Deep-sea Fauna and Pollutants off Pacific Coast of Northern Japan, edited by T. Fujita, National Museum of Nature andScience Monographs, No. 39, pp. 19-23, 2009

Preliminary Report on Deep Water Hydrozoan Species Collected from thePacific Ocean off Northern Japan
Hiroshi Namikawa
Showa Memorial Institute, National Museum of Nature and Science,
1 1 Amakubo 4, Tsukuba City, Ibaraki, 305 0005 Japan
E-mail: namikawa@kahaku.go.jp

Abstract: Hydrozoan specimens gathered by bottom trawl from various depths (between ca. 250 2000 m) in
the Pacific Ocean off northern Japan have disclosed twenty species (one included in Athecata, 19 in Thecata)
identified to date. Noteworthy among the species collected was the wide bathymetric distribution of Hydractinia sp.
Key words: Hydrozoa, Cnidaria, Pacific Ocean, northern Japan.

Introduction
A faunal survey project “Research on Deep-sea Fauna and Pollutants off Pacific Coast ofNorthern Japan” undertaken by the National Museum of Nature and Science, Tokyo, was conducted from 2005 to 2008 (Saito et al., 2009). During the survey, many cnidarians, including hydrozoan species, were obtained from various depths (between ca. 250 2000 m) by bottom trawls.
Because the deep-sea hydrozoan fauna of this region is still poorly known, a preliminary account with species’ identifications is presented here.
Materials and Methods
Cnidarians, including hydrozoa and anthozoa, were collected together with a large assortmentof other benthic material, at many sampling stations using trawls and biological dredges (Table 1),
operated by the R/V Wakataka-maru of the Fisheries Research Agency (FRA) from 2005 to 2007
and the R/V Tansei-maru of the Japan Marine Science and Technology Center (JAMSTEC) in2007 (Fig. 1A). Hydrozoan specimens observed on substrata (for example, shells, rocks and discarded rope) were collected from the assortment of benthic materials. Small detached specimensof hydrozoa were picked out from the remaining rubble (Fig. 1B). Specimens were fixed in 10%
formalin solution on the research vessels and preserved in ca. 75% ethanol in the laboratory immediately after each cruise.
Results and Discussion
Twenty hydrozoan species have been recorded so far (Table 2), based on specimens collectedprimarily at 28 sampling stations. A total of 58 specimens of the athecate hydroid Hydractinia,
each characterized by hydrorhizas with serrated spines (Fig. 2A), upon which the provisional identifications were based, were collected from a number of stations at varying depths during the survey, although other thecate hydroid species were collected much less often (once or twice).
Hydractinia sp. has already been reported from about 70 m depth in the same region by Na-

20

Hiroshi Namikawa

Table 1. Collection data for hydrozoan specimens obtained from the Pacific Ocean off northern Japan during 2005–2007.
* WA: R/V Wakataka-maru, KT: R/V Tansei-maru.
Haul no.*Data

Sampling gear

WA-05-E480
WA-05-E510
WA-05-E550
WA-05-E650
WA-05-E900
WA-05-F425
WA-05-F450
WA-05-F480
WA-05-F510
WA-05-F550
WA-05-G250
WA-05-G350
WA-05-H280
WA-05-H380
WA-05-H900
WA-05-G410
WA-05-G750
WA-06-1200
WA-06-530
WA-06-380
WA-07-A250D
WA-07-C350D
WA-07-D210D
KT-07-29-M-3-1
KT-07-29 M-3-2
KT-07-29 K-2
KT-07-29 E-3
KT-07-29 H-1

2005.10.25
2005.10.25
2005.10.26
2005.10.26
2005.10.26
2005.10.27
2005.10.27
2005.10.27
2005.10.27
2005.10.27
2005.10.29
2005.10.29
2005.10.30
2005.11.1
2005.11.2
2005.11.3
2005.11.10
2006. .
2006. .
2006. .
2007.10.6
2007.10.15
2007.10.18
2007.11.5
2007.11.6
2007.11.7
2007.11.7
2007.11.8

Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
Otter trawl
ND
ND
ND
Biological dredge
Biological dredge
Biological dredge
Beam trawl
Beam trawl
Beam trawl
Beam trawl
Beam trawl

Position in38˚22.6´N, 142˚05.3´E
38˚22.5´N, 142˚06.3´E
38˚22.6´N, 142˚07.3´E
38˚23.0´N, 142˚10.7´E
38˚28.9´N, 142˚21.4´E
37˚44.3´N, 141˚54.8´E
37˚43.6´N, 141˚56.6´E
37˚41.9´N, 141˚59.0´E
37˚39.4´N, 142˚01.2´E
37˚41.0´N, 142˚04.7´E
36˚58.3´N, 141˚25.6´E
36˚56.3´N, 141˚30.9´E
36˚29.4´N, 140˚59.1´E
36˚29.1´N, 141˚00.8´E
36˚30.9´N, 141˚21.0´E
36˚56.8´N, 141˚33.3´E36˚46.2´N, 141˚35.4´ENDNDND
40˚51.0´N, 141˚51.2´E
39˚44.2´N, 142˚16.9´E
38˚57.4´N, 141˚59.7´E
39˚20.0´N, 142˚51.0´E
39˚20.2´N, 142˚51.4´E
42˚30.3´N, 144˚50.5´E
41˚39.1´N, 144˚07.5´E
40˚48.7´N, 142˚00.1´E

Position out
38˚20.9´N, 142˚06.0´E
38˚23.6´N, 142˚05.8´E
38˚23.6´N, 142˚07.5´E
38˚21.8´N, 142˚10.6´E
38˚29.7´N, 142˚21.6´E
37˚42.5´N, 141˚55.0´E
37˚45.3´N, 141˚56.4´E
37˚40.2´N, 141˚59.0´E
37˚38.2´N, 142˚01.1´E
37˚42.0´N, 142˚04.0´E
36˚57.0´N, 141˚24.8´E
36˚58.0´N, 141˚31.5´E
36˚30.8´N, 141˚00.2´E
36˚30.0´N, 141˚01.7´E
36˚30.4´N, 141˚20.3´E
36˚58.1´N, 141˚34.4´E
36˚45.6´N, 141˚34.8´E
NDNDND40˚50.9´N, 141˚51.5´E
39˚44.4´N, 142˚16.9´E
38˚57.7´N, 141˚59.9´E39˚21.8´N, 142˚51.9´E
39˚19.2´N, 142˚49.2´E
42˚30.6´N, 144˚52.2´E
41˚37.2´N, 144˚07.6´E
40˚47.4´N, 142˚00.5´EDepth (m)482 483
514 505
545 561658 657
900 904
424 424
449 449484 480
508 506
551 546251 255
373 356277 281380 384
900 899411 411750 750
1200
530
380
258 258
355 354
213 2131728 1719
1737 1709
1535 1543
1997 2043
497 454

Fig. 1. Specimens caught by an otter trawl from R/V Wakataka-maru. A, a pile of marine animals, including gastropod shells with hydrozoan species and large sea anemones, such as Actinostola carlgreni and Liponemamulticornis (photo: Dr. Narimatsu); B, small specimens separated in a basket.

mikawa (1994), but is now known to occur in depths from 70 2000 m off northern Japan. Elsewhere, Hydractinia species have been reported from limited substrata and depths in Japan (forexample, Stechow, 1909; Goto, 1910; Yamada, 1959; Nagao, 1961; Hirohito, 1988). The widebathymetric distribution of Hydractinia sp., depending on several substrata in accordance with21

Deep Water Hydrozoans from the Pacific Ocean off Northern Japan

Table 2. List of hydrozoan species collected from the Pacific Ocean off northern Japan during 2005 2007.
Species

Depth

Haul no.

Order Athecata
Family Hydractiniidae
Hydractinia sp.

ca. 250 2000 m

WA-05-E510, WA-05-E550, WA-05-E650, WA05-E900, WA-05-F425, WA-05-F450, WA05-F480, WA-05-F510, WA-05-G250, WA05-H280, WA-05-H380, KT-07-29-E3, KT-0729-M-3-2

Order Thecata
Family Haleciidae
Halecium beanii (Johnston, 1847)
Halecium crinis Stechow, 1913
Halecium sp.

506 508 m
449 m
1709 1734 m

WA-05-F510
WA-05-F450
KT-07-29-M-3-2

Family Campanulariidae
Campanularia verticillatus Linnaeus, 1758
Clytia sp.
Obelia bicuspidata Clark, 1875

454 497 m
1200 m
750 m

KT-07-29-H-1
WA-06-1200
WA-05-G750

Family Campanulinidae
Stegolaria sp.

530 m

WA-06-530

Family Lafoeidae
Acryptolaria sp. cf. A. conferta (Allman, 1877)
Cryptolaria exserta Busk, 1858
Grammaria immersa Nutting, 1901
Lafoea benthophila Ritchie, 1909
Lafoea dumosa (Fleming, 1820)
Lafoea sp.
Zygophylax sp.

352 346 m
354 355 m546 561 m
546 551 m
258 m
1709 1734 m
899 900 m

WA-05-G350
WA-07-C350D
WA-05-E550
WA-05-F550
WA-07-A250D
KT-07-29-M-3-1, KT-07-29-M-3-2
WA-05-H900

Family Bonneviellidae
Bonneviella sp.

1535 1543 m

KT-07-29-K-2

380 m
ca. 210 550 m
346 352 m

WA-06-380
WA-05-E480, WA-05-E550, WA-05-F450, WA05-F550, WA-05-G410, WA-07-D210D
WA-05-G350

1200 m

WA-06-1200

Family Sertulariidae
Sertularella sp.
Symplectoscyphus sp.
cf. S. tricuspidatus (Alder, 1856)
Thuiaria sp.
Family Plumulariidae
Halopteris sp.

depth, is noteworthy.
Colonies of Hydractinia sp. were collected from gastropod shells (Buccinidae) (Fig. 2), a
number of the latter also being inhabited by hermit crabs. Although the complete picture is unclear,
it may be that colonies of this hydroid have secured a stable niche based on the continual use ofgastropod shells as substrata, relying on a continuity of new hermit crab hosts. Accordingly, colonies of Hydractinia sp. have become widely distributed in the extensive depths of the Pacific
Ocean off northern Japan, despite the relative lack of hard substrata.
On the other hand, specimens of nineteen thecate species were collected from discarded ropes
or in detached condition from substrata, making any discussion of their bathymetric distribution

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Hiroshi Namikawa

Fig. 2. Hydractinia sp. A, hydrorhizas with serrated spines; B, a specimen collected from WA-05-G250 (ca. 250 min depth); C, a specimen collected from WA-05-E900 (ca. 900 m in depth); D, a specimen collected from KT07-29-E-3 (ca. 2000 m in depth). Scales: 0.2 mm for A, 1 cm for B-D.

difficult.
Acknowledgements
I wish to express my gratitude to the crews of the R/V Wakataka-maru (FRA) and R/V Tansei-maru (JAMSTEC) for their help in collecting specimens, and am very grateful for the generosity of Drs. Shigeaki Kojima (The University of Tokyo) and Yoji Narimatsu (FRA). I also thank Dr.
Graham Hardy, Ngunguru, New Zealand, for his critical revision of the manuscript.
References
Goto, S., 1910. On two species of Hydractinia living in symbiosis with a hermit crab. Journal of Experimental Zoology, 9:469 496.
Hirohito, His Majesty the Showa Emperor, 1988. The hydroids of Sagami Bay. 179+110 pp. Biological Laboratory, Imperial
Household, Tokyo. (In English and Japanese.)
Nagao, Z., 1961. On a new athecate hydroid, Hydractinia uchidai, n. sp. from Akkeshi, Hokkaido. Japanese Journal of Zoology, 13: 1 5.
Namikawa, H., 1994. Four species of hydractiniid hydroids from off Kushiro, Hokkaido, Japan. Memoirs of the National
Science Museum, (40): 79 86 (In Japanese with English summary.)
Saito, H., M. Ito, and T. Fujita, 2009. An outline of “Research on Deep-sea Fauna and Pollutants off Pacific Coast of NorthernDeep Water Hydrozoans from the Pacific Ocean off Northern Japan

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Stechow, E., 1909. Hydroidpolypen der japanische Ostkueste. I. Teil. Athecata und Plumularidae. Abhandlungen der mathematisch-physikalischen Klasse der Königlich Bayerischen Akademie der Wissenschaften, I. Supplement, 1(6): 1 111.
Yamada, M., 1959. Hydroid fauna of Japanese and its adjacent waters. Publications from the Akkeshi Marine Biological Station, 9: 1 101.