Zoom Sharks Shark Glossary

ICE AGE An ice age is a time lasting thousands of years during which the Earth is very cold and largely covered by ice and glaciers.	ICHNOFOSSILS Also known as trace fossils, these are fossilized footprints, nests, dung, gastroliths, etc., but not actual body parts. Ichnofossils record the movement and behavior of animals.	ICHTHYOLOGIST Ichthyologists are scientists who study fish.
ICHTHYOSAUR Ichthyosaurs were prehistoric reptiles that lived in the sea.	IGNEOUS ROCK When molten rock cools, igneous rock is formed.	INDEX FOSSILS Index fossils are commonly found fossils that are limited in time span. They help in dating other fossils. For example: trilobites were common during the Paleozoic, but not found before the Permian period, and ammonites were common during the Mesozoic Era, but not found after the Cretaceous period.

INSECTS Insects have exoskeletons and six legs. They evolved during the Silurian Period, 438 to 408 mya, long before dinosaurs or whales existed.

INTERSPECIFIC COMPETITION Interspecific competition is competition between two different species of organisms (competing for food, territory, etc.).

INTRASPECIFIC COMPETITION Intraspecific competition is competition among members of a species (competing for food, mates, territory, etc.).

INVERTEBRATE Invertebrates are animals without a backbone. Some invertebrates include protozoans, arthropods (insects, arachnids, crustaceans, etc.), worms, jellyfish, sponges, mollusks (like cephalopods [octopus], gastropods, bivalves [clams, oysters, scallops]), and many others.

ISOTOPE An isotope of an element is another form of the same element, that has a different number of neutrons in the nucleus (giving it a different atomic weight).

IZAK CATSHARK The Izak catshark, Holohalaelurus regani, is also known as the Izak shark and the shy eye shark. This shark hides its eyes with is tail when it is caught. It has dark brown skin above, with lighter dots and lines. The belly is much lighter. The Izak shark grows to be up to 2 feet (61 cm) long. It has an anal fin, 5 gill slits, 2 dorsal fins, no fin spines, mouth behind the eyes, slit-like pupils, and nictitating eyelids. It is oviparous, laying eggs (3.5 by 1.5 cm) that were internally fertilized. The Izak catshark was named by Gilchrist in 1922. Classification: Order Carcharhiniformes (ground sharks), Family Scyliorhinidae (catsharks), Genus Holohalaelurus, Species H. regani.

Zoom Sharks Shark Glossary

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