A Sea Slug That Kept Its Shell
Lobiger viridis (Pease, 1863) is one of the most extraordinary sea slugs at our macro dive sites in Romblon, Philippines. Most sea slugs have lost their shell entirely during evolution. Lobiger viridis has not. It retains a small internal spiral shell — making it one of the most primitive sacoglossans alive today. Furthermore, it has four long wing-like parapodial flaps that unfurl to display bright colour patches. It belongs to the order Sacoglossa, family Oxynoidae — a different family from all other Cyerce species in our Marine Life Encyclopedia. Find it on iNaturalist.
Solar Powered on Caulerpa
Lobiger viridis feeds by piercing Caulerpa green algae cells and sucking the sap. It retains the functional chloroplasts from the algae in its digestive gland cells. These chloroplasts continue to photosynthesise inside the animal. As a result, Lobiger viridis gains supplementary energy directly from sunlight — a process called kleptoplasty. Its bright green body provides perfect camouflage on Caulerpa. In addition, when threatened, it unfurls its parapodial flaps to display bright warning colours and appear larger to predators. It can even swim weakly by flapping these wings if dislodged from the algae.
Finding It at Sunset Cove
At Sunset Cove Beach & Dive Resort, our guides find Lobiger viridis on Caulerpa algae patches in very shallow water — typically 1 to 5 metres. The green body blends perfectly with the algae. Therefore, search slowly for the distinctive rolled parapodial flaps along the body sides. For underwater macro photographers in Romblon, photographing the unfurled parachute-like flaps creates one of the most unique images possible from any dive site. Consequently, this species is one of the most exciting and unusual sacoglossans in our entire encyclopedia.