Parvochelus serricaudis, 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 : 211-220

Parvochelus serricaudis sp. nov.

( Figs 5–12 )

Material examined. Holotype: ( MIMB 31912) copulatory male (2.2 mm), KuramBio St. 2-9-S; designated here.

Paratypes: ( MIMB 31913) female (2.1 mm) and copulatory male (1.7 mm), used for dissection, 1 male, 8 females, St. 2-9-S; ( ZMH K- 45099) 17 females, 5 males, St. 2-9-E; ( MIMB 31914) 63 females, 7 males, 2 mancas, St. 02-10-S; ( ZMH K- 45100) 33 females, 8 males, St. 02-10-S.

Additional material: ( ZMH K- 45101) female, St. 01-10-E; ( MIMB 31915) 2 females, St. 01-11-S; ( MIMB 31916) 5 females, St. 7-9-S; ( ZMH K- 45102) 4 females, St. 07-10-E; ( MIMB 31917) female, St. 08-09-S; ( ZMH K- 45103) female, St. 08-12-E; ( MIMB 31918) 3 females, St. 9-9-S; ( ZMH K- 45104) female, St. 09-12-S; ( MIMB 31919) 3 females, 1 manca, St. 10-09-S; ( ZMH K- 45105) male, St. 10-12-E; ( MIMB 31920) 2 females, St. 11-09- S.

Etymology. The name refers to the clearly serrated lateral margins of the pleotelson meaning “serrate tail”.

Diagnosis. Antenna I with 6 articles. Mandibular palp present, incisor process and lacinia mobilis of left mandible with 4 cusps. Maxilliped palp article 3 with distomedial lobe. Pereopod I merus shorter than width, carpus length approx. 2.3 width, slightly produced at basis of claw-seta. Female pleopod II (operculum) length 1.5 width, lateral sides slightly converging toward broadly rounded posterior margin. Pleotelson lateral margins with large serrations, which are visible in dorsal view.

Description. Holotype, male: body ( Fig. 5 A–C) length 3.9 pereonite 2 widths, body height 0.18 body length. Surface of body covered with cuticular folds. Head: length 0.64 width, 0.12 body length. Frons slightly concave in dorsal view, with serrate ridge around antennal sockets, transverse ridge and frons-clypeal furrow present, clypeus horizontal, labrum curved downward, slightly concave.

Pereonite 1 length 0.27 width, 0.06 body length; pereonites 2–7 lengths in relation to pereonite 1 length: 1.2; 1.4; 1.8; 1.9; 1.5; 1.1; length–width ratios: 0.29; 0.38; 0.60; 0.66; 0.51; 0.41. Pereonites 1–3 narrowing posteriorly, anterior margins concave with slightly convex medial parts, posterior margins slightly concave, lateral margins convex. Pereonites 4–5 almost rectangular, with concave lateral margins, posterior margin of pereonite 5 concave.

Pereonites 6–7 trapezoidal, broadening posteriorly. Coxae I–IV bilobed, produced anteriorly, anterior productions acute, culminating in small, spine-like, robust seta, decreasing in size from anterior to posterior pereonites, anterior production of coxa I stout, almost reaching antennal sockets.

Pleotelson oval, length 0.94 width, 0.17 body length, height 0.56 length, lateral margins serrate, posterior margin convex, with few SS, framed by cuticular membrane ( Fig. 9 C). Anus directed ventrally.

Paratype, male: Antenna I ( Fig. 6 A) length about 0.17 body length, with 6 articles. Article 1 length 1.5 width, with 3 small BS distally. Articles 2–6 length–width ratios: 4.8; 2.0; 2.3; 2.5; 1.8; articles 2–6 lengths in relation to article 1 length: 1.7; 0.53; 0.55; 0.37; 0.21. Article 2 with 1 long distal BS reaching 0.9 length of article. Articles 3 and 5 without setae; article 4 with 2 BS; article 6 with 2 SS, 2 BS and 1 aestetasc terminally.

Antenna II ( Fig. 6 B) length about 0.60 body length. Articles 1–6 length–width ratios: 1.0; 0.79; 0.95; 1.0; 2.7; 4.6; articles 2–6 lengths in reation to article 1 length: 0.91; 1.3; 1.0; 4.2; 5.6. Article 3 with robust distolateral UBS; article 5 with 1 small distolateral UBS; article 6 distally with 1 small UBS, 3 BS and 3 SS. Flagellum length 0.39 antenna II length, with 12 articles, article 1 length 0.31 flagellum length; articles bearing numerous fine SS distally.

Mandible ( Fig. 7 A, B) incisor process with 4 cusps. Lacinia mobilis of left mandible with 4 cusps; lacinia mobilis of right mandible serrated; spine row with 3 spines. Molar process triangular, distally with about 7 setae. Palp articles with numerous fine SS, article 1 with 1 distal SS; article 2 length 1.9 article 1 length, article 3 length 1.1 article 1 length, almost straight.

Maxilla I ( Fig. 7 C) lateral endite distally with 10 robust serrate setae; mesial endite width 0.63 lateral endite width, with 1 long and 1 shorter setae distally.

Maxilla II ( Fig. 7 D) lateral endite longest, middle endite shortest, width 0.68 lateral endite width, mesial endite width 1.1 of lateral endite width; endites distally bearing 3 (lateral), 2 (middle) and 5 (mesial) serrate setae respectively and numerous long fine SS.

Maxilliped ( Fig. 7 E) basis length 2.5 width; endite length 2.7 width, 0.53 basis length, with 2 retinaculae, distal margin with 3 fan setae and 1 stout and 2 slender setulate setae. Palp length approximately 0.9 basis length, 1.1 width; articles 3–4 with rounded distomedial lobes, lobe of article 3 length 0.47 article 3 lateral length; article 1 width 0.76 basis width, lateral length 0.17 basis length; articles 2–5 lengths in relation to article 1 lateral length: 2.5; 1.5; 1.1; 0.97; articles 1–3 lateral length to medial length ratios: 1.4; 1.5; 0.56; articles 1–5 lateral length to width ratios: 0.54; 0.98; 0.57; 1.1; 2.7; articles 1, 2, 4 with 1, 2, 2 distomedial SS, respectively, article 3 with 3 medial SS, article 5 with 4 distal SS. Epipod length 2.7 width, 1.2 basis length, distal half narrowing, bent medially; lateral margin with hyaline membrane supported by fine setae; surface covered with cuticular folds.

Pereopod I ( Fig. 6 C) basis to dactylus length-width ratios: 6.4; 1.5; 0.95; 2.3; 3.9; 3.8; length ratios of ischiumdactylus compared to basis length: 0.26; 0.16; 0.52; 0.46; 0.11. Basis with 1 dorsal and 1 distoventral SS; ischium with 1 distoventral SS; merus with 1 distoventral and 1 distodorsal SS. Carpus dorsal and ventral margins parallel, almost straight, distoventral corner slightly produced; ventrally 1 small SS at mid-length and 1 twice longer SS proximally to base of claw-seta; claw-seta length 0.69 propodus length, slender seta between claw-seta and propodus, seta length about 0.85 claw-seta length. Propodus widest proximally, with 2 dorsal and 1 distoventral fine SS, ventral margin with hyaline membrane supported by 3 fine setae. Surface of carpus and propodus covered with cuticular folds. Dactylus dorsal claw 0.22 dactylus length, ventral claw extends beyond dorsal claw.

Pereopod II ( Fig. 8 A) basis to dactylus length-width ratios: 6.8; 2.6; 1.6; 6.8; 5.3; 6.6; length ratios of ischiumdactylus compared to basis length: 0.32; 0.20; 0.76; 0.44; 0.27. Basis with 1 distoventral DSS; ischium with 1 ventral DSS; merus with 1 DSS distoventrally, 1 DSS and 1 SS distodorsally. Carpus dorsal margin with 3 DSS, ventral margin with 4 DSS increasing in size towards propodus. Propodus dorsal margin with 2 long robust DSS, ventral margin with 4 short DSS and 1 distal SS. Ventral margins of carpus and propodus with hyaline membranes. Dactylus with 3 fine distolateral setae, dorsal claw length 0.32 dactylus length, ventral claw length about 0.30 dorsal claw length, 2 setae inserted between claws.

Pereopod III ( Fig. 8 B) basis length 7.0 width, with 3 ventral SS; ischium-dactylus broken, missing.

Pereopod IV ( Fig. 8 C) basis to dactylus length-width ratios: 5.3; 2.4; 1.7; 6.8; 6.5; 9.6; length ratios of ischium-dactylus compared to basis length: 0.42; 0.28; 0.89; 0.59; 0.37. Basis with 1 SS and 1 DSS dorsally, 2 SS and 1 DSS ventrally; ischium with 1 ventral DSS; merus with 1 distoventral and 1 distodorsal DSS; carpus with 4 ventral and 3 dorsal DSS increasing in size towards propodus; propodus with 2 large dorsal DSS; dactylus dorsal claw 0.45 dactylus length, ventral claw length about 0.25 dorsal claw length.

Pereopod V ( Fig. 8 D) basis length 6.7 width, with 1 dorsal SS; ischium length 3.1 width, 0.54 basis length, with 2 dorsal DSS; merus-dactylus broken, missing.

Pereopod VI ( Fig. 8 E) basis to dactylus length-width ratios: 5.7; 2.8; 2.1; 5.7; 7.1; 19.8; length ratios of ischium-dactylus compared to basis length: 0.54; 0.27; 0.86; 0.76; 0.55. Basis with 1 dorsal and 3 ventral fine DSS; ischium with 1 dorsal DSS; merus with 2 SS distoventrally, 1 SS and 1 DSS distodorsally; carpus with 5 ventral and 4 dorsal long DSS, ventral margin with hyaline membranes; propodus dorsal margin with row of 4 long DSS, 1 UBS, 5 long DSS, 1 UBS, ventral margin with 4 long DSS increasing in size towards dactylus; dactylus dorsal claw length 0.30 dactylus length, ventral claw length about half dorsal claw length.

Pereopod VII ( Fig. 8 F) basis to dactylus length-width ratios: 6.7; 3.7; 2.0; 6.7; 7.3; 8.9; length ratios of ischium-dactylus to basis: 0.53; 0.25; 0.86; 0.72; 0.53. Basis with 1 dorsal BS and 2 ventral fine DSS; merus with 1 distodorstal and 2 distoventral fine DSS; carpus with 4 ventral and 3 dorsal long DSS; propodus dorsal margin with row of 2 long DSS, 1 UBS, 4 long DSS, 1 UBS, ventral margin with 1 long DSS; dactylus with 2 SS dorsally, dactylus dorsal claw 0.34 dactylus length, ventral claw about half dorsal claw length, 1 seta inserted between claws.

Pleopod I ( Fig. 9 A) oval, length 1.6 widths, medially with few SS; distolateral lobes not developed, distomedial lobes 0.24 pleopod 1 length, rounded, bearing 8–9 marginal SS.

Pleopod II ( Fig. 9 B) protopod length 3.0 width, with 2 distolateral SS. Endopod basal article length 1.7 width, 0.30 protopod length; stylet length 11.9 width, 1.4 protopod length, sperm duct opening at about 0.16 length of stylet, distal part of stylet narrowing, acute. Exopod length 1.8 width, 0.35 protopod length.

Pleopods III–V similar to those of female (see below).

Uropod ( Fig. 9 C) length 0.43 pleotelson length. Protopod length 1.3 width, with 4 lateral and 1 distomedial UBS. Endopod length 5.4 width, 1.8 protopod length, lateral and distal margins with about 5 BS and 2 SS.

Paratype, female: body ( Fig. 5 D–H) wider, than that of male (length 3.3 width), with larger pereonites 2–4. Pereonites 2–7 length in relation to pereonite 1 length: 1.4; 1.8; 2.2; 1.8; 1.2; 1.3. Coxae with less pronounced anterolateral projections than male. Pleotelson length 1.2 width.

Antenna I ( Fig. 10 A) with 6 articles. Articles 1–6 length–width ratios: 1.4; 4.4; 1.7; 2.0; 3.4; 2.7; articles 2–6 lengths to article 1 length ratios: 2.1; 0.60; 0.67; 0.44; 0.25; article 1 without setae, article 2 with 3 long BS.

Antenna II ( Fig. 10 B) about half body length. Articles 1–6 length–width ratios: 1.2; 0.82; 0.96; 1.2; 6.9; 8.9; articles 2–6 lengths to article 1 length ratios: 0.87; 0.99; 0.99; 4.7; 5.9; article 3 with 1 short robust UBS laterally. Flagellum length 0.39 antenna II length, with 7 articles, flagellar articles 2–6 with 1–2 distal fine SS, article 7 with 6 terminal fine SS.

Mouthparts ( Fig. 10 C–G) and pereopods ( Figs 5 I, 11) similar to those of male, except for minor differences in proportion and setation.

Operculum ( Fig. 12 A) length 1.5 width, lateral sides slightly converging toward posterior margin; posterior margin broadly rounded, with inconspicuous angle medially, framed by hyaline membrane, with 1 SS.

Pleopod III ( Fig. 12 B) protopod length 1.1 width. Endopod length 1.5 width, distal margin broadly rounded, with 3 pappose setae, setae lengths about as long as endopod. Exopod length 0.77 endopod length, narrowing distally, with 1 terminal SS.

Pleopod IV ( Fig. 12 C) protopod length 0.85 width. Endopod length 1.5 width. Exopod length 4.5 width and about 1.1 endopod length, with terminal pappose seta, which about 1.5 times longer than exopod, lateral margin with fine SS.

Pleopod V ( Fig. 12 D) endopod length 2.8 width, with 1 distal SS, lateral margin with fine SS.

Uropod ( Fig. 12 E) protopod length 1.8 width.

Remarks. The habitus of P. serricaudis sp. nov. and the type species P. russus are similar, however, the new species has more pronounced serrations on the pleotelson lateral sides, which are clearly visible on a total view. P. serricaudis sp. nov. can easily be distinguished from P. russus by the shape of pereopod I, which in the new species is much stouter and enlarged when compared to pereopod II, its carpus length 2.3 times longer than wide, slightly produced at the base of the claw-seta. In contrast, the pereopod I of P. russus is slender, not enlarged, possessing a weak chela with a long slender carpus (3.7 times longer than wide), which is not produced at the base of the clawseta. The mandibles of P. russus lack palps. In P. serricaudis sp. nov. the mandibular palps are present but fragile and easily break when specimens are handled. The female operculum in P. serricaudis has almost parallel lateral sides, slightly converging toward the posterior margin; the latter is broadly rounded, with the inconspicuous indentation medially. In P. russus the female operculum is tapering toward the distal end. Furthermore, the two species differ in the number of antennal articles and the mouthparts morphology.

Distribution. Northwest Pacific to the east of the Kuril-Kamchatka Trench, from 40.2210°N, 148.1038°E – 40.2062°N, 148.0905°E to 46.2268°N, 155.5567°E – 46.2487°N, 155.5428°E, at depth ranges from 4830–4863 to 5423–5429 m.

Figures

FIGURE 5. Parvochelus serricaudis sp. nov. (A – C) Male, holotype; (D – G) female, paratype; (H, I) female, paratype: (A, E) dorsal view; (B, D) lateral view; (C, F) pleotelson, ventral view; (H) pleotelson, pleopods removed; (G) head, anterolateral view; (I) pereopod I. Scale bar = 0.3 mm.

FIGURE 6. Parvochelus serricaudis sp. nov. Male, paratype: (A, B) antennae I, II; (C) pereopod I. Scale bar = 0.1 mm.

FIGURE 7. Parvochelus serricaudis sp. nov. Male, paratype: (A, B) right and left mandibles; (C, D) maxillae I, II; (E) maxilliped. Scale bar = 0.1 mm.

FIGURE 8. Parvochelus serricaudis sp. nov. Male, paratype: (A) pereopod II; (B) pereopod III, basis; (C) pereopod IV; (D) pereopod V, basis and ischium; (E, F) pereopods VI, VII. Scale bar = 0.1 mm.

FIGURE 9. Parvochelus serricaudis sp. nov. Male, paratype: (A, B) pleopods I, II; (C) uropods. Scale bar = 0.1 mm.

FIGURE 10. Parvochelus serricaudis sp. nov. Female, paratype: (A, B) antennae I, II; (C, D) right and left mandibles; (E, F) maxillae I, II; (G) maxilliped. Scale bar = 0.1 mm.

FIGURE 11. Parvochelus serricaudis sp. nov. Female, paratype: (A) pereopod II; (B) pereopod IV; (C, D) pereopods V, VI; (E) pereopod VII, basis and ischium. Scale bar = 0.1 mm.

FIGURE 12. Parvochelus serricaudis sp. nov. Female, paratype: (A) operculum; (B – D) pleopods III – V; (E) uropod. Scale bar = 0.1 mm.