Mygalomorphs are relatively large and long-lived spiders. They are one of the oldest terrestrial invetebrate groups in the fossil record and have remained almost unchanged for many millions of years. Because they evolved earlier than araneomorphs or 'modern spiders' they are sometimes known as 'primitive spiders'. Australian Mygalomorph groups include trapdoor, funnelweb, wishbone, curtain-web and mouse spiders. One group, the Australian Theraphosids or tarantulas, are also known as whistling spiders. Mygalomorphs are mostly heavily built, often quite slow moving and are burrow-dwelling. Their fangs point backwards towards the rear of the body rather than towards each other as in the araneomorphs. They have two pairs of book lungs and usually only four or even as few as two spinnerets. Because of their size mygalomorphs are an important food for large reptiles, mammals such as bandicoots and bilbies, and some birds.