Entosiphon Stein, 1878 (ref. ID; 4950)
Order Heteronematales (ref. ID; 4852)

[ref. ID; 1618]
Oval, flattened; more or less rigid; flagella arise from a cytostome, one flagellum trailing; protrusible cytopharynx a long conical tubule almost reaching posterior end; nucleus centro-lateral; fresh water. (ref. ID; 1618)

Entosiphon cuneatiformis Lackey, 1962 (ref. ID; 3090 original paper)
Description; It is almost circular in outline, almost flat ventrally, and with six folds, deep anteriorly and gradually flattening out posteriorly, forming five lobes on the dorsal anterior surface. The innermost the these rather overhangs the mouth opening but the middle two and two lateral lobes terminate at about the level of the mouth, so that there appears to be an anterior median papilla. The pellicle is rigid and thick. The gullet-reservoir-vacuole system is characteristic, as are the two a flagella which emerge from the reservoir floor. The anterior one, about 30 um in length has a wavy action, and the cell is pulled forward in a series of small jerks, much like locomotion in E. sulcatum, The trailing flagellum is about 60 um long, of uniform size, and easily seen. The siphon (whose function is still unknown in this genus) is quite short and stout. It resembles a wedge driven into the cytoplasm. In most other species of Entosiphon, the siphon extends to the posterior end, at times appearing to pierce the pellicle, so this is a radical variation. The nucleus is nearer median than lateral and endosomes may be present or absent. The cytoplasm is homogenous and inclusions appear to be small numerous discs of paramylum and a few large spheres, possibly lipids. Nutrition is saprozoic. Division stages were not found. (ref. ID; 3090)
Etymology; The species name is given because of the appearance of the siphon. (ref. ID; 3090)
Type locality; This organism has been found only in salt water, in the sand at the Narragansett Marine Laboratory and in the surf, presumably from the sand, at the Scripps Institution of Oceanography. (ref. ID; 3090)
Measurements; It is about 40 um in diameter, and about 15-20 um thick. (ref. ID; 3090)
Entosiphon ovatum Stokes (ref. ID; 1618, 3517, 4950)
Description; Anterior end rounded; 10-12 longitudinal striae. (ref. ID; 1618)
Measurements; About 25-28 um long. (ref. ID; 1618)
Entosiphon sulcatum Dujardin (ref. ID; 1618) or (Dujardin) Stein (ref. ID; 3342, 3645, 4254, 4950) reported author and year? (ref. ID; 4826)
Syn; Anisonema entosiphon (Stein) Klebs (ref. ID; 4950); Anisonema sulcatum Dujardin (ref. ID; 4950)
Description; The flagella and feeding apparatus emerge from a deep depression at the anterior end of the cell, the vestibulum. The feeding apparatus, called the siphon, is an elongate tube extending the length of the cell. The flagellar canal and reservoir lie adjacent to the siphon. The basal bodies lie parallel to the siphon and are positioned in a ribosome-free invagination of the nuclear envelope. Microtubules extend from the basal bodies and approach the nuclear envelope. The most conspicuous organelle in the cytoplasm is the feeding apparatus, the overall morphology of which is maintained by dozens of rows of parallel microtubules. Cross-sections show that the microtubules form three triangular bundles arranged in the shape of a "C" with the open side of the "C" facing the nucleus and pointing towards the dorsal surface of the cell. Four cured vanes arise from the microtubular bundles and extend towards the center of the feeding apparatus. An electron-dense thickening covers about two-thirds of each vane on the side closest to the microtubular bundles. Endoplasmic reticulum is intimately associated with the feeding apparatus. It surrounds the perimeter of the siphon and lies adjacent to the thickenings of the vanes. Toward the posterior of the cell, the siphon tapers and the total number of microtubules and vanes is reduced; however, the complexity of the organelle increases dramatically toward the anterior end. The siphon is not an open tube but is covered by a cap which is positioned in the open side of the C-shaped siphon. The plasma membrane is continuous over both the siphon and the cap, the exterior surface of which is covered by a "fuzzy" material. The cytoplasmic side of the cap is subtended by an electron dense layer attached to an elaborates scaffold, which extends about one-quarter of the way down the open side of the feeding apparatus. About six to eight dense fibrous roots project obliquely from the anterior portion of the scaffold and terminate at or near the pellicle. The microtubular bundles of the siphon begin tapering anteriorly from the base of the scaffold. The central vanes also taper as they approach the anterior end of the feeding apparatus. They are no longer connected to the microtubular bundles but surround an elongate invagination of the plasma membrane and ultimately converge on the cell surface in a region of the membrane adjacent to the cap. The anterior portions of the vanes appear striated. The invagination of the plasma membrane extends downward into the siphon for a distance equal to about one-half the length of the scaffold. In cross-section this invagination appears as a circle at the center of the vanes. A large number of elongate vesicles fill the cytoplasm on the open side of the siphon. The greatest complexity is seen at the anterior end of the feeding apparatus. The microtubular bundles have now tapered down to a few rows of microtubules merged of form an incomplete circle. The microtubules of one of the free ends of the siphon merge with the microtubules of the canal. An additional root-like connection is anchored to the opposite side of the siphon and projects towards the pellicle. The rootlets anchoring the cap scaffolding to the pellicle are also seen. A bundle of microfilaments is present on the side of the canal opposite the feeding apparatus. It is attached to the pellicle at one end and associates with the microtubules adjacent to the canal at the other end. Above the bundle of microfilaments and adjacent to the pellicle, a dense thickening is present. Microtubules arise from the ends of the thickening and wrap around the vestibulum. Serial sections demonstrate that some of these microtubules merge with the microtubules anchoring the feeding apparatus to the flagellar canal. Proceeding anteriorly, the siphon projects into the vestibulum. The parallel microtubular bundles of the siphon do not extend to the plasma membrane but end just short of it in an electron-dense material which caps the microtubules. A fuzzy material similar in appearance to that on the cap covers the outer exposed surface of the siphon. (ref. ID; 4254)
Measurements; About 20 um long. (ref. ID; 1618)
23-25 x 7-9 um. (ref. ID; 3342)