Uncowed

Nudibranchs are a highlight of intertidal excursions, which offer periodic sightings of these tiny, tempestous molluscs. Lacking shells, the barenaked snails employ a barrage of defensive strategies to ensure their relative safe passage across a reef of hungry maws and many advertise their unpalatability with markings of strong colour or stark contrast.

One common find in local shores is the polka-dot dorid, a nonplussable devourer of blue sponges that shows up at irregular intervals. The slug's comical garb belies an unpleasant mouthful for most predators, however, as the dark spots on its mantle reveal themselves upon close inspection to be spicule-bearing tubercles. Known as caryophyllidia, these patches, which faintly recall the patterns of Friesian cows, are abrasive deterrents to creatures who seek to treat the nudibranchs as food rather than friends. This individual at Lazarus Island, unfortunately, appears a little worse for wear, with its rhinopores sprouting with ill-symmetry from a somewhat battered head. It's not clear if the defect arose from conflict or congenitality, but it is probably inconsequential to a hunter for whom life is all but blind and love lies afoot.

A different dorid, which is in season at Terumbu Semakau, are the pustulose knobs that navigate the reefs of southern shoals. Small slugs half an inch long dotted the edge of the flat, which abounds with sponges, soft corals and the limp blades of tape seagrasses. Unlike other dorids, phyllidiids hide their gills between mantle and foot, appearing less like a slug than pimply encrustations on a landscape of immoveable feasts. 

Should a curious fish or crab fail to mistake the phyllid for a pebble, the slug signals its discomfort by emitting a milk of sesquiterpene isocyanides, acidic toxins obtained from a diet of sponges that repel most other marine life and ravage every tankmate in ill-thought aquaria. The effectiveness of this defence across deep time has also given rise to mimics – a flatworm, chromodorid and even a holothurian – with shades and shapes that approximate the unpleasant phyllid and permit them to range freely over the reef unmolested and uncowed.

Comments

[anna tambour]

One of your best, though I'm emitting a milk of acidic jealousy. The only nudibranchs I've ever seen in the wild are two Sea Hares (Aplysia dactylomela). Were they involved? I don't know, but I'm all for their mechanisms to protect themselves against canine gourmands and scientists who don't respect their privacy. (See http://www.australiangeographic.com.au/journal/secrets-of-sea-slug-sex-revealed.htm" )

Those "spicule-bearing tubercles" you write of are fascinating. Are the blue sponges that you say this dorid eats siliceous?

[Rick MacPherson]

hey there! looks like i'll be in singapore for a few days on april 27-28(en route to field work in indonesia)... any chance we can meet for coffee or grab some food? my treat!

would be great to meet you!