Ultrastructural and experimental investigations of the euglenoid flagellate. P̲e̲ṟa̲ṉe̲m̲a̲ Ṯṟi̲c̲ẖo̲p̲ẖo̲ṟu̲m̲ (Ehrenberg) Stein, with special reference to flagella, mucocysts and feeding apparatus

With respect to motility, the organism has a conspicuous anterior or leading flagellum and a trailing flagellum which is appressed to the ventral surface of the pellicle. Both short and long nontubular mastigonemes surround the anterior flagellum. Short mastigonemes form a bilateral array parallel to the long axis of the flagellum. Each array consists of tiers which longitudinally overlap each other by one-half of a tier length. Individual short mastigonemes in the tiers are spaced 25 nm apart and are linked by fine fibrils. Tufts of long mastigonemes emanate from spiral rows and curve anteriorly toward the distal end of the flagellum.

Two basal bodies, lying at an angle to each other, are associated with each flagellum at the base of the reservoir. Attached to the basal bodies or originating close to them are microtubular, fibrous and striated roots. Three microtubular roots extend from the basal bodies and continue anteriorly in the reservoir wall. A striated fiber connects microtubular roots to the basal bodies. At least three striated roots, consisting of cross-striations with a periodicity of 30-38 nm, extend from the microtubular roots and the striated fiber to the rodorgan.

Concerning secretion, there are rows of ejectile organelles or mucocysts located beneath the pellicle. Immature mucocysts are tubular structures with amorphous contents. Mucocysts may protrude through the pellicle and discharge a ball of mucilaginous material or may themselves be ejected from the cell through the pellicular grooves. Ejected mucocysts show a uniform structure consisting of an inner tube with helical striations, an outer tube with a diamondshaped pattern, and a dense middle band. Fine fibrils 8-9 nm in diameter emanate from mucocyst tips.

The ingestion or feeding apparatus consists of a prominent rodorgan, a system of complex lamellae and an expandable cytostomal sac, which together form an independent ingestion system lateral to the canal and reservoir. The rodorgan is anchored by lamellae which diverge into the double serrated marginal lamella and the articulating lamella, both of which arch over the rim of the cytostome. A row of microtubules extends along the lower plate of the articulating lamella. Striated roots connect the base of the rodorgan to the flagellar bases.

Typical euglenoid diagnostic features in Peranema include the pellicular striae, helical symmetry, dictyosomes, contractile vacuole and reservoir. Ruthenium red labeling, indicative of acid mucopolysaccharide constituents, is localized in the mucilage strands on the pellicle surface. Atypical of euglenoids are the stacked cristae in some mitochondria and the absence of dense heterochromatin in the interphase nucleus. Endosymbiotic bacteria, rod-shaped structures 1 μm long and 0.3 μm wide, are abundant in the cytoplasm.

This investigation provides a framework for future considerations of phylogenetic affinities among euglenoids and other flagellated algae and protozoans and for biochemical and biophysical investigations of specialized organelles involved in motility, secretion and ingestion.