Myxini Classification Essay

Presentation on theme: "Diversity of Fishes III. Phylum Chordata –Superclass Agnatha Class Pteraspidomorphi † Class Myxini (?) Class Cephalaspidomorphi –Superclass Gnathostomata."— Presentation transcript:

1 Diversity of Fishes III

2 Phylum Chordata –Superclass Agnatha Class Pteraspidomorphi † Class Myxini (?) Class Cephalaspidomorphi –Superclass Gnathostomata Class Placodermi † Class Chondrychthyes Class Acanthodii † Class Sarcopterygii Class Actinopterygii Fish Taxa Diversity

3 Evolution of Fishes

4 Superclass Gnathostomata (still) Class Acanthodii † (“spiny sharks”) –Cartilaginous skeletons with ossified pieces & characteristic spines –Pelagic habitat (FW & SW) –Considered sister group of bony fish

5 Teleostomi or Osteichthyes (Bony Fishes) Sarcopterygi Actinopterygi

6 Superclass Gnathostomata Class Sarcopterygii (lobed fins) –Coelacanths and lungfishes –Osteolepimorphi † Class Actinopterygii (ray fins) -Ray finned fishes

7 Class Sarcopterygii Order Coelacanthiformes –Family Coelacanthidae (coelecanths) -Fleshy lobed fins -Characteristic osteological features (fig 13.6) -Choanae (internal nostrils) -2 spp.

8 Latimeria chalumane (“Old fourlegs”) Marjorie Courtenay-Latimer (1939) J. L. B. Smith –2 nd specimen (1952) Comoro Islands (now Kenia, Madagascar, South Africa…) French embargo Conservation issues Live observations (nocturnal, 200m) Ovoviviparous



11 Mark Erdmann (1998) Indonesia (Sulawesi) Conservation issues Genetics study Live observations Latimeria menadoensis (“King of the Sea”)

12 Other Coelacanth Locations? Meso-american silver jewelry 1800’s

13 Extra Credit: +3% total grade A Fish Caught in Time : The Search for the Coelacanth by Samantha Weinberg ($10.50 @ Read the book, and write a 1 page essay, clearly expressing YOUR interpretation and opinions of it, as well as how the reading affected your opinion on ichthyology.

14 Class Sarcopterygii Infraclass Dipnoi (lungfishes) –Massive toothplates –Maxillae and Premaxillae bones missing –Functional Lung, choanae (internal nostrils) –Family Ceratodontidae (Australia, 1spp.) –Family Lepidosirenidae (S. America, 1spp.) –Family Protopteridae (Africa, 4 spp.)

15 Ceratodontidae Australian lungfish Neoceratus forsteri

16 Lepidosirenidae S. American lungfish Lepidosiren paradoxa Protopteridae African lungfishes Protopterus sp.

17 Class Sarcopterygii Infraclass Osteolepimorphi † –Sister group of modern tetrapods –Similar fins to Devonian Amphibians limbs –Other morphological similarities

18 Teleostomi or Osteichthyes (Bony Fishes) Sarcopterygi Actinopterygi

19 Class Actinopterygii



22 Class Actinopterygii Order Polypteriformes –Family Polypteridae (bichirs & reedfish) 10 spp. (African rivers) Facultative airbreathers (spiracle exhalation) Lobed fins, ganoid scales, heterocercal tail, spiral intestine. Flagfins (vertical spine with horizontal rays)

23 Class Actinopterygii Order Acipenseriformes (secondary cartilaginous skeleton, heterocercal tail, fin rays, spiral valve intestine). Sturgeons and Paddlefish –Family Acipenseridae (sturgeons) 24 spp. (northern hemisphere) 5 rows bony scutes (modified ganoid scales) 4 barbels in front of ventral mouth Fresh water spawning (typically Anadromous)


25 Order Acipenseriformes (secondary cartilaginous skeleton, heterocercal tail, fin rays, spiral valve intestine) –Family Polyodontidae (paddlefishes) 2 spp. (N. American and Chinese paddlefishes) No bony scutes, small scales, ossified head plates Freshwater open water plankton feeders Paddle as electroreceptor? Class Actinopterygii

26 Order Semionotiformes –Family Lepisosteidae (garfish) 7spp. (North and Central America) Ossified skeleton Ganoid scales Slightly heterocercal caudal fin Backwaters in lakes and rivers, predatory fish Toxic eggs

27 Class Actinopterygii Order Amiiformes –Family Amiidae (bowfin) 1 spp. (Amia calva, Eastern North America) Ossified skeleton Slightly heterocercal caudal fin Cycloid scales Swims through dorsal fin ondulations Backwaters in lakes and rivers

By the end of this section, you will be able to:
  • Describe the difference between jawless and jawed fishes
  • Discuss the distinguishing features of sharks and rays compared to other modern fishes

Modern fishes include an estimated 31,000 species. Fishes were the earliest vertebrates, with jawless species being the earliest and jawed species evolving later. They are active feeders, rather than sessile, suspension feeders. Jawless fishes—the hagfishes and lampreys—have a distinct cranium and complex sense organs including eyes, distinguishing them from the invertebrate chordates.

Jawless fishes

Jawless fishes are craniates that represent an ancient vertebrate lineage that arose over one half-billion years ago. In the past, the hagfishes and lampreys were classified together as agnathans. Today, hagfishes and lampreys are recognized as separate clades, primarily because lampreys are true vertebrates, whereas hagfishes are not. A defining feature is the lack of paired lateral appendages (fins). Some of the earliest jawless fishes were the ostracoderms (which translates to “shell-skin”). Ostracoderms were vertebrate fishes encased in bony armor, unlike present-day jawless fishes, which lack bone in their scales.

Myxini: hagfishes

The clade Myxini    includes at least 20 species of hagfishes. Hagfishes are eel-like scavengers that live on the ocean floor and feed on dead invertebrates, other fishes, and marine mammals ( [link] ). Hagfishes are entirely marine and are found in oceans around the world, except for the polar regions. A unique feature of these animals is the slime glands beneath the skin that release mucus through surface pores. This mucus allows the hagfish to escape from the grip of predators. Hagfish can also twist their bodies in a knot to feed and sometimes eat carcasses from the inside out.

The skeleton of a hagfish is composed of cartilage, which includes a cartilaginous notochord that runs the length of the body. This notochord provides support to the hagfish’s body. Hagfishes do not replace the notochord with a vertebral column during development, as do true vertebrates.

Petromyzontidae: lampreys

The clade Petromyzontidae    includes approximately 35–40 or more species of lampreys. Lampreys are similar to hagfishes in size and shape; however, lampreys possess some vertebral elements. Lampreys lack paired appendages and bone, as do the hagfishes. As adults, lampreys are characterized by a toothed, funnel-like sucking mouth. Many species have a parasitic stage of their life cycle during which they are ectoparasites of fishes ( [link] ).

Lampreys live primarily in coastal and fresh waters, and have a worldwide distribution, except for in the tropics and polar regions. Some species are marine, but all species spawn in fresh water. Eggs are fertilized externally, and the larvae distinctly differ from the adult form, spending 3 to 15 years as suspension feeders. Once they attain sexual maturity, the adults reproduce and die within days.

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