Phyllodesmium pinnatum nudibranch octocoral Romblon Philippines

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Pinnate Phyllodesmium

Phyllodesmium pinnatum Moore & Gosliner, 2009

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The Tree-Like Solar Nudibranch

Phyllodesmium pinnatum (Moore & Gosliner, 2009) is one of the most cryptic solar-powered nudibranchs at our macro dive sites in Romblon, Philippines. Its cerata are elongate, flattened and pinnate — branching like tiny trees. This structure matches octocoral colonies almost perfectly. As a result, it is nearly invisible on its prey. It belongs to the order Nudibranchia, suborder Aeolidina, family Myrrhinidae. Furthermore, its type locality is the Philippines — described from Batangas Province. Find it on iNaturalist.

Solar Power Through Octocoral

Like all Phyllodesmium species, Phyllodesmium pinnatum retains zooxanthellae from its octocoral prey. These algae photosynthesise sunlight and provide the animal with supplementary energy. In contrast to Phyllodesmium longicirrum, which feeds on Sarcophyton, this species targets octocorals of the order Alcyonacea. Its close relatives Phyllodesmium colemani, Phyllodesmium jakobsenae and Phyllodesmium koehleri are also in our Marine Life Encyclopedia. Together they represent five different solar-powered strategies documented at Sunset Cove — the most diverse Phyllodesmium collection documented at any single dive resort in the Philippines.

Finding It at Sunset Cove

At Sunset Cove Beach & Dive Resort, our guides search octocoral colonies carefully at 3 to 25 metres depth. The pinnate cerata match coral branches almost exactly. Therefore, look for slightly irregular branch structure on a colony. Approach very slowly — it sits completely still. For underwater macro photographers in Romblon, the tree-like cerata create extraordinary close-up images. Consequently, finding all five Phyllodesmium at our dive sites is one of the great macro photography challenges at Sunset Cove.

Taxonomy & Classification

Order	Nudibranchs (Nudibranchia)
Suborder	Aeolidina (Aeolid Nudibranchs)
Family	Myrrhinidae
Subfamily	Phyllodesmiinae
Genus	Phyllodesmium
WoRMS AphiaID	457930
iNaturalist	496578

Described by Moore & Gosliner (2009) in Zootaxa 2201 alongside P. tuberculatum and P. karenae. Type locality: Devil's Point, Maricaban Island, Batangas Province, Philippines — making the Philippines the type locality for this species. WoRMS AphiaID 457930. Family Myrrhinidae. Solar-powered — retains zooxanthellae from octocoral prey. One of three new Philippine Phyllodesmium described in the same paper.

Morphology

Size	15–40 mm
Colour Variations	Body whitish-grey to brownish-grey. Cerata elongate, flattened and tree-like or pinnate — the most distinctive feature of this species. Zooxanthellae retained from octocoral prey and distributed through cerata — providing supplementary solar energy. Colour closely matches prey octocoral colony making it one of the most cryptic Phyllodesmium species. The pinnate ceratal structure is unique among the Phyllodesmium documented at Sunset Cove.
Identifying Features	Distinguished by its pinnate — feather-like or tree-like — flattened cerata, unique among Phyllodesmium at Romblon. Body whitish-grey to brownish-grey matching octocoral prey. Always found directly on octocoral colonies. Type locality is the Philippines — described from Batangas Province. Distinguished from P. longicirrum by smaller size and pinnate rather than paddle-like cerata. Distinguished from P. colemani and P. jakobsenae by octocoral prey rather than organ pipe or Xenia coral.

Body elongate, up to 40mm. Cerata flattened and pinnate — tree-like branching unique within the Phyllodesmium at Romblon. Zooxanthellae distributed through cerata from octocoral prey. Rhinophores smooth. Lacks cnidosacs — defence relies on chemical compounds from prey and exceptional camouflage. The pinnate ceratal morphology was a key diagnostic feature in the original description by Moore & Gosliner (2009).

Habitat & Ecology

Substrate	coral
Depth Range	3–25 m (most common: 10 m)
Temperature	24–29°C
Primary Prey / Host	Octocorals (soft corals, order Alcyonacea) — highly cryptic on prey colonies

Activity & Behaviour

Active Time	day, night
Seasonal Presence	Year-round — dependent on presence of octocoral colonies
Egg Ribbon	White, coiled ribbon
Spawning Season	Not yet documented at SSC
Chemical Defence	Present
Aposematic Colouring	Absent
Camouflage Strategy	Pinnate tree-like cerata precisely mimic the structure of octocoral colonies. Body colour matches prey coral. One of the most cryptic Phyllodesmium species — nearly impossible to spot without knowing exactly what to look for.
Escape Response	Primary defence is exceptional camouflage on octocoral colonies. Remains motionless when threatened. Chemical deterrents from coral prey.

Scientific Literature

Three new species of Phyllodesmium Ehrenberg (Gastropoda: Nudibranchia: Aeolidoidea), and a revised phylogenetic analysis
Moore, E. & Gosliner, T.M. (2009). Zootaxa 2201: 30–48

Literature for divers

Romblon Field Data

Search carefully on octocoral colonies — the pinnate cerata blend almost perfectly with the coral branches. Look for slightly irregular or mismatched branch structure on a coral colony. Approach very slowly. Use diopters for close-up shots of the pinnate cerata. The tree-like ceratal structure creates extraordinary macro images. Excellent subject for showing the diversity of solar-powered Phyllodesmium strategies found at Sunset Cove alongside P. longicirrum, P. colemani, P. jakobsenae and P. koehleri.

Frequency	rare
First Sighting	2020-01-01
Max Individuals	2