Subject: Evolution occurs in small steps. The Inimicus uses two separated rays of each pectoral fin to crawl over the seabed. This type of walking (which is not limited to species within the genus Inimicus) is believed to be a predecessor to the later progress of similar locomotion (crawling, walking and running) in terrestrial vertebrates.
Technique: To film small subjects or details of bigger subjects, like the modified fin rays in this clip, it is recommended to use a dioptre (US= diopter). Many underwater housings can be fitted with a flip adapter to hold a dioptre or macro lens, so that when the occasion arises the switch from your standard lens to a macro lens is easily realized.