Key to the families of Monadida.
No mouth; 1 or 2 flagella: amœboid with lobose or ray-like pseudopodia Family [Rhizomastigidæ]
Mouth at base of single flagellum; plastic; no pseudopodia Family Cercomonadidæ
One flagellum; inclosed in gelatinous or membranous cups Family [Codonœcidæ]
One flagellum; tentacle like process at base of flagellum; inclosed in cup Family Bikœcidæ
One main flagellum and 1 or 2 accessory flagella Family Heteromonadidæ
Key to marine genera of Monadida.*
Family Rhizomastigidæ:
1. Flagellum repeatedly thrown off and reassumed Genus *[Mastigamœba] in part
2. Flagellum never thrown off 3
3. a. Pseudopodia lobose Genus [Mastigamœba]
b. Pseudopodia ray-like Genus Mastigophrys
Family Codonœcidæ:
1. Goblet-shaped cups adherent by stalk Genus *[Codonœca]
Family Heteromonadidæ:
1. The long flagellum vibratory Genus *[Monas]
2. The long flagellum rigid; shorter one vibrates Genus Sterromonas
* Presence at Woods Hole indicated by asterisk.
Key to marine genera of Choanoflagellida.
1. Without gelatinous or membranous test 3
2. With gelatinous or membranous test 4
3. a. Attached forms:
1. Without a stalk, or with a very short one Genus *[Monosiga]
2. With a long, simple stalk Genus *[Codonosiga]
3. With a long, branched, stalk Genus Codonocladium
b. Free-swimming Genus Desmarella
4. Colonial, and with a gelatinous covering Genus Proterospongia
* Presence at Woods Hole indicated by asterisk.
Key to families and marine genera of Heteromastigida.
1. Two flagella nearly equal in size Family Bodonidæ
One main and 2 accessory flagella Family Trimastigidæ
Family Bodonidæ:
1. Body very plastic, almost amœboid Genus *[Bodo]
Body not plastic; with large anterior cavity, holding flagella Genus *[Oxyrrhis]
Family Trimastigidæ:
1. With an undulatory membrane between accessory flagella Genus Trimastix
Without such membrane; flagella contained in a ventral groove while at rest Genus Costia
* Presence at Woods Hole indicated by asterisk.
Key to marine genera of Polymastigida.
1. Body flattened; ends rounded; sides hollowed; often with wing-like processes; cross section S-shaped Genus Trepomonas
2. Body pyriform; one large asymmetrical groove; 4 flagella Genus Tetramitus
3. Body spherical; many flagella equally distributed Genus Multicilia
Key to families and marine genera of Euglenida.
1. With deeply-insunk pharynx; no mouth 2
With pharynx and distinct mouth Family Peranemidæ
2 Body plastic; usually with chromatophores and eye-spot Family Euglenidæ
Body plastic; no chromatophores; no eye-spot Family Astastidæ
Family Euglenidæ:
Body Euglena-like, inclosed in shell with round opening for exit of flagellum Genus Trachelomonas
Family Astastidæ:
Body with one flagellum Genus *[Astasia]
Family Peranemidæ:
1. Body striped; plastic; two diverse flagella Genus Heteronema
2. Body striped; not plastic; posterior flagellum longer than the other Genus *[Anisonema]
3. Body striped; not plastic; with rod-like organ in pharynx Genus Entosiphon
* Presence at Woods Hole indicated by asterisk.

Genus MASTIGAMŒBA F. E. Schultze '75.

(Kent '81; Bütschli '86; Klebs '92; Senn 1900.)

In general the form is oval and either regular in outline or irregular through the presence of many pseudopodia. One flagellum usually quite large and distinct. Differentiation of ectoplasm and endoplasm distinct or wanting. One to several contractile vacuoles. The pseudopodia are occasionally withdrawn, and the flagellum is the sole means of locomotion. In some cases the flagellum turns into a pseudopodium, and, conversely, the pseudopodium at one end may become a flagellum (see below). In some rare cases the ectoplasm secretes a gelatinous mantle. Reproduction not observed.