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Bonellia viridis, a green marine echiuran worm known since the early 19th century in the Mediterranean Sea, typically lives in sediments or rock crevices at a depth underwater of 3–10 m, causing acquisition of samples to generally require diving. The size of the main body trunk of the female is about 8 cm, whereas the (dwarf) male is 1 to 3 mm long and lives inside the female. The green pigmentation of B. viridis stems from bonellin, a tetrapyrrole macrocycle containing a chlorin chromophore. Bonellin is believed to exert diverse physiological functions (masculinization and sex determination, chemical defense, cytotoxicity, and antimicrobial activity) but not photosynthesis as for the better known native chlorin, chlorophyll. The existence of bonellin poses physiological, biosynthetic, and evolutionary questions. Here, we report in-depth assessment of information concerning tides at a wide shallow beach in Okinawa, identifying narrowly restricted periods when acquisition of Bonellia specimens could be pursued without diving. Indeed, <15 specimens of B. sp. were collected from Odo beach, Itoman city, Okinawa prefecture, Japan [26°09' N, 127°71' E], at midnight on days when the tides were exceptionally low: March 6–12, 2016; December 22–27, 2018; and January 18–25, 2019. The specimens were acquired manually from small tidal pools upon walking near the outer reef flat (~300 m from the shore) during the extremely low tides. Reasonably facile access without diving to Bonellia in a region distant from the Mediterranean should expand study of the diversity of these unusual green worms.
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