be named Raphidomonadida based upon the

Description

validation of the algal class name Raphidophyceae by Silva (1980) . The group has been reviewed by Fott (1968) and by Heywood (1980 , 1990) . A useful taxo nomic guide to th e marine species has been provided by Fukuyo et al. (1990). KEY CHARACTERS 1. Two flagella of unequal length arise from a shallow pit at or near the cell apex. The anteriorly directed flag ellum is approximately as long as the cell and bears stiff , tubular hairs (Heywood , 1980) resembling mastigonemes of other "heterokont" algae (see 19 below) . The posteriorly directed flagellum is up to twice the length of the cell and lacks appendages (Fott , 1968) . Most raphidomonads DIDA contain an extensive flagellar root system , one part of which is a layered structure that appears to be characteristic of the order (Vesk and Moestrup , 1987) . 2 . During locomotion the flagellum that bears tubular mastigonemes projects anteriorly and beats rapidly . The other flagellum trails posteriorly and moves only occasionally . 3. Chloroplast-containing and color-less forms have been described (Fott , 1968) ; the latter are omitted here since evidence is lacking to warrant their inclusion in the order; some recent observations argue against such inclusion . Pigmented genera have many discoid or plano-convex chloroplasts up to 3 x 5 ~m in size in the peripheral layer (termed "ectoplasm" by some authors). Pyrenoids are absent in Gonyostomum , Merotricha , and Vacuo/aria , but are present in some of th e marine species . Chloroplast lamellae consist of three thylakoids between which frequ ent interconnections occur ; a girdle lamella is is present in most species , but absent in some spec ies (Heywood, 1977; Mignot , 1976) . 4 . Chloroplasts may vary in color from bright green to yellow-green to yellow-brown. Ch lorophylls a and c are present (Guillard and Lorenzen , 1972). In Gonyostomum semen and Vacuo/aria virescens (freshwater species) the dominant carotenoids are diadinoxanthin dinoxanthin, B,B-carotene, and hetero~ xanthin , while in Chattonel/a japonica and Fibrocapsa japonica (marine species) the domi nant carotenoids are fucoxanth in fucoxanthinol , B,B-carotene , and viol a~ xanthin (Fiksdahl et al ., 1984) . 5. The chloroplast-containing raphidomonads are photoautotrophic ; possibly some species also utilize heterotrophy . 6. Reserve food material appears to be oil , present as osmiophil ic spheres in the cytop lasmic matrix and in the chloroplast stroma. Lipid-containing structures in Heterosigma akashiwo show diurnal changes (Wada et al ., 1987). The major sterol of Heterosigma akashiwo and Chattonella antiqua is 24-ethylcholesterol (Nichols et al. , 1987) . RAPHIDOMO 7. No eyespots are present. 8. No flagellar swellings have been observed. 9. All species are monads. Cells are ovoid to almost spherical , occasionally pyriform , occasionally lanceolate. They are often flattened dorsoventrally with a furrow on the ventral surface. Some species (e .g. Vacuo/aria virescens , q.v.) may be variable in shape (Fott , 1968 ; Spencer , 1971 ). The variable size and morphology of Chattonella, which made species recognition problematic , has led to the use of monoclonal antibodies for identification (Hiroishi et al. , 1988) . 10. A cell wall is absent , but some species secrete mucus and form palmellae (Heywood , 1980 ) . 11. A contractile vacuole occurs in freshwater genera ( Gonyostomum , Merotricha , and Vacuo/aria) , but is absent in the marine genera. The contractile vacuole may reach 1 0 ~m diameter; it lies between the nucleus and the region of flagellar insertion . In Vacuo/aria virescens a large Golgi body occurs between the anterior surface of the nucleus and the contractile vacuole ; it is thought to be involved in osmoregulation (Heywood , 1978b) . 12. Th e nucleus is large (to 20 ~m long) and contains one or more nucleoli ; interphase chromatin occurs as distinct fine threads (Heywood , 1980; Hovasse , 1945) . Chromosome numbers are large : 97 ± 2 in Vacuo/aria virescens and 65-75 in Gonyos tomum semen (Heywood , 1980) ; chromosome length at metaphase varies from 1 to 12 ~m . In Vacuo/aria virescens kinetochores are present, attached to spindle microtubul es; the latter form around the flagellar basal bodies and enter the nucleus at prophase through polar gaps in the nuclear envelope (Heywood, 1978a). Condensation of chromosomes , dispersion of nuclei , and formation of a metaphase plate of chromosomes resemble similar events in the "classical mitosis " of other organisms. Peculiar features of mitosis in Vacuo/aria virescens are that Golg i bodies and contractile vacuoles occur near the poles of the mitotic nucleus and the original nuclear envelope remains intact until telophase , by which time a new nuclear envelope has begun to form around the daughter nuclei (Heywood , 1978a). 13. Asexual reproduction is by binary fission . Possible sexual reproduction has been reported for Chattonella marina (Subrahmanyan , 1954) . Microfluoro-metric studies of Chattonella antiqua and Chattonella marina suggest a diplontic life cycle in which meiosis precedes encystment (Yamaguchi and lmai , 1994) . 14. Some species form cysts, probably in response to nutrient depletion (Nakamura and Umemori , 1991 ). In Chiarella antiqua , silicon predominates in the cyst wall with magnesium and aluminum also being present (Meksumpun et al. , 1994). 15. Extrusomes (trichocysts or mucocysts) occur in most (but not all) species. The rod- shaped trichocysts of Gonyostomum can discharge mucilaginous threads for distances in excess of 100 ~m . The spherical mucocysts of Vacuo/aria secrete mucilage around the cell. 16 . Freshwater species frequently occur in the plankton , among aquatic plants or immediately above the benthic muds of bogs , ponds , and lakes, the pH of which ranges from 4.0 to 7 .0 . Chattonella , Fibrocapsa , Heterosigma, and 0/isthodiscus occur in marine environments. 17. Diel vertical migrations between lower layers at night where inorganic nutrients are more abundant and euphotic zones during the day, have been observed in both freshwater (Gronberg et al ., 1988) and marine (Watanabe et al. , 1988) species. In Heterosigma akashiwo, phosphate taken up at night in deeper water was accumulated as polyphosphate and subsequently used for photophosphorylation in the photic layer (Watanabe , 1988) . 8. Raphidomonads may occur in large numbers causing mortality to marine organisms (Subrahmanyan, 1954) or health problems to bat hers (Cronberg et a l., 1988) . Red tides of raphidomonads may be co ntrol led by vi ruses (Nagasaki et a l., 1 994) or by hetero t roph preda ti o n (Nakam ura et al. , 1992) . 19 . U ltr ast ru ctura l a n d b iochemica l evidence suggests that the closest relative of the raphidomonads are members of the algal division Heterokontophyta sensu Leedale (see van den Hoek , 1978) which a lso have heterokont flage lla , tubu la r mastigonemes , c hl oroph yll s a and c , thr ee -thy lakoid lamellae in th e chlorop las ts , and oth er common fea tu res . In t hi s book those organisms a re represented by t he Chrysomonad ida (q.v .) (and Heteroc hlo rida) , but they also include severa l major alga l groups such as the diatoms and brown seaweeds. ARTIFICIAL KEY TO SELECTED GENERA b LM TEM 1. Freshwater forms , contract ile vacuole present ....... ......... ........ ..... ..... ... ... ..... .. 2 1'. Brack ish or mari ne forms, con tractile vacuole absent. .. ... ....... .... ..... ....... ... .... 4 2. Ce lls with rod-shap ed tric hocysts ..... . 3 2 ' . Cells with spher ica l mucocysts but lacking rod-sh aped trichocyst .......... .. ........ ... .... ............. .... .... ...... Vacuo/aria 3. Trichocysts mainly in swo llen anterior reg ion of cells ; flag ella arise on latera l surface immed iately below t hi s regio n .. .... .... .. .. ... ......... .... Merotricha 3'. Trichocysts around cell periphery (but may be local ly dense at ce ll anterioa nd/or poste rior ); fl age ll a ar ise near ce ll apex .. ... ... ........ ............ Gonyostomum 4. Fl age ll a arise at or near ce ll apex ....... .......... ....... ........... ...... ..... ... ......... 4 '. Flagella arise sub -ap ical ly to lateral ly on ven tral surface ......... .... ............ ..... 6 ADIDA 5. Pro minent rod-s haped trichocysts pre dominantly present at cell posterior ........ .. ........... .... ... .... ... .. .. .... Fibrocapsa 5' . Mucocysts if prese nt and cons pic uous are not predominan tly groupe d at the ce ll posterio r .. ... .. .. ... .. .... . Chattonella 6. Ch lorop lasts are yellowish-brown to brown ; during swimming , cel l rotates heli ca ll y ................... ..... . Heterosigma 6 ' . Chlo roplasts are yel lowish -green to green; during swimm ing , cell moves without rotation ... ........ 0/isthodiscus Ge nus Chattonella Bi echeler , 1936 Cel l shape is variab le both withi n and between spec ies ; cells are frequently obovate , but vary from globos e to lanceolate , with th e latt er oft en possess ing a distinct ca udus; 2 flagella , about the same length as the ce ll ; many chloroplasts , often present as a single laye r below the plasmalemma , give th e ce ll a ye ll ow-brown co lor ; pyrenoids prese nt in some species ; some species form cysts ; m uc ocy st s p rese nt in some species ; co nt rac til e v ac u o le absen t ; sa lin e , peri odica ll y abundant , causes red tides ; syno nymous with Hornellia (Subra hmanyan , 1954) . See Biec heler (1936) ; Fu kuyo et al. (1990) ; Mignot ( 1976) . T Y PE SPECIE S : C hattonella subsalsa Biec hele r, 1936 (Fig . 6) . Cell 30-5 0 x 15- 25 ~m ; brac kis h and ma rine hab itats, often rich in organic matter (Mignot , 197 6); may reac h hi gh dens ities; 6 other species have be e n recog n iz ed by Fuk uyo et a l, ( 199 0 ): C . antiqua, C. globosa, C. marina (synonymous with Hornellia marina Subra hmanyan) , C . minima, C. ovata, and C. verrucu/osa .

Type species

Figures

Raw text

validation of the algal class name Raphidophyceae
by Silva (1980) . The group has been reviewed
by Fott (1968) and by Heywood (1980 , 1990) .
A useful taxo nomic guide to th e marine species
has been provided by Fukuyo et al. (1990).
KEY CHARACTERS
1. Two flagella of unequal length arise from a
shallow pit at or near the cell apex. The
anteriorly directed flag ellum is approximately
as long as the cell and bears stiff , tubular
hairs (Heywood , 1980) resembling
mastigonemes of other "heterokont" algae (see
19 below) . The posteriorly directed flagellum
is up to twice the length of the cell and lacks
appendages (Fott , 1968) . Most raphidomonads
DIDA
contain an extensive flagellar root system , one
part of which is a layered structure that
appears to be characteristic of the order (Vesk
and Moestrup , 1987) .
2 . During locomotion the flagellum that bears
tubular mastigonemes projects anteriorly and
beats rapidly . The other flagellum trails
posteriorly and moves only occasionally .
3. Chloroplast-containing and color-less
forms have been described (Fott , 1968) ; the
latter are omitted here since evidence is
lacking to warrant their inclusion in the
order; some recent observations argue against
such inclusion . Pigmented genera have many
discoid or plano-convex chloroplasts up to 3 x
5 ~m in size in the peripheral layer (termed
"ectoplasm" by some authors). Pyrenoids are
absent in Gonyostomum , Merotricha , and
Vacuo/aria , but are present in some of th e
marine species . Chloroplast lamellae consist
of three thylakoids between which frequ ent
interconnections occur ; a girdle lamella is is
present in most species , but absent in some
spec ies (Heywood, 1977; Mignot , 1976) .
4 . Chloroplasts may vary in color from bright
green to yellow-green to yellow-brown.
Ch lorophylls a and c are present (Guillard and
Lorenzen , 1972). In Gonyostomum semen and
Vacuo/aria virescens (freshwater species) the
dominant carotenoids are diadinoxanthin
dinoxanthin, B,B-carotene, and hetero~
xanthin , while in Chattonel/a japonica and
Fibrocapsa japonica (marine species) the
domi nant carotenoids are fucoxanth in
fucoxanthinol , B,B-carotene , and viol a~
xanthin (Fiksdahl et al ., 1984) .
5. The chloroplast-containing raphidomonads
are photoautotrophic ; possibly some species
also utilize heterotrophy .
6. Reserve food material appears to be oil ,
present as osmiophil ic spheres in the
cytop lasmic matrix and in the chloroplast
stroma. Lipid-containing structures in
Heterosigma akashiwo show diurnal changes
(Wada et al ., 1987). The major sterol of
Heterosigma akashiwo and Chattonella antiqua
is 24-ethylcholesterol (Nichols et al. , 1987) .
RAPHIDOMO
7. No eyespots are present.
8. No flagellar swellings have been observed.
9. All species are monads. Cells are ovoid to
almost spherical , occasionally pyriform ,
occasionally lanceolate. They are often
flattened dorsoventrally with a furrow on the
ventral surface. Some species (e .g. Vacuo/aria
virescens , q.v.) may be variable in shape
(Fott , 1968 ; Spencer , 1971 ). The variable
size and morphology of Chattonella, which made
species recognition problematic , has led to the
use of monoclonal antibodies for identification
(Hiroishi et al. , 1988) .
10. A cell wall is absent , but some species
secrete mucus and form palmellae (Heywood ,
1980 ) .
11. A contractile vacuole occurs in freshwater
genera ( Gonyostomum , Merotricha , and
Vacuo/aria) , but is absent in the marine
genera. The contractile vacuole may reach 1 0
~m diameter; it lies between the nucleus and
the region of flagellar insertion . In Vacuo/aria
virescens a large Golgi body occurs between the
anterior surface of the nucleus and the
contractile vacuole ; it is thought to be involved
in osmoregulation (Heywood , 1978b) .
12. Th e nucleus is large (to 20 ~m long) and
contains one or more nucleoli ; interphase
chromatin occurs as distinct fine threads
(Heywood , 1980; Hovasse , 1945) .
Chromosome numbers are large : 97 ± 2 in
Vacuo/aria virescens and 65-75 in
Gonyos tomum semen (Heywood , 1980) ;
chromosome length at metaphase varies from 1
to 12 ~m . In Vacuo/aria virescens
kinetochores are present, attached to spindle
microtubul es; the latter form around the
flagellar basal bodies and enter the nucleus at
prophase through polar gaps in the nuclear
envelope (Heywood, 1978a). Condensation of
chromosomes , dispersion of nuclei , and
formation of a metaphase plate of chromosomes
resemble similar events in the "classical
mitosis " of other organisms. Peculiar features
of mitosis in Vacuo/aria virescens are that
Golg i bodies and contractile vacuoles occur
near the poles of the mitotic nucleus and the
original nuclear envelope remains intact until
telophase , by which time a new nuclear
envelope has begun to form around the daughter
nuclei (Heywood , 1978a).
13. Asexual reproduction is by binary fission .
Possible sexual reproduction has been reported
for Chattonella marina (Subrahmanyan ,
1954) . Microfluoro-metric studies of
Chattonella antiqua and Chattonella marina
suggest a diplontic life cycle in which meiosis
precedes encystment (Yamaguchi and lmai ,
1994) .
14. Some species form cysts, probably in
response to nutrient depletion (Nakamura and
Umemori , 1991 ). In Chiarella antiqua ,
silicon predominates in the cyst wall with
magnesium and aluminum also being present
(Meksumpun et al. , 1994).
15. Extrusomes (trichocysts or mucocysts)
occur in most (but not all) species. The rod-
shaped trichocysts of Gonyostomum can
discharge mucilaginous threads for distances
in excess of 100 ~m . The spherical
mucocysts of Vacuo/aria secrete mucilage
around the cell.
16 . Freshwater species frequently occur in
the plankton , among aquatic plants or
immediately above the benthic muds of bogs ,
ponds , and lakes, the pH of which ranges from
4.0 to 7 .0 . Chattonella , Fibrocapsa ,
Heterosigma, and 0/isthodiscus occur in
marine environments.
17. Diel vertical migrations between lower
layers at night where inorganic nutrients are
more abundant and euphotic zones during the
day, have been observed in both freshwater
(Gronberg et al ., 1988) and marine
(Watanabe et al. , 1988) species. In
Heterosigma akashiwo, phosphate taken up at
night in deeper water was accumulated as
polyphosphate and subsequently used for
photophosphorylation in the photic layer
(Watanabe , 1988) .
8. Raphidomonads may occur in large
numbers causing mortality to marine
organisms (Subrahmanyan, 1954) or health
problems to bat hers (Cronberg et a l.,
1988) . Red tides of raphidomonads may be
co ntrol led by vi ruses (Nagasaki et a l.,
1 994) or by hetero t roph preda ti o n
(Nakam ura et al. , 1992) .
19 . U ltr ast ru ctura l a n d b iochemica l
evidence suggests that the closest relative of
the raphidomonads are members of the algal
division Heterokontophyta sensu Leedale (see
van den Hoek , 1978) which a lso have
heterokont flage lla , tubu la r mastigonemes ,
c hl oroph yll s a and c , thr ee -thy lakoid
lamellae in th e chlorop las ts , and oth er
common fea tu res . In t hi s book those
organisms a re represented by t he
Chrysomonad ida (q.v .) (and Heteroc hlo rida) ,
but they also include severa l major alga l
groups such as the diatoms and brown
seaweeds.
ARTIFICIAL KEY TO SELECTED
GENERA
b LM TEM
1. Freshwater forms , contract ile vacuole
present ....... ......... ........ ..... ..... ... ... ..... .. 2
1'. Brack ish or mari ne forms, con tractile
vacuole absent. .. ... ....... .... ..... ....... ... .... 4
2. Ce lls with rod-shap ed tric hocysts ..... . 3
2 ' . Cells with spher ica l mucocysts but
lacking rod-sh aped trichocyst .......... ..
........ ... .... ............. .... .... ...... Vacuo/aria
3. Trichocysts mainly in swo llen anterior
reg ion of cells ; flag ella arise on latera l
surface immed iately below t hi s
regio n .. .... .... .. .. ... ......... .... Merotricha
3'. Trichocysts around cell periphery (but
may be local ly dense at ce ll anterioa nd/or
poste rior ); fl age ll a ar ise near ce ll
apex .. ... ... ........ ............ Gonyostomum
4. Fl age ll a arise at or near ce ll apex
....... .......... ....... ........... ...... ..... ... .........
4 '. Flagella arise sub -ap ical ly to lateral ly
on ven tral surface ......... .... ............ ..... 6
ADIDA
5. Pro minent rod-s haped trichocysts
pre dominantly present at cell posterior
........ .. ........... .... ... .... ... .. .. .... Fibrocapsa
5' . Mucocysts if prese nt and cons pic uous
are not predominan tly groupe d at the
ce ll posterio r .. ... .. .. ... .. .... . Chattonella
6. Ch lorop lasts are yellowish-brown to
brown ; during swimming , cel l rotates
heli ca ll y ................... ..... . Heterosigma
6 ' . Chlo roplasts are yel lowish -green to
green; during swimm ing , cell moves
without rotation ... ........ 0/isthodiscus
Ge nus Chattonella Bi echeler , 1936
Cel l shape is variab le both withi n and between
spec ies ; cells are frequently obovate , but
vary from globos e to lanceolate , with th e
latt er oft en possess ing a distinct ca udus; 2
flagella , about the same length as the ce ll ;
many chloroplasts , often present as a single
laye r below the plasmalemma , give th e ce ll a
ye ll ow-brown co lor ; pyrenoids prese nt in
some species ; some species form cysts ;
m uc ocy st s p rese nt in some species ;
co nt rac til e v ac u o le absen t ; sa lin e ,
peri odica ll y abundant , causes red tides ;
syno nymous with Hornellia (Subra hmanyan ,
1954) . See Biec heler (1936) ; Fu kuyo et al.
(1990) ; Mignot ( 1976) .
T Y PE SPECIE S : C hattonella subsalsa
Biec hele r, 1936 (Fig . 6) . Cell 30-5 0 x 15-
25 ~m ; brac kis h and ma rine hab itats, often
rich in organic matter (Mignot , 197 6); may
reac h hi gh dens ities; 6 other species have
be e n recog n iz ed by Fuk uyo et a l, ( 199 0 ): C .
antiqua, C. globosa, C. marina (synonymous
with Hornellia marina Subra hmanyan) , C .
minima, C. ovata, and C. verrucu/osa .