Thecamoeba quadrilineata (Carter, 1856) Lepşi, 1960
Diagnosis: Stationary amoebae knobby but very little or not at all wrinkled; in locomotion flattened, oblong or elongate elliptical in outline, with broadest point usually just anterior to middle of amoeba and with posterior end usually broadly rounded; several parallel dorsal folds extending far anteriorly common in locomotive forms; hyaloplasm an antero-lateral crescent sometimes extending three-quarters of length posteriorly; nucleus with a single central nucleolus of homogeneous texture: both nucleus and nucleolus highly deformable; a single contractile vacuole, highly deformable, with diameter to 15 µm.
Dimensions: length usually about 35-80 µm (mean 50-55 µm), but giant forms to 170 µm long sometimes found; length: breadth ratio approximately 1.1-2.5 (mean 1.7-1.8); nucleus 7.7-11.0 µm, to 15.0 µm in giant forms, with nucleolus usually 4.6-7.4 µm.
Remarks: Nucleus and nucleolus together are subject to marked deformation, so that they might be spherical, ovoid, or more or less reniform or triangular. The nucleolus is never partly or wholly fragmented as in T. sphaeronucleolus.
Page (1977) writes: Undoubtedly T. quadrilineata has been regularly confused with T. striata ever since the description of the latter species. The only immediately noticeable difference is in nuclear structure. Penard (1890) in his original description of T. striata said: ‘ Noyau clair, oval-allongé, a nucléole divisé en deux croissants étroits qui vont plaquer contre la membrane nucléaire tres fine.’ However, in 1902 he suggested a variety of nuclear structures: ‘ En principe, il renferme un nucléole central, assez gros, en général percé de quelques vacuoles ou lacunes; parfois on n’y trouve plus qu’une grosse vacuole centrale . . . , et la matière chromatique est visible comme un anneau (en realité c’est une sphère creuse); puis eet anneau se voit dans d’autres exemplaires, remplacé par des fragments plus ou moins ronds ou allongés, mais toujours arrondis a leurs extrémités. Enfin on ne voit plus que quelques sphérules pourvues souvent de vacuoles . . . , nageant dans Ie suc cellulaire, qui lui-même est toujours finement granulé. D’autres fois il reste un nucléole central, assez grand encore, et d’autres sphérules tres petites tout autour.’
Cash (1905) did not describe the nucleus of the ‘Amoeba striata‘ which he found other than as ‘ round ‘, but his figures show nuclei resembling those of T. quadrilineata.
Although Carter (1856) gave no adequate textual description of his Amoeba quadrilineata, his drawing shows very clearly the general form, division of hyaloplasm and granuloplasm, dorsal striae, contractile vacuole, and nucleus with structure as described here. This must be recognized as a valid species, while maintaining also the separate existence of a species T. striata. The separation of the two distinct species is based on constancy of nuclear structure in four clonal strains of T. striata and two of T. quadrilineata, as well as other suggestive differences such as growth rate and adhesiveness to a glass sub-stratum. It must be noted that Penard’s varied description of T. striata were based on mixed material collected from the field at different times.