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Polychaetes and other marine worms

Of course, there are many marine worms that are not polychaetes and cannot be identified using this publication. Some worms, such as myzostomes and pogonophorans, have been moved in and out of the Polychaeta as a result of recent research. This rough guide may assist recognition of free-living marine worms and worm-like invertebrates and reduce the confusion about what is a polychaete and what is not. (Other worm-like organisms not mentioned here occur in terrestrial and freshwater environments. Parasitic worms are likewise not surveyed here.)

Even fragments of brittle star arms (ophiuroids) are occasionally mistaken for segmented worms. Detached tentacles from such families as terebellids and cirratulids are also commonly found in benthic samples. With a little experience, worm-like fragments such as these are soon recognised and discarded.

Annelida: Hirudinea
Leeches are segmented worms with short thick muscular bodies with suckers at either end. Segments and chaetae are present but are not easily seen. Hirudinea: Stibarobdella macrothela [illustrator: D.Kowarsky]
Annelida: Oligochaeta Segmented, coelomate, bilaterally symmetrical worms with tapering ends. Anterior extremity, the prostomium, lacks appendages and is followed by the peristomial segment with ventral mouth. Pygidium with terminal anus at posterior extremity. Other segments are similar in form excepting thickened opaque clitellum in sexually mature specimens formed of up to 6 segments in the genital region. Chaetae are typically two pairs of bundles per segment, include both hair-like capillaries and simple or distally-toothed hooks. Compound chaetae absent. insert oligochaete image
Arthropoda: Insecta
insect larvae
Chironomids and other dipterans (flies) have aquatic larvae that are segmented and worm-like. Although predominantly freshwater, they can be quite common in benthic samples from estuaries, and there are even a few marine species. insert insect image
Cnidaria: Anthozoa: Edwardsiidae
burrowing sea anemones
(eg the genus Edwardsia insert edwardsiid image
arrow worms
Narrow-bodied and often transparent, with paired lateral fins and a tail fin and distinctive grasping spines at the mouth. Unsegmented. z0002442.JPG - 7154 Bytes
Echinodermata: Holothuroidea
sea cucumbers
Holothurians are sausage-shaped echinoderms, pentamerously symmetrical in cross-section. Oral tentacles, arranged in a circlet, either bushy of digitate. Soft bodied except for isolated calcareous ossicles in the skin. Tube feet present or absent. Holothuroidea: Chirodotidae [photo: M.Marmach]
spoon worms
Unsegmented marine worms. Body short, wall thick and muscular. Proboscis simple or bifid and non-retractile. Mouth at base of proboscis, anus at the posterior end. Gut long and highly coiled. One pair of chaetae ventrally immediatedly posterior to the mouth; 1-2 rings of chaetae may also encircle the anus. insert echiuran image
Hemichordata: Enteropneusta
acorn worms
R:12 C:2 insert hemichordate image
Mollusca: Aplacophora Worm-like burrowing molluscs that lack a foot and have a covering felt of calcareous spicules. Aplacophora: Falcidens chiastos
Mollusca: Bivalvia: Teredinidae
teredos or ship worms
Wood-boring bivalves with worm-like bodies and modified shell at the anterior end, at the opening to the burrow, which has a calcareous lining. insert teredo image
Mollusca: Scaphopoda - tusk shells Molluscs in a tapering, slightly curved calcareous shell. Scaphopoda: Fustiaria caesura
Myzostomida Worms with inconspicuous segmentation, flattened discs (mostly), and commensal on echinoderms, especially crinoids. Often classified within the Polychaeta as Myzostomida or Myzostomidae but no longer thought to belong within the Polychaeta. insert myzostome image
ribbon worms
Unsegmented acoelomate bilaterally symmetrical worms. Digestive tract with seperate mouth and anus, and an eversible proboscis dorsal to the gut in a tubular cavity. The proboscis pore is ventrally located at the anterior end. Most species nondescript in pigmentation, but some have stripes, bands, spots or other distinctive patterns. Nemertea [photo: M.Marmach]
round worms
Small thread-like unsegmented worms, often with no obvious structure and pointed at both ends, sometimes with copulatory apparatus. Cuticle highly irridescent. insert nematode image
Phoronida Phoronids are tubiculous often constructing sandy tubes which resemble those of the oweniid polychaete Owenia, with branchial crown but lacking distinct segmentation or chaetae. Others are found embedded in the tube walls of burrowing anemones. insert phoronid image
Acoelomate bilaterally symmetrical worms, strongly dorso-ventrally flattened. Mouth ventral, gut sack-like, anus absent. Often brightly coloured in life, tropical species spectacularly so. Free living, commensal and parasitic forms. Pseudoceros bifurcus [photo: L. Newman & A. Flowers]
Pogonophora, including Vestimentifera A small conical prostomium and a peristomium bearing one, 2 or many palps. Treated as Phyla separate from the Annelida by many authors but now known to be polychaetes, family Siboglinidae insert siboglinid image
Priapula Unsegmented marine worms with bilaterally symmetrical bodies. Anterior region is the introvert with mouth and eversible pharynx. Introvert with 20 or 25 longitudinal rows of chitinous papilla-like scalids. Posterior region is the abdomen, with terminal anus. Abdomen with 30-100 circular muscle bands visible as annulations. Priapula [illustrator: Damon Kowarsky]
peanut worms
Unsegmented marine worms lacking chaetae. Body divided into a trunk and a slender, retractable introvert with terminal mouth, often surrounded by tentacles. Body usually with a distinctively "leathery" texture and covered with papillae. Gut typically coiled in a tight helix. Sipuncula [photo: M.Marmach]