(redirected from Cephalocarids)


(invertebrate zoology)
A subclass of Crustacea erected to include the primitive crustacean Hutchinsoniella macracantha.



a subclass of small primitive crustaceans. The body is elongate, measuring as much as 3 mm in length. It consists of a head, a ten-segmented thorax with legs, and a nine-segmented legless abdomen. At the end of the body is a ramus with two long bristles. The legs are used for locomotion and respiration, as well as for directing food toward the mouth opening. There are two pairs of antennae on the head, small upper jaws, and two pairs of lower jaws, which are practically indistinguishable from the thoracic limbs. The animals lack eyes, a condition related to their burrowing way of life. The female lays eggs into an egg sac located on the last segment of the thorax. Nauplii are hatched from the eggs and become adults only after 18 molts.

The subclass Cephalocarida was discovered in 1957. Its first identified representative, Hutchinsoniella macracantha, was found on the Atlantic coast of the USA. Other species have been found on the eastern and western coasts of North America and near Japan. Three genera, embracing four silt-dwelling species, are known.


Zhizn’ zhivotnykh, vol. 2. Moscow, 1968.
Dogel’, V. A. Zoologiia bespozvonochnykh, 6th ed. Moscow, 1975.


References in periodicals archive ?
Thus although cephalocarids can tell little about the interrelationships within Crustacea, they may tell much about the roots of the crustacean radiation.
In the cephalocarids the muscle fiber remains as a single unit which is punctuated with triads) (Fig.
As mentioned above, only the ostracods and cephalocarids have muscles that lack myofibrils.
In contrast, neuromuscular synaptic contacts occur on a highly elaborated sarcoplasmic reticulum amongst the decapods (Atwood, 1976; Govind and Atwood, 1982), reflecting a more extensive repertoire of movements than that of the cephalocarids.
The cephalocarid body is composed of cephalon, thorax, and abdomen.
The tubule system in these cephalocarid muscles consists of the transverse tubules (t-tubules), which invaginate from the sarcolemma at the level of the 1-band and Z-line, with branches in the A-band region forming part of a triad (Fig.
The fine structure of the abdominal muscles of the cephalocarid H.
In comparison, the cephalocarid muscle with its triad denoting two tubules of the sarcoplasmic reticulum represents a less elaborate and much simpler system.
Accordingly, ostracod and cephalocarid muscles with scattered triads (Fig.
As a result, diads and triads occur scattered over the muscle fiber as in the cephalocarid muscle.
The fine structure of motor nerve terminals in the abdominal muscles of the cephalocarid is similar to that seen in the decapods (Govind and Atwood, 1982).