Philine auriformis on the California coast

Your questions take me back to some of the first research I did on opisthobranchs in New Zealand. You seem to have found my published papers on Philine ( Numbers 5, 15, 16) in my list of publications.

For background information, philinids are bubble-shells which have specialised for burrowing through sand and mud. They have a very stream-lined body and the shell is reduced to a thin internal plate-like shell in the back "posterior shield" region of the body. In the photo above it covers the brownish digestive gland. The bright white region is the muscular gizzard which contains three large calcareous plates which are used to crush the shells of the bivalves it feeds on. Species of Philine show an interesting evolutionary progression through species with small chitinous plates to species like Philine angasi which has two huge calcareous plates and a small third plate. Philine auriformis has three identically shaped plates.

My main aim was to compare the functional anatomy of various common bullomorph or cephalaspidean opisthobranchs. We knew little about the biology of any species then and unfortunately there are still major gaps in our knowledge. I don't know of any subsequent studies in New Zealand on Philine auriformis. To answer some of your specific questions:

•As a burrower it is seldom seen unless you are specifically studying it. I remember digging up and seiving huge areas of sandy mudflats in search of Philine and being happy to find 8 or 9 specimens per low tide. The only subtidal records I know of are from dredge samples, the deepest to about 12 fathoms (=72 feet, = 22 meters), but that could be because that is the limit of small naturalist dredge operations. So I can't say what its natural limits are.
•Again I can't be sure how deep it burrows but in most substrates I sampled the sediment became anoxic below about 10 to 15 cms and neither Philine nor its food Nucula were found in such conditions. I am not an expert on nuculid bivalves but Nucula hartvigiana is very common close to the surface in the top couple of centimetres. It is found in fine muddy sands of estuaries and coarser sands of more open beaches.

•The jelly-like egg masses of Philine are about 2 centimetres long, and are anchored in the sand by a long thread. The individual eggs are arranged inside the egg mass in a coil.
•I know of no predators of Philine auriformis but at times the aglajid bubble-shell Philinopsis taronga, a well-known predator of bubble-shells, was commonly found in the same area. Perhaps in California such spectacular aglajids as the huge Aglaja inermis (Navanax) could be feeding on this antipodean invader.

It seems this work would be an excellent excuse to apply for a grant to study these animals in New Zealand.

A good reference is: Gosliner, T. 1995. The introduction and spread of Philine auriformis (Gastropoda: Opisthobranchia) from New Zealand to San Francisco Bay and Bodega Harbor. Marine Biology, 122: 249-255.

A summary of the invasion story has been prepared by Terry Gosliner .. Bill Rudman