| TERM | GROUP | DEFINITION | |
|---|---|---|---|
| OBLIGATE ANAEROBE | NP | BACTERIA | Pronunciation: Etymology: An obligate anaerobe is a cell that is poisoned in the presence of free oxygen. |
| OCELLUS (OCELLI) | N | ANIMALS, PROTISTS | Pronunciation: Etymology: An ocellus (ocelli, pl.) is a simple eye or eyespot characteristic of many invertebrate groups. |
| ONCHOSPHERE | N | ANIMALS | Pronunciation: Etymology: An onchosphere (also called a coracidium) is the first encapsulated larval stage of certain tapeworms. It is ciliated and has 6 hooks. |
| OOCYST | N | PROTISTS | Pronunciation: Etymology: An oocyst is an encysted zygote in many microbial eukaryotes (e.g. coccidians and heliozoans). |
| OOGAMOUS | ADJ | ANIMALS, PLANTS, PROTISTS, FUNGI | Click here |
| OOGONIUM | N | ANIMALS, PLANTS, PROTISTS, FUNGI | Pronunciation & Etymology: Oogonium is a specialized structure (gametangium) that contains the ovum or egg of an oogamous taxon. |
| OPERCULUM (OPERCULA) | N | ANIMALS, PLANTS | Pronunciation: Etymology: Cap-like structure at the tip of the capsule. |
| OPISTHOKONT | N OR ADJ | ANIMALS, PROTISTS | Pronunciation: Etymology: Flagellum located in posterior position. |
| OPISTHOSOMA | N | ANIMALS | Pronunciation: Etymology: An opisthosoma is the chelicerate abdomen or the hind body region of the pogonophora. |
| ORAL PAPILLA (ORAL PAPILLAE) | NP | ANIMALS | Pronunciation: Etymology: Oral papillae are paired finger-like appendages on either side of the mouth, which release a sticky substance used to capture prey in onychophorans. |
| ORDER | NP | SYSTEMATICS | Pronunciation: Etymology: Order is the taxonomic level that contains one or more families. |
| OSCULUM (OSCULA) | N | ANIMALS | Pronunciation: Etymology: An osculum (oscula, plural) is the excurrent opening of a sponge. |
| OSTEOLATE | ADJ | PLANTS | Pronunciation: Etymology: Pericarp with hole on it. |
| OSTIUM (OSTIA) | N | ANIMALS | Click here |
| OVERTOPPING | N | EVOLUTION | Pronunciation: Etymology: Overtopping is a type of growth pattern in which there is unequal dichotomous branching. This produces a larger stem and a smaller lateral stem. |
| OVIDUCT | N | ANIMALS | Click here |
| OVIGEROUS LEGS | NP | ANIMALS | Pronunciation: Etymology: Ovigerous leg are legs adapted to carrying eggs. |
| OVIPAROUS | ADJ | ANIMALS | Pronunciation: Etymology: An oviparous (adj.) animal is one that releases eggs in its life cycle. They may be fertilized internally or externally. |
| OVULARY | N | PLANTS | Pronunciation: Etymology: An ovulary is the part of the pistil that contains the ovules. Sometimes this is called an ovary. |
| OVULE | N | PLANTS | Pronunciation: Etymology: An ovule is a structure that contains the megagametophyte in seed plants. The megagametophyte remains within the megasporangium (the nucellus), which is surrounded by layers of integuments. After fertilization, the ovule develops into a seed. |
| OXIDASE | N | Pronunciation: Etymology: Oxidases are catalytic enzymes that use oxygen as an electron acceptor. |
