Wednesday, October 3, 2012

Discovering the Newest Calyptraeid Species

It’s official.  This week the newest calyptraeid species officially got a name, Crepipatella occulta.   This gives me a great excuse to talk about the process of discovering and describing new species... And just how long it can take.

The Discovery
It all started several years ago when my friend David Veliz was a student in Coquimbo, Chile.  His thesis project was to use allozymes (a genetic technique) to see how closely related the calyptraeid species in Coquimbo are.  Two of these were Crepipatella dilatata and Crepipatella fecunda.  But at that time they were placed in the genus Crepidula.  Anyway, he kept getting very strange results for these two species.  Results his advisor told him were impossible.

Now, it is very difficult to distinguish C. fecunda from C. dilatata from the adults -  they are very similar in size, shape, and color -  but they have different development and if they are brooding we can distinguish them on how the embryos look. C. fecunda makes lots of small eggs that all develop into feeding larvae. C. dilatata makes many small eggs - about the same size as C. dilatata - but only a few of these even begin to develop.  The few embryos that develop eat the eggs that don’t develop -called nurse eggs- and grow into juveniles before they hatch from the capsule.  David knew this and carefully placed all of the animals with lots of small developing embryos into the C. fecunda sample and all of the animals with large embryos mixed with a few round yolky eggs into the C. dilatata sample.

So what could have gone wrong?

Crepipatella dilatata. The normal
embryo looks like a small snail with
a coiled shell but the nurse eggs are
show no structure. They are simply
balls of yolk
Crepipatella occulta. In this species
The nurse eggs begin to develop and
you can see that they are blobs of
yolk surrounded by more transparent

David in 1999 with his new species
When he went back to collect more samples he found that some of the adults had eggs that did not really fit either of these types. Some snails had broods where normal developing embryos were mixed with embryos that had begun to develop but had arrested development.  These nurse eggs were not perfectly round like the nurse eggs from C. dilatata, they were balls of cells covered with a thin epithelium and sometimes even had cilia beating on the outside.  He found that early in development the broods looked just like C. fecunda with all the eggs developing in the same way.  But later in development when they had eaten all of the nurse eggs they look just like C. dilatata. 

When these 3 species were separated his genetic results made perfect sense and showed that the third species is genetically distinct. 

About this time, I was a student traveling around collecting calyptreaid snails in order to sequence their DNA to figure out their relationships.  I visited Coquimbo where David helped me collect samples of all 3 Crepipatella species, and my DNA data verified his results .

These data showed clearly that the third species is different from C. dilatata and C. fecunda BUT it didn’t tell us if it was officially a new species - that is one that has never been described and named.

In the next post we will describe how we demonstrated that this third species was new and needed a name.

For more information about these species and to see the papers we've published on this work:

Veliz et al. 2003.  Developmental and genetic evidence for the existence of three morphologically cryptic species of Crepidula in northern Chile. Marine Biology 143: 131–142.

Collin et al. 2007. Molecular phylogenetic and embryological evidence that feeding larvae have been reacquired in a marine gastropod.  Biological Bulletin  212:  83-92.
Veliz et al. 2012.  Crepipatella occulta sp. nov. (Gastropoda : Calyptraeidae), a morphologically cryptic species from northern Chile.  Molluscan Research.  32:  145-153.

Here are a few more photos of the development of our new species, taken by Matt Starr.

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