Chapter 10. Part 1: Cartilaginous Fishes

Transcription

1 Chapter 10 Part 1: Cartilaginous Fishes

2 Objectives Understand how hagfishes and lampreys differ from all other fishes. Describe how sharks, skates, and rays are related. Differentiate between cartilaginous fishes and bony fishes. List the morphological features that make sharks perfectly adapted for their environment.

3 Fishes Fishes are vertebrates 530 mya evolved from chordate ancestors Tunicates, lancelets Primitive fishes lacked paired fins and jaws Agnathans

4 I. Jawless Fishes (crazy, creepy fishies) Lack both jaws and paired appendages Have skeletons of cartilage Lack scales Hagfish also lack vertebrae (some scientists consider them invertebrates)

5 A. Hagfishes Bottom dwelling slime eels Skins are used to make leather goods Hagfish feeding apparatus is composed of two dental plates containing horny cusps, used to grasp the prey s flesh feed on live prey and scavenge

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7 B. Lampreys Have oral disk and rasping tongue covered with tooth-like keratin plates 38 species 9 found in the ocean Reproduction Anadramous Breed in freshwater/ live in salt water

8 II. Cartilaginous Fishes Class Chondrichthyes e.g. sharks, skates, rays, chimaeras Possess jaws and paired fins Have placoid scales 2 major groups: holocephalans (chimaeras or ratfish) elasmobranchs (2 body forms: streamlined or dorso-ventrally flattened)

9 A. Sharks Characteristics Excellent swimmers with streamlined bodies swim with powerful, sideways sweeps of the caudal fin (tail) heterocercal tail caudal fin in which the dorsal lobe is longer than the ventral

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11 Sharks Characteristics continued Buoyancy sink if they stop swimming large livers produce squalene an oily material with a density less than seawater squalene offsets the shark s higher density to help maintain buoyancy

12 1. Shark Sensory Systems A. Vision a clear nictitating membrane covers and protects each lidless eye many species seem to have color vision B. Olfaction more important than vision almost 2/3 of the shark s brain cells are involved in processing olfactory information sharks are sometimes referred to as swimming noses

13 Shark Sensory Systems C. Lateral line system canals running the length of the animal s body and over the head detect vibrations in the fluid which alert the shark to movements in the water

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15 Shark Sensory Systems D. Ampullae of Lorenzini organs scattered over the top and sides of the animal s head sense electrical currents in the water

16 2. Digestion in Sharks Blade-like, triangular teeth Food is swallowed whole (sharks cannot move their jaws back and forth to chew)

17 2. Digestion in Sharks Food passes through stomach to a short intestine containing a spiral valve spiral valve similar to surface area of large intestine Undigestable material is excreted through the cloaca

18 3. Osmoregulation in Sharks Maintain an internal solute concentration > or = to the seawater retain large amounts of nitrogenous wastes, mostly urea Gills and intestine work to excrete excess sodium chloride Kidney excretes other salts into muscle tissue

19 3. Reproduction in Sharks Sperm produced in paired testes are transferred to the female through grooves in the claspers 3 Types of Reproductive Development Oviparity Viviparity Ovoviviparity

20 Reproduction in Sharks a. Oviparity most primitive mode eggs are laid outside the body and the embryos develop in a protective case e.g. chain dogfish, bullhead sharks (heterodontiformes)

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24 Reproduction in Sharks b. Ovoviviparity most common mode eggs hatch within the mother s uterus but no placental connection is formed young are nourished by yolk from the egg e.g. basking, thresher, great white, & sand tiger sharks *intrauterine cannibalism is common in this type of reproduction

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28 Reproduction in Sharks c. Viviparity most recent mode to evolve either the young directly attach to the mother s uterine wall or the mother s uterus produces uterine milk that is absorbed by the embryo e.g. requiem sharks, hammerhead sharks

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30 B. Skates and Rays

31 Differences between Skates and Rays Rays: swim by moving fins up and down streamlined tails with venomous barbs or spines larger size Skates: create a wave from the forward to backward fin edges fleshier tails with small fins and no spines smaller size ovoviviparous mostly oviparous

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33 Defense Mechanisms Electric rays 220 V Stingrays Toxic barb on caudal fin Sawfishes and guitarfishes barbs along their rostrums

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38 C. Chimaeras Subclass Holocephali e.g. ratfish, rabbitfish, spookfish Large pointed heads and long, slender tails Gills covered by operculum; water inhaled through the nostrils Males have claspers on their heads and pelvic fins

39 Chimaeras Oviparous produce large eggs in a leathery case Have flat plates for crushing prey instead of teeth Generally bottom dwellers

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