Taking a closer look

That's right, those strange claw like arrows you found all over the sea urchin are important. But you knew this from the literature of Tortonese (1965), did you not? The most sensible thing to do in this situation is to observe them under the microscope to test the validity of Tortoneses findings.

Sample stored in ethanol

The dry sample

If you are interested what those pedicellaria are good for follow this link.

Stereomicroscope view 20x magnified

So, we can confirm and successfully reproduced the findings of Tortonese over 55 years ago (status 2021). The pedicellaria on the left seems to express a hook like structure at the tip of the flap. This phenotypic feature seems to be absent on the pedicellaria on the right.

Based on this observation we can confirm, that the individual on the left is a Cidaris cidaris. Since we know from the literature that the most common other deep sea sea-urchin of the Mediterranean Sea is Stylocidaris affinis, we can for now assume that the individual on the right belongs to this taxon.

But what other distinguishing features can we find? Let's move on and maybe we can even extend Tortonese's list.

Because it was difficult to take pictures of the hook at the tip of the pedicellaria, we thought to add some schematic drawings. Cidaris cidaris expresses this hook like structure at the tip of each pedicellaria (and there are all three types present on the test).

The top depicts a globiferous pedicellaria.

The bottom a tridactylous pedicellaria.

Drawing Copyright Paul Rivas Luginbühl