Bull. Natl. Mus. Nat. Sci., Ser. B, 35(4), pp. 183–187, December 22, 2009

The Identity of the Endozoic Red Alga Rhodochortonopsis spongicola
Yamada (Acrochaetiales, Rhodophyta)
Taiju Kitayama
Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, 305–0005 Japan
E-mail: kitayama@kahaku.go.jp

Abstract The identity and status of the unusual endozoic red alga, Rhodochortonopsis spongicola Yamada (Acrochaetiales, Rhodophyta) was reassessed, by reexamining the type specimens(TNS). This species was originally described as the only representative of the monospecific genus
Rhodochortonopsis by Yamada (1944), based on material collected by the Emperor Showa. Yamada (1944) observed single stichidia (specialized branches bearing tetrasporangia) and consideredthem as the discriminant character to distinguish this genus from all the members of the orderAcrochaetiales. This study shows that these specimens are actually belonging to the species
Acrochaetium spongicola Weber-van Bosse. The presence of “stichidia” is actually an artifact, due
to a cover of sponge spicules, forming bundles originally mistaken as part of the alga. Consequently, the genus Rhodochortonopsis has no entity.
Key words : Acrochaetiales, Acrochaetium spongicola, endozoic red alga, Rhodochortonopsis
spongicola, Rhodophyta.

Introduction
Epizoic and endozoic marine algae (i.e. living
on or inside animal bodies) have been little studied. This is inherent to the difficulties of collecting, isolating from the animal host (especially forendozoic algae) and making voucher specimens
for further reexamination. More than half acentury ago, the unusual endozoic red alga,
Rhodochortonopsis spongicola (Acrochaetiales,Rhodophyta), was described by Yamada (1944),
for which he created a new genus. The diagnosesof the species and the genus were based on themicroscopic plants within the tubes of polychaete
worms, which were collected by the Emperor
Showa (1901–1989) in the sea off Hayama, Sagami Bay, Japan. The main characteristic of thegenus Rhodochortonopsis lies in the “very peculiar stichidia” harbouring many zonately divided
tetrasporangia (Fig. 1). After the original description, however, this alga has not been collectedagain in Japan. Only Norris (1991) recorded asimilar algal species from Natal (South Africa)and suggested a possible relationship of
Rhodochortonopsis to the order Gigartinales (andnot Acrochaetiales) because of the cystocarpic
structures of the female plants and the presenceof a structure similar to Yamada’s “stichidia”. In
this research the identity of this species is reassessed by examination of the type specimens.
Materials and Methods
Type material of Rhodochortonopsis spongicola Yamada stored in the herbarium of the Showa
Memorial Institute, the National Museum ofNature and Science (TNS), Tsukuba, Japan wasreexamined. The fragments from the materials
were immersed in glycerin or stained using 1%
acidified aniline blue and observed using amicroscope.

Observations and Discussion
ORDER ACROCHAETIALES Feldmann 1953:12184

Taiju Kitayama

Fig. 1. Illustrations of “Rhodochortonopsis spongicola” Yamada in the original description.
A. A part of the frond. ca. 470. B. Stichidia. ca. 40. C. Cross-section of a stichidium. ca. 330 (after Yamada
1944, p. 24, f. 8).

Family Acrochaetiaceae Fritsch ex Taylor 1957:
209, 210, nom. cons.
Acrochaetium spongicola Weber-van Bosse
1921: 195 (as “Acrochaetium spongiocolum”).
(Figs. 2–8)
Synonyms: Audouinella spongicola (Weber-vanBosse) Stegenga 1985: 314, fig. 18 (as“Audouinella spongiocola”).
Colaconemam spongiocolum (Weber-vanBosse) Woelkerling 1971: 41A–F. 195.
Rhodochortonopsis spongicola Yamada 1944:
23, figs 7, 8.
Specimens examined: Off Sashima (Hayama),Sagami Prov. (Kanagawa Pref.), Japan (15 Aug.
1939), Coll. Showa Tenno, TNS-AL-R L-212 (y.
no. 1859, holotype of Rhodochortonopsisspongicola).
The type material is composed of several tubes

of polychaete worms, mainly made of spongespicules (Fig. 2). Pseudoparenchymatous structures consisting of algal vegetative filaments
were observed (Fig. 3, arrowhead). The filaments
are uniseriate, irregularly branched, Colaconemalike in shape (Fig. 4, arrowhead). Vegetative cells
are cylindrical, 4–7 m m in diameter and 8–38 m min length, irregularly branched and forming a network on the surface of bundles of sponge spiclues. In addition the filaments are covering astem-like structure made of sponge spicules. Theaccumulation of the filaments often makes acrustose on the terminal portion of the stalk(Figs. 5 and 6). As a result, this structure appears
to be the same as the “stichidium” reported in theoriginal description of the species (Yamada,1944, f. 8b) (Figs. 1 and 5). The stalks of the“stichidia”-structures are cylindrical, 70–95 m m
in diameter. A number of erect filaments are rising from the surface of the crustose having an

Rhodochortonopsis spongicola

185

Figs. 2–8. “Rhodochortonopsis spongicola” Yamada (TNS-AL-R 212, holotype). 2. Parasitized polychaete tube, madeof sponge spicules. 3, 4. View of vegetative filaments (arrowhead) growing between the spicules (surface view of thepolychaete tube). 5. “Stichidium” with a long stipe (arrow). 6. Surface of stipe of “stichidium” showing covered withvegetative filaments. 7. Terminal portion of the “stichidium”-structure showing a bundle of sponge spicules inside thestructure (arrows). 8. Surface of the terminal portion of the “stichidium”-structure showing a putative monosporangia(double arrow).

axis of sponge skeletons inside (Fig. 7, arrows).
Erect filaments often have a putative monosporangium on their terminals (Fig. 8, doublearrow).
Stichidia (sing. Stichidium) are specialized
branches bearing tetrasporangia in Rhodophyta,

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Taiju Kitayama

usually enlarged over the vegetative axes (Boldand Wynne, 1985). Yamada (1944) described the“stichidia” in the alga as an important feature forthe genus Rhodochortonopsis. The “stichidium”
illustrated in his description (f. 8B) coincides
with the structures observed in the typespecimens (long cylindrical stalk, 75–125 m m indiameter) (Fig. 1). However, the “stichidium”structure observed in the type specimens of
Rhodochortonopsis spongicola Yamada is notpart of the macroalgal thallus but is in fact consisting of “axes” of sponge spicules and coveredby vegetative filaments of Audouinella or
Acrochaetium on their surface. It is consideredthat the constant diameters of the stalks (i.e. thespicules) are the result of a selection by the polychaete during the elaboration of the tube. Therefore, the algal fraction of the type material isconsidered as Acrochaetium spongicola Webervan Bosse or Audouinella spongicola (Weber-vanBosse) Stegenga, and in either case it is suggested that Rhodochortonopsis spongicola Yamada is
not a separate species and its monotypic genera
Rhodochortonopsis has no entity.
The generic taxonomy of Acrochaetioid algae(Acrochaetiales) including several genera,
Acrochaetium,
Audouinella,Colaconema,Kylinia, Rhodochorton, etc. is continuing to beconfused and many classification schemes havebeen proposed by many authors (e.g., Drew,1928; Woelkerling, 1983; Garbary and Gabrielson, 1987; Lee and Lee, 1988) depending on
criteria used for defining genera. For example,Silva et al. (1996) treated all acrochaetioid
algae reported from the Indian Ocean as
Acrochaetium, following Feldmann’s proposalthat Acrochaetium includes species in which eachcell has a single chloroplast, whether it be stellate
or laminate, axile or parietal (Feldmann, 1962).
However,mostoftheauthors
did
not make any mention of the genus,
Rhodochortonopsis, including even a recent molecular investigation on Acrochaetiales using
DNA sequence data of Acrochaetium, Audouinella, Colaconema, Rhodochorton (Harper andSaunders, 2002). Probably it was largely a resultof Yamada’s statement, “very peculiar stichidia”
and noted that “owing to lack of cystocarps it isimpossible to determine the systematic positionof the new genus” in his original description(Yamada, 1944, p. 25). Kylin (1956) and Silva
et al. (1996) treated this genus as the one ofgenera of uncertain position in Rhodophyceae(Rhodophyta). Only Yoshida (1998) and Yoshida
et al. (2005) listed this genera in Acrochaetiaceae(Acrochaetiales) with an additional comment
about indeterminacy of its taxonomic position.
Norris (1991), who made the only recorded of
Rhodochortonopsis spongicola after the Yamada’s original description, observed the female
plants and cystocarpic plants collected fromNatal, South Africa in 1990. He suggested
the possibility that this unusual alga,
Rhodochortonopsis spongicola, has a relationship with the Gigartinales, based on the combination of the advanced type of cystocarpic structures on or with the female gametophytes fromSouth Africa and zonate tetrasporangia on theJapanese tetrasporophytes described in the original description. As he noted, however, it cannot
be unequivocally established that his female andcystocarpic plants belong to the same entity as
the tetrasporophytic plants described by Yamada(1944). Thus, since Norris (1991) avoided deciding its final position in the Rhodophyta, thisproblem has been pending for a long time. In thisresearch, it was revealed that the “stichidia” described in the Yamada’s original description weremade of sponge spicules covered with vegetative
filaments and a crustose arising numerous erectfilaments (with probably monosporangia) on theterminal. The Japanese plants are identified as
Acrochaetium spongicola Weber-van Bosse in
the morphology of vegetative filaments forming
network on the sponge skeletons and putativemonosporangia on the crustose. Although theidentity of the South African plants with cystocarps is unknown, I consider that the name of
Rhodochortonopsis spongicola should be synonymized under Acrochaetium spongicola (orAudouinella spongicola), which has been recorded so far from only south hemisphere: Indonesia

Rhodochortonopsis spongicola(type locality: Aru Isls., Weber-van Bosse, 1921)
and South Africa (Stegenga, 1985), southern
Australia (Woelkerling and Womersley, 1994),
while there is no record of the species from thenorth hemisphere.
Acknowledgements
I am grateful to Dr. Hiroshi Namikawa, theShowa Memorial Institute, National Museum ofNature and Science, for his generous support
during my investigation in the herbarium. I thankDr. Frédéric Mineur, School of Biological Sciences, Queen’s University of Belfast, UK, forcorrecting the English of the manuscript.
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