Hesionids are usually small colourful worms, often iridescent purples and greens. They are found in most marine habitats. Some hesionids are active predators often taking prey as large as themselves.
The form of the appendages on the head, palps and antennae are important characters at the generic level. There may be four or five antennae. Palps are usually in two sections (biarticulate) and the relative lengths of the sections is useful at the species level. There may be two or three antennae. Hesionids genera have a variable number of pairs of tentacular cirri. The number and arrangement of these cirri are important characters, but often difficult to see in small specimens and also because they drop off if the specimens are not well preserved. Where the biramous parapodia begin and the form of the parapodia also provides good taxonomic characters. The notopodia is variously reduced in many genera, while shape of the neuropodia and chaetal lobes provide useful species characters. Notochaetae are usually capillaries while the neurochaetae are compound; the shape and length of the blades provide useful characters.
Hesionids could be mistaken for nereids. They differ in the form of the tentacular cirri which are arranged more segmentally than in nereids; the form of the parapodia which are simpler without the various ligules seen in nereids; and the pharynx in hesionids does not have obvious jaws and paragnaths.
| Leocrates sp. 1 |
