Four new species of Peniculisa Wilson, 1917, are described from marine fishes caught in coastal waters of southwestern Japan. Peniculisa elongata n. sp., Peniculisa crassa n. sp., and Peniculisa uchinah n. sp. are distinguishable from Peniculisa furcata (Krøyer, 1863), Peniculisa bellwoodi Boxshall, 1989, and Peniculisa wilsoni Radhakrishnan, 1977, in the lack of rami on legs 1 to 4, the lack of leg 5, and the possession of a trunk with prominent anterior shoulders. Peniculisa elongata n. sp. is separated from the remaining 2 known and 3 new congeners, Peniculisa bicaudata Shiino, 1956, Peniculisa shiinoi Izawa, 1965, P. crassa n. sp., Peniculisa ohirugi n. sp., and P. uchinah n. sp. by a pair of long, slender caudal processes, a compact cephalothorax, and its trunk with posteroventral lobes projecting posteriorly. Peniculisa crassa n. sp. can be discriminated from them by its pair of short, thick caudal processes, a comparatively large and thick cephalothorax in relation to its body, and its abdominal processes widest at base. Peniculisa uchinah n. sp. is distinguished from all other congeners by the possession of a pair of relatively long, slender, and proportionately long caudal processes, and a long abdominal process widest near the posterior end. Peniculisa ohirugi n. sp. is identified by a pair of long, divergent abdominal processes extending the tip of caudal rami, and by the location of leg 4 on the neck region.
Peniculisa include species of pennellid copepods (Siphonostomatoida). There are 5 species in the genus: Peniculisa bellwoodi Boxshall, 1989, Peniculisa bicaudata Shiino, 1956, Peniculisa furcata (Krøyer, 1863), Peniculisa shiinoi Izawa, 1965, and Peniculisa wilsoni Rhadhakrishnan, 1977. Peniculisa bellwoodi was reported from a perciform fish, and the remaining 4 species were described from tetraodontiform fishes (Krøyer, 1863; Wilson, 1906; Leigh-Sharpe, 1934; Shiino, 1956; Izawa, 1965; Rhadhakrishnan, 1977; Boxshall, 1989; Izawa, 1997). Species identification of Peniculisa is very difficult because of their featureless bodies. Important identification characters for these 5 species are mainly the shape and size of the body and caudal process, and the presence or absence of anterior shoulders on the trunk. In the present paper, 4 new species of Peniculisa are described from 8 species of coastal marine fishes collected in Japanese waters.
MATERIALS AND METHODS
Marine fishes were collected by rod and line or during SCUBA diving in coastal waters of southwestern Japan from September 2005 to June 2009. Parasitic copepods infecting the fishes (Fig. 1) were carefully removed from the hosts and preserved in 80% ethanol or 10% formalin. Specimens were soaked in lactophenol for a half, to a whole, day, then dissected and examined using the wooden slide method of Humes and Gooding (1964). Drawings were made with the aid of a drawing tube. Morphological terminology follows Huys and Boxshall (1991). The following copepod body parts were measured using an ocular micrometer and are given in millimeters as the range, followed by the mean and standard deviation in parentheses: total length ( = maximum length of the body, including the caudal processes on the trunk); body length ( = maximum length of the body, from the anterior tip of cephalothorax to posterior end of abdominal process); cephalothorax length ( = maximum length of the cephalothoracic shield); cephalothorax width ( = maximum width of the cephalothoracic shield); trunk length ( = maximum length of the trunk, excluding the neck); trunk width ( = maximum width of the trunk, excluding the neck); caudal process length ( = maximum length of caudal processes on the trunk); caudal process width ( = maximum width of caudal processes on the trunk); abdominal process length ( = maximum length of the abdominal process).
Figure 1
Infection by four new species of Peniculisa on fish. (A) Peniculisa elongata n. sp. on the fin rays of a boxfish; (B) Peniculisa crassa n. sp. on the head of a boxfish; (C) Peniculisa uchinah n. sp. on the body surface of a triggerfish; (D) P. uchinah n. sp. on the fin rays of a filefish.
Type specimens are deposited in the crustacean collection of the National Museum of Nature and Science, Tokyo (NSMT), and the University of the Ryukyus Museum, Fujukan (RUMF), Okinawa. The scientific names of fishes follow those listed by Hayashi (2002a, 2002b, 2002c) and Aonuma and Yoshino (2002).
DESCRIPTIONS
Peniculisa elongata n. sp.
Figure 2
Peniculisa elongata n. sp., postmetamorphic female, holotype NSMT-Cr 20931. (A) Habitus, dorsal. (B) Cephalothorax and free thoracic somites, lateral. (C) Posterior end of trunk, ventral. (D) Caudal ramus, dorsal. Scale bars: A, 1 mm; B, 0.5 mm; C, 0.3 mm; D, 0.02 mm.
Figure 3
Peniculisa elongata n. sp., postmetamorphic female, holotype NSMT-Cr 20931. (A) Antenna, dorsal. (B) Maxillule. (C) Maxilla, anterior. (D) Leg 1. (E) Leg 2. (F) Leg 3. (G) Leg 4. Scale bars: A, G, 0.05 mm; B–C, 0.02 mm; D–F, 0.07 mm.
Diagnosis (based on 7 postmetamorphic adult females)
Body (Fig. 2A) slender, 2.19–2.50 (2.36 ± 0.10) in length, with long caudal processes on trunk, total length 4.07–4.50 (4.24 ± 0.19), covered with sclerotised cuticle. Cephalothorax (Fig. 2B) oval, swollen slightly at posterolateral angles, longer than wide (0.43–0.46 [0.45 ± 0.02] × 0.26–0.28 [0.27 ± 0.01]), with constriction on posterior ¾. Nauplius eye conspicuous. Short neck region (Fig. 2B) comprising first to third pedigerous somites. Fourth pedigerous somite incorporated into trunk. Trunk slender, cylindrical, longer than wide (1.54–1.81 [1.70 ± 0.09] × 0.68–0.80 [0.75 ± 0.05]), with slender caudal processes (1.92–2.39 [2.17 ± 0.15] × 0.18–0.23 [0.20 ± 0.02]) on posterolateral corners and posteroventral lobes with prominent tip (Fig. 2C). Abdominal process (Fig. 2C) 0.24–0.30 (0.26 ± 0.02) long, bilobed, ending at posterior end of trunk (Fig. 2C). Caudal rami located on abdominal process carrying 5 setae. Egg-sacs uniseriate.
Antennule absent. Antenna (Fig. 3A) 2-segmented; proximal segment with 2 distal processes; terminal claw without armature. Maxillule (Fig. 3B) knob with 2 distal setules. Maxilla (Fig. 3C) 2-segmented; proximal segment without armature; distal segment curved with rows of fine setae and setulose, blunt distal tip. Maxilliped absent. Legs 1 to 4 (Fig. 3D–G) represented by blunt triangular protopod without rami. Some specimens with 1 small, simple seta on posterior margin of leg 1. Leg 3 often bearing claw-like distal process. Leg 4 with claw-like process on distal tip. Leg 5 absent.
Taxonomic summary
Type locality and collection date
Off Seragaki (26°30′N, 127°52′E), Okinawa-jima Island, Okinawa, East China Sea, Japan, 1 July 2007.
Remarks
Peniculisa elongata n. sp. differs from P. bicaudata and P. wilsoni in having longer and slender caudal processes. In P. bicaudata and P. wilsoni, the caudal processes are consistently shorter than the trunk in postmetamorphic females (Shiino, 1956; Radhakrishnan, 1977). In P. shiinoi, the caudal processes are as long as or longer than the trunk, but the new species has more slender processes (Izawa, 1965). Furthermore, P. shiinoi is more compact than the new species. Peniculisa bellwoodi has a slender body and caudal processes and lacks anterior shoulders and a distinct boundary at the anterior end of the trunk, which are discrete when compared to the new species. Peniculisa furcata can be easily distinguished from the new species by legs 1 to 4, which possess 2 minute, segmented rami and more divergent caudal processes. Leigh-Sharpe (1934) identified 2 specimens from Ostracion meleagris Shaw (as O. punctatus) as P. furcata, but Shiino (1956) and Izawa (1965) pointed out the possibility that these specimens were not identical to P. furcata. Leigh-Sharpe (1934, Fig. 26) illustrated long, slender caudal processes and well-developed posterior lobes on the abdominal process. Both the caudal and the abdominal processes of the new species resemble Leigh-Sharpe's specimens, which, however, are different from the new species in having a long neck with a gap separating legs 2 to 3.
Peniculisa crassa n. sp.
Figure 4
Peniculisa crassa n. sp., postmetamorphic female, holotype NSMT-Cr 20933. (A) Habitus, dorsal. (B) Cephalothorax and free thoracic somites, lateral. (C) Posterior end of trunk, ventral. (D) Caudal ramus, dorsal. Scale bars: A, 0.8 mm; B, 0.5 mm; C, 0.3 mm; D, 0.02 mm.
Figure 5
Peniculisa crassa n. sp., postmetamorphic female, holotype NSMT-Cr 20933. (A) Antenna, dorsal. (B) Maxillule. (C) Maxilla, anterior. (D) Leg 1. (E) Leg 2. (F) Leg 3. (G) Leg 4. Scale bars: A, D–F, 0.05 mm; B, 0.02 mm; C, 0.03 mm; G, 0.04 mm.
Diagnosis (based on 12 postmetamorphic adult females)
Body (Fig. 4A) rounded, fusiform, 1.71–2.10 (1.89 ± 0.14) in length, with long caudal processes in trunk, total length 2.41–3.30 (2.83 ± 0.27), covered with sclerotized cuticle. Cephalothorax (Fig. 2B) oval, swollen slightly at posterolateral angles, longer than wide (0.33–0.46 [0.40 ± 0.04] × 0.22–0.27 [0.25 ± 0.02]), with constriction on posterior ¾. Nauplius eye conspicuous. Short neck region (Fig. 4B) comprising first to third pedigerous somites. Fourth pedigerous somite incorporated into cylindrical trunk. Trunk rotundiform, cylindrical, gradually wider posteriorly, with prominent anterior shoulders, often laterally swollen at posterior ¾, longer than wide (1.20–1.49 [1.33 ± 0.09] × 0.16–0.19 [0.17 ± 0.01]), bearing blunt, divergent, caudal processes on posterolateral corners and posteroventral lobes (Fig. 4C). Caudal processes longer than wide (0.83–1.39 [1.11 ± 0.19] × 0.20–0.25 [0.23 ± 0.02]). Trunk terminating in dorsally located, bilobed abdominal processes (Fig. 4C). Abdominal process expanded at base and gradually narrowing posteriorly; length 0.20–0.25 (0.23 ± 0.02). Caudal rami located on abdominal process carrying more than 4 setae. Egg-sacs uniseriate.
Antennule absent. Antenna (Fig. 5A) 2-segmented; proximal segment with 2 distal processes; terminal claw without armature. Maxillule (Fig. 5B) knob with 2 distal setules. Maxilla (Fig. 5C) 2-segmented; proximal segment without armature; distal segment curved with rows of fine setae and setulose, blunt distal tip. Maxilliped absent. Legs 1 to 4 (Fig. 5D–G) represented by blunt triangular protopod with fissure on surface, lacking rami. Some specimens with unguiform tip on legs 1 to 3. Leg 4 with unguiform distal tip. Leg 5 absent.
Taxonomic summary
Remarks
The new species differs from P. furcata by the lack of rami on legs 1 to 4. The specimens identified as P. furcata by Leigh-Sharpe (1934) are differentiated from the new species in having slender, long caudal processes and a neck region with a gap separating legs 2 to 3. Peniculisa bellwoodi and P. shiinoi differ from the new species in having long caudal processes in relation to the trunk; P. bicaudata and P. wilsoni the caudal processes shorter than a trunk, but P. bicaudata is separated from the new species by having a 3-segmented antennule. Peniculisa wilsoni has a trunk without prominent anterior shoulders, which is different from that of the new species. In P. elongata n. sp., the caudal processes are longer than those of the new species with a percentage of caudal process length/body length (80.13–100.00 [96.26 ± 7.13] vs. 43.56–72.27 [58.98 ± 9.98]) being higher. They are also more slender than those of the new species with the percentage of caudal process width/caudal process length (7.85–10.78 [9.17 ± 1.10] vs. 11.47–21.61 [16.18 ± 3.36]) being lower (Table I; Fig. 10A, B). Peniculisa elongata n. sp. possesses a slightly smaller cephalothorax than the new species; the percentage of cephalothorax length/body length ranges from 17.84–21.05 (19.02 ± 1.01) in P. elongata (vs. 19.11–22.87 [21.17 ± 1.19] in the new species), and the percentage of cephalothorax width/body length ranges from 10.46–12.28 (11.34 ± 0.64) (vs. 12.35–15.43 [13.31 ± 0.90]) (Table I; Fig. 10C, D).
Table I
Percentages of body parts of postmetamorphic females of Peniculisa elongata n. sp., Peniculisa crassa n. sp., Peniculisa uchinah n. sp., and Peniculisa ohirugi n. sp. The data are shown as minimum–maximum (mean ± standard deviations).*
Peniculisa uchinah n. sp.
Figure 6
Peniculisa uchinah n. sp., postmetamorphic female, holotype NSMT-Cr 20935. (A) Habitus, dorsal. (B) Cephalothorax and free thoracic somites, lateral. (C) Posterior end of trunk, ventral. (D) Caudal ramus, dorsal. Scale bars: A, 1 mm; B, 0.5 mm; C, 0.3 mm; D, 0.02 mm.
Figure 7
Peniculisa uchinah n. sp., postmetamorphic female, holotype NSMT-Cr 20935. (A) Antenna, dorsal. (B) Maxillule. (C) Maxilla, anterior. (D) Leg 1. (E) Leg 2. (F) Leg 3. (G) Leg 4. Scale bars: A, F–G, 0.04 mm; B–C, 0.02 mm; D–E, 0.05 mm.
Diagnosis (based on 13 postmetamorphic adult females)
Body (Fig. 6A) slender, 1.29–1.78 (1.52 ± 0.16) in length, with long caudal processes on trunk, total length 2.23–2.90 (2.51 ± 0.24), covered with sclerotised cuticle. Cephalothorax (Fig. 6B) oval, swollen slightly at posterolateral angles, longer than wide (0.28–0.37 [0.34 ± 0.03] × 0.19–0.23 [0.21 ± 0.01]). Nauplius eye conspicuous. Short neck region (Fig. 6B) comprising first to third pedigerous somites. Fourth pedigerous somite incorporated into cylindrical trunk. Trunk short, sub-cylindrical, wider posteriorly, with prominent anterior shoulders, longer than wide (0.86–1.28 [1.03 ± 0.14] × 0.39–0.56 [0.49 ± 0.05]), bearing caudal processes on posterolateral corners and posteroventral lobes (Fig. 6C). Caudal processes slender, slightly incurved, 1.00–1.39 (1.17 ± 0.14) long, 0.12–0.17 (0.14 ± 0.01) wide. Trunk terminates in dorsally located, bilobed abdominal processes (Fig. 6C). Abdominal process gradually expanding posteriorly, 0.11–0.18 (0.15 ± 0.03) long. Caudal rami (Fig. 6D) located on abdominal process carrying at least 3 setae with 2 knobs. Egg sac uniseriate.
Antennule absent. Antenna (Fig. 7A) 2-segmented; proximal segment with 2 distal processes; terminal claw without armature. Maxillule (Fig. 7B) knob with 2 distal setules. Maxilla (Fig. 7C) 2-segmented; proximal segment without armature; distal segment curved with rows of fine setae and setulose, blunt distal tip. Maxilliped absent. Legs 1 to 4 (Figs. 7D–G) represented by blunt triangular protopod with fissure on surface, without armature. Leg 5 absent.
Taxonomic summary
Other hosts
Balistoides conspicillum (Bloch and Schneider) (Tetraodontiformes: Balistidae), Rhinecanthus aculeatus (L.) (Tetraodontiformes: Balistidae), S. bursa (Bloch and Schneider), S. chrysopterum (Bloch and Schneider), and Pervagor melanocephalus (Bleeker) (Tetraodontiformes: Monacanthidae).
Type locality and collection date
Off Minna-jima Island (26°38′N, 127°48′E), Okinawa, East China Sea, Japan, 25 July 2007.
Other localities and collection dates
Off Ankyaba (28°6′N, 129°20′E), Kakeroma-jima Island, Kagoshima, North Pacific Ocean, 27 May 2005; off Odo Beach (26°5′N, 127°42′E), Okinawa-jima Island, Okinawa, North Pacific Ocean, 1 September 2005; off Ikema-jima Island (24°56′N, 125°14′E), Okinawa, East China Sea, 20 December 2005; off Zamami-jima Island (26°13′N, 127°17′E), Okinawa, East China Sea, 27 May 2006; off Seragaki (26°30′N, 127°52′E), Okinawa-jima Island, Okinawa, East China Sea, 4 July 2007.
Specimens deposited
Holotype female, NSMT-Cr 20935, 1 paratype female (from off Minna-jima Island), NSMT-Cr 20936, 5 paratype females (from off Ankyaba), NSMT-Cr 20937, 1 paratype female (from off Zamami-jima Island), NSMT-Cr 20938, 1 paratype female (from off Seragaki), NSMT-Cr 20939, 1 paratype female (from off Ikema-jima Island), NSMT-Cr 20940, 3 paratype females (from off Odo Beach), RUMF-ZC-01074.
Remarks
The new species differs from P. bicaudata and P. wilsoni in having caudal processes consistently longer than the trunk. The new species is differentiated from P. shiinoi by the lack of a unguiform process on legs 1 to 4. Peniculisa furcata is easily separated from the new species by the possession of rami on legs 1 to 4. The specimens identified as P. furcata by Leigh-Sharpe (1934) bear a gap separating legs 3 to 4, which is not shared with the new species. The new species differs from P. bellwoodi by the lack of leg 5 and the possession of a distinct boundary between the trunk and neck. Peniculisa elongata is distinct from the new species by the possession of the trunk with posteroventral lobes projecting posteriorly and long and slender caudal processes in relation to the body; the percentage of caudal process length/body length ranges from 80.13–100.00 (92.06 ± 7.13) in P. elongata n. sp. (vs. 62.61–90.12 [77.73 ± 9.15] in the new species) and the percentage of caudal process width/length 7.85–10.78 (9.17 ± 1.10) (vs. 10.52–14.43 [12.37 ± 1.24]). The cephalothorax of P. elongata n. sp. is more compact than that of the new species; the percentage of cephalothorax length/body length ranges from 17.84 to 21.05 (19.02 ± 1.01) in P. elongata n. sp. (vs. 19.33–25.59 [22.31 ± 1.63] in the new species) and the percentage of cephalothorax width/body length 10.46 to 12.28 (11.34 ± 0.64) (vs. 11.09–15.71 [13.67 ± 1.26]) (Table I; Fig. 10C, D). The new species is separated from P. crassa n. sp. by the abdominal process, which is longer and gradually diverges posteriorly; the percentage of abdominal process length/body length ranges from 2.75 to 5.05 (4.00 ± 0.69) in the new species (vs. 1.60–4.51 [2.83 ± 0.95] in P. crassa). The new species has longer and more slender caudal processes than those of P. crassa; the percentage of caudal process length/body length ranges from 62.61 to 90.12 (77.73 ± 9.15) in the new species (vs. 43.56–72.27 [58.98 ± 9.98] in P. crassa) and the percentage of caudal process width/length ranges from 10.52 to 14.43 (12.37 ± 1.24) (vs. 11.47–21.61 [16.18 ± 3.36]) (Table 1, Fig. 10A, B, E).
Peniculisa ohirugi n. sp.
Figure 8
Peniculisa ohirugi n. sp., postmetamorphic female, holotype NSMT-Cr 20941. (A) Habitus, dorsal. (B) Cephalothorax and free thoracic somites, lateral. (C) Posterior end of trunk, ventral. (D) Caudal ramus, ventral. Scale bars: A, 0.6 mm; B, 0.3 mm; C, 0.2 mm; D, 0.02 mm.
Figure 9
Peniculisa ohirugi n. sp., postmetamorphic female, holotype NSMT-Cr 20941. (A) Antenna, dorsal. (B) Maxillule. (C) Maxilla, anterior. (D) Leg 1. (E) Leg 2. (F) Leg 3. (G) Leg 4. Scale bars: A, 0.04 mm; B–C, 0.02 mm; D–F, 0.03 mm; G, 0.02 mm.
Figure 10
Allometric growth of the caudal process, cephalothorax and abdominal process of P. elongata n. sp., P. crassa n. sp., and P. uchinah n. sp. White circle, P. elongata; black circle, P. crassa; gray circle, P. uchinah. Relationships of the (A) body length to the caudal process length, (B) caudal process length to the caudal process width, (C) body length to the cephalothorax length, (D) body length to the cephalothorax width, and (E) body length to the abdominal process length are shown.
Diagnosis (based on 2 postmetamorphic adult females)
Body (Fig. 8A) slender, 1.85–1.97 (1.91 ± 0.09) long, with long caudal processes on trunk, total length 1.97–2.04 (2.00 ± 0.05). Cephalothorax (Fig. 8B) oval, swollen slightly at posterolateral angles, longer than wide (0.27–0.28 [0.28 ± 0.01] × 0.16–0.18 [0.17 ± 0.01]). Nauplius eye conspicuous. Short neck region (Fig. 8B) comprising 1st to 4th pedigerous somites without distinct boundary between neck and trunk. Trunk cylindrical, longer than wide (1.57 [1.57 ± 0.01] × 0.28 [0.28 ± 0]) bearing slender, sharp, divergent, slightly incurved, caudal processes on posterolateral corner, knob-like posteroventral lobes and 2 small simple setae (Fig. 8C). Caudal processes 0.89–0.94 (0.92 ± 0.04) long, 0.07–0.08 (0.07 ± 0.01) wide. Trunk terminates in dorsally located, abdominal process greatly divergent, as almost long as caudal processes; length 0.79–0.87 (0.83 ± 0.06). Caudal rami located on abdominal process carrying 5 setae. Egg sacs uniseriate.
Antennule absent. Antenna (Fig. 9A) 2-segmented; proximal segment with 2 distal processes; terminal claw small, without armature. Maxillule (Fig. 9B) knob with 2 distal setae. Maxilla (Fig. 9C) 2-segmented; proximal segment without armature; distal segment curved with single small process. Maxilliped absent. Legs 1 to 4 (Fig. 9D–G) represented by blunt triangular protopod with fissure on surface, lacking rami. Legs 1 to 3 with unguiform tips. Holotype specimen bearing 2 and 1 setae on legs 1 and 2, respectively. Leg 5 absent.
DISCUSSION
Five valid species are currently known from Peniculisa, and 4 new species are described in this paper. Of the 4 new species, P. elongata, P. crassa, and P. uchinha are similar in body form, and the differences are very minor between them. In previous studies (Shiino, 1956; Izawa, 1965; Radhakrishnan, 1977; Boxshall, 1989), the proportional length of the caudal process was used as one of the important characters for identification. This is also the case for 4 new species described in this study, but the species of Peniculisa show a wide variation in length of the caudal processes, which depends on the level of metamophosis (Izawa, 1965; Radhakrishnan, 1977). In the present paper, descriptions of the 4 new species are made based only on postmetamorphic females, but many non-postmetamorphic females were found during the study, and the developmental level of their caudal processes is not uniform. It is thus desirable that the caudal processes should be used carefully as a morphological character for identification. Furthermore, in this study, the proportional length of the abdominal process to the body is used as an important character for the discriminating of P. uchinah n. sp. The proportion of the cephalothorax to the body is also useful for the description of P. elongata. However, these proportions are sometimes similar to each other between species, and thus identification is often difficult. For accurate identification, molecular analysis may be helpful.
At present, Peniculisa contains 9 species. Of these, 7 species (P. bicaudata, P. furcata, P. shiinoi, P. wilsoni, P. elongata, P. crassa, and P. uchinah) are the parasites of tetraodontiform fishes (Krøyer, 1863; Wilson, 1906; Leigh-Sharpe, 1934; Shiino, 1956; Izawa, 1965; Radhakrishnan, 1977; this study), whereas the remaining 2 species (P. bellwoodi, P. ohirugi n. sp.) occur on pomacentrid fishes (Boxshall, 1989; this study).
Acknowledgments
We thank Associate Professor Tetsuo Yoshino, Professor Yuichi Hirose, Associate Professor Mamoru Toda, Assistant Professor Tohru Naruse, and Takeshi Sasaki, University of the Ryukyus and Fumihito Iwase, Biological Institute of Kuroshio, Kuroshio Biological Research Foundation, for assistance and permission to use their laboratory facilities. We acknowledge Shigeo Nakamura, University of the Ryukyus, Tomofumi Nagata, Okinawa Environmental Research and Technology, and Hirotaka Toyohara, Kochi University, for help with collection of specimens. We would like to thank Professor Susumu Ohtsuka, Hiroshima University, for valuable suggestions during the study. Part of this work received financial support from the Ocean Exposition Commemorative Park Management Foundation, Okinawa, and Kuroshio Biological Research Foundation, Kochi.
