Nuclear cap - an aggregation of ribosomes that surrounds the nucleus in the zoospores of members of the Blastocladiales. The cap in the Blastocladiales is surrounded by two membranes that are continuous with the outer membrane of the nuclear envelope. Top right is an electron micrograph of a permanganate fixed zoospore of Blastocladiella emersonii showing the arrangement of organelles including the prominant nuclear cap. Bottom right is a light micrograph of five zoospores again of Blastocladiella emersonii. The nuclear cap is visible in all five zoospores.

Oogamous - refers to a type of fertilization in which two heterogametangia come in contact, and the contents of one flow into the other through a pore or tube.

Oogonium - female gametangium containing one or more eggs.

Ooplast - a membrane-bound cellular incision in the oospore of some Oomycota.

Oosphere - a large, naked, nonmotile female gamete.

Oospore - thick-walled spore that develops from an oosphere through either fertilzation or parthenogenesis.

Operculum - lid on a sporangium that, when popped off, or hinged open as here, allows the zoospores to escape. Sporangia that have this type of release mechanism are said to be operculate.

Parthenogenesis - development of the normal product of sexual reproduction from the female gamete alone.

Periplasm - a layer of protoplasm surrounding the oosphere in some Oomycota.

Planogamete - motile gamete.

Planogametic copulation - fusion of naked gametes, one or both of which are motile.

Polycentric - having a number of points of growth and development. Usually producing many sporangia (sp) or reproductive units. Polycentric organisms can be propagated by chopping up the vegetative rhizomycelium (rh) and plating the pieces on an appropriate medium.

Polyplanetic - refers to a species of Oomycota in which there are several swarming periods and incidentally only one type of zoospore (monomorphic). See also monoplanetic and diplanetic.

Rhizomycelium - indeterminate growth form in zoosporic fungi. Effectively, a mycelium except usually much finer filaments that are closer in size to rhizoids.

Rootlet - a system of cytoplasmic microtubules and filaments associated with the kinetosome (basal body) and the nucleus of motile cells. Also known as a rhizoplast.

Sporangiophore - a specialized hypha that bears a sporangium. Seen in several species of Oomycota (Phytophthora, Peronospora, Albugo)

Sporangium - a saclike structure, the entire protoplasmic contents of which become converted into an indefinite number of spores. See also zoosporangium and zoospores.

Zoosporangium - a sporangium that contains zoospores.

Zoospore - a motile, asexually produced spore.

Zostera - a submersed marine aquatic herb used as a substrate by members of the Labyrinthulomycota. A member of the Eel grass family (Monocot, Zosteraceae), it is found all along the coasts of North America and Europe.