P.E. Tompsett, C.J. Neil, & P.A. Gainey
(Polychaetes and Oligochaetes by P.E. Tompsett and C.J. Neil; leeches by P.A. Gainey)
Marine annelids fall into a large and complex phylum, Annelida, the taxonomy of this group is currently under review so the main ‘traditional’ subdivisions are retained in the account below.
Generally, polychaetes have paired, lateral extensions of the body segments known as parapodia, head appendages and several types of chaetae (setae), often in bundles. Chaetae and parapodia give rise to a higher diversity of external morphology in polychaetes than in leeches or oligochaetes. The oligochaetes have fewer, simpler chaetae, rarely in bundles, and lack parapodia or similar structures. The leeches lack parapodia, head appendages and chaetae and have at least one, usually two, terminal suckers. There are no clear ecological boundaries between the groups and all are found in British waters. Polychaetes are almost exclusively marine whilst the oligochaetes have exploited the terrestrial, marine and freshwater environments and, although most leeches are freshwater, there are some 22 or 23 marine species in British seas, all of them parasites of fish.
The systematic sequence and nomenclature followed here is taken from Howson & Picton (1997). The authors would like to acknowledge the invaluable help given by A.S.Y. Mackie, (Amgueddfa Cymru — National Museum Wales), A.I. Muir (The Natural History Museum) and T. Harris (formerly of University of Exeter).
1. Polychaetes ( Bristle Worms)
Polychaetes are widely distributed, often abundant and ecologically important, particularly as a food source for fish and birds. There are some terrestrial and freshwater species but of around 9000 described species worldwide most are marine and of these over 800 have been recorded from British waters. The majority of polychaetes are free-living and they can be found in all marine habitats. They are mostly benthic, but there are a small number of pelagic species. The tiniest live interstitially in spaces in coarse sediments, such as the North Sea species Nerillidium marina which is less than 300μm long. Large species on British coasts include Chaetopterus variopedatus of some 250mm length and the King Rag Nereis virens which can reach 900mm in length. Sedentary or mobile, tube-dwelling or burrowing species live in sediments ranging from rich, organic silts to mobile, coarse sands. Some construct permanent tubes on, or bore into, rocks and shells. Certain species regularly associate with other biota, for example Laminaria holdfasts or other invertebrates. There are commensal and parasitic species, including members of the Myzostomida, a small group historically often considered a separate phylum. Probably the most familiar species are the Lugworms and Ragworms which are dug for use as angling bait.
National distribution data for polychaetes have not yet been assembled and data are relatively scarce. All species listed below have been recorded in fewer than five 10km squares in Cornwall and the Isles of Scilly. The lists have drawn on the few available literature sources and Cornish records for their compilation. They should not be regarded as authoritative. To some extent they reflect recording activity and part of their value will be in prompting more recording. The distribution of some species appears to be affected by temperature zones around the British coast; several are restricted to warmer southern waters.
Conservation concerns for many polychaetes are not known but intertidal populations are threatened locally by pollution such as oil spillages and large-scale disturbance of sediments such as commercial baitdigging. Two polychaetes are listed in Schedule 5 of the Wildlife and Countryside Act, 1981 (amended). One, the Lagoon Sandworm Armandia cirrhosa Filippi, has only been recorded in south Hampshire and is the only RDB polychaete (Bratton, 1991). The other, the Tentacled Lagoon Worm Alkmaria romijni, has been recorded in Cornwall (listed below) and south-west Wales.
The first list below is of species which appear to be rare on Cornish coasts and nationally (pR); this is followed by a list of those with very few local records and which may or may not be nationally scarce. It is hoped that this deficiency of data may encourage a greater recording effort for the future.
Mackie and Erseus (1997) provided the most recent list of British annelids, while Bellan (2001) produced a European register. Helpful references for identification and/or distribution of species include George and Hartmann-Schroder (1985), Hartmann-Schroder (1996), Hayward and Ryland (1990; 1995), Pleijel and Dales (1991), Westheide (1990), Chambers and Muir (1997) and the National Biodiversity Network (NBN) Gateway.
A. Provisionally Rare Species
Lepidasthenia argus1.1.2. Phyllodocidae
Phyllodoce longipes1.1.3. Syllidae
Typosyllis krohni1.1.4. Lopadorrhynchidae
Pelagobia longicirrata1.1.5. Nereididae
Eunice vittata1.2.2. Lumbrineridae
Lumbrineris coccinea1.2.3. Dorvilleidae
Ophryotrocha hartmanni1.2.4. Iphitimidae
Saccocirrus cf. papillocercus
Alkmaria romijni Tentacled Lagoon Worm
Sabella discifera1.9.2. Serpulidae
Vermiliopsis striaticeps1.9.3. Spirorbidae
B. Provisionally Scarce Species (in Cornwall and Isles of Scilly).
Hermonia hystrix1.2. Polynoidae
Malmgrenia marphysae1.3. Phyllodocidae
Eumida punctifera1.4. Glyceridae
Glycera tridactyla1.5. Goniadidae
Goniadella bobretzkii1.6. Sphaerodoridae
Sphaerodorum gracilis1.7. Hesionidae
Podarkeopsis capensis1.8. Syllidae
Typosyllis vittata1.9. Nereididae
Micronereis variegata1.10. Nephtyidae
Aponuphis bilineata2.2. Eunicidae
Nematonereis unicornis2.3. Dorvilleidae
Dorvillea (Schistomeringos) rudolphi
Scolelepis bonnieri4.2. Chaetopteridae
Phyllochaetopterus anglicus4.3. Cirratulidae
Dasybranchus caducus7.2. Maldanidae
Petta pusilla12.2. Sabellariidae
Sabellaria spinulosa12.3. Ampharetidae
Sosane sulcata12.4. Trichobranchidae
Trichobranchus roseus12.5. Terebellidae
2. Brackish and Marine OligochaetesThere are fewer oligochaete species than polychaetes known from the marine environment, but they are often an important part of invertebrate communities in organically-rich, fine sediment habitats. A small number of oligochaete species bridge the gap between fresh and saline water, being found in both, and there is also a small but important group which regularly form the bulk of the macroinvertebrate community on British estuarine mud-flats where they can be found in enormous densities. This group includes sludge worms, a term used to describe species which are commonly identified with organic pollution of marine and freshwater habitats. Aquatic oligochaetes are generally smaller than the terrestrial species and many of the marine species are meiofaunal (less than 1mm in length). Problems with ready identification have undoubtedly deterred the recording of this group so that an assessment of the status and distribution of species is difficult. There are possibly 123 species of oligochaete in British coastal waters (Mackie and Erséus, 1997). These are now classified in just two families which contain brackish and marine species: the Naididae, including the Tubificinae, Rhyacodrilinae, Phallodrilinae and Limnodriloidinae, (see Erseus et al., 2008), and the Enchytraeidae. Within the Naididae, the Naidinae has the fewest marine species - possibly there are only 13 in Britain. The species which is described here as provisionally scarce may be more common than local records suggest.
3. Leeches ( Hirudinea)14 species of leech have been recorded in Cornwall; of these nine species are marine, of which eight can be considered nationally scarce. Useful references are Llewellyn (1966), Hayward & Ryland (1990) and Leigh-Sharpe (1933).