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Amphinomidae
Description
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The prostomium comprises two parts, forming overall a
triangle, rounded and widest anteriorly. The peristomium is
reduced to lips. Paired
lateral antennae and a median antenna are present on the
anterior and posterior prostomial lobes, respectively. The ventro-lateral palps are slender and
located on the anterior prostomium. The nuchal organs are
attached to the edge of the caruncle, which extends posteriorly
from the prostomium; these complex structures
usually comprise several folds and ciliated tracts. The longitudinal muscles are grouped in four
bundles and segmentation is present. The first
segment curves around the prostomium and bears parapodia
similar to those posteriorly. All parapodia are biramous and
bear truncate cylindrical notopodia and tapering neuropodia,
which project beyond the notopodia; dorsal and
ventral cirri are present. The branchiae are branched
structures attached to the notopodial bases. Epidermal
papillae and pygidial cirri are absent, and
lateral organs and dorsal cirrus organs have not been
observed. The thickened muscular lower lip of the mouth is
eversible, rugose and covered with a thick cuticle. A gular membrane is lacking. The gut comprises a straight tube. Mixonephridia are present, and presumed to be
in most segments. A heart body is absent
from the closed circulatory system. Aciculae and other
chaetae, including variously ornamented capillaries and
spines, often dentate, are calcified to some degree and usually very brittle.
The above description is based on Hutchings (2000), which in turn is based on Fauchald & Rouse (1997).
Identification tips
Care should be used in handling amphinomids, especially tropical species which are aptly known as fire worms because of the chaetae which easily break off and become lodged in the skin. These cause a painful irritation and, in some people, an allergic reaction. The chaetae of some tropical amphinomids easily penetrate neoprene gloves.
Recognising the family
Amphinomids are sometimes confused with the Euphrosinidae (in the past both have been considered as belonging to a family, the Amphinomidae sensu lato, eg by Day 1967). For this reason, the interactive key treats both Amphinomidae and Euphrosinidae.
However they are usually treated as distinct families, and can be distinguished as follows. Amphinomids have short or conical notopodia whereas euphrosinids have notopodia as elongated crests. Amphinomids have single tufted notopodial branchiae and furcate chaetae none of which are ringent, whereas euphrosinids have many small branching branchiae along notopodial crests and the furcate chaetae include ringent and non-ringent types.
Distinguishing species
Complete individuals are required for accurate identifications, and the shape and size of the caruncle must be determined. If the front end is coiled up it must be carefully straightened in order to examine the caruncle. The arrangement and branching of the branchiae is also important for generic determination as is the structure of the notopodial chaetae which must be removed and mounted and examined under the microscope. Other characters used to distinguish species include the prostomial morphology, eyes, chaetal types and the distribution of notopodial and neuropodial aciculae.
Description | Identification
tips | Natural History | Diversity
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