Phyllidiella striata

Lore & Background

Phyllidiella striata has a black dorsum with longitudinal grey-pink ridges that are tuberculate and somewhat broken. These ridges form a circle behind the anus and a patch between the rhinophores. The rhinophores are black with pink bases, and the oral tentacles are pale grey, sometimes streaked with black. The front-most tubercles are set obliquely, sloping towards the centre of the back, and the ventral surface is a uniform pale grey.

This species was first described from the Philippines. Its name is often erroneously used for Phyllidiopsis xishaensis. It occurs in the tropical central and western Pacific Ocean and the Indian Ocean at depths down to about 50 m.

Phyllidiella striata feeds on sponges. It has neither a radula, jaws, nor a stomach, and feeds by turning part of its gut inside out, using digestive enzymes to break down sponge tissues and sucking in the liquified product. Like other nudibranchs, it is a hermaphrodite. The genital pore is on the right-hand side of the foot just behind the head. A pair of individuals move close to each other while facing in opposite directions and transfer sperm to each other. Each is then able to produce eggs. There is no larval stage; embryos undergo direct development into juveniles. This species exudes a milky-white substance containing terpenes from its dorsal gland, derived from toxic substances in the sponge it feeds on, which acts to deter predators.

Reader's Guide

Phyllidiella striata is significant as a representative of the family Phyllidiidae, demonstrating a specialized feeding strategy that lacks a radula, jaws, and stomach, instead using an everted gut to digest sponge tissue externally. This adaptation highlights the evolutionary diversity among nudibranchs. Its defensive secretion of terpenes, derived from its sponge prey, illustrates a classic example of chemical defense in marine invertebrates. The species is also notable for its direct development, bypassing a larval stage, which is relatively uncommon among nudibranchs. The frequent misidentification of this species as Phyllidiopsis xishaensis underscores taxonomic challenges in the group. Its distribution across the tropical Pacific and Indian Oceans, first described from the Philippines, places it within a broad Indo-Pacific range. The detailed description of its dorsal ridges, rhinophore coloration, and ventral surface provides clear diagnostic features for field identification. The species' ecological role as a sponge feeder and its hermaphroditic reproductive strategy contribute to understanding the life history of dorid nudibranchs.

Did You Know?

• Phyllidiella striata has neither a radula, jaws, nor a stomach; it feeds by everting its gut to digest sponge tissue externally.
• Phyllidiella striata undergoes direct development with no larval stage; embryos develop directly into juveniles.
• The name Phyllidiella striata is often erroneously used for the species Phyllidiopsis xishaensis.