Mitsuo Chihara

LEPIDODINIUM VIRIDE GEN. ET SP. NOV. (GYMNODINAIALES, DINOPHYTA), A GREEN DINOFLAGELLATE WITH A CHLOROPHYLL A- AND B-CONTAINING ENDOSYMBIONT1,2

A further description of the green dinoflagellate, strain Y‐100, with a chlorophyll a‐ and b‐containing endosymbiont is given with special emphasis on the morphology of the host cell. The host dinoflagellate cell is unarmored and has a gymnodinoid overall appearance. The theca or amphiesma basically consists of the outer membrane and flattened thecal vesicles in which no thecal plates are developed. Unusual hand basket‐shaped scales cover the entire cell surface together with a layer of mucilaginous material. These findings suggest that the organism is a new member of the Gymnodiniaceae (Gymnodiniales). We propose the name Lepidodinium viride gen. et sp. nov. The ultrasturcture of the host cell is typical of the dinoflagellates; however, the organism has 1) an unusual cytoplasmic projection that may be a homologue of the peduncle, 2) a single membrane‐bounded body containing membranous sheets, closely situated next to the endosymbiont, and 3) an electron opaque network‐forming appendage surrounding the transverse flagellum. Name of these features have been found in other dinoflagellates.

A green dinoflagellate with chlorophylls A and B: morphology, fine structure of the chloroplast and chlorophyll composition

A green‐colored marine unicell has been grown in unialgal culture and its morphology, chloroplast fine structure, and chlorophyll composition investigated. The organism is typical of dinoflagellates in its shape, flagellation, nucleus, mitochondria, and trichocysts. It is similar to Gymnodinium but possesses fine body scales. Chloroplasts and two kinds of vesicles bounded by double membranes, but no organelles obviously identifiable as nuclei or mitochondria, are associated in ribosome‐dense cytoplasm separated by a double membrane from the dinophycean cytoplasm. The chloroplasts are unlike any previously reported for dinoflagellates. Each is enclosed by an envelope consisting of a double membrane. Chloroplast lamellae consist of three appressed thylakoids. Interlamellar pyrenoids are present. Pigment analysis reveals chlorophylls a and b but not chlorophyll c. It seems likely that the organism is an undescribed dinoflagellate containing an endosymbiont with chlorophylls a and b and that the reduction of the endosymbiont nucleus and mitochondria has permitted a more initmate symbiosis.

ACARYOCHLORIS MARINA GEN. ET SP. NOV. (CYANOBACTERIA), AN OXYGENIC PHOTOSYNTHETIC PROKARYOTE CONTAINING CHL D AS A MAJOR PIGMENT1

The phylogenetic position of an oxygenic photosynthetic prokaryote containing chl d as a major pigment, which have been tentatively named “Acaryochloris marina,” was analyzed using small subunit rDNA sequences. Phylogenetic relationships inferred among A. marina, selected strains from the Cyanobacteria, and plastids showed that A. marina was within the cyanobacterial radiation. The A. marina lineage diverged independently from other phylogenetic subgroups of the Cyanobacteria. No organism was found to be identical or related closely to A. marina by a similarity search and phylogenetic analysis. Based on these results, in addition to the reported characteristics of the cell morphology, pigment composition, and photosynthesis, a new taxon, Acaryochloris marina Miyashita et Chihara gen. et sp. nov., is formally proposed for the oxy‐genic photosynthetic prokaryote.

Morphology, ultrastructure and taxonomy of the raphidophycean alga Heterosigma akashiwo

Heterosigma akashiwo and its related algae were re-examined by light and electron microscopes using cultured materials including type cultures of bothH. akashiwo andH. inlandica as well as specimens referred to asOlisthodiscus luteus maintained in CCAP and UTEX. All the strains examined were similar to one another in appearance and ultrastructural features. They can be accommodated in a single species,H. akashiwo, which has been invalidly published.In this paper, the genus is validly desribed by providing a Latin diagnosis and designating a type species. Ultrastructural characteristics are also given for the genus.

Productivity of theEcklonia cava community in a bay of Izu Peninsula on the Pacific Coast of Japan

Net production of theEcklonia cava community was monitored on a monthly basis for a year, and annual net production was estimated. Growth rate of blades reached a maximum of about 13 g dry wt·m−2·day−1 in spring and a minimum of about 2 g dry wt·m−2·day−1 in late summer. Annual production of blades was calculated to be 2.84 kg dry wt·m−2·year−1. If the growth of stipes is taken into account, annual net production is estimated to be about 2.9 kg dry wt·m−2·year−1. Standing crop was monitored monthly for two and a half years, and a close negative correlation was found between seasonal change in standing crop and net production. Standing crop reached a maximum of about 3 kg dry wt·m−2 in summer and a minimum of about 1 kg dry wt·m−2 in winter. Low productivity in summer at a period of maximum biomass may be explained by the dense canopy and the large area of reproductive portion occupying a blade, which diminish net assimilation.

Revision of the genusTetraselmis (Class Prasinophyceae)

Information available on the structure of species belonging to the generaTetraselmis, Platymonas andPrasinocladus has been reviewed. Detailed comparison of these data has convinced the authors that species in these genera all belong to the same genus. Stalk development by cast-off thecae, a characteristic used to definePrasinocladus, is variable within different species and is not reliable for separation of a genus. Similarly, the penetration of the pyrenoid by a lobe of the nucleus cannot be held reliable in separation of these genera because it occurs in varying degree in different species.Platymunas G.S. West (1916),Prasinocladus Kuckuck (1894) andAulacochlamys Margalef (1946) are considered to be synonyms ofTetraselmis Stein (1878).Tetraselmis is redescribed using characters visible with light and electron microscopy as well as life-history characteristics. The description reviews information on many species ofTetraselmis that have been found in the western and eastern Pacific as well as species from Great Britain. It is determined that variations in life-histories may be explained by different environmental factors, whereas structure of vegetative cells, as viewed by electron microscopy, seems to be quite stable and characteristic for each species.

ABSOLUTE CONFIGURATION ANALYSIS OF THE FLAGELLAR APPARATUS OF PTEROSPERMA CRISTATUM (PRASINOPHYCEAE) AND CONSIDERATION OF ITS PHYLOGENETIC POSITION1

Pterosperma cristatum Schiller, a member of the Pra‐sinophyceae, was examined with light and electron microscopy with special attention on the absolute configuration of flagellar apparatus components and associated structures. This alga is characterized by asymmetrically arranged basal bodies, connecting fibers and microtubular roots. The microtubular root system is homologous with the cruciate root system, the so‐called X‐2‐X‐2 root system typical of non‐charophycean green algae. Two ducts are associated with microtubular roots. A similar flagellar apparatus and duct system was found in two other prasinophyte genera, Pyramimonas and Halosphaera. The close phylogenetic affinity of these three genera is discussed.

Studies on the ultrastructure and taxonomy of the genusTetraselmis (Prasinophyceae)

Comparative ultrastructural investigations on many isolates ofTetraselmis from Japan and the Pacific coast of North America, and on cultures from the Culture Centre of Algae and Protozoa, Cambridge, England, have revealed that the species have characteristic fine structural features of the pyrenoid. Using the pyrenoid structure as a basic character it is proposed that the genus be subdivided into four subgenera,Tetraselmis, Prasinocladia, Tetrathele andParviselmis. In the present paper, species of the subgenusTetraselmis, includingT. cordiformis, T. ascus, T. convolutae andT. astigmatica sp. nov., are described in detail.

Morphology and ultrastructure ofOlisthodiscus luteus (Raphidophyceae) with special reference to the taxonomy

A flattened discoid flagellate collected from the Seto Inland Sea, Japan, has been examined by light and electron microscopy. This alga agrees well withClisthodiscus luteus Carter. It has two heterodynamic flagella emerging from a furrow on the upward side of the cell that contains six to 13 yellow-green parietal chloroplasts. It does not rotate but smoothly glide while swimming. The cell has a thin periplast lying between the plasmalemma and chloroplasts. Neither lipid bodies nor mucocysts are seen in the periplast. The pyrenoid matrix being free from thylakoids is penetrated by several cytoplasmic canals from various directions. There are no vesicles of periplastidal network in the narrow space between chloroplast envelope and chloroplast ER.The ultrastructural features ofO. luteus are unique, sharing certain characters with the raphidophycean algae but others withPseudopedinella pyriformis, a unique member of the Chrysophyceae.

Ultrastructure and taxonomy of fibrocapsa japonica class raphidophyceae

Abstract The cell morphology and ultrastructure of Fibrocapsa japonica were examined and compared with those of related taxa. The results suggested that Fibrocapsa must be treated as an autonomous genus separate from Chattonella , and its circumscription should follow the description of Toriumi and Takano (1975) with some amendments based on the new criteria presented in this study.