Description
by PAUL KUGRENS, ROBERT E. LEE and DAVID R. A. HILL The cryptomonads are a relatively small but distinct taxonomic group of unicellular flagellates that are cosmopolitan in distribution and are important primary producers in both freshwater a and marine habitats (Gillott, 1990 ; Klaveness 1988). Cryptomonads are common in many phytoplankton samples, but because their cells are extremely delicate, they rupture when fixatives are added or when temperatures are elevated; their J. numbers generally are underestimated in preserved samples. In sub-ice habitats and in early spring and late fall populations of temperate m lakes and reservoirs , they often become dominant. In fact, the structural diversity discovered by using specialized electron-microscopic techniques . (Hill, 1990 , 1991 b ; Hill and Wetherbee, 1 986 , 1988, 1989 , 1990 ; Kugrens and Lee, 1 9 8 7 , 1991, Kugrens et al., 1986a, 1987; Lee and Kugrens, 1986) strongly suggest that the numbers of species in this group of organisms probably has been significantly underestimated (Andersen, 1992). e . general features of a cryptomonad cell and the relative locations of cellular structures. The periplast plates impart a serated appearance to the periplast (arrow) . Important cell structures include a chloroplast (C) with a pyrenoid (Py) traversed by a pair of thylakoids and a stigma (S); a nucleus (N); a nucleomorph (Nm); a golgi apparatus (G); ejectosomes (E); and starch in the periplastidal space. Scale=1 iJm . 1 1 12 CRYPTOMONA showing vestibulum (V) and absence of a furrow . Flagella (F) are inserted on the right side of the vestibulum. Scale=1 IJm. (From Kugrens et. al. , 1986) Fig . 3. SEM of the anterior end of Campylomonas reflexa showing the simple furrow (Fu) and a gullet posterior to the furrow (arrow). At the anterior end and on the dorsal side of the vestibulum is a vestibular ligule (VL) . Scale=1 IJm. (Kugrens et al . 1986) . Fig . 4. SEM of Cryptomonas tetrapyrenoidosa showing a complex furrow which consists of furrow ridges (FR) , furrow folds (FF) , and a posterior stoma (S) . Scale=1 IJm . (Kugrens et al. , 1986) DIDA Cryptomonads are quite complex (Fig . 1), and their fine structure reveals , that except for Goniomonas, their cells are derived from a eukaryotic endosymbiosis as well as the common prokaryotic (mitochondria and chloroplasts) endosymbioses (Douglas et al. , 1991; Gillott , 1990; Ludwig and Gibbs, 1985, 19 8 9 ; McKerracher and Gibbs, 1982 ; Anderson , 1992) . The host nuclear encoded rRNA appears to be related to the Acanthamoeba and green algal lineage , whereas the nucleomorph encoded rRNA appears to be related to red algae (Douglas et al ., 1984, 1987, 1991 ; Sespenwol , 1973). Owing to their unicellularity and small size , current and future classification schemes for cryptomonads must continue to rely upon ultrastructural features . By using information from the structu re s discussed in the following section , specifically the furrow/ gullet complex and periplast types , it has been possible to delineate 15 genera of crypt o- monads. It is significant that the number of genera has increased since the review articles of Santore (1984 , 1987) and the systematic treatment by Gillott (1990) , when only six genera were recognized. Features recognized by freeze- fracture in the TEM and in the SEM are importan t characters for species and some generic distinctions (Brett and Wetherbee , 1986; Dwarte and Vesk, 1983 ; Grim and Staehelin , 1984; Hi II , 1990, 1991b; Hill andWetherbee , 1986, 1988 , 1989; Klaveness, 1985 ; Kugrens and Lee, 1 9 8 7 , 1991; Kugrens et al., 1986, 1987; Munawar and Bistricki, 1979; Wetherbee et al. , 1986, 1987). For information on earlier classification schemes , the publications by Bourrelly (1970) , Huber - Pestalozzi (1950) , and Skuja (1939, 1948) are recommended for freshwater cryptomonads , whereas the treatise by Butcher ( 1967) deals with the marine forms . The external architecture of the cell is asymmetrical due to a furrow/gullet complex. , All cells , whether they are oval , compressed , lunate , caudate, acute , elongate , sigmoid , o r contorted, possess an anterior , outwardly facing depression called a vestibulum , from which the flagella arise on the right side (Fig . 2) . CRYPTOMONAD Rhodomonas ova/is. Periplast plates (PP) appear round with tapered anteriors. Also shown is the furrow (Fu) and one of the flagella (F). Scale=1 IJm . Fig . 6 Hexagona l surface periplast plates of Komma sp. Scale=1 m. (From Kugrens and Lee , 1991 ). Fig . 7. Inne r periplast sheet of Storeatula rhinosa with pores (a rrows ) through which ejectisomes project. A portion of the cell membrane (CM) is visible toward th e outside of the ce ll . Scale= 1 IJm . IDA 1 113 In addition , there may be a furrow , a gullet, or combination of both . Furrows are ventral grooves originating in the vestibulum extending posteriorly, but terminating in the anterior half of the cell. A gullet is a tubular invagination which extends posteriorly from the vestibulum or the end of the furrow. Variations in these features are illustrated in Figs. 2-4 . Ejectisomes flank the furrow and/or gullet. The contractile vacuole discharges into a predetermined site in the dorsal portion of the vestibulum . In some genera, a vestibular ligule covers the discharge site of the contractile vacuole (Kugrens and Lee , 1991) . Periplasts (Figs. 5-7) are unique conformation to cryptomonads. Periplasts consist of the plasma membrane and the inner and surface components (Hill , 1990, 1991 b; Hill and Wetherbee , 1986, 1988, 1989 ; Kugrens and Lee, 1987, 1991 ; Wetherbee et al. , 1987, 1986) and both can be variable in their composition . The inner periplast component (IPC) is protein (Gantt , 1971 ; Faust, 197 4) and may be composed of many variously shaped plates or a sheet. The surface periplast component (SPC) may consist of plates , heptagonal scales , mucilage , or combinations of these. The plates of the inner periplast component are connected to the cell membrane by intramembrane particles or proteins (Brett and Wetherbee , 1986; Kugens and Lee , 1987; Wetherbee et al., 1986 , 1987) . The arrangement of these IMP domains conform to the plate shapes which have been used to characterize genera. The periplast has pores (Fig . 7) through which the ejectisomes dock with the cell membrane (Grim and Staehelin, 1984). With the exception of Goniomonas, cells have two subapically inserted subequal flagella (Fig . 8 ) with tubular hairs on at least one of them . There are at least five variations in the arrangement of . the tubular and non-tubular hairs on the flagella. In the most common , the longer dorsal flagellum bears two laterally opposed rows of tubular hairs and the shorter ventral flagellum bears a single row of hairs (Fig. 8) . Tubular hairs on the dorsal flagellum have one terminal filament and tubular 1 1 14 CRYPTOMONADID hairs of the ventral flagellum have two unequal terminal filaments . In addition flagella may bear heptagonal scales (Lee and Kugrens , 1 9 8 6 ; Pennick, 1981 ). Goniomonas has a unilateral row of curved spikes on one of its flagella instead of tubular hairs and fine non-tubular hairs on both flagella (Kugre ns and Lee , 1987, 1991) . In addition , the flagella of Goniomonas are inserted on the dorsal side of the vestibulum (Fig 13) . The flagellar transition region is unique in cryptomonads and consists of a doublet system of septa (Fig. 9) (Grain et al. , 1988; Kugrens and Lee , 1991 ). A rhizostyle is an intergral component of the flagellar apparatus in most The dorsal flagellum (DF) bears two rows of tubular hairs , whereas the ventral flagellum (VF) has only one row of tubular hairs . Scal e= 1 IJm . Fig . 9 . TEM of transiti on regions of both flagella of Chroomonas coerulea displaying the double septate nature of this region (arrows). Scale=1 IJm . A (LE) are located near the furrow (Fu) , and the small ejectosomes (SE) are situated beneath the cell membrane. Scale=1 IJm. Fig . 11 . Portion of Komma caudata showing the location of the nucleomorph (Nm) near the nucleus (N) and chloroplast (C) in the periplastidal compartment. (PER) periplastiidal endoplasmic reticulum ; (S) -starch. Scale=1 IJm . Fig . 12 . Portion of a chloroplast of Komma caudata showing the paired arrangement of thylakoides . Scale=1 IJm . CRYPTOMONADID cryptomonads , and it consists of microtubules that originate near the basal bodies and then extend posteriorly into the cell. One type of rhizostyle, found in Chilomonas (Roberts et al., 1981 ; Kugrens and Lee , 1991) Cryptomonas phi (Gillott, 1990; Gillot and Gibbs, 1983) Te/eau/ax (Hi II , 1990) , Storeatula (Hill, 1990) , Geminigera (Hill , 1990), and Proteomonas (Hill and Wetherbee , 1986) passes close to the nucleus and terminates near the posterior end of the cell. Each microtubule has a wing-like extension (lamella) and the length of these lamellae may vary with the respective microtubule (Gillot and Gibbs, 1983) . A second type of rhizostyle, reported for Cryptomonas ovata (Roberts, 1984 ; Hill , 1 9 9 0) and Cryptomonas theta (=Guillardia theta)(Gillot and Gibbs, 1983), lacks wings on the microtubules. This rhizostyle terminates anterior to the nucleus (Roberts, 1984) . Ejectisomes are the extrusive organelles of a II cryptomonads, and they appear to be identical in all genera investigated . Two sizes of ejectisomes (Fig. 10) are found in cryptomonad cells (Dodge, 1969 ; Schuster, 1968, 1970; Moral! and Greenwood , 1980; Santore, 1982a, 1984). Large ejectisomes are associated with the furrow / gullet and small ejectisomes are found beneath the periplast in other regions of the cell. Ejectisomes consist of two different-sized, tightly coiled and tapered ribbons, which are joined , and both are surrounded by a membrane (Fig . 10). Upon discharge the ribb ons roll up to form a tube . A crystalline substructure , similar to some prasinophyte ejectosomes has been reported by Morrall and Greenwood (1980) and Grim and Staehel in (1981 ). Cryptomonads have a single reticulate mitochondrion with flattened cristae (Santore, 1977; Roberts et al., 1981 ; Kugrens and Lee , 1991 ). Chloroplasts may be olive green, brown , blue-green , or red, depending upon the pigments present. Pigments found in cryptomonads are chlorophylls a and c 2 , and ~carotene, alloxanthin , diadinoxanthin , and several forms of blue and red phycobilliproteins called Cr-phycocyanin and C r- phycoerythrin to differentiate them from A 1 1 15 cyanobacterial and red algal phyco-biliproteins . With the exception of a marine endosymbiont (Hibberd , 1977), pigmented cells have only one or two chloroplasts . Either Cr-phycocyanin or Cr-phycoerythrin is located in the intrathylakoidal lumina of photosynthetic lamellae (Faust and Gantt, 1973; Gantt, 1979, 1980; Gantt et al. , 1971; Ludwig and Gibbs, 1 989 ) . Chloroplasts are surrounded by a double- membraned endoplasmic reticulum (Fig.11) called the periplastidial envelope , periplastidal complex , or chloroplast endoplasmic reticulum , which originates from an evagination of the outer membrane of the nuclear envelope and surrounds the chloroplast, starch grains, and a reduced nucleus known as the nucleomorph (Gillott and Gibbs, 1980; Ludwig and Gibbs , 1985; Santore , 1982c). Starch grains are formed within the periplastidal compartment, not within the chloroplast, and they generally are associated with a pyrenoid, if present. The number of thylakoids penetrating the pyrenoid has been used as a taxonomic character (Santore , 1984) . relationships between the dorsal flagella (F), furrow (Fu), and infundibulum. Scale=1 IJm . Fig . 14 . Comparatively short furrow (arrow) of Chilomonas paramecium. Scale=1 IJm . Thylakoids in the chloroplasts usually are arranged in pairs (Fig. 12) (Dwarte and Vesk, 1982 , 1983 ; Gantt et al. , 1971), sometimes in groups of three (Kiaveness , 1981 ; Hill, 1 991 b) , or in stacks of variable number (Hill, 1991 b) . 11 16 CRYPTOMONA Chilomonas has a reduced chloroplast which lacks pigments and is called a leucoplast. Goniomonas lacks plastids and a nucleomorph; consequently it also lacks the periplastidial compartment. (Falcomonas daucoides). (E) ejectisome ; (F) flagellum (Fu) furrow ; (Py) pyrenoid ; (S) starch. Scale=1 1-Jm Nucleomorphs (Figs. 1,11) are located in the periplastidial compartment (Gillott and Gibbs, 1980; Kugrens and Lee , 1989, 1 9 91 ; McKerracher and Gibbs, 1982 ; Ludwig and Gibbs, 1985; Morrall and Greenwood, 1982 ; Santore, 1982c, 1984, 1987) . They represent a vestigial nucleus which remains from an ancestral red algal endosymbiont . (Douglas et al., 1991 ). The nucleomorph is small , is limited by a double membrane , and contains DNA (Ludwig and Gibbs, 1985; Douglas et al. , 1991 ). In addition, the nucleomorph contains a fibrillar-granular region and dense bodies (Fig . 11 ). Its location within the compartment may have systematic applications (Santore , 1984; Hill and Wetherbee , 1989) . In Rhodomonas the nucleomorph is located in the pyrenoidal bridge (Hill and Wetherbee , 1989) . DIDA With the exception of Goniomonas and Chilomonas, which are heterotrophs, all cryptomonads are obligate phototrophs. Goniomonas is phagocytic , whereas Chilomonas is strictly osmotrophic, and i t does not ingest particulate materials as was previously assumed. One species of Chroomonas is mixotrophic (Kugrens and Lee, 1991 ) , but there is no evidence that other cryptomonads are also mixotrophic. Reproduction usually occurs by mitotic divisions , although sexual cycles have been documented for Proteomonas (Hill and Wetherbee, 1986) and Chroomonas (Kugrens and Lee, 1988) . Cysts may be produced to withstand adverse conditions. KEY CHARACTERS 1. Two apically inserted subequal flagella with tubular hairs on at least one of them . Most commonly, the dorsal flagellum bears two laterally opposed rows of tubular hairs, while the ventral flagellum bears only a single row of hairs. 2. Cells asymmetrical with an anterior vestibular depression and gullet/furrow complex . 3. Unique cell covering, the periplast , comprised of plates, protein sheets, heptagonal scales, mucilage, or some combination of these. 4. Most have a rhizostyle consisting of ; microtubules that originate near the basal bodies . and pass to the posterior close to, or anterior to, the nucleus. 5. A single reticulate mitochondrion with flattened cristae. 6. Two sizes of tightly coiled tapered ribbon-like ejectisomes associated with the gullet/furrow complex and periplast. 7. May be pigmented or colorless . One or two chloroplasts per cell, may be olive green , brown , blue-green, or red depending upon the pigments present. 8. In addition to a usual eukaryotic nucleus, most possess in the periplastidal compartment a vestigial nucleus known as a nucleomorph . CRYPTOM b LM SEM TEM 90 Q 1. Cells colorless .... ..... ... ... .. ... ...... .... ........... ...... ... 2 1'. Cells pigmented ...... .. ............ .. .. ... .... ..... .. .. .... .... . 3 2. Cells lack plastids ........ ....... .. .. ..... .. Goniomonas 2' . Cells with leucoplasts .. ..... .... ..... .... Chilomonas 3. Chloroplasts blue-green ..... ....... .. ........... ..... ..... 4 3'. Chloroplasts red , olive-green, or brown ... ... .. .. 6 4. Cells with a gullet only .... ...................... .. ........ 5 4'. Cells with a furrow .... ... ....... .. .... .. Falcomonas 5. Retangular periplast plates .. .. ...... Chroomonas 5'. Hexagonal periplast plates ........ .. .. ............ Koma 6. Life history with two dissimilar phases .... .. .. .. .. . ........ ... ...... ... ...... .. .......... .......... ... Proteomonas 6'. Life history with one phase .... .. ...................... 7 7. Cells with a furrow or gullet only .................. 8 7'. Cells with a furrow/gullet complex ...... ... ... . 12 8. Cells with a gullet only .. ... .. ..... .. ........ .... ........ 9 8'. Cells with a furrow only ...... ..... .. .... Te/eau/ax 9. Periplast components of inner & outer hexa- gonal plates .. ... ..... .. .. ... ........... .. ... .. ....... .... .. ... . 10 9'. Inner periplast component a sheet .. .. .... ........ . 11 10. Nucleomorph located in a cytoplasmic evagin- ation into pyrenoid .... .... ... .. .. ...... .. Rhinomonas 1O'. Nucleomorph located anterior to pyrenoid and not located in pyrenoid ..... .... .. .... Hemiselmis 11. Outer periplast component of large, irregular, longitudinally oriented plates ..... Guillardia 11 '. Outer periplast component of coarse fibrils .... . . . .. . .. .. . . .. . .. . . .. . . .. . . .. . . . . .. . . . .. . . .. . . .. . . .. . 12 . Cells with a simple furrow .. ... .. ...... ... .... ..... 13 12'. Cells with a complex furrow ... Cryptomonas 13 . Inner periplast component consists of a sheet. .. ... .... ...... ............... .... ... .. .... ................. ........... 14 ONADIDA 11 17 13' . Inner periplast component consists of multiple plates ... ... ... ... ....... ..... .... ... ... ..... .... Rhodomonas 14. Surface periplast component consists of heptagonal plates .... ..... .. ... ... .... .... .. Geminigera 14'. Surface periplast component lacking or com- prised of diffuse fibrils ....... Campylomonas
Type species
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by PAUL KUGRENS, ROBERT E. LEE and DAVID R. A. HILL The cryptomonads are a relatively small but distinct taxonomic group of unicellular flagellates that are cosmopolitan in distribution and are important primary producers in both freshwater a and marine habitats (Gillott, 1990 ; Klaveness 1988). Cryptomonads are common in many phytoplankton samples, but because their cells are extremely delicate, they rupture when fixatives are added or when temperatures are elevated; their J. numbers generally are underestimated in preserved samples. In sub-ice habitats and in early spring and late fall populations of temperate m lakes and reservoirs , they often become dominant. In fact, the structural diversity discovered by using specialized electron-microscopic techniques . (Hill, 1990 , 1991 b ; Hill and Wetherbee, 1 986 , 1988, 1989 , 1990 ; Kugrens and Lee, 1 9 8 7 , 1991, Kugrens et al., 1986a, 1987; Lee and Kugrens, 1986) strongly suggest that the numbers of species in this group of organisms probably has been significantly underestimated (Andersen, 1992). e . general features of a cryptomonad cell and the relative locations of cellular structures. The periplast plates impart a serated appearance to the periplast (arrow) . Important cell structures include a chloroplast (C) with a pyrenoid (Py) traversed by a pair of thylakoids and a stigma (S); a nucleus (N); a nucleomorph (Nm); a golgi apparatus (G); ejectosomes (E); and starch in the periplastidal space. Scale=1 iJm . 1 1 12 CRYPTOMONA showing vestibulum (V) and absence of a furrow . Flagella (F) are inserted on the right side of the vestibulum. Scale=1 IJm. (From Kugrens et. al. , 1986) Fig . 3. SEM of the anterior end of Campylomonas reflexa showing the simple furrow (Fu) and a gullet posterior to the furrow (arrow). At the anterior end and on the dorsal side of the vestibulum is a vestibular ligule (VL) . Scale=1 IJm. (Kugrens et al . 1986) . Fig . 4. SEM of Cryptomonas tetrapyrenoidosa showing a complex furrow which consists of furrow ridges (FR) , furrow folds (FF) , and a posterior stoma (S) . Scale=1 IJm . (Kugrens et al. , 1986) DIDA Cryptomonads are quite complex (Fig . 1), and their fine structure reveals , that except for Goniomonas, their cells are derived from a eukaryotic endosymbiosis as well as the common prokaryotic (mitochondria and chloroplasts) endosymbioses (Douglas et al. , 1991; Gillott , 1990; Ludwig and Gibbs, 1985, 19 8 9 ; McKerracher and Gibbs, 1982 ; Anderson , 1992) . The host nuclear encoded rRNA appears to be related to the Acanthamoeba and green algal lineage , whereas the nucleomorph encoded rRNA appears to be related to red algae (Douglas et al ., 1984, 1987, 1991 ; Sespenwol , 1973). Owing to their unicellularity and small size , current and future classification schemes for cryptomonads must continue to rely upon ultrastructural features . By using information from the structu re s discussed in the following section , specifically the furrow/ gullet complex and periplast types , it has been possible to delineate 15 genera of crypt o- monads. It is significant that the number of genera has increased since the review articles of Santore (1984 , 1987) and the systematic treatment by Gillott (1990) , when only six genera were recognized. Features recognized by freeze- fracture in the TEM and in the SEM are importan t characters for species and some generic distinctions (Brett and Wetherbee , 1986; Dwarte and Vesk, 1983 ; Grim and Staehelin , 1984; Hi II , 1990, 1991b; Hill andWetherbee , 1986, 1988 , 1989; Klaveness, 1985 ; Kugrens and Lee, 1 9 8 7 , 1991; Kugrens et al., 1986, 1987; Munawar and Bistricki, 1979; Wetherbee et al. , 1986, 1987). For information on earlier classification schemes , the publications by Bourrelly (1970) , Huber - Pestalozzi (1950) , and Skuja (1939, 1948) are recommended for freshwater cryptomonads , whereas the treatise by Butcher ( 1967) deals with the marine forms . The external architecture of the cell is asymmetrical due to a furrow/gullet complex. , All cells , whether they are oval , compressed , lunate , caudate, acute , elongate , sigmoid , o r contorted, possess an anterior , outwardly facing depression called a vestibulum , from which the flagella arise on the right side (Fig . 2) . CRYPTOMONAD Rhodomonas ova/is. Periplast plates (PP) appear round with tapered anteriors. Also shown is the furrow (Fu) and one of the flagella (F). Scale=1 IJm . Fig . 6 Hexagona l surface periplast plates of Komma sp. Scale=1 m. (From Kugrens and Lee , 1991 ). Fig . 7. Inne r periplast sheet of Storeatula rhinosa with pores (a rrows ) through which ejectisomes project. A portion of the cell membrane (CM) is visible toward th e outside of the ce ll . Scale= 1 IJm . IDA 1 113 In addition , there may be a furrow , a gullet, or combination of both . Furrows are ventral grooves originating in the vestibulum extending posteriorly, but terminating in the anterior half of the cell. A gullet is a tubular invagination which extends posteriorly from the vestibulum or the end of the furrow. Variations in these features are illustrated in Figs. 2-4 . Ejectisomes flank the furrow and/or gullet. The contractile vacuole discharges into a predetermined site in the dorsal portion of the vestibulum . In some genera, a vestibular ligule covers the discharge site of the contractile vacuole (Kugrens and Lee , 1991) . Periplasts (Figs. 5-7) are unique conformation to cryptomonads. Periplasts consist of the plasma membrane and the inner and surface components (Hill , 1990, 1991 b; Hill and Wetherbee , 1986, 1988, 1989 ; Kugrens and Lee, 1987, 1991 ; Wetherbee et al. , 1987, 1986) and both can be variable in their composition . The inner periplast component (IPC) is protein (Gantt , 1971 ; Faust, 197 4) and may be composed of many variously shaped plates or a sheet. The surface periplast component (SPC) may consist of plates , heptagonal scales , mucilage , or combinations of these. The plates of the inner periplast component are connected to the cell membrane by intramembrane particles or proteins (Brett and Wetherbee , 1986; Kugens and Lee , 1987; Wetherbee et al., 1986 , 1987) . The arrangement of these IMP domains conform to the plate shapes which have been used to characterize genera. The periplast has pores (Fig . 7) through which the ejectisomes dock with the cell membrane (Grim and Staehelin, 1984). With the exception of Goniomonas, cells have two subapically inserted subequal flagella (Fig . 8 ) with tubular hairs on at least one of them . There are at least five variations in the arrangement of . the tubular and non-tubular hairs on the flagella. In the most common , the longer dorsal flagellum bears two laterally opposed rows of tubular hairs and the shorter ventral flagellum bears a single row of hairs (Fig. 8) . Tubular hairs on the dorsal flagellum have one terminal filament and tubular 1 1 14 CRYPTOMONADID hairs of the ventral flagellum have two unequal terminal filaments . In addition flagella may bear heptagonal scales (Lee and Kugrens , 1 9 8 6 ; Pennick, 1981 ). Goniomonas has a unilateral row of curved spikes on one of its flagella instead of tubular hairs and fine non-tubular hairs on both flagella (Kugre ns and Lee , 1987, 1991) . In addition , the flagella of Goniomonas are inserted on the dorsal side of the vestibulum (Fig 13) . The flagellar transition region is unique in cryptomonads and consists of a doublet system of septa (Fig. 9) (Grain et al. , 1988; Kugrens and Lee , 1991 ). A rhizostyle is an intergral component of the flagellar apparatus in most The dorsal flagellum (DF) bears two rows of tubular hairs , whereas the ventral flagellum (VF) has only one row of tubular hairs . Scal e= 1 IJm . Fig . 9 . TEM of transiti on regions of both flagella of Chroomonas coerulea displaying the double septate nature of this region (arrows). Scale=1 IJm . A (LE) are located near the furrow (Fu) , and the small ejectosomes (SE) are situated beneath the cell membrane. Scale=1 IJm. Fig . 11 . Portion of Komma caudata showing the location of the nucleomorph (Nm) near the nucleus (N) and chloroplast (C) in the periplastidal compartment. (PER) periplastiidal endoplasmic reticulum ; (S) -starch. Scale=1 IJm . Fig . 12 . Portion of a chloroplast of Komma caudata showing the paired arrangement of thylakoides . Scale=1 IJm . CRYPTOMONADID cryptomonads , and it consists of microtubules that originate near the basal bodies and then extend posteriorly into the cell. One type of rhizostyle, found in Chilomonas (Roberts et al., 1981 ; Kugrens and Lee , 1991) Cryptomonas phi (Gillott, 1990; Gillot and Gibbs, 1983) Te/eau/ax (Hi II , 1990) , Storeatula (Hill, 1990) , Geminigera (Hill , 1990), and Proteomonas (Hill and Wetherbee , 1986) passes close to the nucleus and terminates near the posterior end of the cell. Each microtubule has a wing-like extension (lamella) and the length of these lamellae may vary with the respective microtubule (Gillot and Gibbs, 1983) . A second type of rhizostyle, reported for Cryptomonas ovata (Roberts, 1984 ; Hill , 1 9 9 0) and Cryptomonas theta (=Guillardia theta)(Gillot and Gibbs, 1983), lacks wings on the microtubules. This rhizostyle terminates anterior to the nucleus (Roberts, 1984) . Ejectisomes are the extrusive organelles of a II cryptomonads, and they appear to be identical in all genera investigated . Two sizes of ejectisomes (Fig. 10) are found in cryptomonad cells (Dodge, 1969 ; Schuster, 1968, 1970; Moral! and Greenwood , 1980; Santore, 1982a, 1984). Large ejectisomes are associated with the furrow / gullet and small ejectisomes are found beneath the periplast in other regions of the cell. Ejectisomes consist of two different-sized, tightly coiled and tapered ribbons, which are joined , and both are surrounded by a membrane (Fig . 10). Upon discharge the ribb ons roll up to form a tube . A crystalline substructure , similar to some prasinophyte ejectosomes has been reported by Morrall and Greenwood (1980) and Grim and Staehel in (1981 ). Cryptomonads have a single reticulate mitochondrion with flattened cristae (Santore, 1977; Roberts et al., 1981 ; Kugrens and Lee , 1991 ). Chloroplasts may be olive green, brown , blue-green , or red, depending upon the pigments present. Pigments found in cryptomonads are chlorophylls a and c 2 , and ~carotene, alloxanthin , diadinoxanthin , and several forms of blue and red phycobilliproteins called Cr-phycocyanin and C r- phycoerythrin to differentiate them from A 1 1 15 cyanobacterial and red algal phyco-biliproteins . With the exception of a marine endosymbiont (Hibberd , 1977), pigmented cells have only one or two chloroplasts . Either Cr-phycocyanin or Cr-phycoerythrin is located in the intrathylakoidal lumina of photosynthetic lamellae (Faust and Gantt, 1973; Gantt, 1979, 1980; Gantt et al. , 1971; Ludwig and Gibbs, 1 989 ) . Chloroplasts are surrounded by a double- membraned endoplasmic reticulum (Fig.11) called the periplastidial envelope , periplastidal complex , or chloroplast endoplasmic reticulum , which originates from an evagination of the outer membrane of the nuclear envelope and surrounds the chloroplast, starch grains, and a reduced nucleus known as the nucleomorph (Gillott and Gibbs, 1980; Ludwig and Gibbs , 1985; Santore , 1982c). Starch grains are formed within the periplastidal compartment, not within the chloroplast, and they generally are associated with a pyrenoid, if present. The number of thylakoids penetrating the pyrenoid has been used as a taxonomic character (Santore , 1984) . relationships between the dorsal flagella (F), furrow (Fu), and infundibulum. Scale=1 IJm . Fig . 14 . Comparatively short furrow (arrow) of Chilomonas paramecium. Scale=1 IJm . Thylakoids in the chloroplasts usually are arranged in pairs (Fig. 12) (Dwarte and Vesk, 1982 , 1983 ; Gantt et al. , 1971), sometimes in groups of three (Kiaveness , 1981 ; Hill, 1 991 b) , or in stacks of variable number (Hill, 1991 b) . 11 16 CRYPTOMONA Chilomonas has a reduced chloroplast which lacks pigments and is called a leucoplast. Goniomonas lacks plastids and a nucleomorph; consequently it also lacks the periplastidial compartment. (Falcomonas daucoides). (E) ejectisome ; (F) flagellum (Fu) furrow ; (Py) pyrenoid ; (S) starch. Scale=1 1-Jm Nucleomorphs (Figs. 1,11) are located in the periplastidial compartment (Gillott and Gibbs, 1980; Kugrens and Lee , 1989, 1 9 91 ; McKerracher and Gibbs, 1982 ; Ludwig and Gibbs, 1985; Morrall and Greenwood, 1982 ; Santore, 1982c, 1984, 1987) . They represent a vestigial nucleus which remains from an ancestral red algal endosymbiont . (Douglas et al., 1991 ). The nucleomorph is small , is limited by a double membrane , and contains DNA (Ludwig and Gibbs, 1985; Douglas et al. , 1991 ). In addition, the nucleomorph contains a fibrillar-granular region and dense bodies (Fig . 11 ). Its location within the compartment may have systematic applications (Santore , 1984; Hill and Wetherbee , 1989) . In Rhodomonas the nucleomorph is located in the pyrenoidal bridge (Hill and Wetherbee , 1989) . DIDA With the exception of Goniomonas and Chilomonas, which are heterotrophs, all cryptomonads are obligate phototrophs. Goniomonas is phagocytic , whereas Chilomonas is strictly osmotrophic, and i t does not ingest particulate materials as was previously assumed. One species of Chroomonas is mixotrophic (Kugrens and Lee, 1991 ) , but there is no evidence that other cryptomonads are also mixotrophic. Reproduction usually occurs by mitotic divisions , although sexual cycles have been documented for Proteomonas (Hill and Wetherbee, 1986) and Chroomonas (Kugrens and Lee, 1988) . Cysts may be produced to withstand adverse conditions. KEY CHARACTERS 1. Two apically inserted subequal flagella with tubular hairs on at least one of them . Most commonly, the dorsal flagellum bears two laterally opposed rows of tubular hairs, while the ventral flagellum bears only a single row of hairs. 2. Cells asymmetrical with an anterior vestibular depression and gullet/furrow complex . 3. Unique cell covering, the periplast , comprised of plates, protein sheets, heptagonal scales, mucilage, or some combination of these. 4. Most have a rhizostyle consisting of ; microtubules that originate near the basal bodies . and pass to the posterior close to, or anterior to, the nucleus. 5. A single reticulate mitochondrion with flattened cristae. 6. Two sizes of tightly coiled tapered ribbon-like ejectisomes associated with the gullet/furrow complex and periplast. 7. May be pigmented or colorless . One or two chloroplasts per cell, may be olive green , brown , blue-green, or red depending upon the pigments present. 8. In addition to a usual eukaryotic nucleus, most possess in the periplastidal compartment a vestigial nucleus known as a nucleomorph . CRYPTOM b LM SEM TEM 90 Q 1. Cells colorless .... ..... ... ... .. ... ...... .... ........... ...... ... 2 1'. Cells pigmented ...... .. ............ .. .. ... .... ..... .. .. .... .... . 3 2. Cells lack plastids ........ ....... .. .. ..... .. Goniomonas 2' . Cells with leucoplasts .. ..... .... ..... .... Chilomonas 3. Chloroplasts blue-green ..... ....... .. ........... ..... ..... 4 3'. Chloroplasts red , olive-green, or brown ... ... .. .. 6 4. Cells with a gullet only .... ...................... .. ........ 5 4'. Cells with a furrow .... ... ....... .. .... .. Falcomonas 5. Retangular periplast plates .. .. ...... Chroomonas 5'. Hexagonal periplast plates ........ .. .. ............ Koma 6. Life history with two dissimilar phases .... .. .. .. .. . ........ ... ...... ... ...... .. .......... .......... ... Proteomonas 6'. Life history with one phase .... .. ...................... 7 7. Cells with a furrow or gullet only .................. 8 7'. Cells with a furrow/gullet complex ...... ... ... . 12 8. Cells with a gullet only .. ... .. ..... .. ........ .... ........ 9 8'. Cells with a furrow only ...... ..... .. .... Te/eau/ax 9. Periplast components of inner & outer hexa- gonal plates .. ... ..... .. .. ... ........... .. ... .. ....... .... .. ... . 10 9'. Inner periplast component a sheet .. .. .... ........ . 11 10. Nucleomorph located in a cytoplasmic evagin- ation into pyrenoid .... .... ... .. .. ...... .. Rhinomonas 1O'. Nucleomorph located anterior to pyrenoid and not located in pyrenoid ..... .... .. .... Hemiselmis 11. Outer periplast component of large, irregular, longitudinally oriented plates ..... Guillardia 11 '. Outer periplast component of coarse fibrils .... . . . .. . .. .. . . .. . .. . . .. . . .. . . .. . . . . .. . . . .. . . .. . . .. . . .. . 12 . Cells with a simple furrow .. ... .. ...... ... .... ..... 13 12'. Cells with a complex furrow ... Cryptomonas 13 . Inner periplast component consists of a sheet. .. ... .... ...... ............... .... ... .. .... ................. ........... 14 ONADIDA 11 17 13' . Inner periplast component consists of multiple plates ... ... ... ... ....... ..... .... ... ... ..... .... Rhodomonas 14. Surface periplast component consists of heptagonal plates .... ..... .. ... ... .... .... .. Geminigera 14'. Surface periplast component lacking or com- prised of diffuse fibrils ....... Campylomonas