. Chordate morphology. Morphology (Animals); Chordata. homboid scales caudal fin ACIPENSER scutes P^'^'' fi" pectoral fin Figure 2-3. External features of two chondrosteans. Holosleans and teleosls The Bowfin, Amia, a representa- tive holostean, is a thick-bodied fish with a large head and mouth (Figure 2-4). The head is covered with thick bones but is without scales on the cheek. There is a long dorsal fin, an anal fin, and two pairs of lateral fins. The caudal fin is rounded in outline. The scales of the body are large and cycloid, that is, round in shape and overlapping. The lateral-li
. Chordate morphology. Morphology (Animals); Chordata. homboid scales caudal fin ACIPENSER scutes P^'^'' fi" pectoral fin Figure 2-3. External features of two chondrosteans. Holosleans and teleosls The Bowfin, Amia, a representa- tive holostean, is a thick-bodied fish with a large head and mouth (Figure 2-4). The head is covered with thick bones but is without scales on the cheek. There is a long dorsal fin, an anal fin, and two pairs of lateral fins. The caudal fin is rounded in outline. The scales of the body are large and cycloid, that is, round in shape and overlapping. The lateral-line system is indicated by rows of pores on the head. The eyes are large and lateral. The anterior nasal opening is at the tip of a nasal tube extending from the upper lip; the posterior opening is high on the snout in front of the eye. The opercular covers are free to a point far forward between the halves (rami) of the lower jaw. These margins end at a median plate (gular plate). There is no spiracle. The gar, Lepisosteus, is a very elongated fish with a toothed snout. The nasal capsule with its two openings is at the tip of the snout; the eye lies behind the angle of the mouth. The dermal bones of the head are visible through the skin, and the cheek is covered with an intricate and vari- able pattern of small plates. The opercula are joined across the throat. The body is covered with imbricated rhomboid scales with a glassy surface of an enamel-like material (ganoin). The dorsal fin is far back, and there are two pairs of lateral fins and an anal fin. The tail is heterocercal but the fin is not subdivided. The perch, Perca, a typical teleost, has cycloid scales covering the body and cheeks. These scales have fine spines along their anterior margin and are thus identified as ctenoid. The dorsal fin has an anterior spined half and a posterior soft lobe. The lateral fins have slight, fleshy, basal lobes and like the other fins are formed of a skin membrane supported by jointed f
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Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
