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Eunice sp.

Lei Ren 2015


The genus Eunice is not only the most diverse group of worm-like polychaetes that spreads worldwide, but also the least defined one in family Eunicidae. Member of Eunice typically has five antenna attached to its prostomium and paired posterior cerci. They are important inhabitants in benthic ecosystem, dwelling under sediments. 

A lot of these worms are voracious predators which are versed in ambush tactics. Specifically, as they are gifted with the largest hidden jaw amongst polychaetes class, a nasty bite containing deadly toxin will be injected when attacking prey. Moreover, given a maximum around 1500 segments as adults, they are capable of growing up to an impressive 6 metres in length (Fauchald, 1992). 

Although these worms make the greatest contribution to the biodiversity of class polychaetes, most species remain poorly studied. In Australasia region, out of 30 identified eunicid worms, only 19 has been described (Fauchald, 1986). The specimen observed in this study was collected from the aquarium of The University of Queensland. It’s suspected to be a juvenile of one particular species - Eunice antennata, however, no further convincing characteristics were found that could proof such conclusion because the classification within the genus Eunice has been highly depending on morphology solely in the past.

Figure 1

Physical Description

Eunice sp. has a long but slim body. The whole colouration can vary from purple-brown to reddish brown with purple iridescence (Edgar, 1997). Each segment is paired with two relatively short biramous appendages called parapodia. These movement organs change little by little as the body elongates (Fauchald, 1992). 

The anterior region is always muscular in order to wield the excessively large jaw apparatus. Comb-shaped branchiae are commonly seen on the dorsal side in Eunice sp. As approaching closer to the posterior end, branchiae usually becomes denser. These structures are sometimes misread as parapodia, but the real parapodia are located under them at the base (Fauchald, 1992). 

Species comprising genus Eunice can be distinguished from others by their featured five prostomial antenna as well as the transverse white ring band on the dorsal side of the fourth setiger. 

Figure 2


Eunice sp. have representatives in every level of food chain. They perform various feeding strategy and make up the most of macrobenthic fauna abundance (Hutchings, 1998). Despite of the small size that most species possess, they are often found in large aggregation. During a research conducted by Brown (1991), a large horde of polychaete were measured using the ash free dry weight method and he concluded that these benthic worms were of irreplaceable part of marine productivity. Hutchings (1998) also predicted the potential interactions between macrofauna and microfauna where Eunice plays a role of decomposer. 

On the other hand, Plamer (2010) found that polychaete can be ideal assistant for sand-filters which is part of the treatment of mariculture wastewater system.

In addition, the specimen used in this webpage was found living in a mud tube built by another fellow tubicolous polychaete which belongs to the family Sabellidae. However, both of them seemed unharmed which might infer a possible symbiosis between the two species.

Eunice sp. Mini-Habitat

Life History and Behaviour


Eunice sp. uses advanced branchiae to create water current around it and uses parapodia for anchorage and fixation once settled.

Eunice sp. Movement


Eunice sp. can be either scavengers that forage into the sediment for organic particles or veteran predators that prey on fish and small invertebrates. Species such as the infamous bobbit worm Eunice aphroditois, is capable of capturing preys that exceed its own size.


Most species of Eunice have a free-living life in cracks and crevices of seabed and corals when they are juveniles, others used to secrete sticky chemicals to build nests or move into tubes as they grow larger (Fauchald and Jumars, 1979).


There isn’t sexual dimorphism present in Eunicid worms, so in general most Eunice sp. produce either swimming young or massive gelatinous egg clutches. Others act as broadcast spawners (Fauchald & Rouse, 1997). 

Anatomy and Physiology

The most remarkable feature of Eunice is the eversible pharynx that is located ventrolateral and is strongly muscular. Neropodia is highly developed in Eunice. On the contrary, notopodia in Eunice is reduced (Fauchald, 1977).

Respiration of Eunice sp. is similar to that of other larger polychaetes as the respiratory pigments take form of extracellular haemoglobins (Weber, 1978b).

Evolution and Systematics

Nereis is the name of the first few species that has been described whereas the genus Eunice was first coined in the early 19th century (Fauchald & Rouse, 1997).

Eunice has long been disorderly classified along with other polychaetes as a result of the use of jaw apparatus system. A study conducted by Bergman (1998) pointed out the reversal jaw discovered in polychaete fossil identical to normal jaws which prevent misidentification of new species.

Family Onuphidae is considered as the relative group of Eunicidae due to the share of resemblant jaw, parapodia and antennae. However, detailed classification within family Eunicidae is still ambiguous (Orensanz, 1990). From a paleontological point of view, the group Paulinitidae that once occurred in Carboniferous were considered the only family that could possibly be the ancestor of Eunice. Also, the oldest record of eunicid fossil were found in Europe and North America whereas Australia lacks fossil report (Thompson & Johnson, 1977).

Biogeographic Distribution

Eunice sp. are discretely distributed worldwide, the vast majority of them are found in tropical region, especially indo-west-Pacific. Furthermore, most species also present along the coastal line of Australia, ranging from south-eastern Queensland to Geraldton, WA (Day, 1975).

Figure 3

Conservation and Threats

Marine polychaetes including genus Eunice has been and are still being translocated by anthropogenic activities across previously unlinked continents and regions which has risen severe problem in terms of energy flow in trophic level, decomposition of benthic material and various interspecific relations (Vitosek et al., 1997). Alien Eunicid species, for instance, Eunice antennata are extremely competitive in shallow benthic habitats of eastern Mediterranean and would eventrually out-compete native species which might related to marine production, therefore cause huge economics loss (Çinar, 2013). 
Figure 4



Bergman, C. E. 1998. Reversal in some fossil polychaete jaws. Journal of Palaeontology. 72(4): pp. 632-638.

Çinar, M. E. 2013. Alien polychaete species worldwide: current status and their impacts. Journal of the Marine Biological Association of the United Kingdom. 93(5): pp. 1257-1278.

Day, J. H. 1975. On a collection of polychaeta from intertidal and shallow reefs near Perth, Western Australia. Rec. West. Aust. Mus. 3(3): pp. 167-208.

Edgar, G. J. 1997. Australian Marine Life: the plants and animals of temperate waters. Reed Books, Kew. p. 159.

Fauchald, K. 1977. The polychaete worms. Definitions and keys to the orders, families and genera. Natural History Museum of Los Angeles County. 28: pp. 1-188.

Fauchald, K. and Jumars, P. A. 1979. The diet of worms: a study of polychaete feeding guilds. Oceanogr. Mar. Biol. Annu. Rev. 17: pp. 193-284.

Fauchald, K. 1986. Review of the types and key to the species of Eunice (Eunicidae: Polychaeta) from the Australian Region. Records of the Australian Museum. 38(5): pp. 241-262.

Fauchald, K. 1992. A Review of the Genus Eunice (Polychaeta: Eunicidae) Based upon Type Material. Washington, D.C. Smithsonian Institution Press.

Fauchald, K. and Rouse, G. 1997. Polychaete systematics: past and present. Zool. Scr. 26(2): pp. 71-138.

Hutchings, P. 1998. Biodiversity and functioning of polychaetes in benthic sediments. Biodiversity and Conservation. 7: pp. 1133-1145.

McHugh, D. 2005. Molecular systematics of polychaetes (Annelida). Hydrobiologia. 535/536: pp. 309-318.

Orensanz, J. M. 1990. The Eunicemorph Polychaete Annelids from Antarctic and Subantarctic Seas with addenda to the Eunicemorpha of Argentina, Chile, New Zealand, Australia, and the Southern Indian Ocean. Biology of the Antarctic Seas Antarctic Research Series. 52: pp. 1-183.

Palmer, P. J. 2010. Polychaete-assisted sand filters. Aquaculture. 306: pp. 369-377.

Rouse, G. W. 2000. Polychaetes have evolved feeding larvae numerous times. Bulletin of marine science. 67(1): pp. 391-409.

Schüller, M. and Ebbe, B. 2007. Global distributional patterns of selected deep-sea Polychaeta (Annelida) from the Southern Ocean. Deep-Sea Research II. 54: pp. 1737-1751.

Thompson, I. and Johnson, R. G. New fossil polychaete from Essex, Illinois. Fieldiana Geol. 33(25): pp. 471-87.

Vitosek, P. M., Mooney, H. A., Lubchenco, J. and Melilo, J. M. 1997. Human Domination of Earth’s Ecosystems. Science, New Series. 277(5325): pp. 494-499

Weber, R. E. 1978b. Respiration. In. Physiology of annelids. Academic Press Lodon. pp. 369, 392.

Zanol, Joanal., Fauchald, K. and Paiva, P. C. 2007. A phylogenetic analysis of the genus Eunice (Eunicidae, polychaete, Annelida). Zoological Journal of the Linnean Society. 150: pp. 413-434.


Figure 1 Taken by Lei Ren.

Figure 2 Cropped from Fauchald, 1992.

Figure 3 Retrieved from

Figure 4 Cropped from Çinar, 2013.