The Tiger Butterfly Sea Slug
Cyerce nigra (Bergh, 1870) is one of the most striking sea slugs at our macro dive sites in Romblon, Philippines. Divers call it the Tiger Butterfly Sea Slug. Its bold black and white stripes on large leaf-like cerata make it easy to identify. It belongs to the order Sacoglossa, family Caliphyllidae. Furthermore, scientists documented it globally on iNaturalist. Its close relatives Cyerce blackburnae and Cyerce katiae are also documented in our Marine Life Encyclopedia.
A Remarkable Defence Strategy
Cyerce nigra feeds on green algae of the genus Udotea. It lives on sandy and rubble substrate at 3 to 25 metres depth. When a predator threatens it, the animal sheds its cerata. These cerata continue to writhe on the seafloor after separation. As a result, the predator attacks the moving cerata instead. Meanwhile, the animal escapes. This behaviour is called ceratal autotomy. In addition, its bold aposematic colouration warns predators of its chemical defence compounds.
Photographing It at Sunset Cove
At Sunset Cove Beach & Dive Resort, our guides regularly spot Cyerce nigra on sandy rubble near Udotea algae patches. It reaches 15 to 30 mm in length. Therefore, diopters and high magnification work best. Approach very slowly — it sheds its cerata immediately when startled. For underwater macro photographers in Romblon, the flapping cerata and tiger stripe pattern create outstanding images. Consequently, this species is one of the most popular subjects at our dive sites.