. Fresh-water biology. Freshwater biology. 662 FRESH-WATER BIOLOGY in the position of the eyes. In the Anostraca (Fig. loii) there is no shell-fold and the body, composed of many distinct somites, has an almost worm-like aspect; the Notostraca (Fig. 1012) are also elongated and composed of numerous somites, but are flattened, and their anterior portion is covered dorsally by a broad arched carapace; the bodies of the Conchostraca (Fig. 1013) tend to be laterally com- pressed and are enveloped in a bivalve shell that makes them look hke a small clam. The shell-fold is not attached to the trunk
. Fresh-water biology. Freshwater biology. 662 FRESH-WATER BIOLOGY in the position of the eyes. In the Anostraca (Fig. loii) there is no shell-fold and the body, composed of many distinct somites, has an almost worm-like aspect; the Notostraca (Fig. 1012) are also elongated and composed of numerous somites, but are flattened, and their anterior portion is covered dorsally by a broad arched carapace; the bodies of the Conchostraca (Fig. 1013) tend to be laterally com- pressed and are enveloped in a bivalve shell that makes them look hke a small clam. The shell-fold is not attached to the trunk somites which it envelops. It may be more or less corneous but is never calcified. The eyes are elevated on movable peduncles in the Anostraca but are sessile in all other phyllopods. A peculiar. Fig. ioii. Branchinecta paludosa, male and female, ai, first antenna; 02, second antenna; d, cerco pods or furcal rami; p, penis; ^ telson. X 3. (After Packard.), structure, the frontal (or haft) organ, is variously developed in the different groups; in some it is only a sensory area and in others it has a knob-like pediculated form. The head is distinct from the trunk and the number of trionk- somites is variable. Some notostracans have as many as forty-two trunk-somites; the Conchostraca have from thirteen to twenty- eight, and the number in the Anostraca ranges from nineteen to twenty-three. Apart from the head, the trunk of phyllopods shows no differentiation into distinct regions. The terms "thorax" and "abdomen" have been variously used to designate the pre- or post-genital, or the limb-bearing or limbless, regions respectively. But the limits of these regions do not coincide, even approximately, except in the Anostraca; and "thoracic" and "abdominal" are therefore not appUcable to the group. The last segment, or telson, usually bears a pair of appendages, the furcal rami or cercopods. The appendages are fairly uniform in character, except
Size: 2713px × 921px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
