Triconia onnuri Cho & Böttger-Schnack & Kim & Lee 2019, n. sp.

Triconia onnuri n. sp.

(Figs 6-9; 13B, C; Tables 2-4)

urn:lsid:zoobank.org:act: 515ECE8F-6AAE-47DD-AF7B-55D899441DC7

TYPE LOCALITY. — Northeastern equatorial Pacific Ocean (10°30’N, 131°20’W, 0-100 m).

TYPE MATERIAL. — Holotype. 1♀; NIBRIV0000838008; 10°30’N, 131°20’W; 0-100 m; dissected and mounted on 10 slides, collected from the type locality on 21.VIII.2009 by D. J. Ham.

Paratypes. 3 ♀; NIBRIV0000838009-011; 10°30’N, 131°20’W; 0-100 m; each dissected and mounted on 9 or 10 slides, respectively (lost a slide of urosome with P5 of the third paratype). — 3 ♂; NIBRIV0000838012-014; 10°30’N, 131°20’W; 0-100 m; each dissected and mounted on 10 slides, respectively. — 4♀, 3♂ kept in one vial in alcohol, MNHN-IU-2019-2283. All specimens are from the type locality.

ETYMOLOGY. — The species is named after research vehicle ‘Onnuri’ of the Korea Institute of Ocean Science and Technology (KIOST) to recognize contributions to research activities in the northeastern equatorial Pacific Ocean.

DESCRIPTION

Female

Body length. 784-823 Μm, based on four specimens.

Exoskeleton moderately chitinized. Prosome about 1.9 times length of urosome, excluding caudal rami 1.7 times urosome length including caudal rami. P2-bearing somite without conspicuous dorsoposterior projection in lateral aspect (Fig. 6B). Integumental pores on prosome as indicated in Fig. 6A. Pleural areas of P4-bearing somite with rounded posterolateral corners. One pair of secretory pores discernible on first postgenital somite (Fig. 6D).

Genital double-somite. 2.0 times as long as maximum width (measured in dorsal aspect) and about 2.2 times as long as postgenital somites combined; largest width measured at anterior one third; posterior part tapering gradually (Fig. 6C); surface covered with numerous minute pores or pits near genital apertures (inset of Fig. 13B). Paired genital apertures located dorsally at about 1/3 of distance from anterior margin of genital double-somite (Fig. 6C); armature represented by one long spine and minute spinule (Fig. 13B). Secretory pores on dorsal surface as indicated in Fig. 6C.

Anal somite. About 1.4 times wider than long; slightly longer than caudal rami (Fig. 6C). Ornamentation as in T. komo n. sp.

Caudal ramus. About two times as long as wide. Seta VII about half length of seta IV; seta VI almost same length as seta VII, swollen at base (arrowed in Fig. 6F).

Antennule (Fig. 7A). 6-segmented. Armature formula as for T. komo n. sp.

Antenna (Fig. 7B). 3-segmented. Distal endopod segment with armature and ornamentation as in T. komo n. sp., except for seta I of lateral armature sparsely pinnate, and seta III bipinnate at distal part.

Labrum (Fig. 7G, H). Similar to T. komo n. sp., except for each lobe with stronger and fewer dentiform processes than in T. komo n. sp.

Mandible (Fig. 7C). Maxillule (Fig. 7D) and maxilla (Fig. 7E) as for T. komo n. sp., except for innermost element on outer lobe of maxillule ornamented with small spinules (arrowed in Fig. 7D).

Maxilliped (Fig. 7F). Similar to T. komo n. sp., basis with two bipinnate spiniform elements, nearly equal in length, distal one slightly longer. Distal endopod segment (claw) with row of strong pinnules along proximal 4/5 of concave margin.

Swimming legs 1-4. Biramous (Fig. 8 A-D). With armature as in T. komo n. sp. Intercoxal sclerites of P1-P3 ornamented with few spinules on posterior face (Fig. 8A, B, C); intercoxal sclerite of P4 not observed. Coxae and bases of P1-P4 with ornamentation as shown in Fig. 8 A-D. Basis of P4 with outer seta shorter than in T. komo n. sp. (Fig. 8D).

Exopods. Similar to T. komo n. sp., except for length of outer spine on P3 exp-1 shorter than in T.komo n. sp. (Fig. 8C). Length ratio of outer spine on exp-1 relative to outer spine on exp-2 of P3 and P4 somewhat smaller than in T. komo n. sp. (Table 3).

Endopods. Distal margin of P2-P4 produced into conical process with apical pore. Length ratios of spines different from T. komo n. sp. with length data of spines of five specimens as shown in Table 2; length ranges of outer subdistal spine (OSDS) and outer distal spine (ODS) relative to distal spine (DS) given in Table 3.

P5 (Fig. 6E). With outer basal seta very long and plumose at distal part; exopod segment free. Exopod about 1.9 times longer than wide, bearing two naked setae, bearing stout inner seta and extremely long, slender outer seta about twice of length of inner seta, reaching 4/5 the length of genital double-somite from anterior margin, as far as secretory pores on dorsal surface.

P6 (Fig. 6F). Represented by operculum closing off each genital aperture, ornamented with long spine and minute spinule (Fig. 13B).

Male

Body length. 570-604 Μm, based on three specimens. Sexual dimorphism in antennule, maxilliped, P5-P6, caudal ramus, and in genital segmentation. Prosome 1.8 times urosome length, including caudal rami (Fig. 9A). Cephalosome and P1 bearing somite with conspicuous lateral patterns of pore patches (Figs 9B; 13C). Posterior margin of P5-bearing somite with paired row of minute denticles or spinules ventrally (Fig. 9E).

Genital somite (Fig. 9D). About 1.5 times longer than wide.

Caudal rami. About 1.4 times longer than wide, shorter than in female. Caudal seta with proportional lengths as in female, seta VI swollen at base as in female (arrowed in Fig. 9I). Dorsal surface of genital somite with three secretory pores as indicated in Fig. 9D. Surface of genital flaps ornamented with several rows of small spinules (Fig. 9E, F).

Antennule (Fig. 9C). 4-segmented; armature formula as for T. komo n. sp.

Maxilliped (Fig. 9G, H). 3-segmented. Surface ornamentation on syncoxa not discernible, except for single secretory pore at inner distal margin. Basis robust, with small naked setae within longitudinal cleft, proximal seta about same length as distal one; anterior surface with one-two transverse spinular rows and row of small flat spinules along inner margin; posterior surface with rows of short spinules of graduated length along palmar margin.

Swimming legs. With armature and ornamentation as in female, length data of endopodal spines of three males as shown in Table 2; length ranges of outer subdistal spine (OSDS) and outer distal spine (ODS) relative to distal spine given in Table 4; generally similar to females (cf. Table 3).

P5 (Fig. 9D, F). Exopod not delimited from somite, shorter than in female; outer exopodal seta unornamented and almost equal in length to inner seta; outer basal seta naked and much shorter than in female.

P6. Represented by posterolateral flap closing off genital aperture on either side; covered by pattern of spinules as shown in Fig. 9E; posterolateral corners protruding laterally and visible in dorsal aspect (Fig. 9A, D).

REMARKS

Among species of the similis -subgroup of Triconia, T. onnuri n. sp. is closely related to T. similis, based on the body size and the form of the genital double-somite in the female, but differs in the relative lengths of the outer exopodal seta and the outer basal seta on P5, with both setae reaching over half the distance from anterior to posterior margin of the genital double-somite, and the form of caudal seta VI, which is swollen at its base. The combination of these characters separates the new species also from other described species of the similis -subgroup. Furthermore, T. onnuri n. sp. can be identified by the length to width ratio of P5 exopod, which is intermediate (1.9:1) between those of other species of the similis -subgroup (most are less than 1.5:1, except 3: 1 in T. recta); and in some minor differences in the proportional spine lengths on the endo- and /or exopods of P2-P4. Especially on the endopod of P4, the length ratio values of outer subdistal spine (OSDS) relative to distal spine (DS) is higher in T. onnuri n. sp. (OSDS:DS=0.73-0.86:1) than the range of single values reported for T. similis from three studies (OSDS:DS=0.62-0.67:1, Table 3).

The male of T. onnuri n. sp. shows a distinct modification of seta VI on the caudal ramus, which is basally swollen (Fig. 8I) as in the female (Fig. 5F). Modifications in the form of caudal setae have not been observed in other species of Triconia so far, but have been reported for other oncaeid species, such as species of Spinoncaea (Böttger-Schnack 2003) and Epicalymma (Böttger-Schnack 2009), where they occur in both sexes as well. Thus, in T. onnuri n. sp., the modification of the caudal setae can be used as an additional tool for separating the species from closely related species within the genus. Also in the male, the proportional spine lengths on the endopod of P2-P4 and the length range of the exopodal spines on exp-1 of P3-P4 are similar to the female.