level must await studies of additional genes.
Description
on cell body and flagella and the long basal bodies characteristic of prasinophyceans . x30 ,000. (From Moestrup and Ettl , 1979) 1254 PRASINOPHYCE Key Characters 1. Flagella and cell body covered with sub- microscopic organic scales manufactured in the cisternae of the Golgi apparatus (Figs . 1-5). The flagella may carry up to three layers of scales, of three different types, in addition to hair-shaped ones , which occur in two opposite rows (Figs. 2, 3A) . The same flagellum may sometimes carry more types of hair scales , and other hair-like scales may be present on th e cell surface near the insertion of the flagella . Mesostigma lacks hair-shaped scales . In the most complex species (e .g. Pyramimonas or Tetraselmis) the underlayer scales on the flagella are very small , almost square and arranged in 24 longitudinal rows (Fig. 2) . Two nearly opposite pairs of these are slightly different and the hair scales insert in these rows (Fig . 2) . In some genera the underlayer scales are covered by larger scales in nine longitudinal rows, in others again by rod -like scales in 24 double rows . Body scales occur in up to four layers, each layer usually containing only a single type of scale (Fig. 38). A few genera have naked cells or the scales fuse immediately after release into a waIl-like periplast (formerly known as a 'theca'. Cells usually possess 1, 2, or 4 flagella . Some lack flagella , but a few species of Pyramimonas have 8 or in one species 16 flagella (the only known 1 6 - flagellated photosynthetic flagellate). The flagella on a cell are morphologically identical (isokont) in all genera except in a few genera, e.g. Nephroselmis and Pseudo-scourfieldia , which have anisokont flagella, i.e. the flagella differ in length but are otherwise identical (Figs . 19 ,20). In Mantoniella one of the two flagella is very short and knob-like (Fig . 138), and in Micromonas , the smallest known flagellate, only the proximal part of the (single) flagellum contains a typical axoneme (Fig. 15). The flagella are inserted apically (e.g. Pyramimonas, Tetraselmis) , laterally (e .g. Nephroselmis) or posteriorly (Pseudoscourfieldia). In most genera the flagellar basal bodies are parallel and notably long compared to other green algae (Fig . 1 ) . Multilayered structures resembling those of some other protists and charophycean green algae are associated with one or two microtubular flagellar roots in some members of the Pyramimonadales AE 2. The scales contain 2-keto-sugar acids, a compound not found in any other algal flagellates . 3. Cells contain a single (in a few genera two), green or yellow-green chloroplast , generally with one, rarely more pyrenoids . A few species lack pyrenoids. An eyespot is usually present , occasionally two . The chloroplasts contain chlorophylls a and b, prasinoxanthin (in some genera), Mg 2,4 D (in some genera), and other pigments such as lutein , carotenes , zeaxanthin , violaxanthin, neoxanthin , uriolide, and siphonaxanthin . c.D. S~m prasinophycean Pyramimonas mitra unfolded to show the 24 rows of minute square scales , two opposite pairs of which are arranged in exact longitudinal rows . The small scales are overlain by nine rows of limuloid scales. Hair-shaped scales emanate from the interspace between every third scale in the longitudinal rows of scales , but are not exactly opposite . x42 ,000. (From Moestrup and Hill , 1993) . 4. All species are uninuclear 5. Some species form ejectile organelles or mucilaginous bodies. 6. Freshwater species possess a contractile vacuole system . PRASINOPHYCEAE Nephro form r / 10. Mo marine epiphy -. \ water. .. ; O 11. Ce morpho cannot .. ..' \..·- ''~ electr . '-· ,. ,. ,. - •·. ' I ' .... , .. ~ ,:. ... .' , ,, A I 8 through flagellum , showing three layers of scales , in addition to two alm ost opposite rows of hair-shaped scales . x60 ,000 . B. Tangentia l section of the cell surface showing the scaly periplast. Scal es of the innermost layer are very small and square and overlain by scal es shaped somewhat like a Maltese cross. The covere outermost layer co mpri ses larger, stellate scales . th e c x36 ,000 . (Both figures from Moes trup and Ettl , 1979) and Mo 7. All known species are photosynthetic , and one, Cymbomonas, here considered the most primitive prasinophycean , has been found with food vacuoles containing other eukaryotes (Throndsen , 1 9 8 8) (Fig. 5). This indicates mixotrophy , presently the only case of mixotrophy found in any green alga. 1. Fla The mixotrophic habit is an indication that the sca ancestors of green algae were heterotrophic .. flagellates . 1 ·. F 8. The cells store starch in the chloroplast(s). ty 9. Reproduction is by longitudinal fission. Isogamic sc sexual reproduction has been described in selmis (Suda et al. , 1989). Many species esting cysts . st prasinophyceans are members of the plankton, and a few are benthic or tic . A small number are confined to fresh Many are very widely distributed . ll shape , number of flagella and scale logy are diagnostic features . Several species be identified without the aid of transmission on microscopy of the scales . ". .. l ~- . Pyra mimonas te tra rh y ncus . The ce ll surfa ce i s d by three layers of sca les , all manufactured in i stern ae of th e Golgi apparatus. X24 ,000 . (Walne estrup , 1990 Original ) b LM TEM 9 Q gella with square or nearly square underlayer les often overlain by other scale types ..... ... ... ... .... .. ... .... .. ... ...... ... ... .... ... .. ...... ...... ........ 2 lagella lack square underlayer scales . Only one pe of flagellar scale present in addition to hair ales .. .... ......... ... ....... ......... ... .. .. .. . Mamiellales 1256 PRASINOPHYCEAE 2. Underlayer scales covered with rod-shaped scales in 24 double rows ...... Chlorodendrales 2 '. Underlayer scales covered with limuloid scales or without additional layers of scales .. .. .. .... .. .. .. . .. ..... ...... ...... ...... .... ..... ... ... . Pyramimonadales
Type species
Figures
No linked figures.
Raw text
on cell body and flagella and the long basal bodies characteristic of prasinophyceans . x30 ,000. (From Moestrup and Ettl , 1979) 1254 PRASINOPHYCE Key Characters 1. Flagella and cell body covered with sub- microscopic organic scales manufactured in the cisternae of the Golgi apparatus (Figs . 1-5). The flagella may carry up to three layers of scales, of three different types, in addition to hair-shaped ones , which occur in two opposite rows (Figs. 2, 3A) . The same flagellum may sometimes carry more types of hair scales , and other hair-like scales may be present on th e cell surface near the insertion of the flagella . Mesostigma lacks hair-shaped scales . In the most complex species (e .g. Pyramimonas or Tetraselmis) the underlayer scales on the flagella are very small , almost square and arranged in 24 longitudinal rows (Fig. 2) . Two nearly opposite pairs of these are slightly different and the hair scales insert in these rows (Fig . 2) . In some genera the underlayer scales are covered by larger scales in nine longitudinal rows, in others again by rod -like scales in 24 double rows . Body scales occur in up to four layers, each layer usually containing only a single type of scale (Fig. 38). A few genera have naked cells or the scales fuse immediately after release into a waIl-like periplast (formerly known as a 'theca'. Cells usually possess 1, 2, or 4 flagella . Some lack flagella , but a few species of Pyramimonas have 8 or in one species 16 flagella (the only known 1 6 - flagellated photosynthetic flagellate). The flagella on a cell are morphologically identical (isokont) in all genera except in a few genera, e.g. Nephroselmis and Pseudo-scourfieldia , which have anisokont flagella, i.e. the flagella differ in length but are otherwise identical (Figs . 19 ,20). In Mantoniella one of the two flagella is very short and knob-like (Fig . 138), and in Micromonas , the smallest known flagellate, only the proximal part of the (single) flagellum contains a typical axoneme (Fig. 15). The flagella are inserted apically (e.g. Pyramimonas, Tetraselmis) , laterally (e .g. Nephroselmis) or posteriorly (Pseudoscourfieldia). In most genera the flagellar basal bodies are parallel and notably long compared to other green algae (Fig . 1 ) . Multilayered structures resembling those of some other protists and charophycean green algae are associated with one or two microtubular flagellar roots in some members of the Pyramimonadales AE 2. The scales contain 2-keto-sugar acids, a compound not found in any other algal flagellates . 3. Cells contain a single (in a few genera two), green or yellow-green chloroplast , generally with one, rarely more pyrenoids . A few species lack pyrenoids. An eyespot is usually present , occasionally two . The chloroplasts contain chlorophylls a and b, prasinoxanthin (in some genera), Mg 2,4 D (in some genera), and other pigments such as lutein , carotenes , zeaxanthin , violaxanthin, neoxanthin , uriolide, and siphonaxanthin . c.D. S~m prasinophycean Pyramimonas mitra unfolded to show the 24 rows of minute square scales , two opposite pairs of which are arranged in exact longitudinal rows . The small scales are overlain by nine rows of limuloid scales. Hair-shaped scales emanate from the interspace between every third scale in the longitudinal rows of scales , but are not exactly opposite . x42 ,000. (From Moestrup and Hill , 1993) . 4. All species are uninuclear 5. Some species form ejectile organelles or mucilaginous bodies. 6. Freshwater species possess a contractile vacuole system . PRASINOPHYCEAE Nephro form r / 10. Mo marine epiphy -. \ water. .. ; O 11. Ce morpho cannot .. ..' \..·- ''~ electr . '-· ,. ,. ,. - •·. ' I ' .... , .. ~ ,:. ... .' , ,, A I 8 through flagellum , showing three layers of scales , in addition to two alm ost opposite rows of hair-shaped scales . x60 ,000 . B. Tangentia l section of the cell surface showing the scaly periplast. Scal es of the innermost layer are very small and square and overlain by scal es shaped somewhat like a Maltese cross. The covere outermost layer co mpri ses larger, stellate scales . th e c x36 ,000 . (Both figures from Moes trup and Ettl , 1979) and Mo 7. All known species are photosynthetic , and one, Cymbomonas, here considered the most primitive prasinophycean , has been found with food vacuoles containing other eukaryotes (Throndsen , 1 9 8 8) (Fig. 5). This indicates mixotrophy , presently the only case of mixotrophy found in any green alga. 1. Fla The mixotrophic habit is an indication that the sca ancestors of green algae were heterotrophic .. flagellates . 1 ·. F 8. The cells store starch in the chloroplast(s). ty 9. Reproduction is by longitudinal fission. Isogamic sc sexual reproduction has been described in selmis (Suda et al. , 1989). Many species esting cysts . st prasinophyceans are members of the plankton, and a few are benthic or tic . A small number are confined to fresh Many are very widely distributed . ll shape , number of flagella and scale logy are diagnostic features . Several species be identified without the aid of transmission on microscopy of the scales . ". .. l ~- . Pyra mimonas te tra rh y ncus . The ce ll surfa ce i s d by three layers of sca les , all manufactured in i stern ae of th e Golgi apparatus. X24 ,000 . (Walne estrup , 1990 Original ) b LM TEM 9 Q gella with square or nearly square underlayer les often overlain by other scale types ..... ... ... ... .... .. ... .... .. ... ...... ... ... .... ... .. ...... ...... ........ 2 lagella lack square underlayer scales . Only one pe of flagellar scale present in addition to hair ales .. .... ......... ... ....... ......... ... .. .. .. . Mamiellales 1256 PRASINOPHYCEAE 2. Underlayer scales covered with rod-shaped scales in 24 double rows ...... Chlorodendrales 2 '. Underlayer scales covered with limuloid scales or without additional layers of scales .. .. .. .... .. .. .. . .. ..... ...... ...... ...... .... ..... ... ... . Pyramimonadales