I found these sea squirts recently while getting photos at St Helens boat ramp. They got the attention of one of my ascidian friends, who suggested that they may be Styela Canopus. I thought nothing of it, until he said that hadn’t been officially recorded in Victoria.
I went through the rest of my photos and grabbed all that looked like they potentially had the species. I then checked the species description in Awesome Ascidians.
Awesome Ascidians is this brilliant NZ sea squirt identification guide. It’s one of the first resources that has helped me make sense all the information about ascidians. It is incredibly useful and there is a lot of overlap between countries.
It describes the “Rough Sea Squirt” as:
Body small, erect, oblong, with no stalk and two short closely spaced siphons on the top of the body, one slightly larger than the other. Test tough with warty tubercles occurring around the siphons and longitudinal wrinkles, becoming less distinct on the back of the body. Fine stripes run down the external surface of the siphons and upper body; these may be obscured by wrinkles in the tough leathery test. Gill slits elongate, gills folded, tentacles smooth, testis follicles outside ovary. Colour in life cream to tan, stripes white, or burnt orange brown with purplish tinges
That description didn’t seem like what I had found. It didn’t look ‘leathery’. The colour seems more black or a dark brown.
I checked out SA Marine Guide, another favourite site.
These are its most distinguishing feature, being usually dark brown to black with compass point white stripes on both the inside and outside of the siphons. It is most similar to Polyandrocarpa zorritensis, with which it shares habitat. However, it is visibly larger, with thinner stripes, and does not usually form dense aggregations.
This made more sense. I think the leathery bits are the testes and I don’t know how to tell hat they are. But they still seem to have more than four stripes.
I have no idea whether this species actually is S. Canopus or not, based on the information I’ve read. I learned a lot from the discussion. In many cases, descriptions are based off samples that have been collected. These don’t actually represent what the ascidian looks like in the field. It is important to build up a visual database, especially curated in the one place like iNaturalist, so we have more data to work with. This will be useful when a sample is eventually collected. A good example of this type of observation is Janine Bakers observation on iNaturalist.
If you want to nerd out, there is a paper suggesting that Styela canopus “should be treated as the Styela canopus complex.” That makes me question if this is actually an invasive species – could some species in the complex actually be native? I reckon this is unlikely, considering many are found on man made structures.
I’m not a taxonomist, or scientist. I don’t have the knowledge to understand most of the resources I’ve posted. I don’t know what I’m doing most of the time. This particular observation has highlighted the important in documenting changes.
I don’t think I have the patience to become a proper taxonomist/scientist. I prefer documenting!