Invertebrates constitute the majority of all living animals.
The number of species go well into the millions with many still waiting to be classified. Whereas the well studied vertebrate animals, like mammals, birds, etc. only comprise 1% of all animal species.
In a tropical country like Ecuador that holds true as well and the numbers of insects for e.g. in the tropical rainforests or mollusks in the oceans are unknown. We will be dealing here mainly with the arthropods which are spiders, insects and crustaceans and a little bit with mollusks, which are bivalves, squids and also introduce corals.
The number of insects, like beetles, which are the world's most numerous in species, butterflies, ants, grasshoppers, mantis and stick insects and so on are unknown and very high in the tropical forests. Studies of insect population in the tree crowns of tall tropical trees showed an amazing count of unknown species.
But insects can also be found right up to the glacier of 5000m, where they fulfill an important role as pollinators for high alpine flora.
Spiders also are very numerous and found in all ecosystems.
You encounter the smaller web building ones
and the larger hunting spiders, with the tarantula being the largest.
Crustaceans are mostly found in and near waters and have some important economic species in Ecuador present as is the case of the shrimps and in a lesser degree crabs.
Mollusks are the second largest animal phylum after the before mentioned arthropods with over 50 000 species. They are highly adaptable and found in many ecosystems but their largest numbers are in the oceans of the world. They also have the largest invertebrate of the world in their group, the giant squid, which can weigh up to 2000 kg. Other important members are clams, oysters, snails, slugs and octopuses.
Corals are marine invertebrates with a horny skeleton of protective calcium carbonate. The best known are the corals which build reefs and are found in the shallow and warm ocean waters of the world. The live together in a symbiotic relationship with an algae and therefore need light for photosynthesis by the algae. There exist colonial corals which can be found in the deep waters.
There are 30 or so more phylums of invertebrates, most of them marine dwelling animals, which we will not discuss here.