The body of a lophogastrid is long and shrimplike, with the head and thorax covered by a loosely fitting carapace. The carapace is extended in front as a rostrum, which is an anatomical structure resembling a bird's beak. The rostrum can be very large in one genus of lophogastrids. The rear portion of the carapace may cover from five to seven thoracic somites. It extends over the sides of the animal to the bases of the thoracic legs. Both pairs of lophogastrid antennae are biramous; that is, they have two branches. All lophogastrids have eyes on moveable stalks. The antenna (=second antenna) exopod (outer branch) is shaped like a large scale. The mandible, or lower jaw, is of the rolling crushing type, with a toothed incisor and large crushing molar. The mandible palp, which is a jointed sensory appendage, can be rather large and extends upwards in front of the head to the area between the anten-nular peduncles (small stemlike process at the base of an antenna). In some genera, at least, the maxillules, or first pair of maxillae, possess a backwardly-directed endopod (posterior process) in the form of a palp. On the maxilla (upper jaw), the exopod forms a large setose (bristly) lobe that resembles the scaphognathite (lateral flap on the second maxilla) of decapod crustaceans.
The thoracic limbs of lophogastrids are modified in various ways; however, all have well-developed endopods and ex-opods. The first pair is always modified as a maxilliped because the first thoracic somite is incorporated into the head. In essence, such modifications usually involve shortening of the endopod as well as the development of specialized lobes and setae for handling food. The remaining thoracic limbs, now called pereopods, are numbered from one through seven. The pereopods are all usually similar to one another in the structure of the endopod as well as in the strength of the swimming setae (bristles) on the exopods. In the genus Eucopia, however, the first three pereopods are short and stout with subchelate (pincerlike) tips; the fourth through the sixth pereopods are highly modified as elongate grasping appendages; and the seventh pereopod is reduced to a limb with bristles. Most lophogastrid pereopods bear gills at their base. Oostegites, or brood plates, are present on all seven pairs of pereopods.
All lophogastrids, both males and females, have well-developed biramous propulsive pleopods on the first five abdominal somites, and broad flattened uropods on the sixth abdominal somite. The uropods do not possess statocysts. A flattened and somewhat pointed telson terminates the body. In males of the genus Gnathophausia, the endopod of the second pair of pleopods is slightly modified for sperm transfer.
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