Bristleworms (Class Polychaeta of Phylum Annelida)
Geoff Read
General Description
Polychaetes (bristleworms) are segmented marine worms that have evolved into a wide variety of forms and many different lifestyles. They can occur in great abundance and are usually a major component of the marine biota. Consequently, they are an important food source, with their soft bodies providing a nutritious food for fish, wading birds, and many other predators. Polychaetes are commonly found crawling and burrowing in bottom sediments, but also live in crevice environments, on marine plants and plant-like animal growths, and even occur free swimming in the plankton. They are mostly inconspicuous, at least to the human eye, although evidence of their presence may be seen as feeding traces, burrow openings, castings (faecal pellets), and the like. Some polychaetes may be prominent as large colonies of tubes attached to rock. These structures are built by polychaete species in the families Serpulidae (calcareous tubes) and Sabellariidae (cemented sand grain tubes).
Polychaetes are an ancient group with a long fossil history, despite most having relatively few hard parts that remain after their bodies decompose. Jaw elements, chaetae (bristles), and tubes do get preserved frequently. Remarkably detailed whole-body impressions of worms (apparently quite similar to those of today) have been discovered fossilised in Middle Cambrian shales deposited more than 500 million years ago. Our concept of what belongs in this group, or is closely related to them, is expanding with increasing knowledge of relationships gained from molecular data. Notably the hydrothermal vent tubeworms nourished solely by symbiotic bacteria were until recently regarded as belonging to a separate phylum, the Pogonophora, but are now thought to be a polychaete group. There are about 13,000 polychaetes known in 83 families worldwide. New Zealand has at least 800 species in 68 families with about 50% of the formally described species endemic to New Zealand.
Typically each polychaete worm segment has many chaetae (bristles)-hence the class name. The chaetae erupt in upper and lower groups from variably developed fleshy lateral lobes or "feet" called parapodia. Describing these chaetae as bristles or "hairs" hardly does them justice, as many can appear beautifully sculptured. Each family has unique types of chaetae, specialised for various functions, and they are important for identification. The polychaete head region in wandering, agile species often bears eyes, unique chemosensory structures called nuchal organs, and pairs of antennae, palps, and cirri. These may also be present in related tube-dwelling forms, but typically the permanent tube-dwellers have additional feeding and respiratory appendages, such as the tentacular crown of Sabellidae. Sediment-eating burrowing forms generally have much reduced head appendages. Food in many polychaetes is ingested with the aid of an eversible mouth bulb called the proboscis, and this may be armed with pincer-like jaws, particularly in predatory forms. Polychaetes filter-feed, graze on organic debris, bulk-ingest sediment, or prey on other small animals. Common polychaetes typical of each lifestyle are the sabellid, Megalomma suspicions, the terebellid, Nicolea armilla, the maldanid, Macroclymenella stewartensis, and the glycerid, Glycera ovigera, respectively.
Polychaetes have a range of reproductive strategies-too many to detail here-but one of the more bizarre is the ability of many Syllidae, Eunicidae, and Nereididae to metamorphose into free-swimming forms which swarm to the sea surface at night in order to mate. Larval development in polychaetes may be entirely planktonic or involve varying degrees of parental care. Polychaetes are short-lived, mostly with annual or shorter life spans.
Besides their beneficial role as part of the marine food web, the presence of polychaetes, especially alien invasives, can have economic impact due to unwanted fouling or habitat modification or parasitisation. Notably Polydora group spionids can be a problem in bivalve aquaculture as shell borers and high densities of Chaetopterus tubes can foul scallop nets.
Status
Most polychaetes are very common, but the conservation status of a few species is uncertain or of concern. These include the spionids Spio aequalis and Boccardiella magniovata, and the onuphid Hartmanonuphis pectinata. All three have been reported from only two or three localities and no Spio aequalis have been found for nearly 60 years (detailed analyses prepared by NIWA in unpublished reports to Ministry of Fisheries NABIS endangered species project).
Key Locations
Most New Zealand polychaetes have wide geographic ranges limited only by presence of suitable habitat, so there are few unique locations for them, but there are some locations where their presence is notable. For example, Paterson Inlet, Stewart Island, is an important site for its many large subtidal serpulid reefs, even though the main reef-creating species there, Galeolaria hystrix, occurs throughout New Zealand. Similarly, hydrothermal vent specialist Siboglinidae (formerly Pogonophora) and unusual Polynoidae scale-worms have recently been discovered offshore on the Brothers undersea volcano, but probably will be found at some other hydrothermal sites.
Summary of Threats
Habitat loss for estuarine polychaete species is occurring due to infilling and channelisation of waterways. Destruction of reefs of calcareous tubes built by the serpulid Galeolaria hystrix might occur due to bottom-trawling activities.
Typical Habitats
Polychaetes are present in every marine environment, but are most prominent in soft-bottom sediments at all depths ranging from intertidal flats to abyssal plains. Rather like earthworms on land, many polychaetes thrive burrowing in sediment where they are safe from large predators, and are vulnerable only when they come to the surface to feed, excrete, and mate. They often reach densities of tens of thousands per square metre, outnumbering most other similar-sized fauna, and are useful indicators of the health of an environment, as species have differing tolerances to near-anoxic polluted conditions or high deposition rates of organic matter (eg, at sewerage outfalls). However, polychaetes may surprise with their presence in many very different habitats from bottom mud-transparent pelagic polychaetes such as Tomopteris elegans live in the open ocean, and the scale-worm, Benhamipolynoe antipathicola, lives in black coral trees.
State of Information
At least 828 species are known, although only about 500 of those have published names (about half of those are endemic), and there are likely to be numerous yet-to-be-discovered species. The individual biology of only a handful of species has been studied, although much data has been collected on patterns of polychaete occurrences in environmental surveys. The most pressing research areas are in advancing the state of taxonomic knowledge, and in combining and analysing molecular data with the morphological information. Such work would improve our understanding of the evolutionary relationships and geographic origins of New Zealand polychaetes, including finding out which species have, unknown to us, hitchhiked here on ships to find a new home on our shores.
Significance for Maori
There is no known information regarding the significance of polychaete worms to Maori.
Key References
Glasby, C J, Hutchings, P A, Fauchald, K, Paxton, H, Rouse, G W, Watson Russell, C and R S Wilson. 2000. Class Polychaeta. In: Beesley, P L, Ross, G B and C J Glasby (ed). Polychaetes & Allies: The Southern Synthesis. Fauna of Australia. Vol. 4A Polychaeta, Myzostomida, Pogonophora, Echiura, Sipuncula. CSIRO Publishing, Melbourne, 1-296pp.
Glasby, C J and Read, G B. 1998. A chronological review of polychaete taxonomy in New Zealand. Journal of the Royal Society of New Zealand, 28, 347-374.
Glasby, C J, Read, G B and et al. 2006. In Press Phylum Annelida. Bristleworms, Earthworms, Leeches. In: Gordon, D P (ed). The New Zealand Inventory of Biodiversity: Volume 1. Kingdom Animalia: Radiata, Lophotrochozoa, and Deuterostomia. Canterbury University Press, Christchurch, New Zealand.
Read, G B. 2004 New Zealand polychaetes. Biology and taxonomy. Available from http://www.annelida.net/nz/NewZealPoly.html (accessed April 2006).
Rouse, G W and Pleijel, F. 2001 Polychaetes. Oxford University Press, Oxford, 354pp.
Table 25: Bristleworms (Class Polychaeta of Phylum Annelida) in New Zealand
| Class | Order | Family | Endemic species | Other species | Total species |
|---|---|---|---|---|---|
| Polychaeta | Amphinomida | Amphinomidae | 3 | 5 | 8 |
| Euphrosinidae | 2 | 3 | 5 | ||
| Total | 5 | 5 | 13 | ||
| Eunicida | Diurodrilidae | 0 | 2 | 2 | |
| Dorvilleidae | 3 | 12 | 15 | ||
| Eunicidae | 8 | 14 | 22 | ||
| Lumbrineridae | 12 | 8 | 20 | ||
| Oenonidae | 2 | 6 | 8 | ||
| Onuphidae | 9 | 19 | 28 | ||
| Total | 34 | 61 | 95 | ||
| Phyllodocida | Acoetidae | 1 | 2 | 3 | |
| Alciopidae | 0 | 6 | 6 | ||
| Aphroditidae | 2 | 9 | 11 | ||
| Chrysopetalidae | 0 | 3 | 3 | ||
| Glyceridae | 5 | 7 | 12 | ||
| Goniadidae | 3 | 11 | 14 | ||
| Hesionidae | 3 | 6 | 9 | ||
| Lopadorhynchidae | 0 | 1 | 1 | ||
| Nephtyidae | 1 | 5 | 6 | ||
| Nereididae | 21 | 18 | 39 | ||
| Paralacydoniidae | 0 | 1 | 1 | ||
| Pholoidae | 1 | 2 | 3 | ||
| Phyllodocidae | 12 | 27 | 39 | ||
| Pilargidae | 4 | 0 | 4 | ||
| Pisionidae | 0 | 1 | 1 | ||
| Polynoidae | 25 | 37 | 62 | ||
| Sigalionidae | 6 | 6 | 12 | ||
| Sphaerodoridae | 0 | 4 | 4 | ||
| Syllidae | 10 | 51 | 61 | ||
| Tomopteridae | 0 | 2 | 2 | ||
| Typhloscolecidae | 0 | 1 | 1 | ||
| Total | 94 | 200 | 294 | ||
| Sabellida | Oweniidae | 1 | 6 | 7 | |
| Sabellariidae | 2 | 2 | 4 | ||
| Sabellidae | 9 | 21 | 30 | ||
| Serpulidae | 22 | 53 | 75 | ||
| Siboglinidae | 6 | 8 | 14 | ||
| Total | 40 | 90 | 130 | ||
| Scolecida | Arenicolidae | 1 | 2 | 3 | |
| Capitellidae | 0 | 12 | 12 | ||
| Cossuridae | 1 | 0 | 1 | ||
| Maldanidae | 12 | 9 | 21 | ||
| Opheliidae | 1 | 5 | 6 | ||
| Orbiniidae | 3 | 11 | 14 | ||
| Paraonidae | 0 | 8 | 8 | ||
| Scalibregmatidae | 3 | 10 | 13 | ||
| Total | 21 | 57 | 78 | ||
| Spionida | Apistobranchidae | 0 | 1 | 1 | |
| Chaetopteridae | 0 | 6 | 6 | ||
| Longosomatidae | 0 | 1 | 1 | ||
| Magelonidae | 0 | 3 | 3 | ||
| Poecilochaetidae | 3 | 0 | 3 | ||
| Spionidae | 20 | 49 | 69 | ||
| Trochochaetidae | 0 | 1 | 1 | ||
| Uncispionidae | 0 | 1 | 1 | ||
| Total | 23 | 62 | 85 | ||
| Terebellida | Acrocirridae | 1 | 0 | 1 | |
| Alvinellidae | 1 | 0 | 1 | ||
| Ampharetidae | 2 | 16 | 18 | ||
| Cirratulidae | 3 | 16 | 19 | ||
| Ctenodrilidae | 0 | 1 | 1 | ||
| Fauveliopsidae | 1 | 2 | 3 | ||
| Flabelligeridae | 3 | 9 | 12 | ||
| Pectinariidae | 2 | 1 | 3 | ||
| Sternaspidae | 1 | 1 | 2 | ||
| Terebellidae | 19 | 32 | 51 | ||
| Trichobranchidae | 0 | 7 | 7 | ||
| Total | 33 | 85 | 118 | ||
| incertae sedis | Nerillidae | 0 | 3 | 3 | |
| Protodrilidae | 5 | 2 | 7 | ||
| Protodriloididae | 0 | 1 | 1 | ||
| Saccocirridae | 0 | 1 | 1 | ||
| Aeolosomatidae | 0 | 1 | 1 | ||
| Parergodrilidae | 0 | 1 | 1 | ||
| Psammodrilidae | 0 | 1 | 1 | ||
| Total | 5 | 10 | 15 | ||
| Grand Total | 255 | 573 | 828 |
Figure 71: Spio Spio aequalis annual distribution.
Figure 70: Boccardia Boccardia magniovata annual distribution.
Figure 72: Beachworm Hartmanonuphis pectinata annual distribution.