ENTOMOSTRACA

This article appears in Volume V09, Page 656 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: EMS-EUD

ENTOMOSTRACA . This zoological

term

TERM

, as now restricted, includes the Branchiopoda, Ostracoda and Copepoda. The Ostracoda have the

body

BODY

enclosed in a bivalve shell-covering, and normally unsegmented. The Branchiopoda have a very variable number of

body

BODY

-segments, with or without a shield, simple or bivalved, and some of the postoral appendages normally branchial. The Copepoda have normally a segmented body, not enclosed in a bivalved shell-covering, the segments not exceeding eleven, the limbs not branchial.
Under the heading CRUSTACEA the Entomostraca have already been distinguished not only from the

Thyrostraca

THYROSTRACA

or Cirripedes, but also from the

Malacostraca

MALACOSTRACA

, and an intermediate group of which the true position is still disputed. The choice is open to maintain the last as an independent subclass, and to follow Claus in calling it the Leptostraca, or to introduce it among the

Malacostraca

MALACOSTRACA

as the Nebaliacea, or with -Packard and Sam to make it an entomostracan subdivision under the title Phyllocarida. At present it comprises the single family Nebaliidae. The bivalved carapace has a jointed rostrum, and covers only the front

part

PART

of the body, to which it is only attached quite in front, the valve-like sides being under

control

CONTROL (Fr. contrdle, older form contre rolle, from Med. Lat. contra-rotulus, a counter roll or copy of a document used to check the original; there is no instance in
English
- ENGLISH
of the use of " control " in this, its literal, meaning)

of an adductor muscle. The eyes are stalked and movable. The first antennae have a lamellar appendage at the end of the peduncle, a decidedly non-entomostracan feature. The second antennae, mandibles and two pairs of maxillae may also be claimed as of malacostracan type. To these succeed eight pairs of foliaceous branchial appendages on the front division of the body, followed on the hind division by four pairs of powerful bifurcate

swimming

SWIMMING (from " swim," A.S. swimman, the root being common in Teutonic languages)

feet and two rudimentary pairs, the number, though not the nature, of these appendages being malacostracan. On the other hand, the two limbless segments that precede the caudal furca are decidedly non-malacostracan. The family was

long

LONG, GEORGE (1800-1879)
LONG, JOHN DAVIS (1838– )

limited to the single genus Nebalia (Leach), and the single species N. bipes (O. Fabricius). Recently Sars has added a

Norwegian

NORWEGIAN

species, N. typhlops, not blind but weak-eyed. There are also now two more genera, Paranebalia (Claus, 188o), in which the branchialfeet are much longer than in Nebalia, and Nebaliopsis (Sars, 1887), in which they are much shorter. All the species are marine.

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