Magnus Lundgren / Wild Wonders of China / Socoglossan sea slug (Thuridilla gracilis) Xiaoliuqiu Island, Taiwan

Pascal Kobeh / Lined Thuridilla / Orange-edged sapsucking nudibranch / sea slug (Thuridilla lineolata), Sulu sea, Philippines

Linda Pitkin / Nudibranch (Thuridilla lineolata) Sangeang, off Sumbawa, Indonesia.

Alex Mustard / Slender sapsucking slug (Thuridilla gracilis) on surface of Royal seasquirt (Polycarpa aurata) Aljui Bay, Waigeo Island, Raja Ampat, West Papua, Indonesia. Tropical West Pacific Ocean.

Juergen Freund / Nudibranch (Thuridilla sp.)

Juergen Freund / Sea slug {Thuridilla undula} Indo-pacific

Georgette Douwma / Sea slug {Thuridilla lineolata} Rinca, Indonesia

Constantinos Petrinos / Sea slug {Thuridilla hopei} swimming over sea floor, Serifos Island, Greece

Franco Banfi / Nudibranch (Thuridilla hopei), Punta Campanella Marine Protected Area, Amalfi Coast, Italy, Tyrrhenian Sea, Mediterranean.

Franco Banfi / Nudibranch, (Thuridilla hopei), Ponza island, Italy, Tyrrhenian Sea, Mediterranean