple setae along anterior margin and with a cluster of 2 strong simple setae at the anterior distal corner, posterior margin with few long setae; carpus ¾ as long as merus, with 3 bunches of strong simple setae along posterior margin; propodus linear, more narrow and as long as carpus, with 4 bunches of strong simple setae along posterior margin; dactylus medium (1/2 of propodus), with nail.

Pereopod 4: ( Fig. 4 View FIGURE 4 b) coxa as long as coxa 3, subquadrate, slightly broaded distally, posteriorly slightly excavated; leg is similar to that of the pereopod 3.

Pereopods 5–7 elongated from pereopod 5 to pereopod 7.

Pereopod 5: ( Fig. 4 View FIGURE 4 c) coxa with rounded front margin, with quadrate hind margin and with anterior lobe pulled back and down; basis regular, with posterior wing, slightly narrowed distally, width 2/3 as long, posterior distal corner rectangular, hind margin crenulated, anterior margin with small stout setae; ischium subquadratic; merus slightly broaded medially, with a single strong stout seta at the middle of posterior margin, and with a cluster of 2 strong stout setae at the posterior distal corner; carpus 0.8 as long as merus, with 2 groups of 2 strong stout setae at the anterior margin and with a single clusters of strong stout setae at the anterior and posterior distal corners each; propodus linear, more narrow and as long as carpus, with 2 bunches of strong simple setae along posterior margin; dactylus small (1/3 of propodus), with nail.

Pereopod 6: ( Fig. 4 View FIGURE 4 d) coxa with quadrate hind margin and with anterior lobe pulled back and down; basis regular, with posterior wing, narrowed distally, width 0.56 as long, posterior distal corner acute, hind margin crenulated, anterior margin with small stout setae; ischium subquadratic; merus long, with few short stout simple setae along anterior and posterior margins, and with single clusters of 2-3 strong stout setae at anterior and posterior distal corners each.

Pereopod 7: ( Fig. 4 View FIGURE 4 e) coxa small, without distinct anterior lobe and with rounded posterior lobe; basis regular, with posterior wing, narrowed distally, width 0.6 times length, posterior distal corner acute, hind margin crenulated, anterior margin with small setae; ischium subquadratic; merus similar to that of the pereopod 6.

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

Epimeral plates: ( Fig. 5 View FIGURE 5 a, b, c) plates 1 and 2, hind corner acuminate; plate 1 rounded triangular with 1 diagonal ridge, posterior margin slightly convex with 4–5 notches; plate 2 posterior and ventral margins slightly convex, with oblique crest, posterior margin with 6–7 notches, ventral margin with a row of notches and 4–5 small stout setae; plate 3 hind corner moderately produced, acute, posterior margin concave, with 2 notches, ventral margin with a row of notches and 10 small stout setae.

Pleopods: ( Fig. 5 View FIGURE 5 d, e, f) normal, no sexual dimorphism; peduncle with two specific toothed coupling spines on the inner corner; coupling basis of inner ramus with 9 of specific stout two-pointed plumose setae along inner margin.

Uropod 1: ( Fig. 5 View FIGURE 5 g) peduncle with strong and curved interramal spur; rami subequal in length, slightly shorter than peduncle length; peduncle and rami with tiny simple setae along outer edge, both rami with few tiny simple setae at tip.

Uropod 2: ( Fig. 5 View FIGURE 5 h) peduncle shorter than outer ramus (0.73 ramus length); inner ramus shorter than outer, with numerous simple cuspidate setae along outer margin; uropod 2 shorter than uropod 1.

Telson: ( Fig. 5 View FIGURE 5 i) fully cleft; lobes slender, diverging distally; proximal notch positioned laterally; apical and subapical simple cuspidate setae long.

Female (28 mm). Vital body color grey-olive with an unclear pattern of diffused bands and spots ( Fig. 8 View FIGURE 8 d, e, f). Thoracic segments smooth dorsally, without teeth and humps ( Fig. 6 View FIGURE 6 a, b). Pleon segments 1 with large central tooth, with few indistinct lateral denticles on each side; pleons 2 and 3 with central tooth and 3 denticles. Urosome segment 1 with central tooth and 1 lateral tooth; urosome 2 with 2 pairs of teeth and single cuspidate seta.

Head: ( Fig. 6 View FIGURE 6 a) similar to as in male.

Antenna 1: ( Fig. 6 View FIGURE 6 c) 57% of body length, slender; flagellum exceeding 1.3 length of peduncle, 44 articles, few very thin and short setae scattered along flagellum; peduncle article 1 twice as wide but slightly shorter than article 2; article 3 0.25 times as long as article 2; accessory flagellum 4-articulate.

Antenna 2: ( Fig. 6 View FIGURE 6 d) similar same to as in male.

Mouthparts: ( Figs. 6 View FIGURE 6 e, f, g, h, i; 7a, b, c, d) same as in male.

Pereopod 1: ( Fig. 7 View FIGURE 7 e, f) without sexual dimorphism, same as in male.

Pereopod 2: ( Fig. 8 View FIGURE 8 a) with sexual dimorphism; coxa rounded subquadrate, slightly narrowed distally; basis straight, longer than coxa, with a few long simple setae along posterior margin and with numerous long setae along distal part of anterior margin; merus subrectangular, with long acute protrusion at the posterior distal corner, with a few long setae along posterior margin; carpus broadened distally, 1.7 times shorter than propodus, posterior lobe slightly produced with numerous serrate setae; propodus subrectangular, slightly broadened distally, palm oblique, convex, with stout posterodistal tooth, posterior margin with numerous tufts of serrate setae, palm with small simple setae, and with a dense cluster of serrate setae; dactylus as long as oblique part of palm, curved to the inside of propodus, inner margin with a rare row of short simple setae, outer margin strongly setose, tip of dactylus with acute nail.

Pereopods 3 and 4: ( Fig. 8 View FIGURE 8 b, c) same as in male.

Pereopods 5–7 elongated from pereopod 5 to pereopod 7.

Pereopod 5: ( Fig. 8 View FIGURE 8 d) coxa with rounded front margin, quadrate hind margin and anterior lobe pulled back and down; basis regular, with posterior wing, slightly narrowed distally, width 2/3 of length, posterior distal corner rectangular, hind margin crenulated, anterior margin with small cuspidate setae; ischium subquadratic; merus slightly broadened medially, with two cuspidate setae along posterior margin, and with a cluster of 2 strong stout setae at the posterior distal corner; carpus 0.8 times as long as merus, with 2 groups of 2 strong stout setae at the anterior margin and with a single clusters of strong stout setae at the anterior and posterior distal corners each; propodus linear, more narrow and as long as carpus, with 4 bunches of cuspidate setae along posterior margin; dactylus small (0.25 of propodus), with nail.

Pereopod 6: ( Fig. 8 View FIGURE 8 e) coxa with quadrate hind margin and with anterior lobe pulled back and down; basis regular, with posterior wing, narrowed distally, width 0.56 of length, posterior distal corner rectangular, hind margin crenulated, anterior margin with small cuspidate setae; ischium subquadratic; merus long, with 2–3 cuspidate setae along anterior and posterior margins, and with single clusters of 2−3 strong stout setae at anterior and posterior distal corners each; carpus 0.8 as long as merus, with 3 groups of 2 cuspidate setae at the anterior margin, with a single cluster of cuspidate setae at the posterior margin and with single clusters of cuspidate setae at the anterior and posterior distal corners each; propodus linear, more narrow and as long as carpus, with 4 bunches of cuspidate setae along posterior margin; dactylus small (0.25 of propodus length), with nail.

Pereopod 7: ( Fig. 8 View FIGURE 8 f) coxa small, without distinct anterior lobe and with rounded posterior lobe; basis regular, with posterior wing, narrowed distally, width 0.6 length, posterior distal corner acute, hind margin crenulated, anterior margin with small cuspidate setae; ischium subquadratic; merus and carpus similar to that of pereopod 6; propodus linear, more narrow and as long as carpus, with 6 bunches of cuspidate setae along posterior margin; dactylus small (0.3 of propodus length), with nail.

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

Epimeral plates: ( Fig. 8 View FIGURE 8 g, h, i) plates 1 and 2, hind corner minutely acuminate; plate 1 rounded triangular with 1 diagonal ridge, posterior margin slightly convex with 4–5 notches; plate 2 posterior and ventral margins slightly convex, with oblique crest, posterior margin with 4–5 notches, ventral margin with a row of notches and 4–5 small cuspidate setae; plate 3 hind corner moderately produced, acute, posterior margin concave, with 4 notches, ventral margin with a row of notches and 6–9 cuspidate setae.

Pleopods ( Fig. 9 View FIGURE 9 a–g): normal; peduncle with two specific toothed setae on the inner corner; inner ramus slightly longer than outer, basis of inner ramus with 10 (pleopod 1) or 7 (pleopods 2 and 3) specific stout twopointed plumose setae along inner margin.

Uropod 1: ( Fig. 9 View FIGURE 9 h) peduncle with strong and curved interramal spur; inner ramus slightly shorter than outer, subequal to peduncle length; peduncle and rami with numerous tiny simple setae along outer edge, both rami with few tiny simple seta at tip.

Uropod 2: ( Fig. 9 View FIGURE 9 i) peduncle shorter than outer ramus (0.75 ramus length); inner ramus shorter than outer, with numerous tiny simple cuspidate setae along outer margin both; uropod 2 shorter than uropod 1.

Uropod 3: ( Fig. 9 View FIGURE 9 j) peduncle shorter than peduncle of uropod 1, with two cuspidate setae along anterior margin, with one cuspidate simple seta in the middle of posterior margin and with a row of simple cuspidate setae at the apex; elongate 2-articulate outer ramus (8 times length of inner ramus, longer than urosome), with 6 tufts of small simple stout setae along the anterior margin and with 4 tufts of small simple stout setae along the posterior margin of article 1, article 2 minutely, slightly longer than crowning setae; inner ramous short and ovoid with one cuspidate seta at tip and with single cuspidate seta at the posterior margin.

Telson: ( Fig. 9 View FIGURE 9 k) similar to that in male.

Sexual dimorphism: Only in structure of pereopod 2. Pereopod 2 in male bigger than in female.

Variations: The dorsal tooth on epimeral segment 1 may be with or without small indistinct teeth laterally.

Etymology. Species name similidentata is based on a Latin word simili (similar) and the species name dentata , which is explained by similarity of habit of the new species and of M. dentata .

Ecology. M. similidentata was found in the depth interval 85–90 m on the silt-sand bottom in the layer of constant low temperature (-1.2 to +0.5°C).

Distribution. Only type locality. The north-east shelf of Sakhalin Island, Okhotsk Sea.

Remarks. Megamoera similidentata sp. nov. is most similar to M. dentata (Krøyer, 1842) , M. rafiae Jarret & Bousfield, 1996 , M. bowmani Jarret & Bousfield, 1996 , M. glacialis Jarret & Bousfield, 1996 and M. borealis Jarret & Bousfield, 1996 . Megamoera similidentata differs from M. dentata in having subacute processes on the low margin of anterior head lobe, in the form of dactylus of pereopod 1 (dactylus with nail and with tooth-like protrusion as long as nail above it). It differs from M. rafiae in the size of central dorsal tooth of pleon segments 1– 3 (more than lateral teeth), central tooth of urosome segment 1 not vertical, in the shape of propodus of pereopods 1 and 2, in the shape and armament of telson. Although the dorsal armament of pleon segments 1 and 2 and of urosome segments 1 and 2 are more similar between M. similidentata and M. bowmani , the absence of the medial dorsal tooth of pleon segment 3 and the shape of telson M. bowmani distinguishes these species. Megamoera similidentata differs from M. glacialis in a number of dorsal lateral teeth of pleon segments 1–3 (3, not 2), in the form of propodus of gnathopod 1 and in the form of telson. It differs from M. borealis in having of subacute processes on the low margin of anterior head lobe, and in a number of dorsal lateral teeth of pleon segments 2–3 (3, not 2).

Kingdom

Animalia

Phylum

Arthropoda

Class

Malacostraca

Order

Amphipoda

Family

Melitidae

Genus

Megamoera

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