Bull. Natl. Mus. Nat. Sci., Ser. B, 39(4), pp. 159–164, November 22, 2013

Morphology of Zosterocarpus ogasawaraensis sp. nov.
(Phaeophyceae, Ochrophyta), a New Marine Deep-water
Brown Alga from the Ogasawara Islands, Japan
Taiju Kitayama
Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, Ibaraki 305–0005, Japan
E-mail: kitayama@kahaku.go.jp(Received 23 August 2013; accepted 2 October 2013)

Abstract A new brown alga, Zosterocarpus ogasawaraensis sp. nov. (Phaeophyceae,Ochrophyta) was collected from the deep water (73–82 m in depth) off Haha-jima Island, Ogasawara Islands, Japan. This is the ﬁrst record of the deep-water brown algal genus Zosterocarpus
from the North Paciﬁc Ocean. This genus differs from all other phaeophycean members in having
uniseriate ﬁlaments formed by intercalary meristems and plurilocular sporangia formed peripherally by longitudinal cell division on the surface of parental cells. This new species from Ogasawara Islands is distinguishable from the other species of the genus in having laterals with arounded apex and a quite clear meristematic zone and in lacking swollen tannin-ﬁlled cells.
Key words : brown algae, Japan, Ogasawara Islands, Phaeophyceae, Zosterocarpus ogasawaraensis.

Introduction
There is only a few record of the marine deepwater brown algal genus Zosterocarpus (Phaeophyceae, Ochrophyta) from outside of the Mediterranean Sea. This genus was established byBornet (1890) on the basis of Z. oedogonium(Meneghini ex Kützing) Bornet collected from theAdriatic Sea (inside the Mediterranean Sea) andwas deﬁned the features of the genus as branched
uniseriate thalli formed by diffuse intercalary
growth zones or meristems, outward plurilocularsporangia formed by peripheral divisions of cellsof the laterals, and enlarged tannin-ﬁlled cells
scattered and intercalary in laterals (Bornet,1890; Fritsch, 1945; Hamel, 1931; Berecibar et al.,2009; Guiry and Guiry, 2013). After ﬁfty ﬁve years
the second species for the genus, Z. abyssicola
W.R.Taylor, was described from the Santa Maria
Isl., the Galapagos Islands in the South Paciﬁc
Ocean (Taylor, 1945) and after forty two years
further the third species, Z. australicus Womers-ley was described from the Investigator Straits,off Adelaide, the southern Australia in the Indian
Ocean (Womersley, 1987). Recently the typespecies, Z. oedogonium, was recorded from Berlengas Archipelago in the Atlantic Ocean (Berecibar et al., 2009), though there are no subsequent reports on the other two species. The genus
has not previously been reported from the North
Paciﬁc Ocean. In consequence of the difﬁculty incollecting algal samples from a deep-water ﬂoor,
the taxonomic position of the genus is still
unclear.
Recently, as part of review of geographicalchange in the Japanese marine benthic algalﬂora, the author is investigating deep-water algal
habitats around the Ogasawara Islands, where anotably rare brown alga, Discosporangium
mesarthrocarpum (Meneghini) Hauck (Discosporangiales), is also distributed (Kitayama,2012). In this study, to conﬁrm identity of a species of Zosterocarpus collected from Hahajima
Island, one of the Ogasawara Islands, the author

160

Taiju Kitayama

made anatomical observations on the alga using
a microscope.
Material and Methods
The brown algal material referable to thegenus Zosterocarpus was collected from the deepwater (73–82 m in depth) off Hahajima Island inthe Ogasawara archipelago (＝Bonin Islands),
Japan by dredge using the research vessel, theKoyo (87 tonnage), operated by the Ogasawara
Fisheries Center, Tokyo Metropolitan. For preservation, the material was dried on sheets ofpaper or ﬁxed in 10% Formalin-seawater. Anatomical observations were made on the materialusing a microscope. Voucher specimens weredeposited in the algal herbarium of the National
Museum of Nature and Science (TNS).
Results
Zosterocarpus ogasawaraensis Kitayama sp. nov.
[Figs. 1–24]
Description: Thalli erect, up to 2.5 cm high,densly tufted, ﬁlamentous, brown in colour. Filaments uniseriate, 15–20 μm in diameter, branchedalternately or laterally, lacking a swollen tanninﬁlled cell and a phaeophycean hair. Laterals

straight, arisen from a single cell of the parent
axes, with an intercalary meristem at the base.
Cells cylindrical, 14–78 μm long in the middle
portion. Apical cells cylindrical or globose,
10–12 μm in diameter, obtuse or rounded at theapex. Haptera forked. Plastids numerous, discoid, without pyrenoids. Plurilocular sporangia
peripheral, crustose on the vegetative ﬁlaments.
Holotype: TNS-AL 181520 (Fig. 1) depositedin TNS (National Museum of Nature and Science, Tsukuba, Japan), 5 July 2010, leg. T. Kitayama.
Type locality: Subtidal from 73 m to 82 m indepth, off Hahajima Island, Ogasawara Islands,
Japan (26°44′08–15″N, 142°06′00–21″E).
Etymology: The species epithet ʻogasawaraensisʼ
is from the Japanese name of the islands (＝theBonin Islands).
Japanese name: Rahotsu-midoro (nom. nov.).
Habitat: Growing on or entangled with deadcoral or other benthic algae.
Vegetative morphology: Thalli are erect, up to2.5 cm in height, densly tufted, composed ofnumerous ﬁlaments, medium brown in colour,
epilithic, attached to rocks or entangled withgrains of dead coral (Figs. 1, 2) by rhizoidal
holdfasts. The ﬁlaments are uniseriate, 15–20 μm
in diameter in the middle portion, branched alter-Table 1. Comparisons of habit and morphology among Zosterocarpus ogasawaraensis and other species of thegenus in the world

Height of thalli
Diameter of ﬁlaments
Main portion
Terminal portion
Length of vegetative cells
Basal cells of laterals
Apical cells
Intercalary meristematic
zonesSwollen tannin-ﬁlled cells
Depth of habitat
Distribution

Z. ogasawaraensis(The present study)

Z. australicus(Womersley, 1987)

Z. abyssicola(Taylor, 1945)

Z. oedogonium(Bornet, 1890, Hamel, 1931,
Berecibar et al., 2009)

up to 2.5 cm

1–2 cm

1–2 cm

2–3 cm15–20 μm
10–12 μm
14–78 μm
situated on the single
cell of the parent axis
obtuseclear, situated near thebase of the lateralabsent73–82 mthe North Paciﬁc(Ogasawara Isls.)

20–25 μm
7–9 μm20–75 μm*
situated on the single
cell of the parent axis
acutediffuse, occurred
irregularly
absent31–41 mthe Indian Ocean(S. Australia)

up to 32 μm
11–16 μm
58–65 μm
situated on the septum of 1–3
cells of the parent axis
acutediffuse, occurred
irregularlypresent**
55 m
the South Paciﬁc(Galapagos Isls.)

up to 45 μm
up to 17 μm
up to 65 μm
situated on the septum of twocells of the parent axis
acutediffuse, occurred
irregularlypresent
20–70 mthe Meditteranean Sea(France, Italy, Spain, etc.),
the North Atrantic(Berlengas Archipelago)* Calculated using the “L/B” ratio showed in Womersley (1987, p. 36).
** Taylor (1945, p. 79) considered the swollen tannin-ﬁlled cells as “sporangia”.

Zosterocarpus ogasawaraensis sp. nov.

161

Figs. 1–9. Zosterocarpus ogasawaraensis sp. nov. from Ogasawara Islands, Japan. 1. Habit showing a thallus (Holotype: a dried specimen, TNS-AL 181520). 2. Habit showing tufts of erect ﬁlaments. 3. Erect ﬁlaments with several
intercalary meristems (arrowheads). 4. Intercalary meristems (arrowheads). 5. Young lateral showing a intercalarymeristem (arrowhead) and rounded apex of apical cell (arrow). 6–9. Plurilocular sporangia (p). 6. Young plurilocular sporangia. 7. Mature plurilocular sporangia and empty sporangia (e). 8. Young plurilocular sporangia on alateral with an obtuse apical cell (arrow). 9. Lateral covered by many plurilocular sporangia showing a rounded apex.

162

Taiju Kitayama

Figs. 10–24. Zosterocarpus ogasawaraensis sp. nov. from Ogasawara Islands, Japan. 10. Erect ﬁlaments withseveral intercalary meristems (arrowheads). 11. Terminal portion of erect ﬁlament showing a rounded apicalcell (arrow). 12, 13. Holdfasts with a forked hapteron. 14–18. Various stages of young laterals showing arounded apical cell (arrow) (c: chloroplast). 19–22. Various stages of pulirocular sporangia (p) on laterals
showing discoid chloroplasts (c). 19–21. Young plirilocular sporangia on laterals. 22. Lateral covered by many
mature plurilocular sporangia. 23. Mature plirilocular sporangia in cluster on an erect ﬁlament. 24. Empty
plurilocular sporangia (e) and mature plurilocular sporangia (p) in cluster on an erect ﬁlament.

Zosterocarpus ogasawaraensis sp. nov.

nately or laterally, lacking a swollen tannin-ﬁlled
cell (Fig. 3). Laterals are straight with a quite
clear intercalary meristematic zone (growthzone) near the base (Figs. 3–5, 10, arrowheads).
Each lateral is arisen from the single cell of theparent ﬁlaments at wide angle (Figs. 4, 5,14–17), often appearing perpendicular to the cell(Figs. 9, 14–22). Cells of the erect ﬁlaments arecylindrical, 14–78 μm in length in the middle
portion. Apical cells of the main erect ﬁlaments
are cylindrical or globose, 10–12 μm in diameter,
obtuse or rounded at the apex (Figs. 5, 8, 11, 17,20, arrows). Holdfasts are elongate, cylindrical,rhizoidal, possessing a forked hapteron (Figs.
12–13). Plastids are numerous per cell, discshaped, round to ellipsoidal, 2–4 μm in diameter,
without pyrenoids (Figs. 18, 20).
Reproductive morphology: Plurilocular sporangia are formed by longitudinal cell division
peripherally on the surface of parent ﬁlaments(Fig. 6) and short laterals (Figs. 7–9, 19–22).
Mature or empty sporangia usually composed of
4 locules (Figs. 7, 22–24). Locules are 6–9 μm in
width (Figs. 7, 24). Formation of the plurilocularsporangia occurs in a cluster, resulting in crustose sori covering the ﬁlaments and laterals(Figs. 7–9, 22).
The speciﬁc characters that distinguishedZ. ogasawaraensis from other members of thegenus are shown in Table 1. Z. ogasawaraensis
agrees well with Z. australicus, except for shapeof apical cells on the terminal portion of vegetative ﬁlaments and form of intercalary meristematic zones. The apical cells are acute (angular)
in the known species of the genus, while obtuse(rounded) only in Z. ogasawaraensis. The meristematic zones are quite clear and situated on thebase of the laterals, while unclear and diffuse inother species.
Discussion
The new brown alga from the Ogasawara Islands,
Zosterocarpus ogasawaraensis, possesses several characteristics of the genus Zosterocarpus:
the branched uniseriate ﬁlamentous thalli, the163

diffused intercalary meristematic zones in thevegetative erect ﬁlaments, external plurilocularsporangia formed peripherally on the ﬁlaments.
However, Z. ogasawaraensis has no swollen
tannin-ﬁlled cell, which is also a signiﬁcant
generic feature of Zosterocarpus derived fromthe type species, Z. oedogonium. According toWomersley (1987, p. 36), Z. australicus, which
has been recorded only from the southern Australia since the original description, also does nothave “the occasional swollen cells heavily
packed with physodes”. He did not regard “tannin cells” or the swollen tannin-ﬁlled cells as
indispensable to this genus because his species,
Z. australicus has “numerous centrally aggregated physodes” in each cell of the erect ﬁlaments. In Z. ogasawaraensis the author could notobserve such a structure in any cells. On theother hand, Z. abyssicola from Galapagos Isls. has
the swollen tannin-ﬁlled cells as Z. oedogonium
does, though Taylor (1945) considered theseswollen cells as “sporangia”. In addition, in bothZ. ogasawaraensis and Z. australicus laterals arealways arising from the single cell of the ﬁlaments, while in Z. oedogonium and Z. abyssicola
basal cells of the laterals are situated on the septum of the two or three cells of the parent ﬁlaments (Table 1). Fritsch (1945, p. 55) noted that
“The genus is distinguished by the position of thelaterals opposite the septa and the presence ofenlarged fucosan-cells with greysh contents.”
These features suggest that Z. oedogonium andZ. abyssicola are closely related to eath other andform the genus Zosterocarpus sensu stricto, while
Z. ogasawaraensis and Z. australicus have a possibility of belonging to any other new taxon ingeneric rank outside Zosterocarpus. It may bepossible, for instance, that Z. ogasawaraensis
may relate to the deep-water algal genus
Discosporangium (Discosporangiales), which
has also uniseriate ﬁlaments with round apicalcells, unique plurilocular sporangia and plastids
without pyrenoids, though Discosporangium has
no meristematic zone (Kitayama, 2012).
Bornet (1890), Funk (1955) and Pedersen (1984)
placed this genus under the Tilopteridales because164

Taiju Kitayamaof that weakly developed parenchyma andabsence of phaeophycean hairs in Z. oedogoniumand Z. abyssicola. However, Fritsch (1945, p. 55)
placed Z. oedogonium under the Ectocarpales,
not the Tilopteridales with some doubt and thenmost of the algologists followed the Fritschʼstreatment (e.g., Papenfuss, 1951; Wynne, 1982;
Womersley, 1987; Berecibar et al., 2009). In therecent emendation of circumscription of the order
Ectocarpales by Rousseau and de Reviers (1999),
however, the order was redeﬁned to include only
taxa possessing an exserted, pedunculated pyrenoid. Thus it is difﬁcult to place the genus
Zosterocarpus, which has no pyrenoid, under theEctocarpales.
Because of insufﬁciency of information on thisdeep-water algal genus, which is not easy to collect for the present, the taxonomic position of thegenus Zosterocarpus is unsolved (Berecibar et al.,2009) and the deﬁnition of the genus is unstable.
Therefore the author places tentatively the newspecies from Ogasawara Islands under the genus
Zosterocarpus with Z. australicus. To clarify therelationship among the Z. ogasawaraensis andother species of the genus Zosterocarpus, molecular analyses are required.
Acknowledgments
I am grateful to Mr. Yuji Aoki, director of theOgasawara Fisheries Center, Tokyo Metropolitan,
and the crew of the research vessel, Koyo, forproviding me the facilities to processing the specimens. I thank Drs. Toshihiko Fujita, Kazunori
Hasegawa, Hironori Komatsu, Department ofZoology, National Museum of Nature and Science for their kind help in the ﬁeld study in theisland. This study was undertaken as a part of thesurveys of the ﬂora of Izu and Ogasawara archipelagoes, Japan during 2006–2010, entitled“Study on Environmental Changes in the Sagami
Sea and Adjacent Area with Time Serial Comparison of Fauna and Flora.” A part of this study wassupported by Grants-in-Aid for Scientiﬁc Research(no. 25440225) from the Ministry of Education,Culture, Sports, Science and Technology, Japan.
References
Berecibar, E., Wynne, M. J. and Santos, R. 2009. Reportof the brown alga Zosterocarpus oedogonium (Ectocarpales) from Portugal, its ﬁrst recorded occurrence outside of the Mediterranean Sea. Nova Hedwigia 89:237–244.
Bornet, É. 1890. Note sur deux algues de la Méditerranée:Fauchea et Zosterocarpus. Bulletin de la Société Botanique de France 37: 139–148, 5 ﬁgs, 1 plate.
Fritsch, F. E. 1945. The Structure and Reproduction of theAlgae, Vol. 2. Foreword, Phaeophyceae, Rhodophyceae, Myxophyceae. Cambridge University Press, Cambridge, 939 pp.
Funk, G. 1955. Beiträge zur Kenntnis der Meeresalgenvon Neapel. Zugleich Mikrophotographischer Atlas.
Pubblicazioni della Stazione Zoologica de Napoli 25(Suppl.): i–x, 1–178, 36 ﬁgs.
Guiry, M. D. and Guiry, G. M. 2013. AlgaeBase. Worldwide electronic publication, National University ofIreland, Galway. http://www.algaebase.org; searched on
8 August 2013.
Hamel, G. 1931. Phéophycées de France. Fasc. I. Paris.
pp. 1–80.
Kitayama, T. 2012. First record of Discosporangium
mesarthrocarpum (Meneghini) Hauck (Phaeophyceae,Ochrophyta) from the Ogasawara Islands, Japan. Bulletin of the National Museum of Nature and Science,Series B, 38: 147–152.
Papenfuss, G. F. 1951. Phaeophyta. In: Smith, G. M.
(ed.), Manual of Phycology. pp. 119–158. Chronica
Botanica, Waltham, MA.
Pedersen, P. M. 1984. Studies on primitive brown algae(Fucophyceae). Opera Botanica 74: 1–76, 40 ﬁgs.
Rousseau, F. and de Reviers, B. 1999. Circumscription ofthe order Ectocarpales (Phaeophyceae): bibliographicalsynthesis and molecular evidence. Cryptogamie, Algologie 20: 5–18.
Taylor, W. R. 1945. Paciﬁc marine algae of the Allan
Hancock Expeditions to the Galapagos Islands. AllanHancock Paciﬁc Expeditions 12: 1–316.
Womersley, H. B. S. 1987. The Marine Benthic Flora ofSouthern Australia. Part II. South Australian Government Printing Division, Adelaide, 484 pp.
Wynne, M. J. 1982. Phaeophyceae. In: Parker, S. P. (ed.),Synopsis and classiﬁcation of living organisms 1: 115–125, pls. 15 & 16. McGraw-Hill Book Co., New York.