Tactopoda or Arthropodoidea is a proposed clade of ecdysozoan animals that includes the phyla Tardigrada and Euarthropoda, supported by various morphological observations.

Tardigrada Onychophora Euarthropoda Anatomic arguments for the tactopoda monophyly include similarities in the anatomies of head, legs, and muscles between the arthropods and the tardigrades.

Graham Budd argued that the lack of this system in recent tardigrades is due to their miniature size, which makes a complex circulatory system superfluous; thus, the loss of this feature would be a secondary property, acquired as the tardigrade stem group turned smaller, and both the Euarthropoda+Onychophora circulatory system and a relatively large size should be a feature of the last common ancestor of all three groups.

[6] Budd formed the suggested clade name 'tactopoda' from Greek taktos, ordered, and poda, feet, "with reference to the alleged well-formed stepping motion that characterises the group".

[1] Velvet worms (Onychophora) Eutardigrada Heterotardigrada Mesotardigrada †Trilobitomorpha/Trilobita ?Pycnogonida Xiphosura †Eurypterida †Chasmataspidida Arachnida ?Pycnogonida Symphyla Chilopoda Diplopoda Pauropoda Ostracoda Ichthyostraca Hexanauplia Malacostraca Thecostraca Remipedia Cephalocarida Branchiopoda Collembola Protura ?Diplura ?Diplura Insecta