What is the worlds most common animal?

Phylum: Nematoda (roundworms)

Class: Aves (birds)

Order: Coleoptera (beetles and weevils), Calanoida (zooplankton)

Family: Formicidae. (ants)

Genus: Homo (human), Rattus (rats), Dermatophagoides (dust mite), Anopheles (mosquito)

Species: Homo sapien (modern human), Rattus norvegicus (brown rat), Hypsibius dujardini (Tardigrada)

see also: Ichthyes (Pisces, fish) humans birds or fish