The Tendril Sponge--Weird or what?

Marine sponges are common and abundant in the Pacific Northwest, with well over 250 species reported. They thrive in the plankton-rich, current-swept passages along our shores, often dominating underwater terrains with colourful encrusting carpets, massive, gnarled lumps or supple, swaying fans.

Many PNW sponges are well-known to naturalists and can be relatively easily identified by their shape, colour and size. But there are many others that have yet to be properly described and require detailed examination of the shape and arrangement of their spicules in order to decide where they fit in amongst their fellow sponges. These characters must be compared with those of known species from around the world to determine whether they are an already-known species or something new to science. As you might imagine this is painstaking and difficult work, given that the original descriptions of many species were not terribly thorough and that the original (type) specimens that were used to make the determination may no longer even exist.

Sponge taxonomy isn't exactly a glamorous, high-profile scientific pursuit. Yet in the PNW we are extremely fortunate to have dedicated experts such as Bill Austin, Bruce Ott and Henry Reiswig who tackle this unsung task with dedication and enthusiasm. I'm certainly no taxonomist, but I am an observant diver/photographer, and it has been a pleasure to assist in the process of learning more about our local sponges by collecting and photographing interesting specimens.

It's actually quite amazing what even a "nothing-fancy" dive site in Howe Sound will turn up. Right under our noses, just a few miles from downtown Vancouver, dwell sponges that have never even been reported from these waters before. Undescribed species are, amazingly, quite common. Perhaps that speaks to the amount of time scientists have devoted to lowly sponges as opposed to say, much more flamboyant and certainly better known nudibranchs.

I'll say more about Howe Sound and its enigmatic sponges at a later date, but first to the sponge that inspired this post.

While diving in Sechelt Inlet in February this year I was swimming alongside a rocky bluff at about 80 feet, looking carefully for small encrusting sponges that I wanted to photograph. The rocky slope at this site was quite rich, with thousands of small lampshells (brachiopods) carpeting the bottom and the occasional boot sponge festooned with graceful feather stars. The water was a chilly 8 degrees, and while I was reasonably comfortable inside my neoprene drysuit, I could feel my hands starting to get numb as the dive progressed. As I panned my underwater flashlight across a vertical wall, I spotted two unusual creatures. They were tiny white blobs, only 6 mm in diameter, and attached to each blob was an extremely long, slender tendril, one of which seemed to be at least 100 mm long. They certainly looked to be sponges, but nothing like I had seen in over 40 years of diving on this coast. I had never encountered a sponge with such an unusual, extremely long "whip" or tendril, attached to its body.

Fortunately I had my close-up lens on my digital underwater camera, so first I took some pictures. Then I carefully pried the delicate specimens off the rock using a thin knife and deposited them into a plastic bag. At the surface I preserved the specimens in ethanol and later shipped them over to Bill Austin at the Khoyatan Marine Lab in Saanich. The "tendril sponge" was finally in expert hands...

I asked Andy Lamb if he had ever seen such a thing. "As a matter of fact..." he replied, directing me to PO69 on page 78 of Marine Life of the Pacific Northwest. Sure enough, there was a picture of the same sponge I had found. Bernie Hanby, who had taken the picture back in November of 1992, gave me some background. He remembered finding a single specimen about 50 ft deep on a rock wall in Agamemnon Channel at the entrance to Jervis Inlet, not far from where I had found some. He has never seen another.

Bill examined the specimens with his trusty microscope and advised that they belong to the Family Polymastiidae. There are three members of this family commonly encountered by divers in the PNW: the aggregated nipple sponge (PO17), the aggregated vase sponge (PO18) and the retractable nipple sponge (PO19). Yet while the tendril sponge has characteristic spicules of this family, it looks nothing like these sponges. So here's where it gets interesting. Bill suggests that the tendril sponge could be the asexual budding stage of an existing species, perhaps PO18, Polymastia pacifica. In other species of this family it has been observed that a bud is pinched off the adult sponge which then elongates rapidly and produces smaller buds which break off and develop into new sponges. The long tendril perhaps allows the "mother" sponge some room to grow by placing the new buds at a reasonable distance but on similar suitable substrate. But this is only speculation. If this is indeed a "phase," it most likely would belong to Polymastia pacifica, which is the only one of the three common Polymastiidae actually found close by. Bill suggests that the DNA of the tendril sponge could be compared to Polymastia pacifica--this could provide the definite answer, the "smoking gun" as it were, to this riddle. Is the tendril sponge an entirely new species, or is it a budding phase of a known sponge?

That question remains to be answered. In the meantime we would greatly appreciate input from divers and underwater photographers who happen to encounter this mysterious, seriously weird sponge. Contact the author at neil.mcd@telus.net