Photo of the Week: December 26, 2011

Hi Gang!

This week's POTW is a shot of a relatively small, stunningly gorgeous reef creature that has a common name that belies its appearance. The animal is commonly referred to as a "black and gold sapsucking slug". Maybe its just me, but to me this name simply does not convey the beauty of Mother Nature's handiwork in this case. In fact, the name sounds kind of off-putting to me. But I think this slug is a real stunner! 

The black and gold sapsucking slug, Cyerce nigricans, is a type of opistobranch mollusk that is commonly mistaken as a nudibranch. The sapsucking slug is very closely related to nudibranchs, but opistobranchs and nudibranchs are described in different sub-classes, Opistobranchia and Nudibranchia respectively. As is the case with many opistobranchs, this sapsucking slug lacks the external shell found in many other of it's close mollusk relatives including scallops, snails, mussels and oysters. However, some other sapsucking slugs do have very small external shells, while still others are equipped with internal shells.

The black and gold sapsucking slug occurs in the Indo-Pacific region, and is most common from Fiji to Guam. This week's POTW is from Fiji.

Sapsucking slugs are quite common in many reef communities, but they often go overlooked by sport divers because of their diminutive size and the facts that many species lack the attractive colors and striking features displayed by the black and gold sapsucking slug. The black and gold sapsucking slug attains a maximum length of only a couple of inches, but that still makes it considerably larger than many of it's closest relatives as many are less than 1 cm long.

As it's common name suggests, the black and gold sapsucking slug feeds on various types of seaweeds by sucking their sap. This slug is equipped with a very distinctive, rasping tongue-like organ known as a radula. The radula of a black and gold sapsucking slug has a single row of very sharp, knife-like teeth that are used one tooth at a time. A single tooth is used to penetrate the seaweed cell, and then the content of the cell, the sap, is sucked out with a powerful pump-like tube.

Most sapsucking slugs feed on types of green seaweeds with each species of slug selectively feeding on some preferred species of green seaweeds. That said, it is worth noting that that some sacoglossans prey upon the eggs of other slugs.

In some instances the slug retains parts of the seaweed known as chloroplasts that contain chlorophyll without damaging them. Amazingly, these chloroplasts continue to conduct photosynthesis inside of the slug, a natural thief that has essentially stolen the chloroplasts from the seaweed. The slug benefits by using some of the by-products of the photosynthesis as food for itself. Mother Nature is truly an amazing lady!

In addition to this very clever adaptation some sapsucking slugs can exude a noxious secretion that repels potential predators. And that is still not the entire bag of tricks as some species can raise and flare the projections on their skin known as cerata to help frighten away potential predators.

I captured this week's POTW with a Nikon 60 mm lens mounted on a Nikon D300 camera that, in turn, was inside of a Subal housing that was set up with a flat port. I used a pair of Ikelite DS 160 strobes to light the shot. Two tricky parts of photographing slugs and nudibranchs in the size range of the black and gold sapsucking slug are (1) finding a complimentary background that helps the subject standout in the frame and (2) finding a shooting angle in which the antennae and other body parts don't "get lost" in the background by blending in. With such spectacularly colored subjects it can sometimes be a challenge to remember how easy it is to waste a great photographic opportunity by failing to be extra careful to keep the background and your shooting angle in the forefront of your thoughts when composing your shot.

I hope you enjoy his week's POTW!

See you next week,

Marty

P.S. I am currently on the plane with Captain Steve as we are just beginning our trip to Mexico's Revillagigedo archipelago. I look forward to sharing a few images from our adventure in upcoming POTWs.