Warped Operculum

Windy ride

By  Nicole Webster

I found all this in minutes on the beach:

The horde

The haul (OK I collected them over several days, but it took minutes total)

 

 

What are they? Opercula! These are the ‘doors’ used by gastropods to close the shell aperture for added protection (mostly from predators, but also from dessication for intertidal snails and terrestrial prosobranchs).

I really wish I had a photo of the beach; there is a thick layer of debris near the high tide line, full of unrecognizable bits of shell and coral, but also filled with these distinct round, polished bits – like pearls. They are obviously resistant, but its hard to tell how much wear could occur on the edges without it being obvious.

I can’t be sure of the species, but I did collect several shells like this nearby, with a round, calcareous operculum:

Turbo castanea?

Turbo castanea? – the, or a probably culprit. Credit: N Webster

So that’s pretty cool right? Yeah. I think so, but then I came across something special!

DSCN5058p

There was one in the pack that was distinct. At first I thought it was chipped, but looking at the shape of the spiral (the inside), and the bulbous exterior surface makes me wonder if this wasn’t some severely damaged individual – snails sometimes grow their shell a bit misshapen after serious shell damage. It could simply be another species, but most members of Turbo‘s family Turbinidae have round apertures, and the operculum is fairly distinct (as far as my limited experience knows). The other option is some mutant Turbo with a wonky aperture, or simply a disjointed operculum mechanism.

I really wish I had the shell… *sigh*

PS Wikipedia had this neat link about the history of operculum use in the middle east.

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Xenomorpha – kleptomaniac snails

Windy ride

By  Nicole Webster

Having been in Cuba the past week, I saw some wonderful marine things that you just don’t find in Bamfield.

My favortie was a Xenophora conchyliophora [1] which I found washed up (alive)!

Xenophora conchyliophora apical view.  Cayo Coco, Cuba Credit: N Webster

Xenophora conchyliophora 3cm diameter. Cayo Coco, Cuba Credit: N Webster

DSCN5031

The genus Xenophora is famous for attaching random, or not so random bits of rock and shell to the exterior of the shell. The specimen here seems to have used mostly small shell fragments and rocks, but other species use only bivalve shells, or project long pointed gastropod shells outwards. The Zymogyphic museum has a great collection of photos to give you the first taste of the variety and precision sometimes used by Xenophora.

How do they attach stuff? Very carefully:

“Characteristically, the shell is covered with other shells, shell fragments, coral pieces, or stones that are attached or cemented with secretions from the animal. The shells are attached dead, although there is one account of a live kitten’s paw being attached in an aquarium. All bivalves and bivalve pieces are attached inner side up and gastropods are usually attached with the aperture up. Once an object is selected, it is cleaned (as is the site of intended attachment), and then the object is rotated and fitted to the attachment site. This may take up to 1 1/2 hours. The piece is then held in place with the animal’s foot, snout, and tentacle bases and glued into place. The Xenophora may then lay motionless for up to 10 hours, only rocking in place now and then, seemingly a check on the strength of its new attachment.”

– From Xenophoridae online (defunct) via  Zymogyphic museum.

These snails feed on forams and microscopic algae, and even bury their feces – presumably to reduce chemical signals that could attract predators. The collection is mostly thought to be for camouflage: it breaks up the shell outline, and holds the shell above the substrate so the snail can feed while still remaining under the shell.

For more info, and the key I used for identification:

[1] Ponder, Winston F., 1983. A revision of the Recent Xenophoridae of the world and of the Australian fossil species (Mollusca, Gastropoda). Australian Museum Memoir 17: 1–126, with appendix by W. F. Ponder and J. Cooper. [31 December 1983].

Baby Crepidula!

By Nicole Webster

As tedious and eye-straining as it is to clean my Ceratostoma foliatum shells of epibionts (So I can get accurate weights), I keep coming across all sorts of wonders.

Yesterday my prize was a tiny slipper limpet (Calyptraeidae). It is too small  (3mm in length) to be sure of an identification, but Crepidula sp. seems most likely due to the shape of the ‘shelf’ on the inside of the shell.  Once I peeled him off (chipping his shell), he motored around the dish a good pace, making photography difficult. Once I flipped him upside-down, he struggled valiantly, so I still had a hard time capturing his charm.

Aww! (note the prominent protoconch (larval shell) at the apex) Credit: N Webster

“Let me up!” (a clear view of the large, filtering gills) Credit: N Webster

This is the empty shell showing the typical ‘slipper’ shelf of the shell. Credit: N Webster

Snails in the family Calyptraeidae are not true limpets, but have convergently evolved the same low profile, high expansion shells good for sticking strongly to the substrate. The limpet morphology has evolved at least seven times (depending on the phylogeny you use) in Gastropods.

Calyptraeids are sequential hermaphrodites, most famous for the stacking Crepidula fornicata, in which many smaller males stack on top of a larger females in a mating aggregation. As the males grow, they transform into females and can start their own stack. This little guy is probably too young to be sexually mature, and is perhaps more properly addressed as ‘it’.

The gills are so large and prominent because most Calyptraeids are filter feeders, using their gills to trap plankton, and sucking it in their mouth on a stream of mucous from their radula.

Graduate Student Research at BMSC

by Travis Tai

Below is a subsample of what graduate students are studying RIGHT NOW at BMSC. This isn’t a complete survey of all graduate students at BMSC and it’s also not a complete summary of each person’s research.  If you’re interested in hearing more about anyone’s particular projects, leave a comment below and we’ll feature that student’s research in a separate post.

Suz Anthony, University of Alberta, MSc student with Dr. Rich Palmer

Sea slugs. Delicate, beautiful, DEADLY! These squishy creatures, most notably the opalescent sea slug, have the ability steal stinging capsules (cnidae) from their cnidarian prey, and sequester them in their colourful back projections (cerata). These cnidae are then used to defend the sea slugs from their own predators, including crabs, sea stars, and fish. But not all cnidae are equal; some cnidae can inject toxins, some are long and stringy and will entwine the mouthparts of arthropods, and some are more suited to piercing soft tissue. What I want to know is: If the sea slug is in the presence of a specific predator, will the sea slug preferentially select cnidae that will be most effective against that particular predator?

Mónica Ayala-Díaz, University of Victoria, MSc student

Monica in the field

Credit: M Ayala-Diaz

My name is Mónica Ayala-Díaz. I am doing my Masters degree at the University of Victoria. The purpose of my study is to evaluate the changes in behaviour of the marine snail Littorina sitkana due to the presence of trematodes, as these parasites can alter the behaviour of the snail in order to favour its predation by the next host so they can complete their life cycle. I am focusing on trematodes that have birds as their final host and I am testing if the parasite can get to the bird via direct predation of the snail or if it has another intermediate host. To achieve this, I am performing survival experiments in the field. To test changes in behaviour, I am tracking movement and grazing performance of L. sitkana.

Amanda Kahn, University of Alberta, PhD student with Sally Leys

Amanda on a ship

Credit: A Kahn 2012

I’m studying hexactinellid, or glass, sponges: a unique group of sponges that are unique because they are syncytial, meaning that instead of cells they have many nuclei all encased within a common cell membrane.  While other animals have small syncytial regions in their bodies (for example, human muscles), for the most part other animals (and even all other sponge groups) are composed of cells.  I’m studying how hexactinellid syncytia form and grow–from food capture to assimilation to growth of tissue, and finally excretion–which, beyond being really cool because it’s so unique to this group, is important to understand because a small group of glass sponges form reefs, just like corals, off the coast of British Columbia.  The reefs aren’t known to form anywhere else in the world today and are habitats for fish, crabs, sharks, and invertebrates; however, they are fragile and how the reefs grow and why they are so rare (the same sponge species can be found as individuals elsewhere, but only form reefs in a few places) isn’t understood.  Human activities such as trawling can destroy the fragile glass skeletons that form the reef, so understanding more about how the sponges work and what their effects are on animals living alongside them are the aims of my research.

Danielle Ludeman, University of Alberta, MSc student with Dr. Sally Leys

Danielle in the intertidal

Credit: D Ludeman

I study how the canal system in sponges (Porifera) is designed to allow both water flow and particle capture, and then how sedimentation can impact these filtration systems. Sponges are found in high densities worldwide, and as suspension feeders, they play an important ecological role in the recycling of nutrients.  A single 20-hectare glass sponge reef is estimated to filter 80,000 litres of a second!**  Increasingly, sedimentation from resource exploitation such as oil exploration or fishing trawls is having severe impacts on benthic suspension feeders including sponges, which, as filter feeders, are sensitive to materials that can clog their filtration system.  By understanding how their water filtration system works, we can begin to understand the potential impact of sedimentation. This knowledge can be used to predict what level of sedimentation sponges can tolerate to help manage important ecosystems such as the glass sponge reefs off the coast of British Columbia and the ‘ostur’ in the fjords of Norway.

** Chu WF and Leys SP 2010 MEPS 417:97-113

Travis Tai, University of Victoria, MSc student with Dr. Brad Anholt

Travis in the field

Credit: T Tai

I am a Master’s student at UVic, currently working on the evolution of sex-ratios in Tigriopus californicus.  T. californicus has a natural sex-ratio distribution that is extra-binomial, which suggests a polygenic sex-determination mechanism—multiple genes (environmental and/or heritable) contributing to sex-determination.  I am interested in Fisher’s theory of frequency dependent selection and modelling the heritable and environmental effects on sex-determination.  Fisher predicts that selection should select for balanced sex-ratios with respect to the relative costs of sons and daughters.  If sex-ratio should deviate from the balanced equilibrium, individuals of the less abundant sex will have a higher per-capita genetic contribution and frequency dependent selection will drive the sex-ratio towards equilibrium.  After many rounds of artificial selection for sex-biased genes, I have established population lines with male- and female-biased sex-ratios.  With relaxed artificial selection, I have been measuring brood sex-ratios for each treatment population for 8 generations.

Nicole Webster, University of Alberta, PhD student with Dr. Rich Palmer

Snails

Credit: N Webster

I am a PhD student working on the growth and development of shell ornamentation (ridges, ribs, lamellae, varices) in gastropods (snails). I want to know how a snail controls when and where to put ornaments, and how that affects them. My work at Bamfield is on two species, Ceratostoma foliatum, that has three, regularly spaced varices, that are precisely placed in the same position on each whorl, and Nucella lamellosa, that has many varices placed in a less controlled fashion. It is thought that Ceratostoma knows where to place each varix by encountering the previous one, and growing a new one in the same place, which I am testing with some shell manipulation experiments. I am repeating the experiments in Nucella lamellosa to determine how these less constrained varices differ in their growth pattern.

Want to learn more about any of these students’ research?  Or do you have questions about what you read about here?  Leave your questions or comments below!