May 23, 2017

Magdalena Georgieva of the Natural History Museum, London, UK
Maggie Georgieva with a polycheate collected on the RV Investigator voyage. Maggie's team at the London Natural History Museum are interested in exploring similarities between deep-water polychaetes around Australia and those of the central-eastern Pacific. Image: Asher Flatt

Blogging the abyss iconDay 9: Maggie Georgieva, Natural History Museum, London, UK

In the dark depths of the abyss, living within the fine sediment that covers much of these remote vast plains, are many polychaete worms! These worms belong to the phylum Annelida, which includes the earthworms and leeches that we find on land, but also has an astounding diversity within the oceans.

Polychaete worms occur in many different colours, shapes and sizes, but all have lots of chaetae, or hair-like projections along the sides of their bodies (polychaete literally means many chaetae). They can be found in pretty much all marine environments, from the rocky shore to the ocean trenches at more than 6000-metre depths. Much like their land-based relatives, polychaete worms are highly important members of the ecosystems they are part of, processing organic matter, forming a major part of marine foodwebs and also comprising much of the biodiversity of these areas.

But at depths of 4000 m, polychaetes can be tricky to find, especially as many can be as small as one millimetre in size. Collecting these critters requires some fairly elaborate deep-sea mud sifting and collecting devices, of which we have a range of on the CSIRO RV Investigator. And so far, we have managed to collect a wealth of polychaete types!

A two-millimetre-long sphaerodorid (polycheate worm)
A two-millimetre-long sphaerodorid collected off eastern Tasmania. Little is known about this group of polychaetes, which appear to be widespread, but are not usually found in large numbers. Image: Maggie Georgieva

Our sampling at 25004000 m depths off the Australian coast has turned up several sphaerodorids. These usually tiny polychaetes are covered in tiny orbs known as macro- and micro-tubercles and papillae. Little is known about this group of polychaetes, which appear to pop up in all sorts of places, but never in large numbers.

An opheliid (polycheate worm)
A five-millimetre-long opheliid collected off eastern Tasmania. Image: Maggie Georgieva

One of our sampling sites was replete in opheliids, which are regular players in the deep sea, and are characterised by a silky smooth and often iridescent body that one would almost like to stroke, if they were big enough.

A 2mm syllid (polycheate worm)
A two-millimetre-long syllid collected off eastern Tasmania. Image: Maggie Georgieva
A syllid polycheate worm demonstrating budding
A syllid demonstrates reproduction by budding. Image: Maggie Georgieva

We've also found syllids and plenty of polynoids! Syllids, often beautiful worms, are renowned for their ability to reproduce in all sorts of crazy ways, one of which involves the production of miniature versions of themselves that bud off the end of the original worm. Polynoid polychaetes have a series of scales along their back.

We found the grubby polynoid (pictured below) at a depth of 4000 m at our sampling site in the Flinders Commonwealth Marine Reserve, but don't be fooled by its cute, hedgehog-like appearance! As well as chaetae, it also had massive spines along one side of its body, perhaps to make it not so tasty, and these worms also have prominent jaws which they can shoot out at unsuspecting prey by ejecting their pharynx.

A grubby polynoid (polycheate worm)
A two-millimetre-long grubby polynoid collected from abyssal depths (4000 m) at Flinders Commonwealth Marine Reserve north east of Tasmania. Image: Maggie Georgieva

We've also found paddle worms (phyllodocids), which have modified a portion of their segments into flattened paddle-like shapes with which they zoom around in the ocean, helping them to get ahead of their prey.

Osedax worm
An Osedax worm (zombie worm, or bone-eating worm) retrieved from the whale skull collected from the RV Investigator. Image: Maggie Georgieva


Voyage date: 
Tuesday, May 23, 2017