Phyllidiidae

Lore & Background

The family Phyllidiidae was originally spelled as family Phyllidia, with Jean-Baptiste Lamarck coining the words 'les Phyllidiens' and 'les phyllidéens' (1801; 1809). These were later Latinized by J.G. Children (1823) to Phyllidiana, placed in Hydrobranchiae. The present name Phyllidiidae is attributed to Rafinesque, not Lamarck. There has been much taxonomic confusion, largely due to inadequate early descriptions and the difficulty of classifying a family where all species lack radulae. David J. Brunckhorst reviewed the family, clarifying many species and describing new ones and a genus. Cladistic analysis shows the family is monophyletic, with Ceratophyllidia sister to the rest, Phyllidiopsis sister to the remaining genera, Phyllidiella sister to the remaining, and Reticulidia sister to Phyllidia and Fryeria. This analysis was not entirely supported by a 16S gene study. Many undescribed species are being revealed by DNA analyses. The mantle of these oval nudibranchs is flattened dorsoventrally and covered with hard, colored tubercles, decorated with contrasting colors and patterns as warning signals to predators. The lamellate rhinophores can be retracted. Like other dorid nudibranchs, all species have a dorsal anus, except those in the genus Fryeria, where the anus is posteroventral and protrusible. They lack buccal armature (radulae and jaws). Gill leaflets are ventrolateral, not a dorsomedian circlet. The oral glands and stomach have undergone modifications. The reproductive system is triaulic (two female openings, one male). Most phyllidiids appear conspicuously during daytime, using aposematism (warning colors) to deter predators; only Phyllidiopsis cardinalis was found to be always hidden.

Reader's Guide

The family Phyllidiidae holds significance as a distinct group within the clade Doridacea, characterized by the absence of radulae and jaws, a rare trait among nudibranchs. Their feeding habits are poorly documented, but they are known as predators adapted for sucking on sponges, with specific observations of Phyllidia varicosa feeding on Hymeniacidon and Phyllidia flava on Acanthella acuta. The family's taxonomy has been historically confused, but Brunckhorst's cladistic analysis established a monophyletic framework, though not fully supported by 16S gene data. The presence of many undescribed species, revealed by DNA analyses, underscores ongoing discovery. Their aposematic coloration and chemical defenses highlight evolutionary adaptations for predator deterrence. The triaulic reproductive system aligns with advanced dorids. The family includes five genera (Phyllidia, Ceratophyllidia, Phyllidiella, Phyllidiopsis, Reticulidia) and over 80 species, with Fryeria and Reyfria now considered synonyms of Phyllidia. Their distribution is primarily tropical Indo-Pacific, with a few species in the tropical Atlantic and Mediterranean.

Did You Know?

• Phyllidiidae lack buccal armature (radulae and jaws), unlike most other dorid nudibranchs.
• The anus is dorsal in most species, but in the genus Fryeria it is posteroventral and protrusible.
• Only one species, Phyllidiopsis cardinalis, was observed to be always hidden; most are conspicuous during daytime.
• The family contains more than 80 species across five genera, with many undescribed species revealed by DNA analyses.