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Thalassiothrix frauenfeld var? javanica Grunow 1881 was examined from the type locality and found to be conspecific with Asterionella synedriformis Greville 1865. Scanning electron microscopic examination of the velum structure demonstrated an affinity to Thalassionema but not specifically to Thalassionema frauenfeld, and the new combination Thalassionema synedriforme (Greville) Hasle is thus proposed. Thalassiothrix spathulata sp. nov. differs from other species of the genus by the spineless footpole being expanded, contributing to a spathulate valve outline, and by the marginal location of the labiate process at the footpole.
INTRODUCTION
Thalassionema Grunow ex Mereschowsky and Thalassiothrix Cleve et Grunow are long, needle-shaped, marine, planktonic diatoms belonging to the family Thalassionemataceae Round (in Round et al. 1990). The two genera were originally distinguished by cell polarity and presence or absence of marginal spines (Cleve & Grunow 1880; Van Heurck 1881). However, Hallegraeff (1986) found by using electron microscopy that the fine structure of the areolae was a more consistent diagnostic character.
The preparation of a monograph on Thalassionemataceae has revealed several nomenclatural problems. The typification of Thalassiothrix and Synedra nitzschioides Grunow [Thalassionema nitzschioides (Grunow) Mereschkowsky] has been dealt with previously (Silva & Hasle 1993, 1997). In the present paper, in addition to describing a new species of Thalassiothrix from tropical and subtropical waters, I report the results of a study of the taxonomic status of Thalassiothrix frauenfeld var? javanica Grunow (in Van Heurck 1881). Because Grunow indicated that Asterionella synedriformis Greville (1865) was partly referable to T. frauenfeld, the types of the two names have been studied.
MATERIALS AND METHODS
A syntype of A. synedriformis (slide BM 3229, Greville Collection, J.L. Palmer 1863, Hong Kong, see Williams 1988) and slides W 2172a, b, Grunow Collection, Java, the type locality of T. frauenfeld var. javanica, were examined. Net samples IMBB 1405 and IMBB 1409, Gulf of Thailand, were used for electron microscopy.
The description of the new species is based on net samples from the Gulf of Thailand (IMBB 1405 and IMBB 1409), the Indian Ocean (IMBB 445 and IMBB 446), off Ecuador (IMBB 273, IMBB 279, and IMBB 1467), and off Peru (IMBB 183 and IMBB 185).
The following acronyms are used: BM = British Museum (Natural History), London; W = Naturhistorisches Museum, Vienna; IMBB = Department...