Richard E. Norris

CYTOLOGY AND ULTRASTRUCTURE OF CHLORARACHNION REPTANS (CHLORARACHNIOPHYTA DIVISIO NOVA, CHLORARACHNIOPHYCEAE CLASSIS NOVA)1

The green amoeboid cells of Chlorarachnion reptans Geitler are completely naked and each contains a central nucleus, several bilobed chloroplasts each with a central projecting pyrenoid enveloped by a capping vesicle, several Golgi bodies, mitochondria with tubular cristae, extensive rough ER, and a distinct layer of peripheral vesicles. Complex extrusome‐like organelles occur rarely in both the amoeboid and flagellate stages. The only organelles entering the reticulopodia are mitochondria, but microtubules are also present. The chloroplasts contain chlorophylls a and b, but histochemical tests suggest that the carbohydrate storage product probably is not a starch. The chloroplast lamellae are composed of one to three thylakoids or form deep stacks. A girdle lamella and interlamellar partitions are absent. Each chloroplast is bounded by either four separate membranes, a pair of membranes with vesicular profiles between them, or three membranes; all three arrangements may occur in the same chloroplast. A periplastidal compartment occurs near the base of the pyrenoid where there are always four surrounding membranes. The compartment has a relatively dense matrix and contains ribosome‐like particles and small dense spheres; it extends over and into a deep invagination in the pyrenoid where its contents are enclosed in a double‐membraned envelope which is penetrated by wide pores. The zoospores are ovoid and each bears a single laterally inserted flagellum which appears to be wrapped helically around the cell body during swimming. The flagellum lies in a groove in the cell surface and bears fine lateral hairs. Neither a second flagellum or vestige of one, nor an eyespot, is present. A single microtubular root and a larger homogeneous root run from the flagellar base parallel to the emerging flagellum, between the nuclear envelope and the plasmalemma. In the simple flagellar transition region, fine filaments connect adjacent axonemal doublets. A detailed comparison of C. reptans with all other algal taxa results in the conclusion that it must be segregated in the new class Chlorarachniophyceae, the only class in the new division Chlorarachniophyta. The possibility that C. reptans evolved from a symbiosis between a colorless amoeboid cell and a chlorophyll b‐ containing eukaryote is considered, but the possible affinities of the symbiont remain enigmatic. The implications of the unique chloroplast structure of C. reptans for current hypotheses concerning the origin of chloroplasts are discussed.

Nanoplankton species predominant in the subarctic Pacific in May and June 1978

Abstract Oceanic nanoplankton (2 to 20 μm) collected in May and June of 1978 from surface waters of the Gulf of Alaska (136 to 149°W) was examined in the scanning electron microscope. Species within the Prymnesiophyceae, Bacillariophyceae, and Cryptophyceae were numerically predominant. The most common and abundant forms were: Phaeocystis pouchetii (Hariot) Lagerth. (free-swimming stage), Minidiscus trioculatus (F.J. Taylor) Hasle, Nitzschia cylindrus (Grun.) Hasle cf., 2 Cryptomonas species, 4 choanoflagellate species, 5 new siliceous cysts, and an arcgeomonad cyst. Species within the Dinophyceae, Chrysophyceae, and Prasinophyceae were less important. Reasons are discussed for the success of the methods used for preservation and analysis of nanoplankton.

THE GROWTH AND MORPHOLOGY OF THE SILICOFLAGELLATE DICTYOCHA FIBULA EHRENBERG IN CULTURE1,2

Dictyocha fibula was cultured in an enriched seawater medium from collections taken at Edmonds, Washington. The optimum temperature for growth is 10 C at salinity 24% and 160 ft‐c illumination in Provasoli enriched seawater at the concentration of 7.5 ml/liter seawater. Average generation time is 49 hr. In addition to swimming cells with skeletons, swimming cells without skeletons and nonswimming coenocytes were observed in clonal cultures at 15 C.

AN ABERRANT CHRYSOPHYCEAN ALGA PELAGOCOCCUS SUBVIRIDIS GEN. NOV. ET SP. NOV. FROM THE NORTH PACIFIC OCEAN1,2

A description and Latin diagnosis of the new genus and species Pelagococcus subviridis Norris is presented. Pale green, spherical cells appeared in enrichment cultures initiated from water samples collected at stations between 132°W and 175°W and between 45°N and 50°N in the North Pacific Ocean. The alga is placed in the Chrysophyceae based on organelle fine structure, and presence of chlorophylls a and c, diatoxanthin, diadinoxanthin and two fucoxanthin‐like pigments. There are a number of atypical features however; the two fucoxanthin‐like pigments differ from true fucoxanthin; there is only chlorophyll c2 (not C1+ c2); probably mostly a, not β‐carotene; half of the chlorophyll a is in the form of chlorophyllide a.

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.

FINE STRUCTURE OF CELL DIVISION IN PYRAMIMONAS PARKEAE NORRIS AND PEARSON (CHLOROPHYTA, PRASINOPHYCEAE)1

Cell division in Pyramimonas parkeae is described and compared with some other green algae. The first indication of mitosis is division of the chloroplast, accompanied by growth of a prominent microbody, followed by replication of the 4 basal bodies. Also closely timed with this is the replication of the Golgi and other components of the basal body complex. Two basal body complexes separate, each taking a position at either pole of the nucleus which has migrated to a characteristic position just beneath the plasmalemma of a broadened and flattened flagellar pit. Cytokinesis is accomplished by the fusion of ducts and vesicles with the simultaneous release of scales to the newly formed exterior. Cells swim throughout division.

Siliceous nanoplankton I. Newly discovered cysts from the Gulf of Alaska

Siliceous nanoplankton in the size range 2.5 to 5.5 μm and of a type hitherto undescribed are reported from Eastern Subarctic water samples. Nine distinct cell types were recognizable, each possessing an unusual tetrahedral symmetry, resulting from the arrangement of 8 siliceous plates. Since the cells were abundant (maximum concentration of about 7×105 cells 1-1) and were distributed over a wide oceanic area (136° to 149°W), they could well play an important role in the food web in Subarctic seas. Similar cells were found simultaneously in Antarctic waters (see following paper: Silver et al., 1980), where they were as abundant and widespread as in the Subarctic. Evidence that the siliceous forms are likely a cyst stage and that they may be part of the life cycle of species of siliceous oceanic choanoflagellates is presented.

Plant Chimeras Used to Establish de novo Origin of Shoots.

When African violet leaf explants are cultured in vitro, buds and shoots develop directly from the upper leaf surfaces. Three developmentally different African violet chimeras were cultured, and in each case adventitious shoots that developed into plants had the parent chimera pattern. A multicellular origin of the adventitious buds accounts for these results.

UNUSUAL PHENOMENA IN THE LIFE HISTORIES OF FLORIDEAE IN CULTURE1

Several Florideae grown in natural seawater media under defined laboratory conditions have interesting and unusual life histories. Antithamnion occidentale males of one generation produced tetraspores that gave rise to nonsporangiate males. The functional females of A. pygmaeum developed spermatangia and tetrasporangia; the tetraspores formed new females. Antithamnion defectum tetrasporophytes of one generation bore spermatangia in addition to tetrasporangia; the tetraspores gave rise to typical gametophytes. Tetraspores from successive generations of Callitham‐nion sp. developed into tetrasporophytes and males but no females were produced. Functional female gametophytes of Platythamnion sp. bore abortive tetrasporangia. Field‐collected plants of two species of Fauchea produced tetraspores that yielded additional sporangiate plants: those of F. pygmaea being bispo‐rangiate and tetrasporangiate, and those of F. lacini‐ata being strictly tetrasporangiate.

STRUCTURE AND REPRODUCTION OF AMANSIA AND MELANAMANSIA GEN. NOV. (RHODOPHYTA, RHODOMELACEAE) ON THE SOUTHEASTERN AFRICAN COAST

Four species of Amansia Lamouroux were initially found in Natal. More Complete studies on these species revealed a new genus, Melanamansia, Which is described on the basis of presence of two dorsal pseudopericentral cells in two new species from Natal (M. seagriefii sp. nov. & M. fimbrifolia sp. nov.) in addition to other structural characters and features of pigmentation and reproduction. Pseudopericentral cells are not present in the type species of Amansia, A. multifida Lamouroux. The other two species of Amansia occurring in Natal, A. glomerata C. Agardh & A. loriformis sp. nov., have characters similar to the type species. Comparison of species from other regions of the world has shown that eight additional species, previously assigned to Amansia, belong to the new genus.