Myxilla incrustans (Esper, 1805-14) Common name(s): Rough scallop sponge
Synonyms:  Ectyodoryx parasitica, Myxilla parasitica
Phylum Porifera  Class Demospongiae   Subclass Ceractinomorpha    Order Halochondriida     Family Myxillidae
	Myxilla incrustans sponge on a Chlamys hastata scallop.
	(Photo by: Dave Cowles)

How to Distinguish from Similar Species: The other sponge commonly found encrusting scallops in this area, Mycale adhaerens, is yellow-brown to violet and has styles 290-360 microns long.  M. W. de Laubenfels also said that Mycale adhaerens has a coarser structure, and when torn it reveals prominent fibers thicker than thread, which Myxilla incrustans does not have (Ricketts et al., 1985)
(see picture)

Geographical Range: Pacific coast and Japan.  Most references to it are for the Pacific Northwest so presumably it is much less common elsewhere.

Depth Range:

Habitat: Lives on scallops such as Chlamys hastata and Chlamys rubida.

Biology/Natural History: This is the most common sponge found encrusting scallop shells in the Rosario area.  The sponge seems to only encrust the surface and not bore into the shell at all.  Sponge predators include the nudibranchs Cadlina luteomarginata, Dialula sandiegensis, and Archidoris odhneri; and another nudibranch, Discodoris heathi, has been observed clinging to them.  The symbiosis is likely mutualistic.  If one of the major predators of the scallop, the seastar Evasterias troschelii, encounters the scallop (and the scallop does not swim away) it often turns away if it touches the sponge; likely in response to some secretion or to the spicules from the sponge.  The sponge also appears to make it more difficult for the seastar's tube feet to adhere to the scallop.  If the sponge is removed from the scallop and the scallop is prevented from swimming, it is readily captured by the seastar.  The scallop will also swim from predators of the sponge, such as Archidoris spp, so the sponge is benefited as well.  The swimming scallop may also help carry the sponge into areas with clean water and good currents, and help prevent fouling of the sponge.

Research by Kirt Onthank and Thomas Ewing at the Walla Walla University Rosario Marine Laboratory indicates that sponge encrustation deters scallop predation by octopus Enteroctopus dofleini and Octopus rubescens, both of which may be important scallop predators in our area.  Sponges which live on the scallop are also less vulnerable to predation by nudibranchs such as Anisodoris nobilis and Archidoris montereyensis.

References:

General References:
Harbo, 1999
Kozloff, 1993
Morris et al., 1980
Ricketts et al., 1985

Scientific Articles:
Bloom, S., 1975.  The motile escape response of a sessile prey:  a sponge-scallop mutualism.  J. Exp. Mar. Biol. Ecol. 17: 311-321

Farren, H.M. and D. A. Donovan, 2007.  Effects of sponge and barnacle encrustation on survival of the scallop Chlamys hastata.  Hydrobiology 592: 225-234
 

The large majority of Chlamys rubida and especially Chlamys hastata scallops found subtidally on Sares Head are encrusted with this sponge.


These are torn sponge fragments.  Myxilla incrustans is yellow and Mycale adhaerens is purple.  Note the more stringy appearance of the Mycale.  Scale is millimeters.
Photo by Dave Cowles, July 2005.
 
 

Photos of spicules taken from Myxilla incrustans encrusting a Chlamys hastata scallop.  Spicules isolated by Brooke Reiswig July 2006.  Photos are from a phase-contrast microscope.
Styles (a type of megasclere).  A sigma also appears at the top left. We measured styles from 160-195 microns long.	Sigma (a type of microsclere).  We measured sigmas from 15-20 microns long.	Tridentate isoanchor (a type of microsclere).  This one is wrapped around a style. We measured tridentate isoanchors from 14-17 microns long.