Cryptodius sakhalinensis, Labay, 2019

Labay, Vjacheslav S., 2019, Review of amphipods of the genus Cryptodius Moore, 1992 (Amphipoda: Ochlesidae) from the coastal waters of Sakhalin Island (Far East of Russia), Zootaxa 4603 (3), pp. 501-519 : 504-513

Cryptodius sakhalinensis sp. nov.

Figures 1–9b

Diagnosis. Body with dorsal carination on pereonites 5–7 and on all pleonites and urosomites 1 and 3. Pleonite 3 and urosomite 1 with dorsal rectangular keel in posterior half of each. Urosomite 3 dorsally with paired rounded keels. Lateral cephalic lobe subangular. Mandible incisor transverse, crenulated, produced into a cutting edge. Maxilla 1 palp 1-articulate, short, about 1/5 of the outer plate length; with two setae on the distal margin. Maxilliped, inner plate subequal in length to outer plate; palp article 2 distally convex. Carpus lobe of preopod 2 (gnathopod 2) exceeding 1/3 of propodus length. Coxa 1 with concave anterior margin. Basis of pereopods 5–7 with a broadly rounded posterior margin. Merus of pereopods 5–7 is wide, with a posterior lobe reaching the distal margin of the carpus. Telson slightly cleft apically.

Type material. Holotype female, 7.3 mm, Х 50440 /Cr-2279, Sea of Okhotsk , the shelf of north-eastern Sakha- lin Island (53°23’ N, 144°09’ E, 256 m), silt, V.N. Chastikov, October 2014.

Type locality. Sea of Okhotsk (53°23’ N, 144°09’ E, 256 m)

Description. Female (7.3 mm). Small size species. Vital body color is unknown; color in alcohol almost colourless, uniformly pale yellow. Body carinated middorsally on pereon, pleon and urosome 1; urosome segment 2 occluded dorsally; urosomite 3 dorsally with paired rounded keels ( Figs. 2a, c , 9b ). Pleon segments 1 (slightly) and 2 (more pronounced, bluntly) midlines with raised posterior tooth, pleon segment 3 medially with posterior rectangular keel. Urosome segment 1 with distinct medial posterior rectangular keel. Sculpture of cover with large punctuation ( Figs. 7a, b ).

Head: ( Figs. 2a, b ) subequal in length to pereonite 1, rostrum well developed, pointed, tapering distally, reach the distal end of peduncular article 1 of antenna 1; lateral cephalic lobe subangular; eye large, curved, subreniform. Pereonite 1 forming a sharp visor on an anterior margin that covers a posterior part of cephalon.

Antenna 1: ( Figs. 2d, e ) gradually decreasing in thickness distally; peduncle less setose, 1.5 times as long as flagellum, length ratio of peduncular articles 1–3=1.00: 0.58: 0.30, accessory flagellum minute, uniarticulate, with 2 plumose setules; flagellum 7-articulate, with tufted setae marginally, proximal article elongate, about 1.3 times as long as peduncular article 3.

Antenna 2: ( Fig. 2f ) slightly shorter than antenna 1; length ratio of peduncular articles 1, 3, 4, 5=1.00: 0.84: 1.17: 1.09; flagellum short, 7-articulate, proximal article elongate, as long as following articles 2–4 combined.

Mouthparts.

Labrum: ( Fig. 3a ) stocky, asymmetrically incised.

Mandible: ( Figs. 3 b–h) narrow conical, incisor transverse, crenulated, produced into a cutting edge, with 8 small blunt teeth on the left mandible and with 10 small blunt teeth on the right, left lacinia 11 dentate, right lacinia lacking; raker setae stout serrated, numerous (15–17); molar placed medially, strong, columnar, truncate and triturative; palp 3-articulate, article 3 with a row of 4 comb-end setae, distally with 3 comb-end setae, the percentage of total length of the articles of the palp 8% (article 1), 43% (article 2) and 49% (article 3).

Labium: ( Fig. 4a ) notched along midline; apices narrow pointed, without setation.

Maxilla 1: ( Figs. 4b, c ) with short 1-articulate palp, about 1/5 of the outer plate length and carrying two simple setae distally; outer plate narrow, pointed, medial inclined margin smooth, densely setose, subapical margin with 9 comb spine-teeth; inner plate short, about 0.43 length of the outer plate, with 2 plumose setae apically.

Maxilla 2: ( Fig. 4d ) outer plate longer (1.2 times as long as inner plate) and narrower than inner, with two rows of plumose setae; inner plate with dense row of stout plumose setae; both plates pubescent.

Maxilliped: ( Fig. 4e ) inner plate elongate, extending 2/3 of length of outer plate, medial margin with row of plumose setae, apical margin with 3 teeth-form setae, surrounded by patch of pubescence; outer plate broad, rounded apically, does not reach the distal end of palp article 3, medial margin straight, with numerous blunt simple setae subapically; palp 4-articulate, the percentage of total length of the articles of the palp 27% (article 1), 31% (article 2), 31% (article 3) and 11% (article 4); article 1 with 3 bifurcate setae on the outer distal corner; article 2, medial margin swollen, with 9 simple setae in the distal half, outer margin with one bifurcate seta medially and with two bifurcate setae distally; article 3 about 1/3 as wide as article 2, with a row of 15–16 pinnate setae in the distal 1/3 of inner margin, surrounded by long bifurcate setae apically; distal article long triangular.

Pereopod 1 (gnathopod 1): ( Figs. 5a, b , 6a , 7a ) chelate, coxa 1 long, curved anteriorly, rounded, pointed distally; the base is slightly widened proximally, with medial convexity at the anterior margin, anterior margin with a brunch of long plumose setae in proximal ¼ and with short simple setae along distal ¾, posterior margin with rare long setae; ischium subrectangular, protruded anterodistally; merus trapezoidal, anterior margin is short; propodus slightly shorter than carpus; palm of propodus forming chela, with distinct finger, distally with short spine; dactylus with thin, long nail, extending beyond end of propodus, with 1 basal and 5 distal pinnate setae.

Pereopod 2 (gnathopod 2): ( Figs. 5c , 6b ) coxa long, 0.29 times as wide as long, slightly curved ahead, unarmed; gills with indistinct peduncle; basis slightly expands medially, ½ times as long as coxa, with a dense row of simple setae along anterior and posterior margins; ischium rectangular, with 4 stout setae posteriorly and with 3 stout setae at the distal posterior corner; merus subrectangular with truncate protrusion at the posterior distal corner, about 1.5 times as long as ischium, with 8 stout simple setae along posterior margin and with a row of 10 stout setae along distal margin; carpus short, carpal lobe elongate, with a row of simple and unipinnate setae distally; propodus ex- panded distally, strong, 0.62 times as wide as long, with 5–6 short setae posteriorly, palm transverse, serrulate, with two spines at palm angle; dactylus subequal to propodus palm, slightly curved, two-claw.

Pereopod 3: ( Fig. 6c ) coxa is similar in shape to coxa 2, long, 0.29 times as wide as long, unarmed; basis gradually broadened distally, slightly curved in the distal ¼, anterior margin with dense row of plumose setae, with simple setae along distal half of posterior margin; ischium long rectangular, with 3 short setae posteriorly and with one seta at the posterodistal corner; merus long, with anterodistal lobe, reaching of ½ of carpus long, with 2–3 short spineformes setae ateriorly and posteriorly and with a bunch of 3 short spineformes setae at anterior and posterior corners each; carpus 0.56 times as long as merus, with 5 groups of strong simple setae along posterior margin; propodus linear, 1.42 times as long as carpus, with 7 groups of short strong simple setae along posterior margin and with 2 strong spineformes setae posterodistally; dactylus medium (0.6 times length of propodus), slightly curved, with nail.

Pereopod 4: ( Figs. 6d, e ) coxa 4 longer and wider than coxa 3, excavate posteroproximally, midposterior margin pointed, expanded backward; segments 2–7 similar to those in pereopod 3.

Pereopods 5–7 subequal in length, except coxal plates.

Pereopod 5: ( Fig. 7c ) coxa is broadly oval, about 1.2 times as long as wide, bilobate, posterior lobe roundly expanded downward; basis with distinct hind distal rounded lobe; posterior margin rounded, width 0.65 times as long, wing of base separated with curved crest, anterior margin concave medially, with a bunch of simple setae in a distal 1/3, hind margin smooth; ischium rectangular, with two short setae anteriorly and with two short spineformes setae at the anterodistal corner; merus broad, 0.61 times as wide as long, overhanging and tapering posterodistally, reach- ing end of carpus, with 4–5 short stout setae along anterior margin, with 5 short stout setae along posterior margin, with a cluster of 2–3 short stout setae at anterior and posterior distal corners each; carpus short, 0.55 times as long as merus, gradually broadened distally, with 2 groups of 1–2 strong setae at the anterior margin and with a cluster of strong stout setae at the anterior distal corner; propodus linear, 1.61 times as long as carpus, with 6 bunches of strong simple setae along anterior margin; dactylus medium (0.55 times length of propodus), slightly curved, with nail.

Pereopod 6: ( Fig. 7d ) coxa 6 subquadrate, smaller than coxa 5, about 1.4 times as long as wide, bilobate, posterior lobe roundly expanded downward, anterior margin slightly concave, with long simple setae; basis with distinct hind distal rounded lobe; posterior margin rounded distally, width 0.72 times as long, wing of base separated with curved crest, anterior margin convex medially, with simple setae anteriorly, hind margin smooth; segments 3–7 similar to those in pereopod 5.

Pereopod 7: ( Fig. 7e ) coxa small, unilobate, about 1.23 times as long as wide; basis regular, with rounded posterior wing, width 0.6 times of length, posterior distal corner rounded, with small stout setae along anterior margin and with long simple setae along proximal half of anterior margin; segments 3–7 similar to those in pereopods 5 and 6.

Coxal gills 2–6. Coxal gill 5 smaller than gill 4; coxal gill 6 is the least.

Marsupial plates long oval, with long simple setae.

Epimeral plates: ( Figs. 7f, g, h ) plate 1 triangular, with oblique crest, posterior margin slightly rounded, lower margin with numerous plumose setae, hind corner rounded; plate 2 ventral margin convex, with oblique crest, posterior margin with 2 indistinct notches, ventral margin with numerous plumose setae in anterior 2/3, posteroventral corner without tooth; plate 3 hind corner produced, subacute, posterior margin concave, with posterolateral upturned acute process, ventral margin convex, with two simple setae in the anterior half.

Pleopods: ( Figs. 8a, b, c ) normal; peduncle with two specific toothed coupling setae on the inner corner, lateral margin with a row of long setae; coupling basis of inner ramus with 4–5 specific stout two-pointed cuspidate setae along inner margin.

Length of uropods 1–3 decreases from 1 to 3.

Uropod 1: ( Fig. 8d ) slender, elongate, peduncle about 1.25 times as long as outer ramus, with rows of numerous dorsolateral and dorsomedial spineformes setae; outer ramus shorter then inner (0.93 times length of inner ramus), with 2 rows of dorsal spineformes setae each.

Uropod 2: ( Fig. 8e ) peduncle short, subequal to outer ramus, with rows of numerous dorsolateral and dorsomedial spineformes setae; outer ramus shorter then inner (0.77 times length of inner ramus), with 2 rows of dorsal spineformes setae each.

Uropod 3: ( Fig. 8f ) peduncle short, subequal to outer ramus, with two dorsolateral and with one dorsomedial spineformes setae; outer ramus shorter then inner (0.6 times length of inner ramus), with 2 rows of dorsal spineformes setae each.

Telson: ( Fig. 8g ) lingulate, slightly cleft apically, with proximal ventral keel; with 2 short setae dorsolaterally, distally with 2 setules.

Males unknown.

Etymology. Named after the type locality on the shelf of Sakhalin Island.

Ecology: C. sakhalinensis was found in the depth 256 m on the silt bottom in the layer of constant low temperature (-1.2—+0.5°C). Female with 7 eggs (0.5 x 0.6 mm) in marsupium was found in October.

Distribution: Only type locality. Sea of Okhotsk, the shelf of north-eastern Sakhalin Island ( Fig. 1 ).

Remarks. Cryptodius sakhalinensis sp. nov. is most similar to Cryptodius kelleri ( Brüggen, 1907) . C. sakhalinensis differs from C. kelleri in the form of armament of dorsal carination of pleosome and urosome ( Figs. 10b, c ): in C. sakhalinensis pleonite 3 and urosomite 1 with dorsal rectangular keel in posterior half of each, urosomite 3 dorsally with paired rounded keels; in C. kelleri pleonit 3 dorsal midline with gibbous hump, urosomite 1 with a protruding tubercle in the central part of the midline, urosomite 3 bearing a single longitudional ridge on either side of the dorsal midline. In C. sakhalinensis palp of maxilla 1 with two setae on the distal margin ( Figs. 4b , 10q ); in other species of the genus Cryptodius palp of maxilla 1 with one seta on the distal margin only ( Figs. 10o, p ). Coxa 1 of C. sakhalinensis concave anteriorly ( Figs. 5a , 7a , 11j ); in other species of the genus Cryptodius coxa 1 convex anteriorly ( Figs. 11h, i ). Telson of C. sakhalinensis slightly cleft apically ( Figs. 8g , 11w ); in other species of the genus Cryptodius telson is entire ( Figs. 11u, v ).

Figures

FIGURE 1. Distribution of Cryptodius species on the shelf of Sakhalin Island.

FIGURE 2. Cryptodius sakhalinensis sp. nov., holotype, female: a—lateral view, b—cephalon, c—urosome segments 2 and 3 dorsally, d—antenna 1, e—accessory flagellum of antenna 1, f—antenna 2; scales: a, b, c, d, f—1 mm; e—0.01 mm.

FIGURE 3. Cryptodius sakhalinensis sp. nov., holotype, female: a—upper lip, b—left mandible, c—molar of the left mandible, d—incisor of the left mandible, e—article 3 of the palp of the left mandible, f—molar of the right mandible, g—incisor of the right mandible, h—raker setae of the right mandible; scales: a, b—1 mm, e—0.1 mm, c, d, f, g—0.05 mm, h—0.02 mm.

FIGURE 4. Cryptodius sakhalinensis sp. nov., holotype, female: a—low lips, b, c—maxilla 1, d—maxilla 2, e—maxilliped; scales: a, b, d, e—1 mm, c—0.1 mm.

FIGURE 5. Cryptodius sakhalinensis sp. nov., holotype, female: a—pereopod 1, outer side, b—pereopod 1, inner side, cpereopod 2; scale: 1 mm.

FIGURE 6. Cryptodius sakhalinensis sp. nov., holotype, female: a—propodus and dactylus of pereopod 1, b—pereopod 2, inner side, c—pereopod 3, d, e—pereopod 4; scales: a—0.1 mm, b–e—1 mm.

FIGURE 7. Cryptodius sakhalinensis sp. nov., holotype, female: a, b—sculpture of surface of coxa 1, c—pereopod 5, d—pereopod 6, e—pereopod 7, f, g, h—epimer 1–3; scales: a—0.2 mm, b—0.01 mm, c–h—1 mm.

FIGURE 8. Cryptodius sakhalinensis sp. nov., holotype, female: a—pleopod 2, b—coupling spines of pleopod 2, c—coupling setae of pleopod 1, d—uropod 1, e—uropod 2, f—uropod 3, g—telson; scales: a, d, e, f, g—1 mm, b, c—0.1 mm.

FIGURE 9. a—Cryptodius kelleri (Brüggen, 1907), female (4.4 mm), Lake Ptich’e, b—Cryptodius sakhalinensis sp. nov., holotype, female (7.3 mm), the shelf of north-eastern Sakhalin Island; scale: 1 mm.

FIGURE 10. Diagnostic characters of genera Cryptodius Moore, 1992 and Odius Liljeborg, 1865 species: a, h, o—Cryptodius unguidactylus Moore, 1992 (from Moore 1992), b, i, p—Cryptodius kelleri (Brüggen, 1907) (from Moore 1992, Kim & Hong 2014), c, j, q—Cryptodius sakhalinensis sp. nov., d, k, r—Odius carinatus (Spence Bate, 1862) (from Sars 1895), e, l, s—Odius cassigerus Gurjanova, 1972 (from Labay, 2010), f, m, t—Odius oclairi (Moore, 1992) (from Moore 1992), g, n, u—Odius polarsterni (Brandt & Vassilenko, 1995) (from Brandt & Vassilenko 1995); a–g—carination of abdomen, arrow marks the keel of epimeron 3, urosomite 1 and urosomite 3, h–n—incisor of mandible; o–u—maxilla 1, the arrow shown setae of the palp.

FIGURE 11. Diagnostic characters of genera Cryptodius Moore, 1992 and Odius Liljeborg, 1865 species: a, h, o, u—Cryptodius unguidactylus Moore, 1992 (from Moore 1992), b, i, p, v—Cryptodius kelleri (Brüggen, 1907) (from Moore 1992, Kim & Hong 2014), c, j, q, w—Cryptodius sakhalinensis sp. nov., d, k, r, x—Odius carinatus (Spence Bate, 1862) (from Sars 1895), e, l, s, y—Odius cassigerus Gurjanova, 1972 (from Labay, 2010), f, m, t, z—Odius oclairi (Moore, 1992) (from Moore 1992), g, n, u, aa—Odius polarsterni (Brandt & Vassilenko, 1995) (from Brandt & Vassilenko 1995); a–g—maxilliped, h–n—coxa 1; o–u—pereopod 7, u–z, aa—telson.