Bull. Natl. Mus. Nat. Sci., Ser. B, 43(2), pp. 45–50, May 22, 2017

Fragilaria asterionelloides, A New Planktonic Species of Fragilaria
from Japanese Reservoirs That Forms Star-Shaped Colonies
Akihiro Tuji1,* and David Williams2
1

Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, Ibaraki 305–0005, Japan2
Department of Life Sciences, the Natural History Museum,Cromwell Road, London SW7 5BD, UK*E-mail: tuji@kahaku.go.jp(Received 17 February 2017; accepted 22 March 2017)

Abstract A new species of Fragilaria, Fragilaria asterionelloides, is described. It is found inJapanese reservoirs. Fragilaria asterionelloides forms a characteristic star-shaped colony and iseasily distinguished from most other species of Fragilaria because of this feature. Fragilaria asterionelloides is most similar to Fragilaria tenera var. lemanensis but differs in the outline of thefrustule, the ﬁne density of striae and the swollen central area. Synedra acus var. ostenfeldii also
forms a star-like colony but has no central area. The frustule (valves and girdle) of Fragilaria asterionelloides also resemble those of Fragilaria crotonensis but differ from these by the ﬁne densityof striae and the swollen central area.
Key words : Fragilaria tenera var. lemanensis, Synedra acus var. ostenfeldii, Fragilaria crotonensis, plankton, reservoir.

Introduction
The freshwater planktonic diatom ﬂora inJapanese reservoirs and lakes has been studied
by a number of researchers (e.g. Kobayasi andInoue, 1985; Watanabe and Kanechika, 1986)
and the taxonomy of some species has been clariﬁed (e.g. Tuji and Houki, 2001, 2004; Tuji andWilliams, 2006, 2007).
In August 2009, the phytoplankton ﬂora from109 Japanese artiﬁcial reservoirs (Tuji, 2015)
was examined and a very large and assumed
unknown ʻaraphidʼ species which formed a characteristic star-like colony was found. It was dominant in Kanayama reservoir, Hokkaido, Japan(Figs. 1, 2). Similar specimens were found in
Takisato reservoir, Hokkaido (2009 summer) andMoniwakko reservoir, Fukushima Prefecture(Surikamigawa-dam, 2011 autumn).
In this paper, the unknown ʻaraphidʼ species is

described as new and named Fragilaria asterionelloides.
Materials and Methods
The same material and methods as described inTuji (2015) were used for this report. About 18
litres of surface water samples from 109 Japanese
artiﬁcial reservoirs were collected in August 2009
(during the summer) and sent to the laboratory,
after refrigeration, within three days (mostly twodays) and without ﬁxation. In addition, samples
from 50 selected sites from the 109 total were collected from March to May 2010 (spring) and 22
sites were collected from September to October
2011 (autumn), were examined.
About one liter of surface water sample was ﬁltered using PTFE membrane ﬁlters having 1.0 μm
openings (JAWP04700, Millipore) and dried withan incubator (ITD-20E, ALP) at 60°C. The mem-46

Akihiro Tuji and David Williams

brane ﬁlters were then cut into small pieces (about5 mm square) and attached to an SEM stub using
carbon adhesive tape. These stubs were sputteredcoated with platinum and examined using a SEM(JSM-6390 with LaB6 gun, JEOL).
One drop of formalin ﬁxed specimen wasplaced on a coverslip and then placed on a grassplate (Laboratory protection plate, Schott). The
plate was put on a stove burner and baked for 30
minutes. The coverslip was carefully washedusing distilled water and then mounted with Zrax
(Microlife services, Somerset, U.K.). The perma-nent slides were examined and photographedusing an Axiophot, Zeiss microscope.
All samples, SEM stubs and photographs arehoused in the micro-algal herbarium in National
Museum of Nature and Science (TNS).
Taxonomic description
Fragilaria asterionelloides Tuji et D.M.Williams
sp. nov. (ﬁgs. 1, 2, 5–18)
Holotype: A colony in a slide TNS-AL-58931
in TNS (Department of Botany, National Museumof Nature and Sciences＝Fig. 12)

Figs. 1–4. Scanning electron microscopy. 1–2. Fragilaria asterionelloides, 1. bar＝50 μm, 2. bar＝2 μm. 3.
Asterionella formosa, bar＝10 μm. 4. Nitzchia fruticosa, bar＝10 μm.

Fragilaria asterionelloides, a New Species from Japan

47

length 60–70 μm, breath 2 μm. Small spines
located at valve at face—mantle junction, mostsituated on a virga, some across a pair of virgae.
Spines short, taper towards tips; spines at valve
centre mostly bifurcate; spines at poles not bifurcating, but tilting towards respective pole. Somespines occur above each polar ocellulimbus(Figs. 15–18); ocellulimbus composed of threerows and three columns of pores (Figs. 17, 18).
Striae alternate, in single rows, parallel throughout valve, not all opposite either side of central
sternum, 22–23 per 10 μm. Sternum relatively
thin, 1/5 of valve width. One rimoportula perfrustule, situated on valve face (Figs. 15, 16).
Girdle of 3＋ (?) bands, appear open although
not clearly so (Figs. 17, 18).
Results and Discussions

Figs. 5–11. Fragilaria asterionelloides, lightmicroscopy, bar＝10 μm, TNS-AL-58931.

Type locality: Kanayama reservoir, Hokkaido,Japan.
Other localities: Takisato reservoir, Hokkaido,
Moniwakko reservoir (Surikamigawa-dam),
Fukushima Prefecture, and Lake Ashi, Kanagawa
Prefecture, Japan.
In situ, frustules connected in star-shaped colonies; frustules overlap at poles. Valves lanceolate, tapering towards round to capitate poles.
Each valve with expanded central area; valve

A few planktonic ʻaraphidʼ species are known
to have star-shaped colonies. For example, Asterionella formosa Hassall (and some of its varieties and forms: Asterionella formosa var. acaroides Lemmermann 1903 and Asterionella formosavar. tatrica Woloszynsaka 1934, amongst others)
form these kinds of colonies (see also Körner,1970a, b) (Fig. 3). The connecting part of thecolony of Fragilaria asterionelloides is, however, irregular and closely ﬁtting (Fig. 2), so canbe easily distinguished from those seen in A. formosa when using SEM and LM (Fig. 3). The
robust diatom Nitzchia fruticosa Hust. alsomakes similar colonies (Fig. 4), but is quite a different diatom; a number of other diatoms also
form these colonies but few could be confusedwith any ʻaraphidʼ species. Thus, Fragilaria asterionelloides is easily distinguished from otherknown Japanese planktonic diatoms.
As the specimens have one rimoportula per
frustule (Fig. 15), small spines, alternate striae
consisting of single rows, and open girdle bands, itshould, at present, belong in the genus Fragilaria(see Williams and Round, 1987, Round, 1991).
There are two taxa that have a star-shaped colony that are worth comparison. One has beenplaced in Fragilaria the other in Synedra sensu

48

Akihiro Tuji and David WilliamsFig. 12.

Fragilaria asterionelloides, light microscopy, bar＝10 μm, TNS-AL-58931. Holotype individual.

lato. Fragilaria tenera var. lemanensis Druart,Lavigne et Robert was recently described fromLake Geneva, Switzerland (Druart et al., 2007:284). The taxon was illustrated with only threelight micrographs, but later Lange-Bertalot andUlrich documented it in much greater detail using
specimens from Lake Constance, Germany; they
provided a lengthy discussion of Fragilaria tenera
and its varieties (Lange-Bertalot and Ulrich, 2014:9–15). Fragilaria asterionelloides has a swollen
and clear central area allowing it to be distinguished from F. tenera var. lemanensis. The den-sity of valve striation differ as well: 18–20 str. per
10 μm for F. tenera var. lemanensis; 22–23 str. for
Fragilaria asterionelloides.
The second relevant taxon that has beenreported with star-shaped colonies is Synedra acus
var. ostenfeldii Krieger, which has a similar striae
density to Fragilaria asterionelloides (22–24 str.
per 10 μm). Inspection of Kreigerʼs original illustration shows that the valves do not have a central
area and hence differs from Fragilaria asterionelloides, although the illustrations are difﬁcult tointerpret and Kriegerʼs material has not been

Fragilaria asterionelloides, a New Species from Japan49

Figs. 13–18. Fragilaria asterionelloides, scanning electron microscopy. 13. Whole frustule, bar＝10 μm. 14.
Slightly swollen central area with small spines positioned at the margin and on a virga, bar＝1 μm. 15. Valvepoles with apical pore ﬁeld (ocellulimbus) and rimportula, bar＝0.5 μm. 16. Valve apices with apical pore ﬁeld(ocellulimbus) but lacking any rimportula, bar＝0.5 μm. 17–18. Valve apices with open bands, bar＝1 μm.

examined or yet to be traced (Krieger, 1927: taf. 3,ﬁg 29b, after Ostenfeld, 1905: Pl. II, Figs. 16, 17).
The valve outline (Figs. 5–13) is similar tothat recorded for Fragilaria crotonensis Kitton(e.g. Crawford et al., 1985), although the form of
its colony is very different. There are a numberof SEM images of specimens named as Fragilaria crotonensis (see listing in Gaul et al.,
1993, Henderson et al., 2003) and a number ofvarieties and forms of Fragilaria crotonensis
have been described. With respect to the SEM
images, most are hard to evaluate as they do notshow sufﬁcient detail to determine anythingother than the basic characters, with the exception of the images in Lange-Bertalot and Ulrich(2014). One constant is that the colonies areformed by the central portion being attached byspines.
With respect to the many named varieties andforms, these too are hard to evaluate as most areeither illustrated with just simple line drawings,
not illustrated at all or are apparently publishedin obscure items difﬁcult to ﬁnd.
The density of striae in Fragilaria asterionel-50

Akihiro Tuji and David Williams

loides is 22–23 in 10 μm, ﬁner than recorded formost descriptions of F. crotonensis (e.g. 15–18 in
10 μm by Patrick and Reimer, 1966). Fragilaria
asterionelloides also has a slightly swollen central area, which distinguishes it from F. crotonensis. However, morphological variation in F. crotonensis is very high and will possibly include
several cryptic taxa (Tuji pers. obs.), so it isimportant to distinguish Fragilaria asterionelloides from F. crotonensis by an examination of itscolony. Since the type material also include specimens of F. crotonensis, only colony forming
valves were examined with valves not yet studied.
Acknowledgments
A.T. would like to thank Dr. Hidetaka Ichiyanagi, Water Resources Environment Center.
We also with to extend my thanks to Dr. Yuko
Niiyama and Dr. Kaoru Ogane for helping the ﬁltration of so much samples, and Mrs. Yuri Inamifor taking many SEM photographs presented inthis study. Part of this work was supported byWatershed Ecology Research Group.
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