Tintinnoinea
Morphologic outline

The body of tintinnids is typically made up of a contractile cell which is attached by a stalk to the posterior portion of the lorica (Cymatocylis convallaria intro). In most cases, the cell fills a little less than half the lorica, its volume varying with food availability and the life cycle stage. It has one micronucleus and 2 or more macronuclei, and the commonest cytoplasmic inclusions are mitochondria, vesicular endoplasmic reticulum, lipid and digestive vacuoles, granules of lorica-building material (tintinnid reproduction 1), and endocytoplasmic bacteria. Major external features include the ciliary and infraciliary components located in the somatic and buccal regions (Brownlee, 1977; Laval-Peuto et al., 1979; Laval-Peuto and Brownlee, 1986; Sleigh, 1989). The adoral membranelles (Cymatocylis convallaria intro, cell intro, oral membranelles, striae), around the buccal region, commonly forming a closed spiral that comprises 2 or 3 longitudinal rows of kinetosomas; the paroral membrane (cell intro), which consists of a single row of kinetosomas. The capsules (= extrusomes), membrane-bound extrusible bodies usually sub-pelicularly located (Corliss, 1979), of variable shape, size and number; these capsules are aligned in striae (oral membranelles, striae) associated to the adoral membranelles, and are probably involved in feeding processes (Laval, 1971, 1972; Laval-Peuto et al., 1979; Capriulo et al., 1986). The entire cell, including the adoral membranelles, the paroral membrane and the striae, is enclosed by a continuous membrane known as perilemma (Laval-Peuto, 1975; Cymatocylis convallaria intro). Based on their cytological characteristics, tintinnids are included in the suborder of the Ciliophora in the class Polyhymenophorea, subclass Spirotrichia (Levine et al., 1980).

The lorica of a tintinnid consists of a proteic bowl which is always open at its anterior (oral) end, and usually (but not always; see E. fraknoi, C.? melchersi) closed at the posterior (aboral) end (Cymatocylis convallaria intro). The oral end of the lorica typically presents a collar which may be fenestrated (Dictyocysta, D. mitra 6, D. elegans 13), annulated (Codonellopsis; C. gaussi 3), everted (Cyttarocylis and Salpingella; C. cassis/ plagiostoma and Salpingella acuminata respectively), or constricted (Codonella; C. amphorella). The aboral end often bears a horn or a pedicel (a horn provided with a knob or a skirt, and a lance; X. paradoxa, X. heros, X. pulchra). The characteristics of the oral end are quite constant generically, thus an important diagnostic element. On the other hand, the aboral end and all structures related to it (knob, lance, skirt) are highly variable in length, width and general morphology, even at the intraspecific level. The various processes involved in building the lorica, and changes in the lorica during the tintinnid life cycle are thought to explain, at least in part, the high intraspecific polymorphism observed in most species (Alder, 1995), particularly in Antarctic ( van der Spoel, 1986; Boltovskoy et al., 1990; Williams et al., 1994; Alder, 1995) and Arctic (Burkovskii, 1973; Davis, 1978, 1981) forms.

The lorica is built from posterior to anterior end. Lorical material (a chitin-like substance) is poured out through a pore or gutter, and then distributed around the cell by the beating of the somatic ciliature (Laval-Peuto, 1981). If the first lorica (protolorica) built by the mother cell (proter) is lost, the naked mother cell (trophont) is capable of building a new, totally spiralled one (paralorica = coxliella form) which can only be modified through the addition of helical epiloricae (tintinnid reproduction 1, tintinnid reproduction 2, types of epilorca 1, types of epilorca 2, types of epilorca 3; Laval-Peuto, 1977; Laval-Peuto and Brownlee, 1986). The structure of the lorica wall (continuous in most protoloricae; partially to totally spiralled in paraloricae, epiloricae, and some protoloricae; may be highly variable intraspecifically, whereas its texture (which depends on its chemical composition and the degree of hardening of the lorical material) is less variable (Laval-Peuto, 1981).

Some genera may accrete biogenic and/or mineral particles to their loricae. These particles may cover the whole lorica (Tintinnopsis complex; for illustrations see species listed under genus Tintinnopsis), or mainly its bowl (genus Codonellopsis; for illustrations see species listed). Although species typically with such an agglutinated lorica may often have a hyaline lorica in the open ocean, genera lacking this capability (genus Cymatocylis; for illustrations see species listed) always remain hyaline, even in waters with abundant sediment suspended from the sea floor and/or the continental margin. Generally, larger species have a hyaline lorica, while agglutinated ones are far more common in the smaller taxa. Apparently, this phenomenon is an evolutionary adaptation to predation (Capriulo et al., 1982).