Impressed – sunk in.

Indented – notched.

Indigenous species – a species that occurs naturally within an area.

Infauna – buried benthos.

Inflated – swollen, fat.

Intertidal – between high and low tide levels (sometimes including splash zone).

Iridescent – lustrous; changing color in changing reflected light.

Isolume – plane connecting points of equal light intensity.

Isopods – a large order of crustaceans whose members are characterized by flat, segmented bodies.

Isotherm – plane connecting points of equal temperature.

IUCN – International Union for the Conservation of Nature.  This is now called The World Conservation Union.

Keel – continuous ridge or raised surface.

Krill – tiny, free-swimming, shrimp-like crustaceans (euphausiids) which occur in huge numbers in the open sea and are a major part of the diet of many baleen whales.

Labrador current – cold south-flowing current along coast of eastern Canada.

Lagoon – a shallow marine area separated from the sea by a reef or barrier beach or island.

Lamelliform – leaf shaped.

Lamina – thin layer.

Laminate – formed of thin layers.

Lateral – side.

Laver – the green algae, Ulva, dried and sold for food.

Lecithotrophic – said of larvae that are nourished from nutrients in the egg rather than by feeding on plankton.

Leptocephali – a developmental stage in the Anguilla life cycle following the egg when the organism floats from the birth site toward freshwater.

Ligament – dark brown band of tough elastic tissue connecting the valves along the hinge line; its action opposes the pull of the adductor muscles and tends to keep the valves spread open.

Limnobiontic – occurring only in standing (nonflowing) waters.

Limnophilous – occurring mainly in standing waters, but also found in flowing waters.

Lingual ribbon – the radula in molluscs.

Lip – edge of the body whorl bordering the aperture; peritreme.

Littoral zone – the area between the high- and low-water marks on the seashore.

Lobtailing – making a loud splash by forcefully slapping the flukes against the surface of the water while most of the animal remains under the surface.

Lotic – flowing waters habitats.

Lunate – crescent shaped.

Lunule – heart-shaped impression on either side of the hinge line in front of the beaks.