There are many differences within the Toothcomb Blennies family, some eat algae whilst others eat zooplankton. There are many families of Blennies, this is merely one of them.
What they have in common are their oblong shape and long dorsal fin. Some species have small "legs" used to move around the bottom.
These Blennies do not normally get very big and are therefore a good choice for both small and large aquaria. They are not often very colorful, but many have a fun personality which many aquarists fall for.
The species of the families Aspidontus and Plagiotremus imitate Cleaner Wrasses and can therefore be difficult to identify.
Fish in the genus Salarias are often used to combat algae growth, especially the Jewelled Blenny is popular and is seen in many aquaria. There is little difference in what these fish eat, but they often remove the filamentous algal layer and detritus from glass and rock. Some individuals eat also other kinds of algae, like i.e. green hair algae.
Be aware that they can be very aggressive towards other Blennies. Also in some instances towards food competitors, like the Surgeonfish, Rabbitfish or similar.