- obligate
-
Required.
- ocean coasts, dunes
-
areas dominated by accumulations of sand which is shaped and formed by the action of wind and/or water. This habitat type also includes desert dune areas and lake coasts characterized by dune formation.
- oceanic islands
-
islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.
- oceanic vent
-
Areas of the deep sea floor where continental plates are being pushed apart. Oceanic vents are places where hot sulfur-rich water is released from the ocean floor. An aquatic biome.
- oceanodromous
-
Referring to fish that live entirely within oceans.
- oestrus cycle
-
See estrus cycle.
- ommatidia
-
The individual optical units of a compound eye. Found in Arthropoda.
- omnivore
-
an animal that mainly eats all kinds of things, including plants and animals
- organism
-
a living thing (plant, animal, or microbe)
- oriental
-
found in the oriental region of the world. In other words, India and southeast Asia.
- osmoregulatory
-
referring to the means by which water content and salt and mineral concentrations of body fluids are controlled in animals and protozoans.
- ossicle
-
any small bony or chitinous structure found in various skeletal parts of animals. Usually used to refer to the bones of the middle ear in vertebrates.
- ostia
-
plural form of ostium, which is any small opening in a body organ or part. Usually used to refer to small openings or pores in the tissues of sponges (Phylum Porifera).
- other polygyny
-
any form of polygyny that is not characterized as resource defense, female defense, or lekking polygyny
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- ovoviviparous
-
reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.