A new brackish water diatom, Achnanthes secretitaeniata, from Japan

Abstract

A new monoraphid diatom, Achnanthes secretitaeniata, is decribed from brackish water in the coast, Yamada-machi, Shimohei-gun, Iwate Pref., Japan. Cell shape is more or less linear with rounded extremities. Rapheless sternum grows close to the margin of the araphid valve. Araphid valve margin is well developed, but does not form marginal ridge as in A. yaquinensis and A. subconstricta. Valvocopulae and copulae are open- ended at both poles of valve. This species is closely related to A. brevipes C. Agardh var. intermedia (Kütz.) Cleve, but, they can be easily distinguished from each other by the position of rapheless sternum and the structure of valve margin on their araphid valves.

Full text

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Achnanthes Bory sensu stricto includes
monoraphid, hetelovalver diatoms, which
have cribrate areolae on both valve and
cingulum (e.g., Round et al. 1990, Toyoda et
al. 2005b). The taxa are widely distributed
and occur mainly in marine and brackish
waters, rarely in freshwater (e.g., Bory 1822,
Kützing 1844, Cleve 1895, Hustedt 1937,
McIntire and Reimer 1974, Round et al.
1990, Witkowski et al. 2000, Werum and
Lange-Bertalot 2004, Metzeltin et al. 2005).
For instance, A. brevipes C. Agardh var.
brevipes, which is the type species of the
genus, A. longipes C. Agardh and A.
subconstricta (F. Meister) Toyoda occur in
marine waters; A. angustata Grev. and A.
kuwaitensis Hust. occur in brackish waters,
and A. crenulata Grunow and A. inflata
(Kütz.) Grunow occur in freshwaters (Cleve
1895, Cleve and Grunow 1880, Toyoda et al.
2003, Toyoda et al. 2005a, Metzeltin et al.
2005). The genus has a confused taxonomic
background since its original establishment
by Bory, however, it has been gradually or-
ganized by recent studies of Achnanthes
sensu lato. For instance, Round and
Bukhtiyarova (1996) redefined the genus,
and established three new genera, with a fur-
ther seven new genera also established by
them (Bukhtiyarova and Round 1996, Round
and Bukhtiyarova 1996, Round and Basson
1997). Toyoda et al. (2005b) advocated the
genus Achnanthes s. s. on the basis of the
morphological information recently pub-
lished with detailed figures within
Achnanthes s. l. taxa (e.g., Toyoda et al.
2003, Toyoda and Williams 2004, Potapova
and Ponader 2004, Flower 2005). But we
need more specific information on the
ultrastructure of eads species using electron
J. Jpn. Bot. 84: 19–26 (2009)
A New Brackish Water Diatom, Achnanthes secretitaeniata, from Japan
Kensuke TOYODAa, Jiro TANAKAband David M. WILLIAMSc
aNational Research Institute of Fisheries and Environment of Inland Sea Fisheries Research Agency,
Hatsukaichi-shi, Hiroshima, 739-0452 JAPAN;
E-mail: toyoda@diatom.jp
bDepartment of Ocean Science, Tokyo University of Marine Science and Technology,
Konan, Minato-ku, Tokyo, 108-8477 JAPAN;
cDepartment of Botany, The Natural History Museum, Cromwell Road, London, SW7 5BD, U.K.
(Received on April 28, 2008)
A new monoraphid diatom, Achnanthes secretitaeniata,isdecribed from brackish
water in the coast, Yamada-machi, Shimohei-gun, Iwate Pref., Japan. Cell shape is more
or less linear with rounded extremities. Rapheless sternum grows close to the margin of
the araphid valve. Araphid valve margin is well developed, but does not form marginal
ridge as in A. yaquinensis and A. subconstricta.Valvocopulae and copulae are open-
ended at both poles of valve. This species is closely related to A. brevipes C. Agardh var.
intermedia (Kütz.) Cleve, but, they can be easily distinguished from each other by the po-
sition of rapheless sternum and the structure of valve margin on their araphid valves.
Key words:Achnanthes secretitaeniata,Achnanthes sensu stricto, brackish water, mor-
phology, new species.

microscopy to fully understand these genera.
At the present study, one new species of
Achnanthes s.s. is described by scanning
electron microscopy (SEM) comparing with
the closely related taxa in the genus.
Materials and Methods
The material was obtained from the
Japanese coast as follows: Yamada-machi
(39°27 
N, 142°01 
E), Shimohei-gun, Iwate
Pref., Japan, brackish water, epiphytic to
Cladophora sp. (Chlorophyceae), 29 July
1999, coll. Matsuyama, preserved in the pri-
vate collection of K. Toyoda (KT 1101).
Fixed material with formaldehyde was
cleaned by a bleaching method (Nagumo and
Kobayasi 1990). In LM (light microscope)
observation, because of the heterovalvar
structure of Achnanthes taxa, to avoid the
possibility of mis-identifications when only
one side of a frustule being observed, the
raphid valve (RV) face and araphid valve
(ARV) face of the same individual were ex-
amined using a double-faced slide nipped
with two cover slips. The cleaned material
was also examined using scanning electron
microscope (Hitachi S-4000, Philip XL-30
FEG). Valve terminology follows by the
Working Party on Diatom Terminology
(Anonymous 1975, Ross et al. 1979) with
supplementary details from Toyoda et al.
(2003).
Slides of the present specimens were de-
posited in the herbaria of the Natural History
Museum, London and the National Museum
of Nature and Science (former National
Science Museum, Tokyo).
Diagnosis
Achnanthes secretitaeniata K. Toyoda &
Ji. Tanaka, sp. nov. [Figs. 1–24]
Frustula haterovalvaria. Valvae lineares,
breves, facientes, 33–41 µm longae, 10–
11 µm latae. Raphovalva introflexa, con-
vexa. Areovalva retroflexa, concava, sterno
incurrete angsto orae areovalva. Areolae
uniseriatae. Cingulum ex taeniae secretus
extremus.
TYPE: Slide BM101174 (holotype). Slide
BM101175, Slide TNS-AL-53981 (isotype).
Type locality: Yamada-machi, Shimohei-
gun, Iwate Pref., Japan (39°29
N, 142°01
E).
Habitat: Occurs in brackish water around
marine coast, epiphytic on filamentous
Cladophora sp.
Etymology: The epithet is referred to the
special structure of open-ended bands.
Observations and Discussion
In LM observation, valve is more or less
linear, not pointed at the terminal (Figs. 1–
7), 33–41 µm long, 10–11 µm wide. Striae
are uniseriate on both valves, with 10–11
costae in 10 µm on RV, and 10.5–11.0 on
ARV. On RV, costae occur on both sides of
the raphe, being opposite with each other.
Raphe fissure extends to the entire length of
a valve with central area forming a distinct,
well developed stauros (Figs. 1–3, 4a). The
rapheless sternum on ARV grows at the
margin of ARV and occasionally appears
biconvex, there are no terminal orbiculi on
the end of ARV (Figs. 4b, 5–7). Rows of
areolae are visible on the girdle (Fig. 8).
In SEM observation, the outer surface of
RV is slightly rounded (Fig. 9). On both
valves, there are cribrate areolae, which are
often supported by more than 5 pegs (Fig.
10). These areolae are usually rounded or
squarish shaped, creating peripheral slits
curved (Fig. 10). The central raphe fissures
are slightly expanded and unilaterally de-
flected (Fig. 11), while the terminal fissures
are deflected to the opposite side over the
valve apices (Fig. 13). The stauros reaches
the valve margin (Fig. 11). Internal views of
RV reveal the slightly thickened stauros and
additional thickening on the transverse
virgae (often thickened and referred to as
costae), distal to the raphe slit (Fig. 12).
Internal raphe fissures are almost straight,
the central endings (pores) hooked to one
植物研究雑誌 第84巻第1号平成21年2月20

side (Fig. 15) and the terminal fissures
curved slightly in the opposite direction into
small helictoglossae (Figs. 14, a–b). The ex-
ternal surface of ARV lacks any ridge or
spine, but there is a well developed margin
(Fig. 16), and no terminal orbiculus (Fig.
18). Some individuals form small kind of
spines at the pole of ARV (Fig. 19, arrow-
head). Rapheless sternum grows close to the
margin on ARV (Figs. 16, 19). Intervening
areolae appear sunken, and costae well de-
veloped in the inside of ARV, and transverse
virgae connect with rapheless sternum (Figs.
17, 20). The pole of ARV has an indented
end (Fig. 21). Valvocopulae (both RV and
ARV sides) are open-ended at both poles of
a valve (Figs. 14a, 14b), and have areolae
occluded by complex cribra with volae (Fig.
24), valvocopula has two rows of areolae
(Fig. 22). Some of bands develop as lateral
outgrowths from a longitudinal axis (Fig.
23).
Achnanthes secretitaeniata resembles A.
brevipes var. intermedia in some common
characteristics: the valves are more or less
linear, no terminal orbiculi, and occurring in
brackish water (cf. Toyoda and Williams
2004). However, these taxa can be easily dis-
tinguished by the structure of the margin and
the position of a rapheless sternum on ARV.
Achnanthes secretitaeniata has a well devel-
oped valve margin on ARV, and the
Journal of Japanese Botany Vol. 84 No. 1February 2009 21
Figs. 1–8. Achnanthes secretitaeniata, cleaned material under LM, all the same
magnification. Figs. 1–3. RV views. Fig. 4. RV (a) and ARV (b) views of
the same individual cell. Figs. 5–7. ARV views. Fig. 8. Girdle view showing
the convex ARV, and the concave RV.

植物研究雑誌 第84巻第1号平成21年2月22
Figs. 9–15. Achnanthes secretitaeniata, SEM observations of RV and valvocopula. Fig. 9.
External view of RV showing a filiform raphe fissure. Fig. 10. External view of
cribrate areolae with volae, which are often supported by more than 5 pegs. Fig. 11.
External view of RV centre showing a transverse stauros. Fig. 12. Internal view of
RV with valvocopula. Arrowhead show positions of open ended band. Fig. 13.
Terminal view of raphefissure, showing a curved end. Figs. 14a, 14b. Enlarged views
of Fig. 12, showing openended valvocopulae at both poles of a valve. 14a and 15b
correspond to an arrowhead and double arrowhead in Fig. 12, respectively. Fig. 15.
Internal view of a stauros, showing the central endings of raphe fissures hooked to
one side.

rapheless sternum grows close to margin of
ARV, while A. brevipes var. intermedia has
a round margin on ARV, and the rapheless
sternum on ARV grows slightly laterally and
occasionally appears biconvex. Furthermore,
A. coarctata Bébisson in W. Sm. (1855)
Grunow in Cleve and Grunow (1880) also
resembles the present taxon in the valve.
However, A. coarctata has a smaller valve
with closer arranged striae on its valve com-
pared with A. secretitaeniata.Onthe other
points, A. subsessilis Kütz. is also like A.
secretitaeniata in forming well developed
margin on ARV (Toyoda 2004 unpubl. data)
Journal of Japanese Botany Vol. 84 No. 1February 2009 23
Figs. 16–21. Achnanthes secretitaeniata, SEM observations of ARV. Fig. 16. External
view of a whole ARV. Fig. 17. Internal view, showing the transverse virgae connect-
ing with rapheless sternum. Fig. 18. External view at the pole, with no terminal
orbiculi. Fig. 19. External view at the pole, with spines (arrowhead). Fig. 20.
Enlarged view of Fig 17, rapheless sternum and transverse virgae coming to the in-
side of ARV. Fig. 21. Internal view at the pole, showing indent end.

but the former has a more rounded shape at
the poles of the valve face compared with the
latter.
It was observed that A. secretitaeniata has
valvocopulae which are open-ended at both
poles. Commonly, Achnanthes taxa form
bands with some bands open at one side,
which are combined and piled up by turns
(e.g., Novarino 1992, Toyoda et al. 2003,
Toyoda and Williams 2004, Toyoda et al.
2005a, 2005b, 2005c). These open-ended
bands strengthen the structure of cell wall.
In other genera, Cocconeis stauroneiformis
(Rabenh.) Okuno, which is also a mono-
raphid diatom, forms open-ended valvo-
copulae at both poles (cf. Suzuki and
Nagumo 2003). Also, second band is open-
ended at both poles, but short in length.
Furthermore, third band is open-ended. So
the strength of the cell in C. stauroneiformis
is compensated by short bands and third
band. In this study, however, such short or
closed bands were not observed in A.
secretitaeniata.InAchnanthes s. s., A.
inflata (Kütz.) Grunow also forms a
cingulum which is open-ended at both poles
(Toyoda in preparation). How and where the
difference on the development process of
bands (cingulum) occurs remains uncertain.
Usually, Achnanthes taxa are generally
identified at the rank of species by 1) shape
of valve, 2) position of rapheless sternum, 3)
existence of terminal orbiculi, 4) number of
striae between costae, and 5) shape of plastid
(e.g., Toyoda et al. 2005b, 2006). Identifica-
tion is difficult only with light microscopic
observations. As for Achnanthes taxa we
often need an electron microscopic observa-
tion. In particular, A. brevipes C. Agardh and
related taxa cannot be identified without
植物研究雑誌 第84巻第1号平成21年2月24
Figs. 22–24. Achnanthes secretitaeniata, SEM observations of bands. Fig. 22. Second or
third band, showing two rows of areolae. Fig. 23. Enlarged view of sequenced second
or third band development, showing around the silica deposits (arrowhead). Fig. 24.
External view of RV with valvocopula (upper part) with cribrate areolae.

SEM observations. For instance, when com-
paring A. brevipes var. brevipes and var.
intermedia, these two varieties resemble
each other on their valve shape. The former
forms quite flat valve face, on the other
hand, the latter forms rounded valve face
(cf. Toyoda and Williams 2004, Toyoda et
al. 2005b). These structures can be con-
firmed only using SEM observations. As for
A. secretitaeniata, well developed ARV mar-
gin and open-ended bands at both poles, are
specific structures among Achnanthes taxa,
and they cannot be recognized in LM obser-
vation.
We are grateful to Dr Geraldine Reid,
Natural History Museum, London, for proof-
reading this manuscript and providing us
with the slides numbers in the herbarium of
Natural History Museum, London.
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植物研究雑誌 第84巻第1号平成21年2月26
豊田健介a,田中次郎b,D. M. ウィリアムスc：
日本の汽水産珪藻の 1新種 Achnanthes
s
ecretitaeniata
岩手県下閉伊郡山田町の沿岸汽水水域より採集
した珪藻を新種 Achnanthes secretitaeniata K.
Toyoda & Ji. Tanaka として記載した. 本種の被殻
は棒状で, 殻端部に丸みを帯びる. 殻長は33–41
µm, 殻幅10–11 µm,条線は10 µm あたり10–11本
が並ぶ. 無縦溝殻において, 頂軸域は殻縁付近に
伸び, 殻端肋や殻縁肋は形成されない. 帯片には
点紋列が並び, 両殻端において開放型であった.
本種は A. brevipes C. Agardh var. intermedia (Kütz)
Cleve と類似する形態を持つが, 被殻殻端部の形
状, 頂軸域の位置, そして, 両殻端において開放
型の帯片の構造において区別される.
(a水産総合研究センター瀬戸内海区水産研究所,
b東京海洋大学海洋科学部,
c自然史博物館 (ロンドン) 植物研究部)