Melibe engeli ghost nudibranch Romblon Philippines

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Ghost Melibe

Melibe engeli Risbec, 1937

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A Master of Invisibility

Melibe engeli (Risbec, 1937) is one of the most extraordinary nudibranchs at our macro dive sites in Romblon, Philippines. Its body is almost entirely transparent. This makes it one of the most cryptic nudibranchs in the Indo-Pacific. In addition, brown zooxanthellae — photosynthetic algae — are visible as tiny speckles through the transparent body wall. Remarkably, Melibe engeli captures these algae from the water column during feeding, rather than from its prey. As a result, it gains additional energy from sunlight. It belongs to the order Nudibranchia, suborder Dendronotina, family Tethydidae. You can find it on iNaturalist.

How It Hunts

Like all Melibe species, Melibe engeli is an active predator. It uses a large, expandable oral hood to catch small crustaceans and copepods. The hood opens wide, then contracts rapidly when prey is detected. Notably, this species has no radula at all — it swallows prey whole. It is closely related to Melibe colemani, also documented in our Marine Life Encyclopedia. Both species share the same family and the same hunting strategy. Originally described from New Caledonia, Gosliner and Smith first documented it in the Philippines in 2003 — confirming Romblon as part of its range.

Finding It at Sunset Cove

At Sunset Cove Beach & Dive Resort, Melibe engeli is one of the rarest finds possible. Its transparency makes it almost invisible against sandy rubble. Therefore, finding it requires a slow search and a trained eye. Night dives offer the best chance — the oral hood is often extended during active feeding. For underwater macro photographers in Romblon, a shot of this species against a dark background reveals its ghostly transparent body. Consequently, it is one of the most prized images from our dive sites.

Taxonomy & Classification

Order	Nudibranchs (Nudibranchia)
Suborder	Dendronotina
Family	Tethydida
Subfamily	Melibinae
Genus	Melibe
WoRMS AphiaID	593362
iNaturalist	467983

Originally described from New Caledonia by Risbec (1937). Long considered restricted to its type locality until Gosliner & Smith (2003) documented it from Hawaii and the Philippines — representing significant range extensions. WoRMS AphiaID 593362. Family Tethydidae, suborder Dendronotina. Sister species to M. digitata and M. tuberculata. Closely related to M. colemani, also documented at Sunset Cove. The zooxanthellae symbiosis is unique among Melibe in that symbionts are obtained from the water column, not from prey — documented by Burghardt & Wägele (2014).

Morphology

Size	30–60 mm
Colour Variations	Body almost entirely transparent — one of the most translucent nudibranchs in the Indo-Pacific. Brown zooxanthellae (Symbiodinium sp.) scattered throughout the body and visible through the transparent integument, giving a faint brownish tinge. Cylindrical cerata bear visible internal digestive gland ramifications. No significant colour variation documented — the transparency itself is the defining feature. Juveniles are even more transparent than adults.
Identifying Features	Transparent to near-invisible body with cylindrical cerata. Distinguishable from the closely related Melibe colemani by its smaller oral hood and cylindrical (not flattened) cerata. Zooxanthellae visible as brown speckles throughout body under magnification. Oral hood net-like with sensory papillae of equal length — a key distinguishing feature from other Melibe species. Closely related to M. digitata and M. tuberculata but M. engeli's papillae are equal in length rather than graduated.

Body elongate, transparent, approximately 60mm. Cerata cylindrical, arranged in 4–6 pairs along dorsum. Oral hood large, expandable, net-like with fringe of sensory tentacles — thrown forward to trap prey. Rhinophores short, rounded, earlike. Lacks radula — prey swallowed whole. Digestive gland ramified only within cerata. Also harbour zooxanthellae (Symbiodinium sp.) in specialised carrier cells, obtained as bycatch from water column during feeding rather than from prey — a unique adaptation documented by Burghardt & Wägele (2014).

Habitat & Ecology

Substrate	sand, rubble
Depth Range	3–25 m (most common: 10 m)
Temperature	24–29°C
Primary Prey / Host	Small crustaceans, amphipods and copepods — caught using expandable oral hood

Activity & Behaviour

Active Time	day, night
Seasonal Presence	Year-round — easily overlooked due to near-total transparency
Egg Ribbon	White, coiled ribbon
Spawning Season	Not yet documented at SSC
Chemical Defence	Absent
Aposematic Colouring	Absent
Camouflage Strategy	Near-total transparency — one of the most cryptic nudibranchs in the Indo-Pacific. Almost invisible in the water column and against substrate, making it extremely difficult to spot without a trained eye.
Escape Response	Relies primarily on transparency for protection. Can contract body rapidly when disturbed. No ceratal autotomy — unlike Cyerce and Phyllodesmium.

Scientific Literature

Systematic review and phylogenetic analysis of the nudibranch genus Melibe (Opisthobranchia: Dendronotacea) with descriptions of three new species
Gosliner, T.M. & Smith, V.G. (2003). Proceedings of the California Academy of Sciences 54(18): 302–355

Literature for divers

Romblon Field Data

One of the most challenging and rewarding macro subjects at Sunset Cove. Nearly invisible — look for the faint brownish zooxanthellae speckles against sandy or rubble substrate. Best found at night when the oral hood may be extended. Use a dark background technique to reveal the transparent body. Photograph against dark water for maximum impact — the transparency and internal structures create stunning images. Approach extremely slowly as it retracts its hood immediately when disturbed.

Frequency	rare
First Sighting	2019-01-01
Max Individuals	2