 The muscles in a tarantula's legs cause the legs to bend at the joints, but to extend a leg, the tarantula increases the pressure of haemolymph entering the leg.Tarantulas, like almost all other spiders, have their primary spinnerets at the end of the opisthosoma.Unlike most spider species in the infraorder Araneomorphae, which includes the majority of extant spider species, and most of which have six, tarantula species have two or four spinnerets.