Anatomy of finfish and shellfish

Unit 12 - Arthropoda

12.1.4. Nervous System
The nervous system of the white shrimp consists of a brain (supraesophageal ganglion), which is situated dorsally in the head, two circumesophageal connectives that pass on either side of the esophagus and are connected with each other by the tritocerebral commissure, and a ventral nerve cord, which runs posteriorly the entire length of the shrimp and at more or less regular intervals is swollen into bulbous ganglia. The entire central nervous system of the white shrimp, as of other decapod crustaceans, is fundamentally "ladder-type" in structure, but in most regions the two longitudinal halves of the "ladder" have fused. As a consequence, the word "gan¬glion" generally refers to a pair of laterally fused ganglia.
The brain receives nerves from sense organs of the head, notably the eyes and antennae, and supplies nerves to the muscles that operate these sense organs. In the ventral nerve cord, the first ganglion (subesophageal ganglion) and the remaining ventral ganglia (five in the thorax and six in the abdomen) receive nerve fibers from sensory cells widely dis¬persed through the body of the shrimp and supply nerves to muscles that move the mouth parts, thoracic legs, pleopods, and tail.
In addition, lying on the circurnesophageal connectives is a pair of connective ganglia, or stomatogastric ganglia (stö-m¬to-GAS-trik; from the Greek, stoma, mouth; gaster, stomach). The connective ganglia and the stomadeal ganglion on the anterior surface of the çsophagus combine to form the stomadeal system, which supplies nerves to the esophagus and the foregut.
In the forward part of the cephalothorax of the white shrimp, situated on the second, or antennal, segment are the kidneys, which because of their location are often called an¬tennal glands. Each kidney is made up of a small dorsal portion that lies above the brain and a large ventral portion lying beneath the brain. The two portions of each kidney are connected with each other by lateral arms. Part of the ventral portion extends into the antenna on the same side of the animal. A short duct from this portion of each kidney leads to the exterior through an excretory pore, which lies at the base of the antenna on its inner (medial) side. In higher shrimps, the Caridea, a bladder also is present.
There are 19 pairs of gills in Penaeus setiferus. Three pairs occur in each thoracic segment, except the first and last, where there is one pair. In any given segment the gills may be attached to the base of the limb, to the flexible membrane between limb and body, or to the body wall. A gill of the white shrimp consists of a primary supporting axis known as a rachis (RAY-kis; from the Greek, rhakhis, spine, or backbone), from which secondary supporting structures emerge at right angles. On the secondary supporting structures are many gill filaments that in turn protrude at right angles. Each secondary supporting structure with its attached filaments nests against the preceding one. In caridean shrimps, the gill filaments are flattened and plate-like and protrude directly from the primary supporting structure; this type of gill also is found in crabs.