Little Antarctic worm raises big issues!

Bristle worms (polychaetes) are segmented marine worms that occur in all oceans from intertidal to the greatest depths. Ophryotrocha species are typically small worms (2-5mm long) occurring predominantly in nutrient-rich environments (whale-falls, wood-falls, polluted areas). They have a rounded head with sense organs (eyes and antennae) and well-defined segments with leg-like appendages. A complex jaw apparatus with many tiny teeth allows them to graze on their surroundings (e.g. bacteria, algae, detritus). They undergo direct development, producing large yolky eggs that develop directly into juveniles in a protective tube and are cared for by both parents. In this way they can rapidly increase their numbers and are considered opportunists.

The specimens were collected near Casey station, East Antarctica and sent to me for identification. I studied their external morphology with light and scanning electron microscopy (SEM) and sent some specimens to colleagues at the Natural History Museum London for DNA analysis. These studies confirmed that they were O. orensanzi, a species described originally from the South Shetland Islands near the opposite side of the continent, living in and on experimentally deployed whale bones thousands of kilometres away from Casey station, where the same species occurred in unpolluted, intertidal surroundings. Once their identity was confirmed, the study allowed us to make some interesting observations.

The morphology study revealed previously unknown features of the jaw apparatus and the presence of a sensory structure in the neck region that had not been documented before.

The genetic study demonstrated that the widely separated populations belong indeed to the same species, that the two populations are genetically connected and this species is circumpolar, challenging the general assumption that organisms with direct development have limited genetic flow between distant populations.

Furthermore, it had generally been stated that Ophryotrocha species are specialists of organically enriched substrates (e.g. whale-bones at original Deception Island collecting site). Since the Casey station worms were collected in a clean, unpolluted area, we are also challenging this opinion, suggesting that at least O. orensanzi and probably also other Ophryotrocha species can also be unspecialised opportunists, able to exist in the most pristine environments (like Casey station) and because of their direct development and brood-care have the ability to rapidly increase their population sizes under favourable conditions.

Thus, a little worm, collected unintentionally together with other organisms, is challenging some generally held opinions.

Hannelore Paxton, Research Associate

More Information:

• Paxton, H., Wiklund, H., Alexander, F., Taboada, S. (2017). Is the Antarctic Ophryotrocha orensanzi (Annelida: Dorvilleidae) a circumpolar non-specialized opportunist? Systematics and Biodiversity. 15(2): 105–114. *This paper was nominated for the Outstanding Paper Award for 2017 by the journal.