gogol

Invertebrate animals range in size from microscopic worms, free-living and symbiotic, to huge forms such as huge giant squids, which, including their longest tentacles, can be as much as 20 m in length. Within this size range, the variety of forms derives from a combination of various appendages attached to bodies that may or may not be segmented, but that are usually bilaterally symmetrical. Colors range throughout the possible spectrum and are combined in sometimes extraordinary ways. The invertebrates include insects and snails, star-fish and corals, and worms of all kinds--in all, about a million different species. And all of them are consumers.

The term predator is usually reserved for animals that hunt their prey. A lion preys on zebras and antelopes, an octopus often preys on crabs, many spiders prey on insects, and so on. We do not think of zebras or antelopes as preying on grass; nor do crabs that browse on algae or butterflies that obtain nectar from flowers strike us as predators. Nonetheless, in all these cases, a similar function is carried out; this includes locating, and orienting to food, attaining it by capture or simply moving up to it (to graze, for example), and then ingesting it. Predators are simply the most dramatic example of this set of common coordinated behaviors. And underlying these behaviors is a set of common structural features. Notably, there is a nervous system for sensing and coordinating; a muscular systemfor moving, which also demands some sort of skeleton for muscle attachment and for transforming muscular action into mechanical action. And these are all integrated with a functional mouth for ingestion.