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Zooming into Nudibranchs: Sap Sucking Sea Slugs

Zooming into Nudibranchs:
Sap Sucking Sea Slugs

Written by Roy Kittrell 27 February 2024.

All over the ocean there are multitudes of different kinds of sea slugs, a type of mollusk found in the subclass Heterobranchia. Nudibranchs, in the superorder Nudipleura, are perhaps the most well-known of this variety of animals found all over the reefs of SE Asia. However, it is their close cousin, the wonderfully named Sacoglossan Sap Sucking Sea Slugs in the superorder Sacoglossa that we will be discussing in this article. Just for the sake of abbreviation, I shall henceforth refer to them collectively as the SSS.

As you will see, they are an utterly remarkable kind of animal, not just because of how utterly cute they are – like the infamous Shawn the sheep in the picture above, but because of their amazing superpower: the ability to photosynthesize!

As you can see the pictures in this article; there is one common denomination between all of the slugs listed here; they are wonderfully bright and vivid shades of green, perfectly themed for the month of March and St Patrick’s day! The key to how they get to be this color is found in their name, they get it by eating and digesting seaweed and plant material in the shallow water.

They don’t just eat the seaweed though. Some slugs, like Shaun the sheep, can incorporate the photosynthetic cells from the seaweed into their tissue, giving them the ability to derive energy from photosynthesis. The ability to steal living tissue and use it in your own body has a name in Biology; it is a process known as ‘kleptoplasty’. Amazing to see such a tiny animal do something so incredible. 

That’s not the end of their abilities though. The sap sucking slug Elysia marginata, seen below, has the ability to, (and let me just check my notes here again… ) sever its own head and re-grow its entire body from scratch!

That’s correct. This relatively normal looking green slug has the absolutely astonishing ability to regenerate its entire body from just the head alone. It’s thought that this is a quick way for the slug to be able to rid its body of parasites quickly, rather than expend energy trying to clean them off in other ways.Sacoglossan sea slugs are relatively easy to find on most of the diving trips with Flow, and you can start looking for them by finding their preferred habitats: sea weed. Shawn the sheep is almost exclusively found on the Elephant’s Ear seaweed, so whenever you see a patch be sure to get up close and personal and have a look to see if any are hanging out and want to say hello! Bubble sea weed is also another habitat where you are likely to find them.

You can join us on our next macro dive trip to Semporna in November and we will surely keep a close look for these amazing SSS on this trip!


-Roy Kittrell is an avid naturalist and underwater photographer, his work can be found on Instagram @roythedivebro

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