The prostomium is reduced to a narrow ridge, and the
peristomium is represented only as lips around the mouth. A pair of small lateral antennae is present; a
median unpaired antenna is located more posteriorly on the
prostomium. Although palps are lacking
palpal nerves are present, and run to the ventro-lateral lips; the position of these nerves correspond to
those of the palpal nerves in amphinomids, suggesting a loss
of palps. The nuchal organ/caruncle process is three-lobed
with longitudinal ciliated ridges, attached frontally and
projecting as free lobes posteriorly. The longitudinal muscles
form bundles and segmentation is distinct. The first segment
is distinct and is curved dorso-laterally around the
prostomium so that the first parapodia project anteriorly on
both sides of the prostomium without being fused to it. The notopodia comprise transverse ridges
which nearly meet medially; the neuropodia project laterally,
tapering to blunt tips. Dorsal and ventral cirri are present. The
branchiae are divided into small branching bundles behind the
notopodia. One pair of inflated pygidial cirri
is present. Epidermal papillae are absent and lateral organs
and dorsal cirrus organs have not been observed. The buccal
organ is a thick, eversible ventral muscle mass covered with
thickened cuticle. A gular membrane is absent; the gut is a
straight tube. The segmental organs are
mixonephridia and are present in most segments. The
circulatory system is closed and a heart body is lacking.
Aciculae are present and chaetae are calcified. Furcate
and capillary chaetae are present, but most
chaetae are spine-like with characteristic ‘ringent’
ornamentation.
The above description is based on Hutchings (2000), which in turn is based on Fauchald & Rouse (1997).
Identification tips
Recognising the family
Euphrosinids are closely related to the Amphinomidae (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 here treated as distinct families. Euphrosinids have short, stout bodies, oval in outline with relatively few segments, whereas amphinomids have elongate bodies with numerous segments. The chaetae of euphrosinids are calcareous and sometimes heavily calcified but are not hollow and venom-filled as in amphinomids.
Amphinomids have short or conical notopodia whereas euphrosinids have notopodia as elongated crests. Amphinomids have single tufted notopodial branchiae and furcate chaetae non 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
Characters used to distinguish species of euphrosinids include the relative length of the notochaetal prongs, and the notochaetal length relative to body length. These characters are often consistent for a species although they vary along the body and within chaetal fascicles.
