See diatom.

Plural of diatom.

Species identification key comprising pairs of alternative choices arranged in a series of couplets, used commonly in ichthyological papers.

A division of organisms into two groups, typically based on a characteristic present in one group and absent in the other.

Having two different colour forms independant of sex or age.

The quality or condition of being dichromatic.

Exhibiting dimorphism.

In biology, the occurrence within a species of two forms which differ distinctly from one another in one or more characters, e.g., colour pattern or morphology.

Within a species, having the male and female reproductive organs in separate individuals.

Containing two complete sets of chromosomes, i.e., one from each parent.

Distinctly separated from one another.

Distribution.

The concentration of oxygen dissolved in a water body. Normally expressed in milligrams per liter, parts per million, or percentage saturation.

Located away from the point or origin of attachment or a central point of the body. Opposite of proximal.

Capable of being distended or extended; able to stretch.

Type of stream or river that branches off and flows away from a main channel. Particularly common in river deltas, but also occur inland in some cases.

Fish or group of fish, typically inhabiting open water in the mid-to-upper water column, used by aquarists to reduce innate shyness in other species.

Of, relating to, or occuring during daylight hours; having a daily cycle. Opposite of nocturnal.

See circadian rhythm.

The state of being divergent.