Bull. Natl. Mus. Nat. Sci., Ser. B, 47(1), pp. 27–35, February 22, 2021

Morphology of Codium arenicola M.E.Chacana &P.C.Silva (Codiaceae, Ulvophyceae) from the Ogasawara Islands, Japan
Taiju Kitayama
Department of Botany, National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki 305–0005, Japan
E-mail: kitayama@kahaku.go.jp(Received 18 August 2020; accepted 23 December 2020)

Abstract A benthic marine green alga, Codium arenicola M.E.Chacana & P.C.Silva (Codiaceae,
Bryopsidales, Ulvophyceae) was collected from the mesophotic zone (46–54 m in depth) oﬀ Chichijima Island and Nishijima Island, Ogasawara Islands, Japan. This alga is diﬀerent from theother species of the genus Codium in having an erect, terete (1–5 mm in diameter), sparsely dichotomous branches, a holdfast with sand-binding rhizoidal ﬁlaments, and cylindrical to obovate or
obconical utricles (105–430 μm in diameter, 294–588 μm in length). Scatter plot of diameter versus length in the utricles revealed a wide variation in shapes of the utricles is caused by diﬀerent
developmental stages. It is suggested that the shape of the utricles of C. arenicola is more various
than illustrated and stated as “claviform to muﬃn-shaped” in the original description.
Key words : benthic marine green alga, Codiaceae, Codium arenicola, Japan, Ogasawara Islands,
Ulvophyceae.

The marine green algal genus Codium (Codiaceae, Bryopsidales, Ulvophyceae), which wasestablished by Stackhouse (1797), has 120–144
species in the world (Huisman et al., 2015; Guiry
and Guiry, 2020). Although the thalli of thisgenus are composed of unicellular siphons (multinucleate tubular units), they are very various in
the external form ranging from unbranched semispherical thalli to erect branched cylinders. In
Japan, 21 species of Codium have been recorded(Chacana and Silva, 2014; Yoshida et al., 2015),
of which seven are composed of erect, terete,dichotomously branched thalli: C. arenicola
M.E.Chacana & P.C.Silva, C. barbatum Okamura, C. contractum Kjellman, C. cylindricum
Holmes, C. fragile (Suringar) Hariot, C. subtubulosum Okamura, and C. yezoense (Tokida)
K.L.Vinogradova. These Japanese species are
distinguishable from each other by their external
forms and microscopic shapes of utricles.
© 2021 National Museum of Nature and Science

The Ogasawara Islands (also called the Bonin
Islands) are oceanic islands located ca. 1,000 km
south of the Izu Peninsula, central Japan. In
recent investigations of algal ﬂora around theislands, several rare algae were found from themesophotic zone or middle light zone (30–150 m
in depth) using a dredging aparatus: for example,
mesophotic marine algae, Discosporangia mesarthrocarpum (Meneghini) Hauck (Kitayama,2012), Zosterocarpus ogasawaraensis Kitayama(Kitayama, 2013), Aneurianna ogasawaraensis
Kitayama (Kitayama, 2014), Codium mamillosum Harvey (Kitayama, 2017), Lychaete bainesii(F.Müller & Harvey ex Harvey) M.J.Wynne(Kitayama, 2019). The presence of these algal
species suggested that the Ogasawara Islands hasa unique marine algal ﬂora diﬀerent from theones of the Japanese Archipelago. In thisresearch, Codium arenicola M.E.Chacana &P.C.Silva, which is new to the Ogasawara
Islands, is observed in morphology using materials collected from the mesophotic zones oﬀ the28

Taiju Kitayama

Ogasawara Islands, for unraveling the algal ﬂoraof this sea area.
Materials and Methods
The green algal materials referred to as
Codium arenicola M.E.Chacana & P.C.Silva
were collected from the mesophotic zone (46–54 m in depth) oﬀ Chichijima Island and Nishijima Island in the Ogasawara Islands, Japan by adredge using the research vessel “The Koyo” (87tonnage) on 8 July 2010 and 13 July 2016, andthe ﬁshing vessel “The 7th Ushiwo-maru” (6.7
tonnage) on 17 July 2017. For preservation, thematerial was ﬁxed and stored in 10% formalinseawater, and specimens were mounted in glycerin jelly. Anatomical observations were made on
the material by a microscope. Voucher specimens
were deposited in the herbarium of National
Museum of Nature and Science (TNS).
Results
Class Ulvophyceae K.R.Mattox& K.D.Stewart, 1984
Order Bryopsidales J.H.Schaﬀner, 1922
Family Codiaceae Kützing, 1843
Codium arenicola M.E.Chacana & P.C.Silva
Nova Hedwigia 98: 249, ﬁgs. 1–3 (2014).
[Figs. 1–18][Type locality: Indonesia: Sulawesi: E side,
Kudingareng Keke Island (Chacana and Silva,
2014: 249)]
Habitat: Grew on sandy bottoms in the mesophotic zone (46–54 m in depth).
Morphology: Thalli are light green, erect, up
to 23 cm in height, with a cuneate stipe (Figs.
1–3). Holdfast attached to sandy bottom by sandbinding rhizoidal ﬁlaments (Fig. 3). Branching issparse with elongate internodes (Figs. 1–2),
irregularly dichotomous or sub-dichotomous, andup to 4 orders. Branches are mostly terete,
1–5 mm in width, becoming slightly compressedat dichotomies. Hairs grow from the surface ofbranches (Fig. 4), green, terete, 20–52 μm in

diameter, elongated, up to several millimeters,with a round apex (Fig. 5). The thalli are composed of numerous medullary ﬁlaments and individual utricles. Medullary ﬁlaments are colorless,siphonous, elongated, and 18–64 μm in diameter(Fig. 6). Utricles are connected to other ones by
2–4 medullary ﬁlaments issued from the basal
portion (Fig. 7). Apices of the utricles arerounded or ﬂattened, often depressed, with thinwalls (Fig. 6). Hair scars are abundant on theupper portion of utricles (Fig. 8). The shape ofthe utricles varies depending on the development(Figs. 9–17). Young utricles are cylindrical toclavate, (78–)105–194 μm in diameter, (228–)
294–560 μm in length. Mature utricles are clavate to obovate or obconical, 220–430(–486) μm
in diameter, 382–588(–690) μm in length, tapering toward the base (Figs. 13–17). Plugs inside
medullary ﬁlaments are located beneath the utricles, 1–3 per utricle (Figs. 9–17).
Specimens examined: The Ogasawara Islands,
Japan: Oﬀ Kurazonone (53.5–53.9 m), Chichijima
Island (27°30′55″N, 142°6′20″E), 17 July 2017,leg. T. Kitayama (TNS-AL 213459) (Fig. 1); Oﬀ
Nishijima Island (47.9–52.3 m) (27°7′27″N,
142°10′26″E), 13 July 2016, leg. T. Kitayama(TNS-AL 213460) (Fig. 2). Oﬀ Nishijima Island(46.2–50.8 m) (27°7′14″N, 142°10′42″E), 8 July
2010, leg. T. Kitayama (TNS-AL 213461) (Fig.
3).
Japanese name: Otohime-miru (nov.).
Distribution: The Indian Ocean: Indonesia:
Sulawesi (type locality); Komodo Island;
Samaloa Island; Barang Lompo Island; Western
Australia: Dampier Archipelago; The Paciﬁc
Ocean: Thailand: Songkhla; New Caledonia:
Balabio Island; Philippines: Sulu; Japan: Oki
Islands; Tanegashima Island; Amami Island(Chacana and Silva, 2014); the Ogasawara
Islands (the present study).
A scatter plot with the variations in diameterand the variations in length in the utricles of
Codium arenicola M.E.Chacana & P.C.Silva isshown in Fig. 18. The morphology, the habitatand distribution in the six species of Codium
having erect, terete, dichotomously branchedMorphology of Codium arenicola

29

Figs. 1–8. Codium arenicola M.E.Chacana & P.C.Silva from Ogasawara Islands, Japan. 1. Living thallus from
Chichijima Island (TNS-AL 213459). 2. Herbarium specimen from Nishijima Island, having considerable
sparse ramiﬁcation (TNS-AL 213460). 3. Herbarium specimen from Nishijima Island, showing the holdfast
with sand-binding rhizoidal ﬁlaments (TNS-AL 213461). 4. Apical portion of thallus with many hairs (h). 5.
Apex of hair. 6. Utricles with medullary ﬁlaments (m) and plugs (p). Arrow shows a depression on the apex ofutricle. 7. Young utricle and mature utricle connecting with a medullary ﬁlament (m) and hair (h) protrudingfrom the apex of the utricle. 8. Apex of utricle with hair scars (arrowheads).

30

Taiju Kitayama

Figs. 9–17. Various shapes of utricles of Codium arenicola M.E.Chacana & P.C.Silva from Ogasawara Islands
depending on the developmental stages. 9–11. Young utricles. 12. Young utricle with a long hair (h). 13.
Mature utricle with hair scares (arrowheads), medullary ﬁlaments (m) and plugs (p). 14. Mature utricle showing a depression on the apex (arrow). 15–17. Mature utricles. Arrow shows a depression on the apex.

thalli and bearing cylindrical to conical utricles
are shown in Table 1.
Discussion
The present alga collected from the mesophotic zone oﬀ the Ogasawara Islands resembles
Codium arenicola M.E.Chacana & P.C.Silva(Chacana and Silva, 2014), C. barbatum Okamura (Okamura, 1930), C. campanulatum
P.C.Silva & M.E.Chacana (Abbott and Huisman,
2004; Silva and Chacana, 2014), Codium cicatrix
P.C.Silva (Silva, 1959), C. profundum P.C.Silva& M.E.Chacana (Oliveira et al., 2010; Silva andChacana, 2010) and C. tenue (Kützing) Kützing(Kützing, 1856; Silva, 1959; Huisman et al.,Morphology of Codium arenicola

Fig. 18. Scatter plot with the variations in diameter and the variations in length in the utricles of
Codium arenicola M.E.Chacana & P.C.Silva
from Chichijima Island, Ogasawara Islands,
Japan.

2015) in appearance of thalli and/or shape ofutricles (Table 1). The commonality that these
species share is having erect, terete, dichotomously branched thalli composed of cylindricalto obconical utricules.
In particular, the present alga relates mostclosely with Codium arenicola, which occurs
widely in the Indo-Paciﬁc Ocean, in having
sparsely ramiﬁed branches (up to 4 orders) withlong internodes and a holdfast with sand-binding
rhizoids. The width of branches of the present
alga may be close to ones of C. arenicola.
Although branches of C. arenicola were written
as “Internodes terete or slightly ﬂattened,
6–10 mm broad, nodes ﬂattened, cuneate, to 2 cm
broad” in the original description (Chacana andSilva, 2014, ﬁg. 2), the ones in the photograph ofthe holotype specimen were 1–5 mm in width.
The present alga has obovate or obconical utricles in mature, while only “stout claviform to
muﬃn-shaped” utricles were observed in the31

original description of C. arenicola (Chacana andSilva, 2014, ﬁg. 3). In this research, however, it
was revealed that the shape of the utricles varies
depending on the developmental stages (Figs. 7,
9–18). For such an alga there is a danger thatpartial observation on utricles may underestimate
the morphological variation depending on development. In addition, the present alga agrees tothe original description of C. arenicola in abundance of depressed apices of utricles, hairs (orhair scars), light green fronds, and “deep-water”
habitat (Table 1). C. arenicola was recorded fromthe sandy bottoms at depth of 20–30 m (Chacana
and Silva, 2014).
Before the deﬁnition of Codium arenicola by
Chacana and Silva (2014), there are confusions
with the other species with swollen utricles. The
alga recorded as C. arenicola from Samoan
Archipelago, South Paciﬁc by Skelton and South(2007) is not conspeciﬁc with the genuine C. arenicola in having dense ramiﬁcation of compressed branches, which forms often palmate
fronds (ﬁgs. 702–703). Verbruggen and Costa(2015) has observed C. arenicola at the southern
Madagascar, but it does not correspond with thespecies in possessing the dense ramiﬁcation ofcompressed branches.
Chacana and Silva (2014) noted the similarity
in the shape of utricles between Codium arenicola and the two other “deep-water” species, C.
campanulatum (endemic to Hawaii) and C. profundum (Atlantic species), though they have thinner branches than the ones of C. arenicola andthe present alga from the Ogasawara Islands:
1.5–2.3 mm in C. campanulatum (Abbott andHuisman, 2004) and less than 3 mm in C. profundum (Silva and Chacana, 2010) (Table 1).
C. tenue, which is recorded from the Indian
Ocean, grows in shallow waters of estuaries andhas abundant ramiﬁcation with thick utricles:(135–)200–700 μm in diameter (Silva, 1959) or
200–550 μm in diameter (Huisman et al., 2015).
According to Chacana and Silva (2014),
C. tenue, which Børgesen (1948) reported from
Mauritius, is only C. arenicola. Also C. cicatrix,
which is widely distributed in the Indian Ocean,up to 15

C. tenue (Kützing)
Kützing (Silva, 1959)

cuboid, obovate,
oblongstoutly cylindrical,
campanulate,turbunate, pyriform,
obovate, orbicular,
quadratecylindrical, clavate

cylindrical, clavate,obovate, obconicalstoutly claviform to
muﬃn-shapedForm(135–)200–700(175–)200–350(145–)235–390

120–125(–360)

200–300(78–)105–430(–486)(180–)200–250(–330)

Diameter(μm)

Utricles(330–)500–800

350–550

630–920

310–440

460–483(228–)294–588(–680)(500–)600–780(–800)

Length(μm)*) Estimated from the ﬁg. 2 in Chacana and Sliva (2014). **) Estimated from the pl. 10, f. 1 in Okamura (1930).

up to 3(2–)4–5

1.5–2.3

up to 3

1–5

“6–10”
1–5*

Width
(mm)

subcylindrical topyriform, gobletshaped, bell-shaped,
muﬃn-shaped
up to 45 1–5(–22) clavate, pyriform,
turbinate, quadrata,
obovate, orbicularup to10(–15)

12–40

up to ca. 8

up to 6

up to 10up to 10**up to 19

up to 23

up to 4

C. arenicola M.E.
Chacana & P.C.Silva(the present study)
C. barbatum Okamura,
1930
C. campanulatum P.C.
Silva & M.E.
Chacana (Abbott andHuisman, 2004)

up to 9“up to 40”
ca. 20*

up to 4*

Codium arenicola M.E.
Chacana & P.C.Silva,
2014

C. cicatrix P.C.Silva,
1959
C. profundum P.C.Silva& M.E.Chacana, 2010

Height(cm)

Branching
order

Taxon

External form

Estuaries and lagoons,silt-covered rocks,
shells, jetty piles

Epiphytic on
Cymodocea ciliata
up to 70 m, calcareous
rubble or crustosecorallines

56–185 m

cast up ashore

46–54 m, sandy
bottoms

20–30 m, sandy
bottoms

Depth and substrata

Indian Ocean: South
Africa (Knysna to Port
St. Johns)

Indian Ocean: MozambiqueAtlantic Ocean: Bermuda,
Brazil, Canary Is.,
Florida, Louisiana

Paciﬁc Ocean: Japan,
Korea
Paciﬁc Ocean: Hawaii

Paciﬁc Ocean: Indonesia(type locality), Japan,
Philippines, Thailand
Indian Ocean: Indonesia,
Western Australia
Paciﬁc Ocean: Japan(Ogasawara Isls.)

Distribution

Table 1. Comparison of the morphology, the habitat and distribution among the species of erect, terete, dichotomously branched Codium bearing cylindrical to obconical, obovate utricles

32
Taiju Kitayama

Morphology of Codium arenicola

has similarity to the present alga, though the species in the original description (Silva, 1959) is
diﬀerent from the present alga in ramiﬁcation of
branches (up to 9 orders), length of utricles (upto 920 μm), and habitat (epiphytic on a seagrass,
Cymodocea ciliata Forsskål [now Thalassodendron ciliatum (Forsskål) Hartog)]. On the other
hand, Egerod (1974) reported “C. cicatrix” fromThailand (Andaman Sea), though it is not conspeciﬁc with the species but is similar to C. arenicola in the habitat and habit. Verbruggen andCosta (2015) also recorded “C. cicatrix” from
Madagascar, which is mixed with two diﬀerent
species (ﬁgs. 8, 9). Both thalli do not correspondwith C. cicatrix and the thallus shown in ﬁg. 8 in
Verbruggen and Costa (2015) is close to C. arenicola in habit. Moreover, C. cicatrix recorded by
Van den Heede and Coppejans (1996) is not similar to both of C. arenicola and C. cicatrix in thesmall compressed thalli. Codium barbatum Okamura, whose type locality (Hachijo Island) is close
to the Ogasawara Islands, bears “cuboid or obovate
or oblong, short” utricles (Okamura 1930). This33

species is also diﬀerent from C. arenicola in having a small thallus (below 10 cm in height) with aconical holdfast and slender branches (less than
3 mm in width). Silva et al. (1997) noted that collections reported as “C. tenue” by Okamura (1918,
61, pl. CLXV, ﬁgs. 11–13) from Japan are referable to C. barbatum and thus C. tenue is restricted
to South African estuaries.
As a result, the author identify the present algaas Codium arenicola M.E.Chacana & P.C.Silva,
which has thin branches with sparse ramiﬁcationand cylindrical to obconical, obovate utricles. It
is suggested that this species has a wide distribution in mesophotic zone (20–60 m in depth) in
the Indo-Paciﬁc Ocean. To clarify the whole distribution of this species, anatomical observations
and molecular analyses on more samples fromvarious ﬁelds and more specimens in various
herbaria are required. Presently, it is clear thatseven species of Codium having erect, terete,dichotomously branched thalli are distributed
throughout Japan, and their “key to species” isshown as follows.

Key to the species of Codium having erect, terete, dichotomously branched thalli in Japan
1a. Thallus growing on sandy bottoms ..................................................................................C. arenicola
1b. Thallus growing on rocks or boulders................................................................................................22a. Thallus shorter, usually 10–30 cm in height .......................................................................................32b. Thallus longer, 0.3–1(–15) m in height, ﬂattened at dichotomies .....................................................4
3a. Apices of branches clavate ............................................................................................C. contractum
3b. Apices of branches tapering ...............................................................................................................54a. Utricles 100–140 μm in diameter, 660–850 μm in length.........................................C. subtubulosum
4b. Utricles 400–500(–900) μm in diameter, 2–3 mm in length ........................................C. cylindricum
5a. Utricles with an acute apices ................................................................................................ C. fragile
5b. Utricles with rounded or ﬂattened apices...........................................................................................66a. Utricles cylindrical to clavate............................................................................................C. yezoense
6b. Utricles cuboid to obovate .............................................................................................. C. barbatum

34

Taiju Kitayama

Acknowledgments
I am grateful to Mr. Yoshiyasu Takase, theOgasawara-jima Fisheries Cooperative for collecting the material by dredging using his ship. I
thank Mr. Masataka Kikuchi, the union representative of the Ogasawara-jima Fisheries Cooperative for permission and cooperation for collecting, and Mr. Kotaro Seno, Mr. Takayuki
Miyazaki and Mr. Yuhei Tanaka, the Ogasawara
Fisheries Center, Tokyo Metropolitan for providing me the facilities to process the specimens. I
am also thankful to Ms. Lauren Morris, Wisconsin, USA, for her correction of English in thismanuscript. This study was supported by Grantsin-Aid for Scientiﬁc Research (no. 16K07496)
from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
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