Colourful Nudibranchs

The WWF has posted photos (such as the one below) of vibrantly coloured Nudibranchs taken in Anilao, Batangas, in the Philippines. There are at least 3,000 known species of the soft gastropods, which take their name from their exposed gills.

Unlike other mollusks, Nudibranchs - often referred to as 'sea slugs' - have no shell to protect them. They are believed to rely on their often fabulous colours to either blend in with their environment or warn predators that their bodies contain chemicals that render them distasteful. Quite tasteful (if you're a mollusk predator) nudibranchs also display colourful warning signals, which mimic the patterns of genuinely inedible, related but distinct species.

You can find several examples of aposematic colouration, as the evolutionary strategy of using colour signals to put predators off making a meal of you is termed, here. Here's a pair of unrelated dead ringers below:

The flatworm of the genus Pseudobiceros (upper photo) mimics the colour pattern of Chromodoris magnifica (lower photo), which is known from Australia, Papua New Guinea, Indonesia and the Philippines. (PHOTOS ©  Michael D. Miller, The Slug Site).

A neotenic tune: 'The Axolotl Song'

The retention of juvenile traits in adulthood – failing to grow up, really – is called neoteny: in some species, developmental biologists will tell you, the juveniles never actually develop into the adult form; you could say that they grow old without growing up.

Peter Pan is as neotenous as it gets, and so is probably some pathetically immature ex-boyfriend or girlfriend you walked out on years ago. Among other species, the axolotl (Ambystoma mexicanum), a Mexican mole salamander, is perhaps the most famous example of neoteny: axolotl larvae fail to undergo complete metamorphosis, and the adults, instead of becoming salamanders equipped with lungs, retain their gills and remain fully aquatic (Dr Freud would have loved this one – think of all these people who never leave the amniotic safety of the womb, kind of thing).

The Axolotl Song, spotted on Arbroath, is a delightful little video featuring a lyrical axolotl that made the grade to salamanderhood.