Eugerdella kurabyssalis, Golovan, Olga A., 2015

Golovan, Olga A., 2015, Description of two ubiquitous species of Desmosomatidae (Isopoda: Asellota) from the Northwest Pacific Basin east of the Kuril-Kamchatka Trench, Zootaxa 4039 (2), pp. 201-224 : 204-211

Eugerdella kurabyssalis sp. nov.

( Figs 1–4 )

Material examined. Holotype: ( MIMB 31898) preparatory female (2.8 mm), KuramBio St. 9-9-S; designated here.

Paratypes: ( MIMB 31899) female (2.3 mm) and copulatory male (2.3 mm), used for dissection, copulatory male (2.2 mm), 4 females, St. 9-9-S; ( ZMH K- 45095) 3 females, St. 9-9-E; ( MIMB 31900) 13 females, 5 males, St. 9-12-E; ( ZMH K- 45096) 2 females, 1 male, 2 mancas, St. 9-12-E.

Additional material: ( MIMB 31901) 4 females, 2 males, St. 01-10-S; ( MIMB 31902) 2 females, 2 males, St. 2- 9-S; ( ZMH K- 45097) 4 females, St. 2-9-E; ( MIMB 31903) 3 females, St. 3-9-S; ( MIMB 31904) 3 females, 1 male, St. 5-9-S; ( MIMB 31905) female, St. 6-11-S; ( MIMB 31906) 2 females, 1 manca, St. 7-9-S; ( MIMB 31907) 2 females, St. 7-9-E; ( MIMB 31908) 3 females, 1 male, St. 08-09-S; ( ZMH K- 45098) 3 females, 3 mancas, St. 08-09- E; ( MIMB 31909) 2 females, 1 manca, St. 10-9-S; ( MIMB 31910) 3 females, 1 male, St. 11-9-S; ( MIMB 31911) 2 females, St. 12-4-S.

Etymology. The species name derives from the abbreviation of “kurilensis” and “abyssalis”, that refers to the type locality of the species.

Diagnosis. Body length 3.7–4.4 width, widest at pereonite 2, narrowing posteriorly. Pereonite 1 length 1.2 pereonite 2 length. Pleotelson with small posterolateral spines. Coxae I–II in female and coxae I–IV in male produced anteriorly, acute, culminating in a robust, spine-like seta; anterior production of coxa I longest compared to more posterior coxae. Mandibular incisor process of left mandible with 4 cusps, lacinia mobilis with 5 cusps; palp absent. Pereopod I stout; carpus enlarged, length 1.3 width, width 2.4 pereopod II width, ventral margin at proximal two thirds convex, at distal third straight, with row of 4 robust UBDS of irregular size and 1 minute distal UBDS at base of penultimate seta; ischium length 1.2 width, with 5 robust distodorsal UBDS. Operculum truncate, slightly concave distally, length 1.2 width.

Description. Holotype, female: body ( Fig. 1 A–D) length 3.7 pereonite 2 width, body height 0.18 length. Head: length 0.65 width and 0.12 body length. Frons smooth, without transverse ridge, frons-clypeal furrow present. Pereonite 1 length 0.38 width, 0.10 body length; pereonites 2–7 length in relation to pereonite 1 length: 0.86; 0.80; 0.96; 1.2; 1.2; 1.0; length–width ratios: 0.31; 0.31; 0.47; 0.68; 0.72; 0.66. Pereonites 1–3 narrowing posteriorly, anterior margins slightly concave, posterior margins slightly convex, lateral margins convex. Pereonite 4 with concave anterior margin and straight lateral and posterior margins. Pereonites 5–7 almost rectangular, with almost straight margins. Coxae I–IV bilobed, coxae I–II produced anteriorly, anterior production of coxa I longest, narrow and acute, culminating in small spine-like, robust seta; lobes of coxae III and IV rounded.

Pleotelson length 1.3 width, 0.17 body length, lateral margins straight, subparallel, small posterolateral spines present, located at 0.82 length posteriorly to anterior margin of pleotelson, posterior margin rounded, convex.

Paratype, female: Antenna I ( Fig. 2 A) about 0.18 body length, with 6 articles. Article 1 length 1.6 width, with 1 BS and 1 SS distally. Articles 2–6 length-width ratios: 6.5; 2.9; 2.7; 3.5; 5.3; articles 2–6 lengths in relation to article 1 length: 2.5; 0.79; 0.65; 0.63; 0.56. Article 2 with 3 BS at distal half, 1 long distal BS reaching 1.3 length of article. Article 3 with small SS; article 4 with small BS; article 6 with few long SS terminally.

Antenna II ( Fig. 2 B) length 0.38 body length. Articles 1–6 length-width ratios: 0.74; 0.67; 0.97; 0.68; 5.9; 7.9; articles 2–6 lengths in relation to article 1 length: 0.80; 1.1; 0.65; 5.1; 5.7. Article 1 with distal robust UBS; article 3 with robust distolateral UBS; articles 5–6 with few SS and 2 distal BS. Flagellum length 0.43 antenna II length, with 8 articles, bearing few long fine SS distally.

Mandible ( Fig. 2 C, D) incisor process with 4 cusps on left mandible and 3 cusps on right mandible. Lacinia mobilis of left mandible with 6 cusps; spine row with 6 spines. Spine row of right mandible with 8 spines, 2 distal spines stout, serrated. Molar process triangular, distally with about 8–11 setae. Palp absent.

Maxilla I ( Fig. 2 E) lateral endite distally with 12 robust serrate setae and laterally with few long, fine SS; mesial endite width 0.76 lateral endite width, with numerous long fine SS laterally and distally.

Maxilla II ( Fig. 2 F) lateral endite longest, middle endite shortest, as wide as lateral endite, mesial endite width 1.3 lateral endite width; lateral and middle endites distally with 3 serrate setae, mesial endite distally with 4 serrate setae and distomedially with 1 long SS, all endites with numerous long fine SS.

Maxilliped ( Fig. 2 G) basis length 1.9 width, with few SS, laterally with fine setae; endite length 2.9 width, 0.57 basis length, with 2 retinaculae, distal margin with 2 fan setae and 3 SS. Palp length approximately 1.1 basis length; article 1 width 0.87 basis width, lateral length 0.25 basis length; articles 2–5 to article 1 lateral length ratios: 2.0; 0.59; 0.96; 0.68; articles 1–3 lateral length to medial length ratios: 2.4; 1.7; 0.33; articles 1–5 lateral lengths to width ratios: 0.54; 0.95; 0.33; 1.4; 2.1; article 1 with 1 distolateral SS; articles 2–3 with 4–5 SS near medial margin and 1 stout seta distolaterally; article 4 with 3 distomedial and 1 distolateral SS; article 5 with 1 lateral and 3 distal SS. Epipod length 3.0 width, 1.2 basis length, narrowing distally, lateral margin and distal half of medial margin with hyaline membrane.

Pereopod I ( Fig. 1 H) basis to dactylus length-width ratios: 3.0; 1.2; 0.61; 1.3; 2.6; 7.9; ischium-dactylus lengths in relation to basis length: 0.45; 0.25; 0.86; 0.84; 0.50. Basis with 1 distoventral long stout seta (broken) and few fine SS; ischium with 2 ventral and 5 distodorsal robust UBDS; merus with 2 ventral and 2 distodorsal robust UBDS. Carpus ventral margin at proximal two thirds convex, at distal third straight, with row of 4 robust UBDS of varying sizes (short setae alternate with long setae) and 1 tiny distal UBDS at base of penultimate seta, penultimate seta length 0.70 propodus length, carpus extended ventrally, distal margin with gap between penultimate seta and insertion of propodus. Propodus with 2 dorsal and 1 distoventral fine SS, ventral margin with hyaline membrane supported by 8 fine setae. Surface of carpus and propodus covered with cuticular scales. Dactylus claw length 0.19 dactylus length, 2 slender setae inserted ventrally.

Pereopod II ( Fig. 3 A) basis to dactylus length-width ratios: 3.6; 2.3; 1.7; 4.3; 4.9; 5.4; length ratios of ischiumdactylus lengths in relation to basis length: 0.60; 0.32; 0.94; 0.59; 0.34. Basis with 1 distoventral DSS and few fine SS; ischium with 2 ventral robust UBS and 1 distodorsal SS; merus with 1 ventral robust UBS, 1 distoventral long robust UBDS and 1 distodorsal SS. Carpus with dorsolateral row of 3 robust UBS, 1 short UBS and 1 BS distodorsally and ventral row of 8 robust UBDS, increasing in size towards propodus. Propodus with 3 robust ventral and 4 long robust dorsal UBS and 1 distoventral SS. Dactylus claw length 0.27 dactylus length, 2 long slender SS inserted ventrally.

Pereopod III ( Fig. 3 B) basis to carpus length-width ratios: 5.9; 3.7; 1.8; 5.0; ischium-carpus lengths in relation to basis length: 0.48; 0.17; 0.55; propodus and dactylus broken and missing. Setation similar to that of pereopod II, but merus with 1 UBS ventrally, carpus with 4 DSS ventrally and 3 dorsally.

Pereopod IV ( Fig. 3 C) basis to dactylus length-width ratios: 5.9; 3.6; 1.8; 5.8; 5.0; 9.5; length ratios of ischium-dactylus in relation to basis length: 0.57; 0.27; 0.72; 0.56; 0.38. Setation of basis–merus similar with that of pereopod II. Carpus with dorsolateral row of 3 DSS and ventral row of 7 DSS. Propodus with dorsal row of 4 DSS and ventral row of 4 UBS, 1 SS distoventrally. Dactylus claw length 0.29 dactylus length.

Pereopod V ( Fig. 3 D) basis to dactylus length-width ratios: 4.3; 2.3; 1.7; 3.5; 4.9; 16.6; ischium-dactylus lengths in relation to basis length: 0.49; 0.23; 0.68; 0.51; 0.51. Basis with 3 BS and few fine SS; ischium distodorsally with 1 DSS and 2 UBS; merus with 1 SS distoventrally, 1 SS and 1 DSS distodorsally; carpus with 5 ventral and dorsal long slender DSS and 1 distodorsal UBS; propodus with 7 long slender DSS and 1 SS ventrally and row of 2 DSS, 1 UBS, 2 DSS, 1 UBS dorsally. Dactylus claw length 0.32 dactylus length, with 1 distodorsal DSS and 1 distoventral UBS.

Pereopod VI ( Fig. 3 E) basis to dactylus length-width ratios: 4.1; 2.3; 1.3; 4.0; 5.7; 13.2; ischium-dactylus lengths in relation to basis length: 0.49; 0.20; 0.61; 0.47; 0.48, similar to pereopod V.

Pereopod VII ( Fig. 3 F) basis to dactylus length-width ratios: 4.5; 2.2; 1.1; 4.5; 5.4; 12.0; ischium-dactylus lengths in relation to basis length: 0.38; 0.16; 0.59; 0.49; 0.54. Basis with few fine SS; merus with distodorsal DSS and 2 small ventral SS; carpus with 3 long slender UBDS ventrally and 3 long slender DSS, 1 BS and 1 UBS dorsally; propodus with 1 seta (broken, type unknown), 1 small SS and 2 long slender UBDS ventrally and 1 long slender DSS, 1 BS and 1 UBS distodorsally. Dactylus claw length 0.34 dactylus length, with 1 long slender dorsal SS and 2 long slender SS ventrally to claw.

Operculum ( Fig. 4 D, E) truncate, length 1.2 widths, height 0.17 length, slightly higher medially than proximally and distally, lateral sides convex, posterior margin slightly concave, with about 12 SS on distal margin.

Pleopod III ( Fig. 4 B) protopod length 0.82 width. Endopod length 1.5 width, distal margin broadly rounded, with 3 plumose setae, setae lengths 1.2 endopod length. Exopod length 1.9 width, 0.52 endopod length, oval, with 1 terminal SS, lateral margin with fine SS.

Pleopod IV ( Fig. 4 C) protopod length 0.58 width. Endopod length 1.8 width. Exopod length 5.9 widths, about 1.1 endopod length, with terminal plumose seta, seta length about 1.1 exopod length.

Uropod ( Fig. 4 A) length 0.61 pleotelson length. Protopod length 1.9 width, with 2 distolateral and 2 distomedial UBS. Endopod length 6.6 width, 2.5 protopod length, with 2 long BS and articulations of 3 broken BS distally, 1 medial and 1 distal SS and 3 small BS. Exopod length 1.5 widths, 0.10 endopod length, with 2 terminal UBS.

Paratype, male: body ( Fig. 1 E–G) more slender compared to female (length 4.4 width), pereonites 1–3 narrower than in female, pereonites 4–7 of about similar width. Coxae I–IV produced anteriorly, culminating in spine-like, robust seta; length of anterior productions and apical setae decreasing from pereonites 1 through 4, seta of coxa I constitutes 0.5 of production length and reaches article 2 of antenna I. Posterolateral spines of pleotelson longer in relation to pleotelson length than those of female.

Antenna I ( Fig. 4 F) articles 1–6 length–width ratios: 1.7; 6.3; 2.9; 2.5; 3.3; 3.3; articles 2–6 lengths in relation to article 1 length: 1.8; 0.59; 0.46; 0.38; 0.36. Setation similar with that of female, article 6 with 1 BS, 2 SS and 1 aestetasc.

Antenna II ( Fig. 4 G) length about 0.43 body length. Articles 1–6 length–width ratios: 0.82; 0.68; 0.70; 0.91; 3.6; 4.0; articles 2–6 lengths in relation to article 1 length: 0.87; 1.1; 0.98; 5.1; 4.5. Article 3 distolaterally with stout seta; articles 5–6 distomedially with 1 and 2 BS and few fine SS. Flagellum length 0.40 antenna II length, with 11 articles, article 1 length 0.21 flagellum length; articles bearing few fine SS distally.

Mouthparts and pereopods similar to those of female.

Pleopod I ( Fig. 4 H) length 2.3 proximal widths, lateral sides concave, bearing few fine SS distomedially; distomedial lobes length 0.20 pleopod I length, width equal length, extending 0.06 pleopod I length beyond lateral lobes, rounded distally, each lobe distally with 5 SS and distolaterally with 6 fine SS; distolateral lobes lengths 2.5 width.

Pleopod II ( Fig. 4 I) protopod length 2.1 width, distolaterally with 8 SS. Endopod basal article length 2.1 width, 0.23 protopod length; stylet length 5.5 width, 0.59 protopod length, sperm duct opening at about 0.40 length of stylet, distal part of stylet narrowing, acute. Exopod length 1.5 width, 0.27 protopod length.

Pleopods III–IV and uropod similar to those of female.

Remarks. E. kurabyssalis sp. nov. is rather similar to E. theodori Brix, 2007 from the Angola Basin (South Atlantic) and E. minutula Mezhov, 1986 from the Gulf of Alaska (Northeast Pacific), sharing the following characters: the body is compact, narrowing posteriorly; pereonite 1 is slightly longer than pereonite 2; the pleotelson has small posterolateral spines; the anterior lobes of the coxae I–IV are more ( E. theodori , E. kurabyssalis sp. nov.) or less ( E. minutula ) produced and acute. The productions at the coxae I are the longest; in the males of E. theodori and E. kurabyssalis sp. nov. they are longer than in the females. The character states of the mouthparts of these three species are quite similar (although the description of E. minutula is incomplete), the mandibles lack palp. Pereopod I is stout, with the enlarged carpus, whose ventral margin is convex at the proximal two thirds and almost straight distally, bearing a row of 4 ( E. theodori , E. kurabyssalis sp. nov.) or 5 ( E. minutula ) robust setae of varying size (short setae alternate with long setae). E. theodori and E. kurabyssalis sp. nov. also have an extremely small distal seta in addition to this row and a gap between this seta and the insertion of the propodus, which (gap) E. minutula lacks. In E. kurabyssalis sp. nov. and E. minutula the carpus of pereopod I is 1.3 times longer than wide, while in E. theodori it is 1.8 times longer than wide. E. minutula differs from E. kurabyssalis sp. nov. and E. theodori by the tiny terminal article of antenna I and by the suncircular female operculum, which is slightly wider than long (versus the elongate operculum, which is 1.2-times longer than wide).

E. kurabyssalis sp. nov. can be distinguished from the mentioned species by the number of cusps of the mandibular incisor process (4 cusps on the left mandible versus 5 in E. theodori ) and lacinia mobilis (5 cusps versus 3 in E. minutula and 6 in E. theodori ), relatively stouter pereopods and presence of 5 robust UBDS at the distodorsal angle of the pereopod I ischium ( E. theodori has 3 robust SS at this location, E. minutula lacks setae).

E. kurabyssalis sp. nov. is clearly distinguishable from the other species of the genus by the body shape and proportions and by the shape and setation of the pereopod I articles. The key to the species of Eugerdella is presented in Schnurr & Brix (2012).

Distribution. Northwest Pacific to the east of the Kuril-Kamchatka Trench, from 39.7300°N, 147.1813°E – 39.7082°N, 147.1562°E to 47.2307°N, 154.6982°E – 47.2477°N, 154.7197°E, at depth ranges from 4830–4863 to 5423–5429 m.

Figures

FIGURE 1. Eugerdella kurabyssalis sp. nov. (A – D) Female, holotype; (E – G) male, paratype; (H) female, paratype: (A, F) dorsal view; (B, E) lateral view; (C) head, anterolateral view; (D, G) pleotelson, ventral view; (H) pereopod I. Scale bar = 0.3 mm.

FIGURE 2. Eugerdella kurabyssalis sp. nov. Female, paratype: (A, B) antennae I, II; (C, D) left and right mandibles; (E, F) maxillae I, II; (G) maxilliped. Scale bar = 0.1 mm.

FIGURE 3. Eugerdella kurabyssalis sp. nov. Female, paratype: (A) pereopod II; (B) pereopod III, basis – carpus; (C – F) pereopods IV – VII. Scale bar = 0.3 mm.

FIGURE 4. Eugerdella kurabyssalis sp. nov. (A – E) Female, paratype; (F – I) male, paratype: (A) uropod; (B – C) pleopods III and IV; (D) operculum, ventral view; (E) operculum, lateral view; (F, G) antennae I, II; (H, I) pleopods I, II. Scale bar = 0.1 mm.