The spine is completely ossified. The skull, with the exception of the superior occipital region, is bony. The type of skull is amphistilic. Usually there is a gular plate. Ganoid or bone scales. A cellular bladder with cellular walls serves as an additional respiratory organ. There is a spiral valve in the intestine, in the heart - an arterial cone. Nowadays, living fish are united in 2 orders: Amoeiformes and Carapace.
Squad amoeiformes –amiiformes
The snout is shortened, rounded. Long dorsal fin. Scales cycloid. There is a gular plate. The type of vertebrae is amphicelic.
Family Eel fish - Amiidae
Genus Silt fish - Amia.
Silt fish - A. calva Linne. Reaches 90 cm in length (Fig. 68, b). Inhabits freshwater bodies of North America (southeastern part). Able to breathe atmospheric air. Caviar lays in a nest of aquatic plants.
Squadron-like order –lepisosteiformes
An arrow-shaped body covered with ganoid scales. Short dorsal fin, located above the anal. The caudal fin is shortened heterocercal: the hypuralia is supported by the end of the spine bent upwards. The snout is elongated and, unlike other fish, the preorbital bone, divided into 6-8 bones carrying teeth, is involved in the formation of the upper jaw. The lower jaw consists of 6 paired bone elements. There is no gull plate; there are 3 rays of the gill membrane. The integumentary bones of the head are covered with ganoin. Vertebral vertebrae.
Family Carapace, or Cayman - Lepisosteidae
Genus Carapace - Lepisosteus. Includes 6-7 species. All inhabitants of North and Central America (to the north go to the headwaters of the Mississippi, to the south - to Costa Rica, south-western Cuba).
Long-snouted carapace - L. osseus (Linne). It reaches 1.5 m in length (Fig. 68, c). Common in fresh waters, but adults are found in brackish and marine individuals along the Atlantic coast of America.
Questions for self-testing:
What are the main features of the Bone fish class?
State the differences between the signs of the Bone class and fish from the Cartilaginous class.
What subclasses are in the Bone fish class?
What are the features that characterize these subclasses?
What representatives have gular plates, ganoid scales, a beaded type of paired fins, an autostylic type of skull?
What is the name of the brushworm and its habitat?
What is the systematic position of the multipope and where does it live?
What species are known to you among breathless? Where are they common?
What systematic group does shell pike and silt fish belong to? How do they differ morphologically? Where do they live?
Theme 12. The superorder of cartilaginous ganoids –chondrosteimorpha
The task. When considering representatives of cartilaginous ganoids, attention should be paid to: a heterocercal tail with the remains of ganoid scales and fulcra, the presence or absence of five rows of bone bugs, the peculiarity of attachment of gill membranes to the intercostal space, the shape of the mouth, the presence or absence of spatter, the shape of the rostrum, the structure of the lower lip, the location and nature of the antennae, the number of lateral bugs, the nature of the bone plates between the rows of bugs.
General characteristics of cartilaginous ganoids. The body is spindle-shaped, elongated, bare or covered with five rows of bone bugs. There is a rostrum, lower mouth. The tail is heterocercal; on the upper lobe there are ganoid scales and fulcra. One dorsal fin. Paired fins are located horizontally in relation to the body, the anus is located near the ventral fins. The skeleton consists mainly of cartilage. Cartilage endocranium, with well-developed integument bones. The chord is not dissected, there are only cartilaginous arches. In the heart there is an arterial cone, in the intestine there is a spiral valve. The swim bladder is connected by a canal to the esophagus. The living people are represented by one detachment - Sturgeon-like and the families of Sturgeon and Paddlefish.