The purple-loving barnacle

Andrew Hosie's blog | Created 2 years ago

The Purple-Loving Barnacle

A new species of barnacle, Membranobalanus porphyrophilus, has now been named and described. The barnacle was recently discovered living on the reefs around Rottnest Island during local fieldwork by the Aquatic Zoology Department. Searching in the collections of both the Western Austrailan and South Australian Museums revealed that the barnacle had also been collected in the waters around Kangaroo Island in South Australia. Scientists from the WA Museum and  Curtin University utilised a diverse array of tools including light microscopy, DNA sequences, scanning electron microscope images and micro-CT scans to build a comprehensive description of the new species. 

A 3D model of the purple-loving barnacle Membranobalanus porphyrophilus, reconstructed from micro-CT scans by wamuseum on Sketchfab

Unlike a typical barnacle that attaches to rocks, this species exploits a very different strategy. M. porphyrophilus belongs to a group of barnacles that live solely in symbiosis with marine sponges. It is completely embedded within the sponge body with only a small hole allowing the barnacle to extend its feathery limbs, called cirri, into the surrounding water to trap food such as plankton. Interestingly, M. porphyrophilus is only known to inhabit one species of sponge, the vibrantly purple Spheciospongia purpurea. The sponge is endemic to southern Australia from Geraldton to southern New South Wales. The shell plates of the barnacle should be white and the body mostly transparent, but they are deeply stained by the pigments of the host. The sponge even retains the purple colour even when dried or preserved in ethanol. The barnacle's species name, porphyrophilus, translates as purple-loving in reference to the coloration of the only known host. 

Left, the newly described Membranobalanus porphyrophilus. Right, the host sponge

Left, the newly described Membranobalanus porphyrophilus. Right, the host sponge, Spheciospongia purpurea at Rottnest Island
Image copyright WA Museum 

How the barnacle becomes embedded within the sponge is still a bit of a mystery, but they prevent the sponge from completely overgrowing them by rasping the sponge tissues using a variety of spines and teeth on the cirri. Sponge-inhabiting barnacles are a diverse group with more than 80 species world-wide and approximately 20 in Western Australia. However, current research is showing that many more are yet to be formally named and described.  

Scanning electron (left) and light (right) microscope images of the teeth and sp

Scanning electron (left) and light (right) microscope images of the teeth and spines on the cirri used by the barnacle to scrape away encroaching sponge tissue.
Image copyright WA Museum 

The barnacle species’ description was recently published in the scientific journal Zookeys and is a small part of a large collaborative project between a team of researchers from the WA Museum and Curtin University, funded in part by the Australian Biological Resources Study and the Gorgon Net Conservation Benefits Fund. The newly published paper can be viewed here: DOI: 10.3897/zookeys.873.35421