Journal of Plant Biology, June 2004, 47(2) : 12%132

Prorocentrum vietnamensis sp. nov. (Prorocentraceae Dinophyta): A New Armored Dinoflagellate from Vietnam Coastal Waters

Jong Su Yoo 1, Jin Hwan Lee 2 . , and Yasuwo Fukuyo 3 ~Research Institute of Science and Technology, Korea Maritime University, Busan 606-791, Korea

2Department of Biology, Sangmyung University, Seoul 110-743, Korea 3Asian Natural Environmental Science Center, The University of Tokyo, Tokyo 113-8657, Japan

The Prorocentrum species, which are primarily marine, are distributed worldwide and occur in ocean, neritic, and littoral environments. Prorocentrum is either a planktonic or benthic genus, with some species possibly being both. Until now, about 35 species had been reported including two that are fresh-water. Some species contain toxic substances. As one of many currently active studies, we collected P. vietnamensis sp. nov. from Hon M~, Gulf of Tongkin, Vietnam. Based on its cell shape, smooth valve surface, arrangement of valves and marginal pores, plus characteristics of the central pyrenoid, we propose that P. vietnamensis is a new species. Its attributes include straight cell sides that are parallel to each other, as well as anterior and posterior areas with rounded ends that form a short, rod-shaped cell that is unique to this species.

Keywords: morphology, Prorocentrum vietnamensis, taxonomy, Vietnam

Prorocentrum species are distributed worldwide and are important ecosystem components (Steidinger, 1983; Faust, 1997). These species, which are mostly marine or estuarine (Dodge, 1975; Croome and Tyler, 1987; Faust, 1997), can be planktonic, benthic, or both (Fukuyo, 1981; Dodge, 1982; Faust, 1991). None of the reported species have any known fossil records (Fen- some et al., 1993), nor do form cysts.

Prorocentrum (Ehrenberg, 1833) is one of the oldest taxa. Originally, Prorocentrum Ehrenberg and Exuviaella Cienkowski were distinguished by the presence or absence of an apical spine (Schiller, 1933). However, Ab6 (1967) suggested that both these genera could be placed under Prorocentrum, stressing that no taxonomic demarcation existed, because many intermediate forms and one incompletely explored aberrant had been recorded. Later, Dodge (1975) revised the genus Pro- rocentrum to include Exuviaella, while also reducing 64 known species to 21 and dividing the genus into five sections according to morphological characteris- tics. Those groupings were based on the existence of valve ornamentation (i.e., spinules, depressions, tri- chocyst pores), anterior spines, and cell shape. Fol- lowing that revision, 16 benthic and 2 freshwater species of Prorocentrum were newly described (Fukuyo, 1981; Croome and Tyler, 1987; Faust, 1997). Steidinger and Tangen (1996) then further differentiated the spe- cies of this genus according to size and shape, presence

*Corresponding author; fax +82-2-395-1895 e~mail jhlee@smu.ac.kr

of apical process, shape of periflagellar area, number and pattern of periflagellar plates, number and size of aerolae or poroids, pore pattern, and markings on intercalary bands. Recently, some species of Prorocen- trum have been found to contain a ciguatera-related toxin and okadaic acid (Murakami et al., 1982; Taylor et al., 1995). In the study presented here, we describe a new species, Prorocentrum vietnamensis, that was obtained in Vietnam coastal waters. This species is distinguished by its cell shape as well as the number and arrangement of valve and marginal pores.

MATERIALS A N D M E T H O D S

We used a 20 ~m mesh-sized plankton net to col- lect samples of unidentified Prorocentrum at a 10-m depth at Hon M6, Gulf of Tongkin (18"74'54"N, 105"83'85"E), Vietnam, in October of 1997. Taxonomic observations were made under a light microscope with differential interference contrast optics. The valves were examined after separating the theca in a sodium hypochlorite solution and staining it with chloral hydrate KI-12 (Yoo et al., 2000).

RESULTS A N D D I S C U S S I O N

Prorocentrum vietnamensis Yoo and Fukuyo sp. nov. (Fig. 1)

Diagnosis: Cellulae photosyntheticae, brevis bacilli-

129

130 Yoo et al. J. Plant Biol. Vol. 47, No. 2, 2004

formis, 42 to 50 pm Iongae et 36 to 42 ~tm latae. Uterque valvae poris 58 to 72 centralibus et 65 to 75 marginal- ibus. Apex valvae dextrae area periflagellare V-formata latae. Porus flagellaris et porus auxiliaris inaequalis. Porus flagellaris magnus et porus apicalis parvulus et sine spina apicale et vollum apicale. Nucleus in regione postica cellulae. Pyrenoides in regione centralis.

Type locality: Vietnam. At Hon M6 in the Gulf of Tongkin; species associated with floating detritus, October 1997. Mr. Chu Van Thuoc of the Haiphong Institute of Oceanology, National Center for Natural Science and Technology of Vietnam.

Holotype: Slide No. Y4404 (Fig. 1-1), deposited at the Research Institute of Marine Science and Technol- ogy, Korea Maritime University.

Isotype: Y4407 (Fig. 1-2), Y4411 (Fig. 1-3), Y4414 (Fig. 1-4). Research Institute of Marine Science and

Figure 1. Light microscopy with differential interference con- trast optics of Prorocentrum vietnamensis sp. nov.. (1) Cells are short and rod-shaped, and have straight, parallel sides. (2) Right valve (R), periflagellar area at anterior cell end; Left valve (L), anterior end of left valve is asymmetrical and slightly concave. Arrow indicates pyrenoid in center of valve. (3, 4) Unevenly distributed valve pores. Center of valve is devoid of pores, and evenly spaced marginal pores are located at mar- gin of cell (arrow, valve pore; arrow head, marginal pore).

Technology, Korea Maritime University. Etymology: Designating the origin of the collection

area. Prorocentrum vietnamensis is about medium in size

compared with other species in this genus. It is short and rod-shaped in its valve view, and has very straight sides (Fig. 1-1 ). The thecal surfaces of the two valves are smooth except for the pore openings. Valve pores, which number 58 to 72 per valve, are distributed unevenly except in the central area (Fig. 1-3). Marginal pores are generally rod-shaped and evenly spaced in a row on the cell flange. The number of marginal pores ranges from 65 to 75 on each valve (Fig. 1-3 and 1-4). The anterior end of the cell is indented; the right valve has a broad V-shaped depression on the periflagellar area (Fig. 1-1 and 1-4). The anterior end of the left valve is irregularly shaped, having a flat to slightly concave formation (Fig. 1-2). P. vietnamensis has a clear pyrenoid in the center of each valve, and also possesses a pos- terior nucleus.

Dodge (1975) revised this genus based on the pres- ence or absence of valve ornamentation, anterior spines, and cell shape. Faust (1997) further rearranged 18 species of benthic Prorocentrum according to cell size, ornamentation, pore arrangement, apical area, and metacytic zone. Some dinoflagellate groups cannot be easily delineated by cell shape. For example, the Alexandrium species are almost impossible to distin- guish only by shape (Balech, 1995; Taylor et al., 1995), whereas the Ceratium species have extensive mor- phological variations according to growth stage and hab- itat (Reinecke, 1973). Nevertheless, except for some similar species such as Prorocentrum lima, P. minimum, and P. concavum (Hulburt, 1965; Yoo, 2004), cell shape is the most important taxonomic key for classifying members of this genus.

The Prorocentrum species previously described had cells that were ovate, rotundate, elliptic, cordiform, or lanceolate (Dodge, 1975; Fukuyo, 1981; Faust, 1997). However, P. vietnamensis has short, rod-shaped cells with round anterior and posterior ends, as well as parallel cell sides that differ greatly from the currently known, general shape for this genus (Table 1). Those species with pore arrangements on the surface that exclude the central area include P. vietnamensis sp. nov., P. caribbaeum, P. maculosum, P. emaginatum, P. lima, and P. concavum (Fukuyo, 1981 ; Faust, 1993a, b). The first three are radially arranged types while P. concavum is distinguished by its 1,000 to 1,100 areolae per valve and a lack of marginal pores (Faust, 1990). Although Prorocentrum lima shares some common characteris- tics with P. vietnamensis, e.g., valve arrangement, mar-

Prorocentrum vietnamensis sp. nov . ( P r o r o c e n t r a c e a e D i n o p h y t a ) 131

Table 1. C o m p a r i s o n o f m a j o r m o r p h o l o g i c a l character is t ics in s o m e mar ine Prorocentrum species. Charac ters are des ignated as

present (+ ) or absent (-) . Shape; oval o r ova te (1), py r i f o rm (2), round ish (3), b road ly o b l o n g (4), t r iangular (5), short rod (6), poster ior

a t t e n u a t i o n (7), a n d pos ter ia l e n d is p o i n t e d (8); ap ica l sp ine (9), va l ve o n a m e n t a i o n ; a r e o l a t e (10), r e t i cu l a te (11), s m o o t h

dp ress ion (12), s m o o t h (13), a n d va lve sp ine (14), va l ve p o r e (15), rad ia l l y a r r a n g e d (16), s ca tee ted p o r e a r ranged (17) a n d

u n c o m p l i c a t e d l l y a r r a n g e d .

M o r p h o l o g i c a l Charac to rs

species 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Lenth

R arenarium - - + . . . . . . . . . + - + - + - 3 0 - 3 2

R balt icum + - + . . . . . + . . . . + + - + - 9 - 1 0

P. belzeanum + . . . . . . . . + . . . . + - + - 5 5 - 6 0

R caribbaeum - + . . . . + - + - - + - - + + - - 4 0 - 4 5

R compressum + - + . . . . . + - - + . . . . . . 3 0 - 5 0

P. concavum + . . . . . . . . . . + - - + - - - 5 0 ~ 5 5

P. dentatum - - - + - - - + . . . . . + . . . . 3 6 - 6 0

R elegans + . . . . . . . . . . . + - + - - + 15 ~ 2 0

P. emarginatum + . . . . . . . + - - - + - + + - - 3 0 - 4 0

P. gracil - + . . . . + + + - - + - - + - + - 4 0 ~ 60

P. hoffmannianum + + . . . . . . . + . . . . + - + - 4 5 ~ 5 5

P. l ima + . . . . . . . . . . . + - + - + - 3 1 - 4 7

P. maculosum + . . . . . . . . . . + - - + - + - 4 0 ~ 5 0

R mexicanum + . . . . . . + - - + - - + + - - 3 0 - 3 8

R micans - + . . . . + + + - - + - - + + - - 3 5 ~ 7 0

R min imum + - - - + - - - + . . . . + + - + - 1 4 ~ 2 2

R reticulatum + . . . . . . . . . + - - - + - + - 5 5 ~ 6 0

R ruetzlerianum + - + . . . . . . + . . . . + - + - 2 8 - - 3 5

R sabulosum + - + . . . . . . + . . . . + - - - 4 8 - 5 0

R sculptile + . . . . . . . + - - + + - + - - - 3 2 - 3 7

R triestinum - + . . . . + + + - - - + - + - + - 1 8 - - 2 2

R tropicalis + . . . . . . . . . . + - - + - + - 5 0 - - 5 5

R venetum . . . . + - - - + - - - + - + - - + 1 9 ~ 2 1

R vietnamesis . . . . . + . . . . . . + - + - + - 4 2 - 5 0

Sources o f i n f o r m a t i o n : D o d g e (1975) , T o l o m i o and C a v o l o (1985) , S te id inger and Tangen (1996) , Faust (1997) , and th is paper .

g ina l p o r e s , a n d a c l e a r c e n t r a l p y r e n o i d , t h e f o r m e r is

c l e a r l y d i s t i n g u i s h e d b y i ts w i d e o v o i d - s h a p e d c e n t r a l

i n f e r i o r a r e a . In f ac t , R v ie tnamens is is t h e o n l y s p e c i e s

in t h e g e n u s h a v i n g s h o r t , r o d - s h a p e d ce l l s w i t h v e r y

s t r a i g h t s ides .

ACKNOWLEDGEMENTS

W e w o u l d l i k e t o t h a n k K i i r s t e n F l y n n a t t h e C e n t e r

f o r S c i e n c e E d u c a t i o n f o r Eng l i sh r e v i s i o n , a n d Dr .

R i c h a r d R. P e t e r s e n a t P o r t l a n d S t a t e U n i v e r s i t y f o r

c r i t i c a l r e v i e w a n d c o m m e n t s o n t h i s d r a f t .

Rece i ved Feb rua ry 5, 2 0 0 4 ; a c c e p t e d M a r c h 17, 2 0 0 4 .

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