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The genus Palusphaera Lecal-Schlauder emend. R.E. Norris is a distinctive modern coccolithophore that accommodates monomorphic, monothecate coccospheres with one type of spine-bearing heterococcoliths. Having examined a set of scanning electron microscopy images from our collections, we were able to demonstrate that four distinct species of Palusphaera exist in the modern oceans, including the type species Palusphaera vandelii, an informally proposed form, Palusphaera sp. 1 (type robusta) that is herein taxonomically ratified as Palusphaera crosiae sp. nov., and a distinctive morphotype, which is formally described as Palusphaera bownii sp. nov. Biometric analyses and observations on the morphologies of numerous P. vandelii specimens revealed the existence of a further form, and its commonly distinguished coccolith morphotypes are therefore taxonomically separated from Palusphaera vandelii and established as a discrete species, Palusphaera probertii sp. nov.

Coccolithophores are cosmopolitan, major calcifying protists that have significant roles in marine carbon cycling. Although the influence of temperature and irradiance fluctuation on coccolithophor...

The haptophyte symbiont Chrysochromulina andersonii sp. nov. isolated from the polycystine radiolarian Dictyocoryne truncatum was examined using both natural and cultured materials by light, scanni...

Seawater samples from the lower photic zone, obtained from shallow hydrocasts during an investigation of the eastern Indian Ocean, revealed the presence of two new species of the coccolithophorid genus Vexillarius: V. iaculifera sp. nov. and V. cereus sp. nov. Both possess dimorphic coccospheres: simple dishlike body coccoliths and coccoliths with an elongate, quadrangular central appendage. The main difference between these species and the type species, V. cancellifer, is the appendage shape: flaring (V. cancellifer), dart-shaped (V. iaculifer), or tapered (V. cereus). Furthermore, a recently described genus and species (Porsildia acerviphora) from the Arctic closely resembles V. cereus, but differs in having ‘irregularly piled elements' in the central area that are not connected to the body coccolith wall. Since it possesses the characteristic features of Vexillarius, it is transferred to the genus as V. acerviphora comb. nov. It is believed that Vexillarius is closely related to Turrilithus a...

We isolated 17 strains of Chrysotila stipitata and 10 strains of Chrysotila lamellosa from samples collected at exposed chalk surfaces, Westgate, Kent, England, which is the type locality for C. stipitata (generitype) and C. lamellosa. The nuclear-encoded small subunit and large subunit rRNA were used in a molecular phylogenetic analysis. We also examined the cells using light microscopy. Chrysotila stipitata had two chloroplasts per cell, as originally described, and it was positioned within the Coccolithales (Prymnesiophyceae) in a RAxML tree. Chrysotila stipitata gene sequences formed a clade with Pleurochrysis, and because Chrysotila has priority, Pleurochrysis was placed in synonymy. New nomenclatural combinations were also made. Chrysotila lamellosa was located within the order Isochrysidales, and like other members of the order, C. lamellosa had one chloroplast per cell. We reinstated the generic name Ruttnera to accommodate this species (Ruttnera lamellosa comb. nov.). We also showed that several ...

A new taxon, Syracosphaera pemmadiscus sp. nov., collected from the southwest Pacific Ocean near New Zealand, was described based on the morphological structure of both exo-and endothecal coccoliths. Both the elliptical exo- and endothecal coccoliths of Syracosphaera pemmadiscus were very small (

Grant B., Waller R.F. and Wetherbee R. 2011. Platychrysis moestrupii sp. nov. (Prymnesiophyceae): a new dimorphic, sand-dwelling haptophyte species from southeastern Australia. Phycologia 50: 608–615. DOI: 10.2216/11-14.1 A marine prymnesiophyte, Platychrysis moestrupii sp. nov., is described. Clonal cultures were established from field samples collected during the summer of 2009 from Stewart's Bay, Tasmania, Australia. Cells of P. moestrupii have two distinct morphologies, a motile swimming phase and an adhesive benthic phase. Motile cells are oblong to cylindrical with a posterior rounded protuberance and are 50–65 µm long and 20–25 µm wide. The cells possess two equal to subequal homodynamic flagella and a flexible noncoiling haptonema (8–10 µm long). Benthic cells are irregularly discoid with a diameter of 50–65 µm and are adherent to the substrate. Cells possess scales of two types, both of which are elliptical and 300 by 500 nm. Distal scales are unique amongst Platychrysis and have a marginal serie...

Zingone A., Forlani G., Percopo I. and Montresor M. 2011. Morphological characterization of Phaeocystis antarctica (Prymnesiophyceae). Phycologia 50: 650–660. DOI: 10.2216/11-36.1 Different stages of the life cycle of Phaeocystis antarctica are described by light and electron microscopy on the basis of cultured material isolated from the Atlantic Sector of the Antarctic Circumpolar Convergence, relatively close to the type locality. Species identity was confirmed molecularly on the basis of small-subunit ribosomal DNA. Colonies (up to 2000 µm in diameter) are surrounded by a rather thick membrane and are generally spherical, in some cases presenting a conical protrusion with a pointed end at one side. Colonial cells (4–6 µm) have a rounded or slightly quadrangular outline and possess two chloroplasts. In small and medium-sized colonies, cells may be densely packed under the peripheral colony skin; otherwise they are more or less evenly spaced. Nonmotile cells within or outside the colonies often show one ...

S. SEOANE ,W. E IKREM ,R. P IENAAR AND B. EDVARDSEN. 2009. Chrysochromulina palpebralis sp. nov. (Prymnesio- phyceae): a haptophyte, possessing two alternative morphologies. Phycologia 48: 165-176. DOI: 10.2216/08-63.1. A marine haptophyte flagellate, Chrysochromulina palpebralis sp. nov., is described from cultures originating from the Nervion River estuary in the Cantabrian Sea, northern Spain. In addition, cultures of similar organisms originating from Japanese and South African waters have been studied. Cells of C. palpebralis had an ovoid shape with an anterior shoulder and were 8-13 mm long and 6-9 mm wide. The cells possessed two equal to subequal flagella that measured 20- 27 mm and a haptonema (7-15 mm long) that was flexible and shorter than the flagella. The life cycle included two motile cell forms indistinguishable at the light microscope level. At the electron microscope level, the two cell forms could be distinguished by having different types of body scales. Flow cytometric ploidy analysis showed that the nuclei of the two forms differ in DNA content by a factor of about four. One cell form ,f .palpebralis, assumed to be tetraploid, was covered by three scale types, one with a central spiny projection and a peripheral rim with about 20 projections and two types of ovoid plate scales. The other form, f. bisquamata, assumed to be haploid, had two types of plate scales. The first cell form is known from the literature as 'eyelash Chrysochromulina' and has previously been recorded from coastal waters in Australia, Japan and South Africa. Phylogenetic analyses based on the nuclear encoded SSU and LSU ribosomal DNA sequences suggest that C. palpebralis is closely related to some nonsaddle-shaped Chrysochromulina species, clustering with C. polylepis and C. kappa as its closest relatives. Chrysochromulina palpebralis was nontoxic to nauplii of brine shrimp.

The coccolithophorids are a well-established group of unicellular algae whose bodies are covered by calcareous scales. They are usually assigned to the class Haptophyceae or Prymnesiophyceae, but we present arguments in favor of the name Coccolithophyceae. The taxonomic diversity within the coccolithophorids far exceeds that within the remaining members of the class. Molecular evidence shows phylogenetic closeness of coccolithophorids to certain haptophytes that do not form coccoliths, suggesting that the ability to produce calcareous scales has arisen only once and has been lost in some haptophytes. Electron microscopical detection of weak calcification in noncoccolithophorid haptophytes further supports the view that calcification is distributed throughout the class. Of three available names for the class, Coccolithophyceae Rothmaler 1951 has priority over Prymnesiophyceae Casper ex Hibberd 1976 and Haptophyceae Christensen ex P.C. Silva 1980. We urge the use of the name Coccolithophyceae for t...

J. BOLLMANN, M.Y. CORTES ,A. K LEIJNE, J.B. O STERGAARD ANDJ.R. YOUNG. 2006. Solisphaera gen. nov. (Prymnesiophyceae), a new coccolithophore genus from the lower photic zone. Phycologia 45: 465-477. DOI: 10.2216/05-14.1 Solisphaera gen. nov. (Prymnesiophyceae) is described from the lower photic zone of the Pacific Ocean, the North Atlantic Ocean and the Gulf of Mexico. Differences in coccolith morphology between Solisphaera and members of Rhabdosphaer- aceae are certainly substantial enough to warrant the erection of a separate genus that should probably be categorised as incertae sedis aff. Rhabdosphaeraceae. The new genus accommodates three new species, S. emidasia sp. nov., S. blagna- censis sp. nov. and S. helianthiformis sp. nov. and the presence of a corona of process-bearing coccoliths around the cell is a key feature that unites the three species in the new genus Solisphaera, while the shape of these coronal coccoliths provides the main character for separating them at species level. A remarkable feature of this genus is the tight interlocking of the coronal coccoliths, in almost all collapsed coccospheres the circle of coronal coccoliths remains intact. This is evidently due to the presence of notches at the base of the process into which the rims of adjacent coccoliths lock. All three species are restricted to the lower photic zone in the areas studied and apparent preferences for different depth levels of S. emidasia and S. blagnacensis, as well as their nutrient and light requirements, have to be confirmed by further analysis.

We isolated a novel haptophyte alga from the coastal waters of the northern part of Japan. The cell is asymmetrical spindle-to knife-shaped and possesses two nearly equal flagella and a haptonema from the anterior tip. Two yellowish chloroplasts including immersed pyrenoids are situated asymmetrically. Two types of organic scales, small elliptical and large rhomboidal scales, cover the cell. The rhomboidal scale has two tubular projections at the longitudinal poles and closely touched to each other. The transition region of the flagellum includes only one transitional plate, which is probably homologous with the distal plate in other prymnesiophyceans. The flagellar apparatus of this alga has basic components found in other prymnesiophyceans. Developed root 1 (R1) is divided into two components that join again. The R1 extends toward the posterior tip of the cell with associated endoplasmic reticulum (ER) and forms a cytoplasmic tongue. A fibrous root, which has only been reported in some coccolit...

The posttranslational modifications of tubulin of Chrysochromulina parva were determined using specific antibodies. Haptonematal microtubules were acetylated, monoglutamylated and weakly detyrosinated, a pattern distinct from that of the flagella of C. parva. The Ca2+-binding protein centrin was present in the basal apparatus, the proximal parts of both flagella and in the haptonema. In the haptonema, centrin was detected in a small dot-like structure located mostly near the distal end. These observations are discussed with respect to haptonematal contractility.

Most haptophytes are unicellular, photosynthetic flagellates, although some have coccoid, colonial, amoeboid, or filamentous stages. Nearly all have a characteristic filamentous appendage, the haptonema, arising between the two flagella. The small subunit ribosomal RNA gene (l8S ribosomal DNA) from 18 haptophyte species has been sequenced, and the sequences aligned with those of more than 300 published and unpublished chlorophyll a + c algae. Phylogenies were constructed using maximum likelihood, neighbor-joining, and weighted maximum parsimony analyses. The high divergence (6%) between members of Pavlova and the remaining haptophytes supports the division of Haptophyta into two classes: Prymnesiophyceae and Pavlovophyceae. Three major clades that correspond to known taxa within the Prymnesiophyceae were identified: one clade embraces Phaeocystis spp.; the second includes members of the genera Chrysochromulina, Prymnesium, and Imantonia; and the third includes coccolithophorid genera and the genu...

A new, small, saddle-shaped species of Chrysochromulina with a coiling haptonema is described from Danish coastal waters. The scale cover of C. ahrengotii sp. nov. comprises an inner layer of plate scales and an outer layer of spine-bearing scales. Chrysochromulina ahrengotii bears close morphological resemblance to C. scutellum Eikrem et Moestrup, another species of Chrysochromulina recently described, but differs in details of the scales and in having only one type of spine scale. Details of the flagellar apparatus and some observations on scale formation are reported. The spine scales are formed in T-shaped cisternae of the Golgi apparatus, a very unusual feature somewhat resembling the formation of the flat scales in C. chiton Manton seen by Manton in 1967. The flagellar apparatus is similar to that of other saddle-shaped species such as C. scutellum, C. simplex Estep, Davis, Hargraves et Sieburth, C. apheles Moestrup et Thomsen, and C. acantha Leadbeater et Manton. Chrysochromulina ahrengoti...

Chrysochromulina fragaria sp. nov. was one of the dominant species during the 1994 and 1995 Chrysochromulina blooms off the southern coast of Norway. It was isolated by the serial dilution culture method from a surface water sample collected during the bloom in May–June 1994. The cells are spherical, 4 to 8 μm in diameter, and possess a coiling haptonema that is shorter than the two equal to subequal flagella. Each cell contains two chloroplasts, a nucleus, and one mitochondrion, which appears to be reticulate. The periplast is covered by monomorphic scales (scale faces with identical pattern) of two types arranged in layers. The scale faces have a pattern of radiating ribs arranged in quadrants. One type has inflexed rims, whereas the other type has erect rims. The first internal transcribed spacer (ITS1) rDNA sequence and scale morphology of C. fragaria are compared with that of Chrysochromulina sp. CCMP 1204. Despite the great similarities in scale morphology, their ITS1 rDNA regions are very ...

During a study of the modern coccolithophore flora in the central and western Pacific, a hitherto undescribed taxon belonging to the genus Gladiolithus Jordan et Chamberlain was recorded. Here, Gladiolithus striatus sp. nov. is described. The new species resembles Gladiolithus flabellatus (Halldal et Markali) Jordan et Chamberlain in the general construction of the coccosphere, but there are differences in coccolith morphology. The major differences are (1) horizontal grooves occur on the external side of the tubular coccoliths; (2) the lepidolith is a rectangular plate with a finely grooved external surface (G. flabellatus has an oval disc with a smooth external surface); and (3) the suture line separating the two platelets of the lepidolith runs diagonally (it runs along the short axis in G. flabellatus).

In 1991, a Chrysochromulina Lackey species identified as C. leadbeateri Estep et al. was the dominant species in a toxic algal bloom in Vestfjorden, northern Norway, that killed caged salmon. For the first time, living cells of this species could be studied and material sectioned for fine structural investigations. The scale morphology and microanatomy of the species are described from cultured material obtained from the bloom and are compared with natural material from the same event, as well as with unpublished information from the Mediterranean and the Norwegian coasts, and with previously published information on scale morphology for specimens assigned to this species. Differences in scale morphology between specimens identified as C. leadbeateri are evident, but no subdivision of the species is proposed at present.

Chrysochromulina throndsenii sp. nov. was isolated from the Norwegian Skagerrak coast using the serial dilution culture method. It has also been observed in Danish waters. Chrysochromulina throndsenii is a new representative of the small saddle-shaped Chrysochromulina species. It has two approximately equal and homodynamic flagella and a long coiling haptonema emerging subapically from the ventral side. One flagellum is autofluorescent in blue light. The cell body is covered by two scale types, both having spiral and radiating patterns of fibrils. In both scale types the ornamentation of the inner and outer scale faces is identical. The scales in the outer layer possess an upright rim.

The flagellar apparatus of Prymnesium nemamethecum Pienaar et Birkhead is more similar to that of P. patelliferum Green, Hibberd et Pienaar than to any other prymnesiophyte yet described. This includes the arrangement of the appendages, the origins and pathways of the microtubular roots, and the system of fibrous and striated connectives. There is, however, a major difference in the presence of a compound broad root in interphase cells of P. nemamethecum. Other differences include the number of constituent microtubules in some roots, the extent of development of a root (herein designated R7) associated with the right basal body, and an additional accessory band (AB3) in P. nemamethecum. The transitional region of the flagella is also described. It resembles that of P. parvum Carter, as both species have two transitional plates separated by a form of stellate structure. P. nemamethecum also has a distal axosome and a series of tubular rings between the outer doublets and the flagellar membrane. Th...

It is shown that the haptonema plays an important role as a food capture and transport device in the processes of phagocytosis in the marine flagellate, Chrysochromulina hirta Manton (Prymnesiophyceae). The capture offood and its transport by the haptonema were observed only when the cells were swimming with the haptonema fully extended forward and the two flagella beating backwards alongside the body of the cell. Food particles become attached and adhere to the haptonema. They then move down to a particular point on the haptonema, the particle-aggregating centre, where they accumulate. The cell stops swimming, and the aggregated food moves toward the tip of the haptonema. After the food aggregate reaches the tip, the haptonema bends and delivers it to the lateral posterior surface of the cell. The food aggregate is then translocated to the posterior end of the cell, where it is taken into the cell by phagocytosis. The haptonema bends even when it does not carry any particles, suggesting that it ...

Trigonaspis gen. nov. (Prymnesiophyceae) is described on the basis of electron microscopy of shadowcast whole mounts, prepared from water samples collected at Godhavn (West Greenland) in July and August 1977. Members of the genus are small biflagellate coccolithophorids with a short coiling haptonema. The periplast is composed of tower-like coccoliths around the flagellar pole, flattened or slightly elevated coccoliths elsewhere on the cell. Below the coccolith base-plates is a layer of small always unmineralized scales. The coccolith crystallites are triangular plates. Apparently normal cells with unmineralized coccoliths are commonly found. Two species are described, the type species T. diskoensis sp. nov. and T. minutissima sp. nov., both appearing in large numbers in the Greenland cold water samples, but also occurring in Danish coastal waters.

An investigation into the ultrastructure of Chrysocamponula spinifera Fournier is reported. Attention is drawn to the unusual method of production of the long spine scales and the marked similarity in cell structure between Chrysocampanula Fournier and Chrysochromulina Lackey. In view of their similarities Chrysocampanula spinifera Fournier has been transferred to Chrysochromulina Lackey as Chrysochromulina spinifera (Fournier) comb. nov.

Numerous occurrences of Hymenomonas roseola, a freshwater coccolithophorid, and Spiniferomonas trioralis, a recently described chrysophycean flagellate, have been noted in collections from Saginaw Bay of Lake Huron. These constitute the first known records of either entity from the Laurentian Great Lakes.

Papposphaera and Pappomonas are coccolithophorid genera that have recently been described, but there has been little attempt to relate them to known genera and families. Analysis of coccolith structure from Indian Ocean material and the literature has revealed a relationship of these genera to a species, Defiandrius intercisus, known in fossil form from the late Cretaceous. This species and genus typify the family Deflandriaceae, defined here in the original narrow sense, and have characteristics in coccolith structure to allow Papposphaera and Pappomonas to be admitted to this family. A coccolith that may be the same as Defiandrius intercisus was discovered in the Indian Ocean extant nanoplankton flora. Two species of Papposphaera, P. sarion and P. thomsenii sp. nov., were also found in the Indian Ocean samples.

Pleurochrysis carlerae var. dentala var. nov. was isolated into culture from a shallow, saline pond near Roswell, New Mexico, USA. This taxon is similar to Pleurochrysis carlerae (Braarud & Fagerland) Christensen, but differs in cricolith morphology and in thermal tolerance. Internal ultrastructure is very similar to that found in other representatives of the Hymenomonadaceae. Two plastids are present, each with a bulging pyrenoid traversed by paired thylakoids. A single Golgi apparatus with peculiar dilations is positioned anteriorly, and appears to be the site of scale and coccolith production. A central nucleus, vacuole, several mitochondria, and numerous coccolithosomes are also evident. The haptonema is evident in noncoccolith-bearing swarmers, but has not been observed in coccolith-bearing motile cells. This taxon grows best in waters high in divalent cations, with optimal growth observed in SERI Type I water at 25°C and 25 mmhos cm−1 conductivity. Growth was also good in artificial seawate...

Deux nouvelles especes de Platychrysis (Prymnesiophyceae) sont decrites: P. pienaarii et P. simplex. Elles ont le caractere commun de manquer de cinetide visible au microscope optique, dans l'etat palmelloide, contrairement a l'espece-type P. pigra Geitler. Les deux especes sont principalement caracterisees par la structure fine de leurs ecailles superficielles: ecailles internes plates, pluristratifiees, ecailles externes unistratifiees, en forme de coupe a bord droit. Chez P. pienaarii, ces ecailles externes sont caracterisees par la presence de cloisons radiales qui sont absentes chez l'autre espece. Les principaux caracteres ultrastructuraux sont decrits a propos de chaque taxon.

The red algal genus Gloiophloea J. Agardh (Galaxauraceae, Nemaliales) includes multiaxial, dichotomously branched plants that are composed internally of a filamentous central axis, radiating dichotomously branched medullary filaments, and a loose cortex of spherical, pigmented cells. An examination of the three species presently included has shown that only the type species, G. scinaioides J. Agardh, should be maintained. Gloiophloea articulata Weber-van Bosse from Cargados Carajos, near Mauritius, is known only from a single collection of sterile plants. It differs from G. scinaioides in lacking an apical pit, having periclinal medullary filaments which loosely fill the internal cavity rather than being restricted to a central axis, and producing a cortex composed of files of closely appressing cells, rather than a loose matrix. Gloiophloea articulata appears more closely allied to the family Gymnoploeaceae of the order Gigartinales, in particular the genus Nemastoma J. Agardh. Sexual material needs to be examined, however, before the species can be placed without doubt. Gloiophloea perrinae Levring from southern Australia was distinguished from G. scinaioides in having a firmer texture and in minor differences in its cortical composition and cystocarp shape. Variations in these characters occur within the type species, however, and are probably due to age and growing conditions. Gloiophloea perrinae is therefore reduced to synonymy with G. scinaioides. In culture, carpospores of G. scinaioides give rise to a filamentous tetrasporophyte which produces cruciate tetrasporangia. Tetraspores in turn produce a filamentous protonemal gametophyte which gives rise to the fleshy gametophyte directly. The life history of Gloiophloea is therefore identical to that of the closely related genus Scinaia Bivona-Bernardi.

Chrysochromulina breviturrita Nicholls is a freshwater prymnesiophyte which may be an im­ portant indicator of lake acidification (Kling 1981; Nicholls et al 1982; Wehr et al 1985) and also has been reported to form blooms associated with undesirable odours in lakes in north-eastern North America (Nicholls et aI1982). Decreasing pH has long been known as an increasingly im­ portant ecological factor in lakes subject to acidic precipitation (Hendrey et al 1976). Inasmuch as C. breviturrita is an indicator organism of mod­ erate acidification of lakes, it is essential that taxonomic identification of this organism be ac­ curate. Identifications in the Prymnesiophyceae are based primarily on scale morphology and we report here some features of the scales of C. brevi­ turrita which have not been described in pre­ vious studies on this organism (Nicholls 1978; Kling 1981; Kling & Kristiansen 1983). C. breviturrita was isolated from blooms which occurred in three sites: Cinder Lake in Hindon Twp., Haliburton Co., Ontario (78°56'W, 45°04'N) July 1982; Bat Lake, Minden Twp., Haliburton Co., Ontario (78°41'W, 44°56'N) July 1984; Lake 302, Experimental Lakes Area, On­ tario (93°46'W, 49°41'N) August 1984 and grown in an enriched lake water medium prepared by filtering water from the lake through a 0.45 JLm membrane filter and adding 100 JLM (NH4)2P04, 0.3 JLM thiamine and 0.37 nM vitamin BI2 fol­ lowed by autoclaving. The cultures were ren­ dered axenic by a combination of micropipette isolations and antibiotic treatments. Cells for ultrathin sectioning (Fig. 3) were fixed in 2% glutaraldehyde in 0.05 M phosphate buffer

Gyromitus disomatus Skuja has been found in several Ontario lakes. Electron microscopy of specimens from six lakes revealed a covering of scales which are identical in structure to those known for the coccolithophorid Hymellomonas prenallti Lecal. Gyromitus shows no taxonomic relationship to Hymenomonas. The chemical composition of Gyromitus scales is shown by X-ray analysis to be silica, not calcium, and smaller organic scales and a haptonema are not present. It is shown that the original description of Hymellomonas prenanti is incomplete and could well have been of Gyromitus. H. prenanti is probably a superfluous synonym for G. disomatus.

Quaternariella obseura gen. et sp. nov. (Prymnesiophyceae) is described on the basis of electron microscopy of shadow cast whole mounts prepared from water samples collected in the summer 1977, at localities in the vicinity of Godhavn, West Greenland. The new taxon comprises small biflagellate coccolithophorids with a short coiling haptonema. The periplast is composed of at least two layers of organic scales of which the outer larger circular scales support crystallite packages, each a group of four minute rhombohedrons. Small, unmineralized oval scales are present below the coccolith base-plates.

Prymnesium calathiferum sp. nov. is described from samples taken during a summer phytoplankton bloom dominated by Cerataulina pelegica (Cleve) Hendey, which occurred in Bream Bay off Northland, New Zealand. This new species, which is closely related to P. parvum Carter, was implicated in fish and shellfish mortalities in the area. Isolates of P. calathiferum were examined using both light and electron microscopy. Prymnesium calathiferum may be separated from the other six species of Prymnesium by several features. Firstly, P. calathiferum has elaborate wicker-basket-like external scales which are unique to this species, and secondly, it has the greatest ratio of flagella to cell length and the lowest ratio of haptonema to flagella length of all known Prymnesium species.