A single MALT1, cleavage and CLAP : an old story. The type 1 paracaspases are defined by their domain composition with an N-terminal Death-domain, immunoglobulin domains and a caspase-like (paracaspase) domain. Type 1 paracaspases originated in the edicarian geological period before the last common ancestor of bilaterans and cnidarians (planulozoa). Most organisms have a single type 1 paracaspase, except vertebrates where a triplication occurred in the ancestral jawed vertebrate. Mammals have lost two of the paralogs and only contain a single paracaspase (paracaspase-1, MALT1). Cnidarians have several paralog type 1 paracaspases, type 2 paracaspases, and a homolog of Bcl10 (CLAP). Notably in bilaterans, lineages like nematodes and insects lack Bcl10 whereas other lineages such as vertebrates, annelids, molluscs and acorn worms do contain Bcl10. There seems to be a correlation where invertebrates with Bcl10 have type 1 paracaspases which are more similar to the paracaspases found in vertebrates. A proposed evolutionary scenario includes two ancestral type 1 paracaspase paralogs in the bilateran last common ancestor, where one paralog usually is dependent on Bcl10 for its function. Functional analyses of invertebrate type 1 paracaspases and Bcl10 homologs support this scenario and indicate an ancient origin of the Bcl10/paracaspase signalling complex.