Genus Triaenamoeba Bovee, 1953
Diagnosis: Locomotive form generally trapezoidal with long, slender anterior subpseudopodia usually in groups of 2 or more produced from a common mound-like base. Length, including pseudopodia, up to 60 µm although cell body usually only around 17 µm long. Floating form irregularly round with radiating pseudopodia. Spherical nucleus with central nucleolus. No uroid but cells may have a few temporary trailing filaments. Cytoplasm without crystals and often with a few vesicles.
Two described species from coastal regions.
Triaenamoeba jachowskii Sawyer, 1975
Diagnosis: Form in locomotion typical of the genus Triaenamoeba, with two or more filose pseudopods originating from a common base. Anterior advancing margin of protoplasm clear with filose pseudopods which increase in length as they are formed. Body of amoebae not in locomotion usually irregularly spherical
with filopods extending in many directions. Amoebae in locomotion 13.5-22.5 µm long, mean 17; width 7-12 µm, mean 9. Nucleus about 3 µm in diameter and usually obscured by digestive vacuoles in granular endoplasm, nucleolus about 2 µm. Feeding forms ingest bacteria quickly without forming pronounced food cups. Floating or rayed-forms with small irregularly spherical body mass and delicate filose pseudopods of variable length; one or more pseudopods may be twice as long as diameter of body.
Ecology: Marine, surface water of Chincoteague Bay, Virginia.
Remarks: Locomotive form with clear anterior margin and numerous filose pseudopods extended in different directions. Two or more filopods as long or longer than granular body mass. Change of direction frequent and initiated by lateral movement of clear protoplasm and extrusion of new filopodia. Rate of locomotion about 15-20 µm/min, erratic, and frequently interrupted when amoebae are in contact with food organisms. T. jachowskii changes shape continuously and does not have a shape that may be considered typical. Filose pseudopods are extended and retracted continuously from all parts of the granular endoplasm; pseudopods which retract posteriorly resemble uroidal filaments. Light from the microscope lamp causes amoebae to contract and produce abnormally long filopods. Amoebae on agar plates contain many ingested food particles and appear rounded.
Survival and growth occurs in sea water and on sea-water-agar diluted to 6 %o salinity while death and degeneration occur at 3 %o salinity. Floating or rayed-forms are irregularly spherical with numerous short filose pseudopods.
During conversion to the trophic form, or exposure to light from the microscope, the rays vary in length to twice the diameter of the central mass. Rays resemble fine hairs and do not taper from a widened base.
Reproduction: Mitosis typical of the mayorellids. Spherical papillate division stages may be confused with compact floating forms if not observed throughout the mitotic process. Mitotic apparatus indistinct in living or stained specimens because of small size and compacted food vacuoles.