Dinoflagellata

Dinoflagellata, so called by O. Bütschli (= the Cilioflagellata of E. Claparide and H. Lachmann), a group of Protozoa, characterized as Mastigophora, provided with two flagella, the one anterior extended in locomotion, the other coiled round its base, or lying in a transverse groove. The body is bounded by a firm pellicle, often supplemented by an armour (“lorica”) of cuticular cellulose plates, with usually a marked longitudinal groove from which the anterior flagellum springs, and an oblique or spiral transverse groove for the second flagellum. In Polykrikos (fig. 2, 9) there are eight transverse grooves each with its flagellum. The armour-plates are often exquisitely sculptured, and may be produced into spines or perpendicular plates to give greater surface extension, as we find in other plankton organisms. The cortical plasma may protrude pseudopodia in the longitudinal groove; it contains trichocysts in several species, true nematocysts in Polykrikos. It contains chromatophores in many species, coloured by a mixed lipochrome pigment which appears to be distinct from diatomin. The endoplasm is ramified between alveoli; it contains a large nucleus (in Polykrikos there are eight nuclei, accompanied by smaller, more numerous bodies regarded by O. Butschli as micro-nuclei). Besides the other spaces are definite rounded or oval vacuoles with a permanent pellicular wall termed by Schutt “pusules”; these open by a duct or ducts into the longitudinal groove. They enlarge and diminish, and are possibly excretory like the “contractile vacuoles” of other Protista; though it has been suggested that by their communication with the medium they subserve nutrition. Nutrition is of course holozoic or saprophytic in the colourless forms, holophytic in the coloured; but these divergent methods are exhibited by different species of the same genus, or even by individuals of one and the same species under different conditions. Binary fission has been widely observed, both in the active condition or after loss of the flagella: it differs from that of true Flagellates in not being longitudinal, but transverse or oblique (fig, 2, 2). Repeated fission (brood-formation) within a cyst has also been observed, as in Pyrocystis and Ceratium; and possibly the chains of Ceratium and other (fig. 2, 5 and 6) genera are due to the non-separation of the brood-cells. Conjugation of adults has been observed in several species, the most complete account being that of Zederbauer on Ceratium hirundinella (marine): either mate puts forth a tube which meets and opens into that of the other (as in some species of Chlamydomonas and Desmids); the two cell-bodies fuse in this tube, and encyst to form a resting zygospore. The Dinoflagellates are relatively large for Mastigophora, many attaining 50 µ (1/500”) in length. The majority are marine; but some genera (Ceratium, Peridinium) include fresh-water species. Many are highly phosphorescent and some by their abundance colour the water of the sea or pool which they dwell in. Like so many coloured Protista, they frequently possess a pigmented “eye-spot” in which may be sunk a spheroidal refractive body (“lens”).  
  
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Fig. 2.  
From Delage and Hérouard’s Traité de zoologie concrete, by permission of Schleicher Frères.  
  
  
1\. Modified from Schütt, Ornithoceras.  
2\. Diagram of transverse fission of a Dinoflagellate.  
3\. After Schutt, Exuviaeella.  
4\. After Stein, Prorocentrum. | 5, 6. Ceratium, single and series.  
7\. Pouchetia fusus (Schutt).  
8\. Citharistes.  
9\. After Butschli, Polykrikos.  
  
The affinities of the Dinoflagellata are certainly with those Cryptomonadine Flagellates which possess two unequal flagella; the zoospores or young of the Cystoflagellates are practically colourless Dinoflagellates.

1\. Gymnodiniaceae: body naked, or with a simple cellulose or gelatinous envelope; both grooves present. Pyrocystis (Murray), often encysted, spherical or crescentic, becoming free within cyst wall, and escaping whole or after brood-divisions as a form like Gymnodinium; Gymnodinium (Stein); Hemidinium (Stein); Pouchetia (Schütt) (fig. 2, 7) with complex eye-spot; to this group we may refer Polykrikos (Bütschli) (fig. 2, 9), with its metameric transverse grooves and flagella.

2\. Prorocentraceae (Schütt) ( = the Adinida of Bergh); body surrounded by a firm shell of two valves without a girdle band; transverse groove absent; transverse flagellum coiled round base of longitudinal. Exuviaeella (Cienk.) (fig. 2, 3); Prorocentrum (Ehrb.) (fig. 2, 4).

3\. Peridiniaceae (Schütt); body with a shell of plates, a girdle band along the transverse groove, in which the transverse flagellum lies. Genera, Peridinium (Ehrb.) (fig. 1), fresh-water and marine; Ceratium (Schrank) (fig. 2, 5, 6), fresh-water and marine; Citharistes (Stein); Ornithoceras (Claparède and Lachmann) (fig. 2, 1).

Literature.—R. S. Bergh, “Der Organismusder Cilioflagellaten,” Morphol. Jahrbuch, vii. (1881); F. von Stein, Organismus der Infusionsthiere, Abth. 3, 2. Hälfte; Die Naturgeschichte der arthrodelen Flagellaten (1883); Bütschli, “Mastigophora” (in Bronn’s Thierreich, i. Abth. 2), 1881-1887; G. Pouchet, various observations on Dinoflagellates, Journal de l’anatomie et de la physiologie (1885, 1887, 1891); F. Schütt, “Die Peridineen der Plankton Expedition” (Ergebnisse d. Pl. Exed. i. Th. vol. iv. 1895); and “Peridiniales” in Engler and Prantl’s Pflanzenfamilien, vol. i. Abt. 2 b. (1896); Zederbauer, Berichte d. deutschen botanischen Gesellschaft, vol. xx. (1900); Delage and Hérouard, Traité de zoologie concrète, vol. i. La Cellule et les protozoaires (1896).

(M. Ha.)

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