Isotoma are like busses

You wait ages for Isotoma anglicana to come along and then, when you're desperate to find some Isotoma viridis so you can make comparison images of the manubrial teeth, it's anglicana all the way down...

What do these manubrial teeth do? They hook onto the teeth on the rami of the hamula or retinaculum, a catch-like structure which holds the springloaded furca in place under the body. In most other species of Collembola the retinacular teeth hook onto ridges at the inner base of the dentes. Since this is a lock and key type mechanism, the shape and arrangement of teeth varies from one species to another.