Triconia hirsuta Wi, Bottger-Schnack & Soh 2010

Triconia hirsuta Wi, Böttger-Schnack & Soh, 2010

(Figs. 5–8, 9 D, E )

Synonymy. Triconia hirsuta wi, Böttger-Schnack & Soh, 2010, p. 674, 678, 679, Figs. 2, 3, 4 A, B (female).

Type locality. The Western Channel of Korea Strait, 34°05.97'N, 129°47.32'E.

Material examined. Four females (MABIK CR000235318 – CR000235321) dissected on ten slides. Three males (MABIK CR000235322 – CR000235324) each dissected and mounted on seven or nine slides.

All specimens collected from the NE equatorial Pacific (10°30'N, 131°20'W) on 21 August 2009 by D.J. Ham.

Description of female. Body length (measured in lateral aspect): 1070–1160 µm, based on 4 specimens (illustrated female: 1156 µm).

Exoskeleton well chitinized. Prosome about 1.8 times length of urosome length excluding caudal rami, about 1.6 times urosome including caudal rami. P2-bearing somite with conspicuous dorso-posterior projection in lateral aspect (Fig. 5 B). Numerous integumental pores and sensilla on prosome (Fig. 5 A, B). P3-bearing somite with row of about 10 pores near dorso-posterior projection (Fig. 5 A). Pleural areas of P4-bearing somite with more or less rounded posterolateral corners in lateral view (Fig. 5 B).

P5-bearing somite with paired dorso-posterior pore, each with sensillum (Fig. 5 C).

Genital double-somite (Fig. 5 C) barrel-shaped, with paired patches of setules on antero-lateral margins (Figs. 5 C, D, 9D); about 1.6 times as long as maximum width (measured in dorsal aspect) and about 2 times as long as postgenital somites combined; largest width measured at anterior 1/3, posterior part tapering gradually. Paired genital apertures located at 2/5 the distance from anterior margin of genital double-somite. Pore pattern on dorsal surface as indicated in Fig. 5 C.

Anal somite about 1.6 times wider than long; slightly longer than caudal rami (Fig. 5 C).

Caudal rami (Fig. 5 C) about 1.7 times as long as wide; caudal seta VI less than half length of seta IV; seta VII about same length as seta VI, plumose and bi-articulate at base.

Antennule (Fig. 6 A) six-segmented. Armature formula as for T. derivata.

Antenna (Fig. 6 B) three-segmented, distinctly reflexed. Distal endopod segment with armature and ornamentation as in T. derivata, except for ornamentation of setae B–D being bipinnate; seta G shorter than setae A–D and about same length as seta F.

Labrum (Fig. 6 G, H) as described for T. derivata, except for shape of lobes being less elongate and ornamentation of three secretory pores on proximal part of posterior surface orientated in a row and not as a group.

Mandible (Fig. 6 C) as described for T. derivata, with minor differences in the surface ornamentation of the coxa, showing three spinular rows.

Maxillule (Fig. 6 D) similar to T. derivata, except for length of innermost element on outer lobe similar to the strong element next to innermost.

Maxilla (Fig. 6 E) similar to T. derivata. Proximal inner margin with slender pinnate seta and strong basally swollen spine on inner margin, ornamented with single row of shorter spinules along outer margin in addition to double row of very strong spinules along the inner margin.

Maxilliped (Fig. 6 F) similar to T. derivata, with slight differences in ornamentation. Surface of syncoxa and basis ornamented with several spinule rows and distal element on basis with longer spinules than in T. derivata. Distal endopod segment with stout spinules along entire length of concave margin, decreasing in size distally.

Swimming legs (Fig. 7 A–D) with armature and ornamentation as in T. derivata, except for intercoxal sclerites being without ornamentation. Coxae and bases of legs 1–4 with surface ornamentation as in Fig. 7 A–D.

Endopods. Distal margin of P2–P4 produced into conical process, process with apical pore. Distal spines shorter than in T. derivata and not (P2), or only slightly (P3), reaching beyond tip of conical process. Length ratios of spines different from T. derivata with length data of spines of four specimens as shown in Table 1; length ranges of outer subdistal spine (OSDS) and outer distal spine (ODS) relative to distal spine (DS) are given in Table 2.

P5 (Figs. 5 C, D, 9D) with outer basal seta long and plumose distally; exopod segment free, with few denticles on distal margin (Figs. 5 D, arrowed in inset of Fig. 9 D). Exopod 2.4 times longer than wide, bearing short seta (outer) and long seta (inner) ornamented with minute spinules; outer seta half length of inner seta (Figs. 5 C, D, 9D).

P6 (Figs. 5 C, 9E) represented by operculum closing off each genital aperture; armed with long spine and 2 small processes (arrowed in inset of Fig. 9 E).

Holotype female Paratype female

Leg endopod Spines length ratio left side right side left side right side P2 enp-3 OSDS: DS 1.58 1.65 1.78 1.71 ODS: DS 1.79 1.72 1.74 1.68 P3 enp-3 OSDS: DS 1.32 1.27 1.42 1.47 ODS: DS 1.38 1.33 1.32 1.37 P4 enp-3 OSDS: DS 1.04 1.10 0.92 0.91 ODS: DS 0.90 0.99 0.91 0.86 Description of male. Body length: 716–720 µm, based on 3 specimens (illustrated male: 716 µm). Sexual dimorphism in antennule, maxilliped, P5, P6, genital segmentation and CR; slight differences in endopodal spine lengths on P2.

Prosome 2.4 times length of urosome, excluding caudal rami, about 2.1 times urosome length, including caudal rami (Fig. 8 A). Integumental pores on prosome and urosome as figured (Fig. 8 A). Cephalosome with conspicuous posterolateral group of over 20 pores (Fig. 8 B). P3- and P4-bearing somites with conspicuous dorsal patches of pores (Fig. 8 A).

Genital somite (Fig. 8 A, E, F) about 1.6 times longer than wide. Dorsal surface of genital somite covered with numerous pores as figured (Fig. 8 A). Caudal rami (Fig. 8 A, F) similar to female. Surface of genital flaps ornamented with rows of minute spinules (Fig. 8 E, F). Anal somite about 1.6 times wider than long, similar to female.

Antennule (Fig. 8 C) four-segmented; armature formula as for T. derivata.

Maxilliped (Fig. 8 D) three-segmented (damaged, syncoxa not figured). Basis robust, with 2 small naked setae of similar length within longitudinal cleft; anterior surface with 1-2 transverse spinule rows in additional to row of small flat spinules along inner margin between distal seta and endopod; posterior surface with rows of spatulate setules of graduated length along palmar margin.

Swimming legs with armature and ornamentation as in female, lengths of endopodal spines on P2–P4 as shown in Fig. 8 G–I, with distal spine not (P2), or only slightly (P3), reaching beyond tip of conical process as in female. Variation of endopodal spine lengths of three male specimens as listed in Table 1; length ranges of outer subdistal spine (OSDS) and outer distal spine (ODS) relative to distal spine (DS) are given in Table 2. Relative spine lengths of OSDS and ODS on P2 slightly shorter than that of female (Table 2).

P5 (Fig. 8 E) exopod not delimited from somite, shorter than that of female, outer exopodal seta about 3/4 length of inner exopodal and outer basal setae, relatively longer than that of female.

P6 (Fig. 8 F) represented by posterolateral flap closing off genital aperture on either side; covered by pattern of spinules; posterolateral corners protruding laterally so that they are discernible in dorsal aspect (Fig. 8 A).

Remarks. Females of T. hirsuta were originally described from the Korean waters (Wi et al. 2010). Females from our study in the northeastern equatorial Pacific were identified by the conspicuous surface ornamentation of the genital double-somite, showing paired patches of long setules on the antero-lateral margin, which is a unique character not found in any other species of the conifera -subgroup known so far. The morphology of the females from the equatorial Pacific agree in almost all morphological characters with the original description, except for the proportional lengths of spines on the endopod of P2: in our specimens the distal spine was very short, not reaching the tip of the conical process (cf. Fig. 7 B), while in the original description the distal spine was figured as being much longer, reaching beyond the tip of the conical process (Wi et al. 2010, their fig. 3B). Nevertheless, the text of the original description says: “…terminal spine on P2 enp-3 hardly as long as conical process.” (Wi et al. 2010, p. 679).

In order to account for the discrepancy between the text and figures in the original description of T. hirsuta, the female holotype was borrowed from the collections of the National Institute of Biological Resources (NIBR), Incheon, as well as a paratype female held in the personal collection of R. Böttger-Schnack. Both were reexamined and compared. As a result, the distal spine of P2 enp-3 proved to be shorter than the conical process in the holotype; a new figure showing the distal part of the endopods of P2–P4 of the holotype female is given here (Fig. 10 A–C). The resulting length ratios of the outer subdistal spine (OSDS) and outer distal spine (ODS) relative to distal spine (DS) of the holotype and the paratype are given in Table 3. The corrected ratios are within or very close to the range of values reported for specimens from the equatorial Pacific (cf. Table 2).

Our study further adds to the earlier description of female T. hirsuta by providing ornamentation details which were not noted or figured by Wi et al. (2010). These include (1) the conspicuous pore pattern on the prosome, especially the P3-bearing somite, (2) the ornamentation of the inner exopodal seta on P5, with minute spinules on the inner margin, and (3) the microstructures on the cephalic appendages, such as antenna, mandible, maxillule, maxilla, and maxilliped. The anterior face of the labrum has not been examined by Wi et al. (2010, p. 678) and is described in the present study for the first time. Thereby, the presence of integumental pockets typical for species of the conifera -subgroup of Triconia was confirmed. The description of the female genital apertures, examined using scanning electron microscopy, seemed to be slightly different between our study and Wi et al. ’s description: the armature of the genital aperture was described as a spine and a bended process near the base of the spine by Wi et al. (2010, arrowed in their fig. 4B), whereas in our specimens two minute spinous processes close to the spine were apparent (cf. inset of Fig. 9 E), but neither of them was bended. It may be concluded, that the bended process in Wi et al. ’s specimen was caused during its treatment for scanning electron microscopy, but does not seem to be a common characteristic of T. hirsuta. The conspicuous position of CR seta II, articulating almost at right angle in females from Korean waters (Wi et al. 2010, fig. 2A, p. 678) was less pronounced in specimens from the NE equatorial Pacific (Fig. 5 A, C).

The hitherto unknown male of T. hirsuta is described in the present account. It was pre-identified from mating pairs, where the male was attached to the female. The male was also assigned to T. hirsuta by the short distal spine on P2 enp-3, which does not reach as far as the tip of the distal conical process. This is a distinct character, similar to that of the female, and not affected by the slight sexual dimorphism in spine lengths observed during the present study.

Among males of the conifera -subgroup, T. hirsuta males are most similar to those of T. antarctica (Heron, 1977). Both species share a very short distal spine on P2 enp-3 which does not reach as far as the tip of the conical process (cf. Heron 1977, fig. 3d). However, males of T. antarctica differ from T. hirsuta in the proportional spine lengths on the endopods of P3 and P4: the distal spine on P3 enp-3 reaches far beyond the tip of the conical process and is longer than the outer distal spine in T. antarctica (cf. Heron 1977, fig. 3e), while in T. hirsuta the distal spine hardly reaches beyond the tip of the conical process and is shorter than the outer distal spine. Also, on P4 enp-3 the distal spine of T. antarctica is much longer than the outer distal spine (cf. Heron 1977, fig. 3f), while the two spines are almost equal in length in T. hirsuta. In both studies, identification of the males was corroborated by the occurrence of mating pairs (cf. Heron 1977, fig. 4b). In T. antarctica the sexual dimorphism in body length is rather pronounced, as males measure only about half the size of females (670 µm, range: 640–700 µm in males, as compared to 1260 µm, range: 1160–1400 µm in the female). In T. hirsuta sexual dimorphism is less pronounced as males reach about 60–70% of the female´s size (720 µm in males as compared to 1070–1160 µm in the female).

Males of the similis -subgroup of Triconia do not have to be considered for a more detailed comparison with T. hirsuta, because no species of this subgroup exhibits a very short distal spine on P2 enp-3 as observed in T. hirsuta.

Within the conifera -subgroup of Triconia, other five species, such as T. conifera (Giesbrecht, 1891), T. inflexa (Heron, 1977), T. quadrata (Heron & Bradford-Grieve, 1995), T. pararedacta, and T. thoresoni (Heron & Frost, 2000), exhibit a fairly (but not very) short distal spine on P2 enp-3. The same is found in four species of the similis - subgroup [T. gonopleura Böttger-Schnack, 1999, T. minuta (Giesbrecht, 1893 [“1892”]), T. parasimilis Böttger- Schnack, 1999, and T. umerus (Böttger-Schnack & Boxshall, 1990)]. For one of these species (T. gonopleura) the male has not yet been described. In all these species, however, the distal spine on P2 enp-3 reaches as far as the tip of the conical process or slightly beyond, thus being somewhat different from the above mentioned two species (T. antarctica and T. hirsuta). Further differences can be found in the proportional spine lengths of the endopods of P3 and P4, which separate them from T. hirsuta. It remains uncertain, however, whether a clear distinction of males can be achieved between these species within the frame of not yet known natural variability of the specific morphometric characters on P2-P4 enp-3.

The zoogeographical records of T. hirsuta are summarized in Fig. 11, indicating a fairly wide distribution in the Indo-Pacific region.