Cyerce elegans pink butterfly sea slug Romblon Philippines

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Elegant Butterfly Sea Slug

Cyerce elegans Bergh, 1870

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A Pink Icon Reclaims Its Name

Cyerce elegans (Bergh, 1870) is one of the most visually striking butterfly sea slugs at our macro dive sites in Romblon, Philippines. Its body and large leaf-like cerata are a bold, unmistakeable pink. Furthermore, it has a fascinating taxonomic story. For decades, the dive community called this pink species Cyerce sp. 3 or Cyerce sp. 3 (NSSI2). Meanwhile, a different golden species incorrectly carried the name C. elegans. The landmark 2025 molecular revision by Moreno et al. set the record straight — the true Cyerce elegans is this pink species. It belongs to the order Sacoglossa, family Caliphyllidae, and is documented on iNaturalist.

Bold Colour, Bold Defence

Unlike most Cyerce species, Cyerce elegans does not hide. Its pink colouration is aposematic — it warns predators of chemical defence compounds in its body tissue. In addition, like all Cyerce, it performs ceratal autotomy when threatened. The cerata detach and writhe on the seafloor. As a result, the predator targets the moving cerata while the animal escapes. Its close relatives Cyerce nigra, Cyerce blackburnae and Cyerce katiae are all documented in our Marine Life Encyclopedia. Together they represent four of the nine newly revised Cyerce species found in Romblon.

Finding It at Sunset Cove

At Sunset Cove Beach & Dive Resort, our guides find Cyerce elegans on sandy rubble substrate near Udotea green algae patches at 3 to 25 metres. The pink colour makes it easier to spot than other Cyerce. However, approach slowly — it sheds its cerata immediately when startled. For underwater macro photographers in Romblon, the pink cerata photograph beautifully against dark substrate. Consequently, this is one of the most sought-after and photographable butterfly sea slugs at our dive sites.

Taxonomy & Classification

Order	Sacoglossans (Sacoglossa)
Family	Caliphyllidae
Subfamily	Cyercinae
Genus	Cyerce
WoRMS AphiaID	494512
iNaturalist	549234

Originally described by Bergh (1870) from the Philippine Archipelago in Semper's Reisen im Archipel der Philippinen — making it one of the oldest described Cyerce species. For many years, a golden-coloured Cyerce was incorrectly called C. elegans. The landmark 2025 molecular revision by Moreno et al. (Zoological Journal of the Linnean Society) confirmed the true identity — the pink specimen previously called Cyerce sp. 3 (NSSI2) is the genuine Cyerce elegans. WoRMS AphiaID 494512. Family Caliphyllidae.

Morphology

Size	10–25 mm
Colour Variations	Body and cerata striking pink to pinkish-white — the most distinctive feature of this species. Large, flattened, leaf-like cerata typical of the genus Cyerce. Previously known in the dive community as Cyerce sp. 3 or Cyerce sp. 3 (NSSI2). For many years, a golden-coloured Cyerce species was incorrectly identified as C. elegans. The 2025 molecular revision by Moreno et al. confirmed that the true Cyerce elegans is the pink specimen found in Romblon and across the Indo-Pacific.
Identifying Features	Instantly recognisable by its striking pink colouration — unique among Cyerce species at Romblon. Large flattened leaf-like cerata. No other Cyerce at our dive sites shares this pink colour. Bifurcate enrolled rhinophores typical of the genus. Always found near Udotea green algae. The pink colouration provides aposematic warning of chemical defence compounds. Distinguished from Cyerce nigra (black and white), Cyerce blackburnae (yellow-brown) and Cyerce katiae (honeycomb pattern) by colour alone.

Body flattened, ovate. Cerata large, leaf-like, readily autotomised as defence — ceratal autotomy. Rhinophores bifurcate and enrolled. Head shield distinct. Penial stylet present. Body and cerata pink to pinkish-white. One of the most visually striking members of the genus. Originally described by Bergh (1870) from the Philippine Archipelago — making the Philippines the type locality.

Habitat & Ecology

Substrate	sand, rubble
Depth Range	3–25 m (most common: 10 m)
Temperature	24–29°C
Primary Prey / Host	Udotea spp. (green algae, family Udoteaceae)

Activity & Behaviour

Active Time	day, night
Seasonal Presence	Year-round — found on sandy and rubble substrate near Udotea algae
Egg Ribbon	White, coiled ribbon
Spawning Season	Not yet documented at SSC
Chemical Defence	Present
Aposematic Colouring	Absent
Camouflage Strategy	Pink colouration is aposematic — warns predators of chemical defence compounds rather than providing camouflage. Stands out boldly against substrate unlike most other Cyerce species.
Escape Response	Ceratal autotomy — sheds cerata which writhe and distract predators. Chemical defence compounds in body tissue provide additional deterrent.

Scientific Literature

Phylogenetic systematics of the genus Cyerce Bergh, 1870 (Sacoglossa, Caliphyllidae) with descriptions of nine new species
Moreno, K.; Medrano, S.; Gosliner, T.M.; Wilson, N.G.; Krug, P.J.; Valdés, Á. (2025)

Literature for divers

Romblon Field Data

One of the most photogenic Cyerce species at Sunset Cove. The pink colouration photographs beautifully against dark substrate or blue water backgrounds. Search sandy rubble near Udotea algae patches. Use diopters for close-up shots. The flapping cerata and bold pink colour create outstanding macro images. Approach slowly — sheds cerata immediately when startled. Excellent subject for showing the full Cyerce diversity at our dive sites alongside C. nigra, C. blackburnae and C. katiae.

First Sighting	2019-01-01
Max Individuals	3