Specimens and species identification

The littoral earthworm P. litoralis was collected at a sandy region of one of the following beaches^3,8: Wonnapa Beach, Amphoe Mueang Chon Buri, Chonburi, Thailand (13°15′55.6"N 100°55′29.3"E); Kowa Beach, Chita, Aichi Prefecture, Japan (34°46′23.3"N 136°54′52.7"E); and Kira Waikiki Beach, Nishio, Aichi Prefecture, Japan (34°46′55.2"N 137°05′48.3"E). P. longissimus was collected from Tambon Muang Klang, Amphoe Kaper, Ranong, Thailand (9°37′26.7"N 98°28′08.6"E). The earthworms were maintained in native sand in plastic containers sprayed with artificial seawater to keep the sand moist. Species identification was performed based on morphological characteristics by Seesamut et al.⁸. In vivo bioluminescence was photographed in darkness with a Nikon D5500 digital camera (Nikon, Japan). Pontodrilus were stimulated by electricity or rough handling to induce bioluminescence, and in vivo fluorescence was photographed under a handheld UV lamp (365 nm) without mechanical stimulation.