Triconia giesbrechti Böttger-Schnack, 1999

Cho, Kyuhee, Kim, Woong-Seo, Böttger-Schnack, Ruth & Lee, Wonchoel, 2013, A new species of the dentipes-subgroup of Triconia and a redescription of T. giesbrechti and T. elongata (Copepoda: Cyclopoida: Oncaeidae) from the tropical Pacific and the Korea Strait, Journal of Natural History (J. Nat. Hist.) 47 (25 - 28), pp. 1707-1743 : 1730-1738

Triconia giesbrechti Böttger-Schnack, 1999 Pacific form

( Figures 9–12 )

Sampling locality

North-east equatorial Pacific (10 ◦ 30 ′ N, 131 ◦ 20 ′ W, 0–100 m).

Material examined

One female ( NIBRIV0000245010 ) dissected and mounted on 10 slides, collected on 21 August 2009 by D.J. Ham .

Three females ( NIBRIV 0000245011–13), each dissected and mounted on nine slides. Two males ( NIBRIV 0000245014–15), each dissected and mounted on eight or nine slides. All from the sampling locality.

Other material examined

Three females ( NIBRIV0000245021 , 24 , 25 ), each dissected and mounted on eight or nine slides. All from the Korea Strait (33 ◦ 44 ′ 50.50 ′′ N, 128 ◦ 15 ′ 39.02 ′′ E), collected on 7 October 2008 by K.H. Cho .

Description of female

Body length: 519 µm [traditional method: 444 µm] [range: 440–490 µm, n = 7 individuals, based on specimens from the northeast equatorial Pacific; specimens from Korean waters fall into this size range].

Exoskeleton heavily chitinized, entire surface covered with numerous deep pits as exemplified for genital double-somite in Figure 13D, E . Prosome 1.6 times length of urosome, excluding caudal rami, about 1.5 times urosome length including caudal rami ( Figure 9A ). P2-bearing somite without dorsoposterior projection in lateral aspect ( Figure 9B ). Integumental pores on prosome as indicated in Figure 9A, B . Pleural areas of P4-bearing somite with small pointed posterolateral corners.

Genital double-somite 1.7 times as long as maximum width (measured in dorsal aspect) and 1.9 times as long as postgenital somites combined, with oval-rounded form; exoskeleton heavily chitinized ( Figure 13D, E ), largest width measured at about two-fifths distance from anterior margin, lateral margins rounded, posterior part tapering gradually ( Figure 9C ). Paired genital apertures located at about two-fifths distance from anterior margin of genital double-somite; armed with one spine and a minute spinule ( Figures 9E , arrowed in 13C). Secretory pores on dorsal surface as in Figure 9C .

Anal somite slightly wider than long, about 1.5 times longer than caudal rami ( Figure 9C, D ).

Caudal ramus ( Figure 9C ) about 1.4 times as long as wide; length data of setae II–VII of holotype and two paratype females as shown in Table 1; range of variation of setal lengths relative to longest seta V calculated for two undamaged specimens as follows: II: 6 / 11%, III: 14%, IV: 51 / 52%, VI: 16 / 22%, VII: 31 / 41%.

Antennule six-segmented ( Figure 10A ). Armature formula as for T. pacifica .

Antenna three-segmented ( Figure 10B ), relative lengths (%) of segments approximately 41: 34: 25. Surface of coxobasis covered with numerous deep pits (not illustrated), as on entire exoskeleton. Proximal endopodal segment with double row of denticles on posterior inner margin. Distal endopodal segment with armature and ornamentation as in T. pacifica , except for absence of spinular patch on anterior face of distal endopodal segment.

Labrum ( Figure 10G, H ) similar to that of T. pacifica , except for number of five stout and three small dentiform processes medially along distal margin of each lobe. Anterior surface ( Figure 10G ) unornamented (lacking integumental pockets and spinular patch). Posterior surface ( Figure 10H ) with group of three secretory pores located on proximal part of each lobe and additional one on midregion.

Mandible ( Figure 10C ) similar to that of T. pacifica .

Maxillule ( Figure 10D ) similar to T. pacifica , except for slight differences in proportional lengths of elements, with middle element on inner lobe shorter than outermost element and innermost element on outer lobe shorter than the strong element next to the innermost.

Maxilla ( Figure 10E ) similar to that of T. pacifica , except for seta on outer margin of allobasis not reaching as far as tip of allobasal claw.

Maxilliped ( Figure 10F ), with surface of syncoxa sparsely ornamented with spinules. Basis with armature and ornamentation as in T. pacifica , except for fewer spinules between proximal and distal setae ( Figure 10F ).

Swimming legs 1–4 ( Figure 11 A–D) with armature and ornamentation as in T. pacifica . Intercoxal sclerites well developed (P1–P3) or narrow (P4) and unornamented. Surface ornamentation on coxae and bases of P1–P4 difficult to discern, possibly as shown in Figure 11 A–D. Coxa of P4 without tuft of setules at outer margin of posterior surface. Surface of distal exopodal and endopodal segments with few secretory pores, as figured.

Exopods. Hyaline lamellae on outer spines moderately developed (P1, P2) or narrow (P3, P4). Distal spine about equal in length to (P2) or longer than (P1, P3–P4) distal segment.

Endopods. Distal segments of P2–P4 with long, unornamented conical processes at distal margin ( Figure 11 B–D). Length data of spines of holotype and three female paratypes as shown in Table 1; length ranges of outer subdistal spine (OSDS) and outer distal spine (ODS) relative to distal spine are as follows: P2 enp-3, OSDS: 88–136%, ODS: 59–91%; P3 enp-3, OSDS: 56–87%, ODS: 44–50%, P4 enp-3, OSDS: 55–59%, ODS: 35–48%. Proportional lengths of outer subdistal spines on P3 and P4 enp-3 different from T. pacifica , being relatively longer. Distal spine much longer than conical process in P2–P4; outer distal spine not reaching as far as tip of conical process in P2–P4; outer subdistal spine not reaching as far as insertion of outer distal spine in P2–P4. Hyaline lamellae on outer spines as in T. pacifica .

P5 ( Figure 9C, D ) with long plumose outer basal seta, about two times longer than outer exopodal seta, reaching far beyond genital apertures and extending as far as four-fifths the length of genital double-somite ( Figures 9D , 13E ). Exopod a free segment, about as long as wide, bearing short spiniform seta and much longer slender seta, reaching as far as genital apertures; both setae unornamented ( Figure 9C, D ).

P6 ( Figures 9E , 13C ) armed with one long spine and a minute spinule.

Description of male

Body length (traditional method): range: 360–414 µm, x = 390 µm, n = 2 individuals. Sexual dimorphism in antennule, maxilliped, endopodal spine lengths on P3 and P4, P5, P6 and in genital segmentation.

Caudal rami with length to width ratio as in female; length data of setae II–VII of two male paratypes as shown in Table 1, range of variation of setal lengths relative to longest seta V as follows: II: 9%, III: 13 / 14%, IV: 52 / 58%, VI:14 / 15%, VII: 46–53%, similar to female except for slight difference in proportional lengths of setae VII, being relatively longer than in female .

Surface of genital somite covered with numerous deep pits. Secretory pores on dorsal surface as in Figure 12D . Surface ornamentation on genital flaps and on ventral surface of anal segment not fully discerned, probably as indicated in Figure 12E .

Antennule ( Figure 12B ) four-segmented; armature formula as for T. pacifica .

Maxilliped ( Figure 12G, H ) three-segmented. Syncoxa unarmed, single secretory pore on inner distal margin, other surface ornamentation not discernible. Basis robust, with two small naked setae within longitudinal cleft, proximal seta slightly longer than distal one; anterior surface with one to two transverse spinular rows in addition to row of short flat spinules along inner margin, without small expanded flap; posterior face with two to three longitudinal rows of spatulated setules of graduated length ( Figure 12H ).

Swimming legs with armature and ornamentation as in female, length data of endopodal spines of two male paratypes as shown in Table 1; length ranges of outer subdistal spine ( OSDS) and outer distal spine ( ODS) relative to distal spine as follows: P2 enp-3, OSDS: 93 / 127%, ODS: 67 / 73%; P3 enp-3, OSDS: 54%, ODS: 33 / 35%, P4 enp-3, OSDS: 44 / 50%, ODS: 26 / 32%, slight sexual dimorphism in proportional spine lengths on P3 and P4 enp-3, with OSDS and ODS being relatively shorter than in female .

P5 ( Figure 12C, D ) small exopod not delimited from somite, armature and proportional lengths of exopodal setae as in female; outer basal seta ∼1.4 times longer than outer exopodal seta, relatively shorter than corresponding seta in female.

P6 ( Figure 12E ) represented by posterolateral flap closing off genital aperture on either side; spinular pattern on surface as indicated in Figure 12E . Posterolateral corners distinctly pointed and protruding laterally so that they are discernible in dorsal aspect ( Figure 12A, D ), occasionally with bifid tip ( Figure 12F , arrowed).

Remarks

Females of Triconia giesbrechti from the Pacific are similar to the typical T. giesbrechti Böttger-Schnack, 1999 , originally described from the Red Sea, with regard to almost all morphometric characters including the endopodal spine lengths on P4, which have been found to be of relevance for separating sibling species within this subgroup of Triconia (see above). Slight morphometric differences between the two forms appear to be present in (1) the proportional spine length of the outer subdistal spine on P2 enp-3 not reaching as far as the insertion of the outer distal spine in Pacific specimens, but reaching this point in those from the Red Sea, and (2) the relative length of antennary seta F, being somewhat shorter than seta D and about one-third longer than seta G in the Pacific specimens, whereas seta F is about as long as seta D and twice the length of G in the typical form. However, these small morphometric differences were not regarded as sufficient for establishing a new species for Pacific T. giesbrechti , because (1) the proportional spine lengths of endopodal spine(s) on P2 were found to display considerable variation in Pacific specimens (cf. Table 1), but no corresponding systematic information about the variability of these spines had been gathered for the typical form by Böttger-Schnack (1999), though it was occasionally noted for other species of the dentipes -subgroup by this author, and (2) in the case of proportional lengths of distal antennary setae also the difficulties establishing the correct lengths of these setae due to their curved appearance has to be kept in mind.

The ornamentation of the entire exoskeleton with numerous deep pits is likewise found in both form variants of T. giesbrechti , but quite a number of differences in micro-structures of appendages can be found (cf. Table 2), including (1) the additional ornamentation of the antennary coxobasis, (2) the spinular patch either side of the median swelling on the anterior surface of the labrum, (3) the bipinnate ornamentation of the element next to the outermost one on the outer lobe of the maxillule (arrowed in Figure 10D ), (4) the ornamentation of the seta on the outer allobasal margin of the maxilla (arrowed in Figure 10E ), (5) the spinulose ornamentation of the proximal element on the basis of the maxilliped, which is unornamented in the typical form, and (6) the plumose ornamentation of the outer basal seta on P5, being naked in the typical form.

Males of T. giesbrechti have not been recorded before and are described from the equatorial Pacific for the first time. They were identified on the basis of the conspicuous surface ornamentation of the exoskeleton, showing numerous deep pits as in the female, as well as on the proportional spine lengths of the outer basal setae and the two exopodal setae on P5. The sexual dimorphism in the proportional spine lengths on the endopods of P3 and P4, being relatively shorter in the male, is noteworthy. Males of the dentipes -subgroup are difficult to identify because of their great similarity (cf. Böttger-Schnack 1999; Wi et al. 2012), but the distinct surface ornamentation of the entire exoskeleton may be used to separate males of T. giesbrechti from those of the co-occurring T. pacifica and from males of the newly described T. constricta from the Korea Strait ( Wi et al. 2012), which otherwise is very similar in morphology. The latter species also differs from the Pacific T. giesbrechti in proportional lengths of the two exopodal setae on P5, in the relative length and the ornamentation of the outer basal seta on P5, being much shorter and unornamented in T. constricta , as well as in proportional spine lengths on P2 enp-3, showing a relatively short outer subdistal spine, which is only about three-quarters the length of the distal spine, while this spine is similar in length or even longer in the Pacific T. giesbrechti ( Table 1).

Knowledge about the zoogeographical distribution of T. giesbrechti is very limited. In ecological studies, females of this species have been recorded as solitary finds from the north-west subarctic Pacific, Oyashio region, during periods of influence of the Kuroshio current ( Nishibe and Ikeda 2004) and they were also identified in the northeast Indian Ocean, at the shelf break of Australia’s North-west Cape ( McKinnon et al. 2008) and adjacent to Scott Reef ( McKinnon et al. 2013). During a comprehensive study on the species diversity of oncaeid copepods in the Mediterranean Sea, however, T. giesbrechti was not found ( Böttger-Schnack and Schnack 2009), which may indicate that the distribution is confined to Indo-Pacific regions. The present record of the species from the tropical and subtropical Pacific Ocean greatly extends the range of zoogeographical distribution in these areas. The distribution of the form variants, however, is unresolved and still needs to be investigated.

Figures

Figure 9. Triconia giesbrechti NE equatorial Pacific. Female: (A) habitus, dorsal; (B) habitus, lateral; (C) urosome, dorsal; (D) urosome, lateral; (E) P6. Scale bars in µm.

Figure 10. Triconia giesbrechti NE equatorial Pacific. Female: (A) antennule; (B) antenna, posterior; (C) mandible; (D) maxillule; (E) maxilla; (F) maxilliped, anterior, elements on inner margin of basis figured separately, insertion points of elements on basis indicated by stippled line; (G) labrum, anterior; (H) labrum, posterior. Scale bars in µm.

Figure 11. Triconia giesbrechti NE equatorial Pacific. Female: (A) P1, anterior; (B) P2, anterior; (C) P3, anterior; (D) P4, anterior. Scale bars in µm.

Figure 12. Triconia giesbrechti NE equatorial Pacific. Male: (A) habitus, dorsal; (B) antennule; (C) urosome, lateral; (D) urosome, dorsal; (E) urosome, ventral; (F) P6, aberrant posterolateral corner; (G) maxilliped, anterior; (H) maxilliped, medial view. Scale bars in µm.

Figure 13. Triconia pacifica sp. nov. Female (A) P5 and genital double-somite, dorsal; (B) genital aperture, arrows indicating minute spinous processes close to spine. Triconia giesbrechti NE equatorial Pacific. Female: (C) genital aperture; (D) P5 and genital double-somite.