A companion to the identification of cryptomonad flagellates (Cryptophyceae = Cryptomonadea).

This paper provides an annotated synopsis of cryptomonad morphology, ultrastructure, taxonomy and nomenclature. Its aim is to aid cryptomonad identification down to whatever taxonomic level is realistically possible, based on currently used taxonomic criteria. It is intended as a `companion', i.e. a tool to be used in conjunction with the existing literature, rather that a self-contained guide making it possible to identify all known cryptomonads. A nominalistic philosophy is adopted as far as possible, whereby taxa are considered to be acceptable as long as their names have been published in accordance with the nomenclatural rules and prevailing taxonomic practice. A new combination is proposed, Pyrenomonas duplex comb. nov. (basyonym: Rhodomonas duplex Hill & Wetherbee). Although identification keys are provided whenever possible, an empirical, multilateral approach is followed with a view to facilitating cryptomonad identification by non-specialists using only what equipment is available to them at any one time. This approach is based on the fact that different degrees of taxonomic resolution can be achieved by using different combinations of observation techniques. Identification rationales are based on the following techniques (in ascending order of complexity, time-consumption, and financial cost): light microscopy, scanning electron microscopy, and transmission electron microscopy, supplemented by freeze-fracture investigations and spectrophotometry. Information given under any one section is cross-referenced to other relevant sections by means of italicized links. It is envisaged that this paper will constitute the core of an interactive identification tool to be published electronically on the Internet in due course. Amongst the factors contributing to the difficulties of cryptomonad identification, the most important appear to be the following: the state of flux of cryptomonad classification systems; typification difficulties, especially the historical disregard for the type method and the incorrect belief that preserved type materials of cryptomonads do not exist; difficulties in relating `classical' taxa and newer ultrastructural descriptions; the description of monospecific genera; inadequate methodology; and the long-standing gap between ecological studies on the one hand and cryptomonad taxonomy and systematics on the other. A wider use of scanning electron microscopy is advocated wherever possible because it appears to be a highly informative and cost-effective tool for discovering, describing, and mapping cryptomonad biodiversity. It is also to be hoped that collaborative projects between ecologists and taxonomic specialists will start to fluorish soon. [ABSTRACT FROM AUTHOR]