Phestilla viei nudibranch Pavona coral Romblon Philippines

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Vie's Coral Nudibranch

Phestilla viei Mehrotra, Caballer & Chavanich, 2020

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Follow the Trail to Find It

Phestilla viei (Mehrotra, Caballer & Chavanich, 2020) is one of the most cleverly hidden nudibranchs at our macro dive sites in Romblon, Philippines. Its body mimics the surface of its prey coral Pavona explanulata so perfectly that it is nearly invisible. However, there is a reliable way to find it. Look for a linear trail of crescent-shaped egg masses on freshly devoured Pavona coral. Follow the trail to its head — the animal is always there. It belongs to the order Nudibranchia, suborder Aeolidina, family Trinchesiidae. Find it on iNaturalist.

An Obligate Coral Predator

Phestilla viei feeds exclusively on Pavona explanulata coral. It never feeds on any other species — making it an obligate corallivore. Furthermore, it contains symbiotic dinoflagellates (Durusdinium sp.) which give it its brown coloration and may provide supplementary photosynthetic energy. Its cerata are held flat and horizontally, giving the body an extremely flat profile that matches the coral surface. In addition, characteristic bulbous bumps along its pericardium are a key diagnostic feature. It was described in 2020 from Koh Tao, Gulf of Thailand, and named in honour of Mr. Vie Panyarachun — a marine naturalist and citizen science contributor in Thai waters.

Photographing It at Sunset Cove

At Sunset Cove Beach & Dive Resort, our guides find Phestilla viei on Pavona explanulata colonies at 7 to 21 metres depth. Therefore, search any Pavona colony carefully for crescent-shaped egg mass trails. Follow the trail to its end — the animal sits there. For underwater macro photographers in Romblon, the combination of animal and egg mass trail makes a compelling documentary sequence. Consequently, this species rewards patient, methodical searching with one of the most interesting corallivore stories in our Marine Life Encyclopedia.

Taxonomy & Classification

Order	Nudibranchs (Nudibranchia)
Suborder	Aeolidina (Aeolid Nudibranchs)
Family	Trinchesiidae
Genus	Phestilla
WoRMS AphiaID	1435754
iNaturalist	1080284

Described by Mehrotra, Caballer & Chavanich (2020) in Marine Biodiversity 50:36 from Koh Tao, Gulf of Thailand. Named in honour of Mr. Vie Panyarachun for contributions to citizen science and sea slug diversity records in Thai waters. WoRMS AphiaID 1435754 — status listed as uncertain due to ongoing controversy over genus allocation (also placed in Tenellia). Family Trinchesiidae. Sister species to Phestilla fuscostriata based on COI barcoding. Indo-Pacific distribution.

Morphology

Size	5–20 mm
Colour Variations	Body translucent white to pale yellow. Sides pale brown. Cerata held horizontally giving a very flat appearance — mimicking the surface texture of Pavona explanulata coral. Characteristic bulbous bumps on the pericardium at regular intervals along the back — a key diagnostic feature. Brown pigmentation from symbiotic dinoflagellates (Durusdinium sp.) visible through translucent body. Colour and posture provide near-perfect camouflage on Pavona coral.
Identifying Features	Almost perfectly camouflaged on Pavona explanulata coral — looks like the coral surface. Cerata held horizontally and very flat. Characteristic bulbous pericardial bumps. Brown pigmentation from dinoflagellates. Most easily found at the leading end of a distinctive linear trail of crescent-shaped egg masses on freshly devoured Pavona coral. No cnidosacs at ceratal tips — a key character distinguishing Phestilla from other Trinchesiidae. Obligate corallivore — never found away from Pavona explanulata.

Body small, 5–20 mm, translucent white to pale yellow. Cerata wide at base, held laterally and very flat — unique horizontal posture. Pericardium has characteristic bulbous knobs at regular intervals. Rhinophores smooth, semi-white, relatively short. Oral tentacles smooth, 1.5x rhinophore length. No cnidosacs — diagnostic for the genus. Contains symbiotic dinoflagellates (Durusdinium sp.) which give brown pigmentation and may contribute to nutrition via photosynthesis.

Habitat & Ecology

Substrate	coral
Depth Range	7–21 m (most common: 12 m)
Temperature	24–29°C
Primary Prey / Host	Pavona explanulata (Agariciidae coral) — obligate corallivore, feeds on no other species

Activity & Behaviour

Active Time	day, night
Seasonal Presence	Year-round — found exclusively on Pavona explanulata coral colonies
Egg Ribbon	Crescent-shaped egg masses in distinctive linear trails on freshly devoured Pavona coral — 80–120 eggs per mass
Spawning Season	Egg masses deposited in distinctive linear trails on devoured coral — present year-round
Chemical Defence	Absent
Aposematic Colouring	Absent
Camouflage Strategy	Body colour, flat horizontal cerata posture and texture mimic Pavona explanulata coral surface almost exactly. One of the most convincing coral-mimicking nudibranchs in the Indo-Pacific. The brown dinoflagellate pigmentation adds to the coral-like appearance.
Escape Response	Relies entirely on camouflage. Remains motionless on coral. No cnidosacs. No ceratal autotomy. Cryptic behaviour on coral surface is the primary defence.

Scientific Literature

A new species of coral-feeding nudibranch (Mollusca: Gastropoda) from the Gulf of Thailand
Mehrotra, R.; Arnold, S.; Wang, A.; Chavanich, S.; Hoeksema, B.W. & Caballer, M. (2020). Marine Biodiversity 50: 36

Literature for divers

Romblon Field Data

Look for the distinctive linear trail of crescent-shaped egg masses on Pavona explanulata coral — this trail leads directly to the animal at its head. The nudibranch itself is nearly invisible on the coral surface. Photograph from directly above to show the flat horizontal cerata and coral mimicry. Also document the egg mass trail for context — this combination makes a compelling macro photography sequence. Very small — use diopters. The egg mass trail is often more visible than the animal itself.

First Sighting	2021-01-01
Max Individuals	8