Things have been going quite well in the in-line refugium known as Box of Slugs 2.0. Although it might not be considered a plus in most aquaria, algae have been very successful in the new tank. A less sophisticated aquarist might dare to call the tank an eyesore, yet the slugs could not be happier. Here are a few of the youngsters grazing on what I think is Derbesia.
Indeed, it has been a great time for the little guys, and they have been growing like the little slug-weed chimeras that they are. Many have gone beyond the twiggy little worm stage to looking and behaving like proper small slugs.
At this size, I am still unsure that they are all E. clarki. The one below is most likely E. tuca
almost looks like E. chlorotica, or maybe E. subornata, and does not have much in the way of parapodia.
The small slugs below look more convincingly like the adults in the tank. Rolled rhinophores, parapodia starting to ruffle, chloroplasts throughout the body, including the foot, all point to the little guys being the common lettuce slug of the Keys.
Will they get spots and ruffles like the purported parents? Time will tell. [note added later: these are not young E. clarki, as a few of the edits above indicate]
They still have a long way to go to get to full size, as can be seen in this photo of the adult from the photo above grazing on Bryopsis while a youngster wanders about.
One of the more interesting developments is the appearance of very small, dense egg masses in Box of Slugs 2. At first, I attributed them to the small herd of E. crispata that arrived a few weeks ago, since I have no idea of the size or appearance of their egg masses. I need to start putting a ruler or something in the photo for scale, but this clutch is about the size of the first coil of the a standard E. Clarki mass from Box of Slugs 1 (shown here, for example), and the little embryos are packed much more tightly.
As mentioned above, I thought these were eggs from crispata, but was thrown for a bit of a loop when I saw one of the youngsters curved around the mass as if laying them. Can they really be mature enough to lay eggs? I collected the mass below, and am documenting the embryos’ development. They are definitely fertile, as indicated by the classic circling movements inside their eggs, and maybe this time I can get a brood to mature in a controlled environment and find out which species they turn into. Stay tuned.
Terry Gosliner of the California Academy of Sciences was on NPR’s Science Friday this afternoon, talking about…SEA SLUGS!
Mostly he talked about the northward movement of the Hopkins Rose nudibranch (below), and what that tells us about warming temperatures in the Pacific.
Of course, he could not help but mention Solar Sea slugs and kleptoplasty. I mean, who can spend an entire interview talking about a spiky pink abomination when you can talk about green beauties like Elysia? It was a bit disappointing that he referred to Elysia as a nudibranch (we all know that they are not), and implied that they derived as much benefit from their chloroplasts as corals do from their zooxanthellae. Nevertheless, any radio show about sea slugs is a good radio show.
More information and audio can be found on the Science Friday web site.
Not surprisingly, many of the comments that have been posted by others on the blog are spam, and many of these are helpful people with names like “Central Air Conditioning,” and offer assistance in increasing traffic on the site.
To be honest, although I would like for the site to be useful to all of the denizens of the InterWeb, the site is mainly a way for me to keep track of my progress, along with helping me organize the links and literature comprising the world of slugs. So, I am not particularly interested in increasing traffic for the time being.
Nonetheless, maybe it’s time to generate a little click bait. While not to the high standards of “10 things Kim Kardashian will eat today” or “11 things your dog hates,” there are plenty of catchy lists to be made with all the fascinating information from the world of sacoglossan biology.
Here are ten things you should know about Elysia, in no particular order.
1. They suck sap. Like other sacoglossans, they pierce the cell walls of their food plants with rasping mouthparts, the radulla, and suck out the contents.
2. Larvae are lecithotrophic, meaning they live off of stored yolk while they are in the brief free swimming, or veliger, stage. This means that they do not have to find food during this period.
3. Larvae metamorphose rapidly. With some exceptions, the veliger stage lasts only a few days, and the juvenile slugs settle onto their food plants and begin their benthic (bottom dwelling) lives.
4. They like to float randomly. Although this may not apply to all species, captive E. clarki and E. crispata like to release their hold on the substrate from time to time. They often skim the surface layer, and also float around in the water column. This may not be a natural behavior, but I have observed wild E. crispata “going for a float” when launched by the current generated by a passing fish. Whether this behavior aids dispersal or is simply a byproduct of being the same density as seawater is unclear.
5. They are hermaphrodites. Adult Elysia produce both eggs and sperm at the same time. They cannot fertilize themselves, but can mate with anyone of the same species that they encounter. Was it Woody Allen who said it doubles your chance of finding a date on Saturday night?
6. They steal chloroplasts. When they suck the sap from their food plants, the chloroplasts (photosynthetic subcellular structures) are taken and moved to digestive diverticula, which are special outpouchings of the digestive system. The chloroplasts can be maintained for many months, and produce measurable amounts of energy for the slugs. Contrary to earlier reports, however, photosynthesis by these stolen chloroplasts (“kleptoplasts”) is not enough to stave off starvation.
7. Several Elysia species are being studied as sources of potential therapeutics. As can be found in the Natural Products page, the slugs contain chemicals derived from their food plants that may be useful in treatment of cancer and other disorders.
8. Elysia species often eat a variety of food plants. Many slugs, such as nudibranchs, are highly specialized to feed on a single kind of animal or plant. Although this may be the case for some species of Elysia, many will accept multiple plant species. Further, there have been reports that juveniles prefer different plants from adults.
9. They have adapted to many climates and conditions. For example, on the east coast of North America, Elysia species range from Nova Scotia to the Caribbean. As an example of the range of ecological adaptations, Elysia crispata is commonly found on corals reefs, while E. catulus is restricted to seagrass beds.
10. Elysia do not have gills. The large surface area generated by their parapodia allows them to perform gas exchange through their skin, obviating the need for gills. They are frequently, and erroneously referred to as nudibranchs because of their superficial similarity to this group, but nudibranchs have prominent gills, as illustrated by the fact that their name means “naked gills.”