Description
Unicellular algae occurring in 2 very different stages. The main , coccoid , Phycoma stage is spherical , 14-230 J.lm in diameter and surrounded by a double wall . The surface of the wall is smooth , papillose , or poroid and bears 1 or more wings protruding from the surface . The mature Phycoma is initially uninuclear and contains numerous chloroplasts , each with a pyrenoid. Cell divisions give rise to formation of a large number of motile cells , which are released through a slit in the outer wall . Each motile cell possesses 4 flagella , held together as a single , thick 'compound' flagellum behind the sw imming cell . The motile cell contains a chloroplast with a pyrenoid but lacks an eyespot. Extrusomes are also present. All surfaces covered with organ ic scales , the flagella with an underlayer of small square scales overlain by lim uloid ones , in CEAE addition to 2 opposite rows of hair-shaped scales . The cell body has a three-layered scale cover: an inner layer of small square scales and 2 layers of larger, octagonal or nonagonal scales (3-4 types ). The change between Phycoma stage and motile cells is apparently determined by the lunar cycle , release of the motile cells occurring 2-3 days on either side of the new or full moon (Parke et al. , 1978) . The motile stage divides by fission . The Phycoma stage of Pterosperma may be mis identified as a pollen grain , resting spore , etc. It is widely distributed in the marine plankton. The genus probably comprises c. 20 species. Pterosperma moebii (J 0 rgensen) Ostenfeld (Fig. 7) . Phycoma with single , equatorial , undulate wing , 120-200 J.lm in total diameter. Width of the wing c. half the body diameter. The cell body subglobose to ellipsoidal with flattened poles . Motile cells 5-8 x 4-6 x 3-4 J.lm; flagella 4 - 7 times the body length . Cells covered with 4 types of large scales , in addition to small underlayer scales . This species, known from both the North Atlantic and the North Pacific , was studied in detail by Parke et al., ( 1978) . . Genus Pyramimonas Schmarda 1850 More or less radially symmetrical cells with 4 , 8 (rarely), or 16 flagella (one species only ) emerging from an anterior depression in the c e II , wh ich is more or less inversely pyramidal. A single cup-shaped chloroplast and a basal pyrenoid . One or 2 eyespots . Freshwater species with a contractile vacuole system near the flagellar bases. Some species with tubular ejectile organelles . The 16-flagellate species differs in having 2 chloroplasts , 2 pyrenoids , and 4 eyespots. The flagella with square underlayer scales , limuloid scales and two opposite rows of hair-shaped scales on the flagella. Cell body covered with scales in several layers, underlayer scales on the body are overlain by 1 or 2 layers of larger, usually crown or box-like scales. Scales accumulate in a scale reservoir before release through a canal to the ce II surfaces . Mainly distributed in the marine phytoplankton , a few from fresh water. Some species epiphytic or episammic . Probably around PRASINOPHYC 50 species, but most freshwater species have not been adequately examined and some have been shown to belong to the genus Hafniomonas (Volvocales), which lacks scales. Marine species of Pyramimonas occur in all seas. Prasinochloris is a monotypic genus apparently related to Pyramimonas. Cells are unicellular epiphytes surrounded by a thick wall. They multiply by quadriflagellate zoospores resembling Pyramimonas (Belcher, 1966}. view . ch, chloroplast ; cv, contractile vacuole; n, nucleus; p, scaly periplast (only one layer of scales indicated); py, pyrenoid; r, rhizoplast; v, vacuole. In top view the eight chloroplast-lobes are visible , two containing an eyespot. Not to scale. (Ettl and Moestrup , 1980). Pyramimonas tetrarhynchus Schmarda, 1 850 (Fig . 8). Cells 20-28 ~m long, 12-20 ~m wide near the front end. Chloroplast with 8 anterior lobes and 1 basal pyrenoid. Two eyespots in the posterior part of the cell . Ejectile organelles absent. Two contractile vacuoles. Underlayer body scales covered with 2 layers of larger scales , box-shaped scales overlain by crown-like ones. Asexual cysts known. Widely distributed fresh- water species. Type species of the genus.
Type species
Figures
Raw text
Unicellular algae occurring in 2 very different stages. The main , coccoid , Phycoma stage is spherical , 14-230 J.lm in diameter and surrounded by a double wall . The surface of the wall is smooth , papillose , or poroid and bears 1 or more wings protruding from the surface . The mature Phycoma is initially uninuclear and contains numerous chloroplasts , each with a pyrenoid. Cell divisions give rise to formation of a large number of motile cells , which are released through a slit in the outer wall . Each motile cell possesses 4 flagella , held together as a single , thick 'compound' flagellum behind the sw imming cell . The motile cell contains a chloroplast with a pyrenoid but lacks an eyespot. Extrusomes are also present. All surfaces covered with organ ic scales , the flagella with an underlayer of small square scales overlain by lim uloid ones , in CEAE addition to 2 opposite rows of hair-shaped scales . The cell body has a three-layered scale cover: an inner layer of small square scales and 2 layers of larger, octagonal or nonagonal scales (3-4 types ). The change between Phycoma stage and motile cells is apparently determined by the lunar cycle , release of the motile cells occurring 2-3 days on either side of the new or full moon (Parke et al. , 1978) . The motile stage divides by fission . The Phycoma stage of Pterosperma may be mis identified as a pollen grain , resting spore , etc. It is widely distributed in the marine plankton. The genus probably comprises c. 20 species. Pterosperma moebii (J 0 rgensen) Ostenfeld (Fig. 7) . Phycoma with single , equatorial , undulate wing , 120-200 J.lm in total diameter. Width of the wing c. half the body diameter. The cell body subglobose to ellipsoidal with flattened poles . Motile cells 5-8 x 4-6 x 3-4 J.lm; flagella 4 - 7 times the body length . Cells covered with 4 types of large scales , in addition to small underlayer scales . This species, known from both the North Atlantic and the North Pacific , was studied in detail by Parke et al., ( 1978) . . Genus Pyramimonas Schmarda 1850 More or less radially symmetrical cells with 4 , 8 (rarely), or 16 flagella (one species only ) emerging from an anterior depression in the c e II , wh ich is more or less inversely pyramidal. A single cup-shaped chloroplast and a basal pyrenoid . One or 2 eyespots . Freshwater species with a contractile vacuole system near the flagellar bases. Some species with tubular ejectile organelles . The 16-flagellate species differs in having 2 chloroplasts , 2 pyrenoids , and 4 eyespots. The flagella with square underlayer scales , limuloid scales and two opposite rows of hair-shaped scales on the flagella. Cell body covered with scales in several layers, underlayer scales on the body are overlain by 1 or 2 layers of larger, usually crown or box-like scales. Scales accumulate in a scale reservoir before release through a canal to the ce II surfaces . Mainly distributed in the marine phytoplankton , a few from fresh water. Some species epiphytic or episammic . Probably around PRASINOPHYC 50 species, but most freshwater species have not been adequately examined and some have been shown to belong to the genus Hafniomonas (Volvocales), which lacks scales. Marine species of Pyramimonas occur in all seas. Prasinochloris is a monotypic genus apparently related to Pyramimonas. Cells are unicellular epiphytes surrounded by a thick wall. They multiply by quadriflagellate zoospores resembling Pyramimonas (Belcher, 1966}. view . ch, chloroplast ; cv, contractile vacuole; n, nucleus; p, scaly periplast (only one layer of scales indicated); py, pyrenoid; r, rhizoplast; v, vacuole. In top view the eight chloroplast-lobes are visible , two containing an eyespot. Not to scale. (Ettl and Moestrup , 1980). Pyramimonas tetrarhynchus Schmarda, 1 850 (Fig . 8). Cells 20-28 ~m long, 12-20 ~m wide near the front end. Chloroplast with 8 anterior lobes and 1 basal pyrenoid. Two eyespots in the posterior part of the cell . Ejectile organelles absent. Two contractile vacuoles. Underlayer body scales covered with 2 layers of larger scales , box-shaped scales overlain by crown-like ones. Asexual cysts known. Widely distributed fresh- water species. Type species of the genus.