Cuttlefish learn as embryos

In the first known example of visual learning by embryos, unborn cuttlefish are capable of visualising potential prey while still in the egg. Embryos that are exposed to crabs develop into cuttlefish that actively prefer crabs! This is really remarkable - not only in pointing to the high visual development of cuttlefish; it also says a great deal for their intelligence.



Ludovic Dickel and his colleagues at the University of Caen Basse-Normandy, France, made the discovery by placing crabs alongside cuttlefish eggs in a series of laboratory tanks...

Crabs, a common prey of adult cuttlefish, were also placed into the tanks, but enclosed in separate compartments. Crucially, the compartment sides were made of clear glass, so the crabs were in plain view of the eggs.

But the embryos could not smell or hear the crabs. Once the cuttlefish embryos hatched, they were instantly moved, to ensure they could not glimpse the crabs, and were not exposed to any other prey until they were seven days old...

But those embryos exposed to crabs much preferred to hunt crabs after hatching. And the clearer the view of the crabs they were given, the greater their taste for it.

Source

Olm

Olms first came to my attention in a nature programme; my interest was revived at seeing a pickled one in Oxford's Natural History Museum. They are funny-looking little things; surprisingly cute for amphibians - even when pickled. I headed over to the Wikipedia article, as many a researching blogger has done before me, and was delighted to discover that they were far more interesting than I had thought.



This is a picture of an olm. As far as I'm aware, they don't actually exhibit an eery glow.

Before we get started, I must warn you not to confuse olms with axolotls. The two look remarkably similar - see?



Axolotls, though, are something else entirely, and are fairly fascinating in their own right. But that's another post. Back to the olms!

Olms are amphibians, like frogs, toads or newts. Unlike these three, though, olms are completely blind; eyes being unnecessary in the pitch-black caves where they live, they have lost them. Although they develop eyes as larvae, these stop growing and eventually atrophy. In an environment where eyes are useless, it would be a waste of an animal's resources to develop and maintain them. Darwin himself used olms as an example of the reduction of biological structures through disuse:

Far from feeling surprise that some of the cave-animals should be very anomalous... as is the case with blind Proteus with reference to the reptiles of Europe, I am only surprised that more wrecks of ancient life have not been preserved, owing to the less severe competition to which the scanty inhabitants of these dark abodes will have been exposed.

(Proteus is the olm's proper name.)

The olms get by using other senses; they possess a heightened sense of smell, retain some sensitivity to light, and may be able to sense magnetic fields.

Olms are white, almost transparent, but you'll notice they have red frills on either side of their head. These are their gills, and the fact that they protrude from the head in this way is, itself, unusual. External gills are a remnant of the olm's time as a larva (and something the olm shares with the adult axolotl, above). Frog embryos possess external gills, but they are reabsorbed before the tadpoles emerge. Other salamanders also have external gills, but only as larvae. The olm's gills are red because the blood flowing through them is freshly enriched with oxygen.

These are seriously impressive little creatures. Living in caves, they never know when their next meal will come along, and so they are able to go without food for ten years. They may be able to live to the ripe old age of 70, or possibly more.

Yapok

The world's only living semi-aquatic marsupial! Yapoks are pretty nifty. I first heard of them while watching David Attenborough's "Life on Earth" series. They are handsome little beasts, of the opossum family, banded with dark brown or black on pale grey and white, with black patches around their eyes like glasses.



They live in South America, near water, and eat fish, frogs, insects, and other small unfortunates. Since they're not tree-dwelling, their tails are less prehensile than other marsupials' or opossums', and apparently they only really use them for carrying bundles of nest material, neatly rolled up.

The yapok does, as a marsupial, have a pouch. Obviously the babies in there will need to breathe even while the mother is swimming, and so the pouch opens backwards, to prevent water rushing in. More importantly, it's also protected by a strong ring of muscle that contracts and effectively seals the pouch, giving the babies a few minutes of air.

One really intriguing fact - the male also has a pouch. Not needing it for ferrying around babies, he uses it to keep his testicles in when he swims. Apparently he just draws them right up inside it.

The German word for the yapok is 'Schwimmbeutler', which I was unable to translate, but which is a rather nice word nonetheless. 'Yapok' itself comes from the Oyapock River, in northern South America.

The yapok has its own genus, Chironectes, of which it is the sole member.