DOCSLIB.ORG

Lecture 3 - Early Fishes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Lecture 3 - Early Fishes Lecture 3 - Early Fishes 1. Early Chordates 2. Conodonts 3. Early Vertebrates 4. Jawless fishes 5. Agnatha/ Gnathostomes junction 6. Placoderms 7. Chondrichthyes Early Chordates Cephalochordates (lancelets) most primitive chordates? Urochordates (tunicates and salps) notochord: stiffening rod that - lack vertebrae, brain, eyes, provides support & heart • precursor to spinal chord Cephalochordates are sister to vertebrates • embrace your inner lancelet! Craniata (= Vertebrates) Synapomorphies: Cranium present Cartilage or bone or both are present Heart chambered Neural crests Conodonts • 600 – 200 mybp • “elements” were abundant in fossil beds • Not until 1980’s did we find fossilized soft body parts • cartilaginous head skeleton Agnatha - Jawless Fishes Agnatha • appeared 530 mybp • previously given superclass status • now recognized as paraphyletic • Myxinomorphs now considered separate in own superclass • still used as informal adjective for jawless fishes Agnatha – Ostracoderms • Name means “shell-skinned” referring to bony shield that covered head and thorax • heavily armored • first ossified bones evolve • jawless & no pelvic fin Ostracoderms are paraphyletic …making “ostracoderm” a false designation • likely 4 superclasses of jawless fishes Hagfishes - Class Myxini 77 species Live deep – scavengers & predators Strictly marine • isoosmotic - no osmoregulation Hagfishes - Class Mixini • 4 rudimentary hearts • 70-200 pairs of slime glands • eye spots • lack vertebrae Rasping tongue Hagfish feeding Hagfishes - Class Myxini Reproduction….? • cash prize for information on the reproduction of Myxine glutinosa remains unclaimed since 1854 from the Royal Danish Academy of Sciences Development • No larval stage, direct development from eggs Lampreys - Class Petromyzontida ~ 42 species Osmoregulate - found in freshwater and ocean Larval stage called ammocoete Ammocoete undergo metamorphosis Ammocoete filter feeds Lampreys Lampreys Reproduction • semelparous • males build nest • eggs hatch after 12-14 days and ammocoete emerges • ammocoete burrows into mud or silt in river or stream, with head emerged filter feeding • can stay like this for up to seven years Non-parasitic spp. • form spp. pairs with parasitic spp. Agnatha - Gnathostomata Junction Gnathostomes: jawed vertebrates Agnatha - Gnathostomata Junction Gnathostomes: jawed vertebrates Synapomorphies: • Jaws modified from gill arches • Paired limbs • Vertebral centra usually present Previously thought that a shark like ancestor gave rise to all jawed vertebrates but this fossil debunks that hypothesis • characteristics of both Placoderms and Osteichthyans Entelognathus primordialis Entelognathus primordialis, Placoderms “Plate-skinned” • fresh & salt water • arose ~430 mybp • disappeared ~350 mybp Placoderms Synapomorphies: Head and shoulder girdles with dermal bony plates Five gill arches - evolved towards reduced armament Chondrichthyes - Cartilaginous fishes • arose ~420 mybp Chondrichthyes - Cartilaginous fishes • extant cartilaginous fishes Chondrichthyes - Cartilaginous fishes Synapomorphies: • Cartilaginous skeleton, calcified but not ossified • Skull with no sutures Chondrichthyes - Cartilaginous fishes Synapomorphies (cont’d): • Internal fertilization with claspers • High blood concentration of urea Chondrichthyes - Cartilaginous fishes Reproduction oviparous: lay eggs • ~40% species viviparous: live birth • ~10% species ovoviviparous: egg hatches internally and give live birth • ~50% species Chondrichthyes - Cartilaginous fishes Split into two subclasses: Elasmobranchii Holocephali (sharks & rays) (ratfishes) Holocephali • “whole-head” • oviparous Holocephalans - Chimaeras - Ratfish Synapomorphies: Gill cover over 4 gill openings Upper jaw fused to cranium Holocephalans - Chimaeras - Ratfish Some species possess head claspers - more speciose in the past.
Load more

Recommended publications
  • (= Amphioxus) Branchiostoma Floridae
    MARINE ECOLOGY PROGRESS SERIES Vol. 130: 71-84,1996 Published January 11 Mar Ecol Prog Ser Larval settlement, post-settlement growth and secondary production of the Florida lancelet (= amphioxus) Branchiostoma floridae M. D. Stokes* Marine Biology Research Division, Scripps Institution of Oceanography, La Jolla, California 92093-0202, USA ABSTRACT A population of Branch~ostomaflondae in Tampa Bay, Flonda, USA was sieved from the substratum frequently (often daily) from June 1992 through September 1994 Body lengths were mea- sured for 54264 luvenlle and adult lancelets The breedlng season lasted each year from early May through early September and newly metamorphosed lancelets settled as luveniles from late May through mid October, dunng this period of the year dlstinct settlements occurred approxmately every 1 to 3 wk Post-settlement growth was followed as changes in modal length on size-frequency histo- grams Changes in cohort growth over this peliod were compared to several different simple and seasonally oscillating growth models The von Bertalanffy functlon in smple and oscillating forms provided the best estmates of lancelet growth The lancelets grew in summer (almost 0 5 mm d-' in recently settled luveniles), but growth slowed and almost ceased durlng wlnter B flondae can llve at least 2 yr and can reach a maxlmum length of 58 mm The maximal secondary productlon was 61 53 g m-' yrrl (ash-free dry welght) and the productlon to biomass ratio was 11 64 Population den- sities at the study site ranged from about 100 to 1200 lancelets m ' KEY WORDS: Lancelet . Amphioxus . Branchiostorna flondae . Growth . Production . Breeding season .
    [Show full text]
  • Abstract Introduction
    Marine and Freshwater Miscellanea III KEY TRAITS OF AMPHIOXUS SPECIES (CEPHALOCHORDATA) AND THE GOLT1 Daniel Pauly and Elaine Chu Sea Around Us, Institute for the Oceans and Fisheries University of British Columbia, Vancouver, B.C, Canada Email: [email protected] Abstract Major biological traits of amphioxus species (Cephalochordata) are presented with emphasis on the size reached by their 32 valid species in the genera Asymmetron (2 spp.), Branchiostoma (25 spp.), and Epigonichthys (5 spp.) and on related features, i.e., growth parameters and size at first maturity. Overall, these traits combined with features of their respiration, suggest that the cephalochordates conform to the Gill Oxygen Limitation Theory (GOLT), which relates the growth performance of water-breathing ectotherms to the surface area of their respiratory organ(s). Introduction The small fish-like animals know as ‘lancelet‘ or ‘amphioxius’ belong the subphylum Cephalochordata, which is either a sister group, or related to the ancestor of the vertebrate animals (see Garcia-Fernàndez and Benito-Gutierrez 2008). The cephalochordates consist of 3 families (the Asymmetronidae, Epigonichthyidae and Branchiostomidae), with one genus each, Asymmetron (2 spp.), Branchiostoma (24 spp.) and Epigonichthys (6 spp.), as detailed in Table 1 and SeaLifeBase (www.sealifebase.org). This contribution is to assemble some of the basic biological traits of lancelets (Figure 1), notably the maximum size each of their 34 species can reach, which is easily their most important attribute, though it is often ignored (Haldane 1926). Finally, reported lengths at first maturity of cephalochordates were related to the corresponding, population-specific maximum length, to test whether these animals mature as predicted by the Gill- Oxygen Limitation Theory (GOLT; see Pauly 2021a, 2021b).
    [Show full text]
  • Updated Checklist of Marine Fishes (Chordata: Craniata) from Portugal and the Proposed Extension of the Portuguese Continental Shelf
    European Journal of Taxonomy 73: 1-73 ISSN 2118-9773 http://dx.doi.org/10.5852/ejt.2014.73 www.europeanjournaloftaxonomy.eu 2014 · Carneiro M. et al. This work is licensed under a Creative Commons Attribution 3.0 License. Monograph urn:lsid:zoobank.org:pub:9A5F217D-8E7B-448A-9CAB-2CCC9CC6F857 Updated checklist of marine fishes (Chordata: Craniata) from Portugal and the proposed extension of the Portuguese continental shelf Miguel CARNEIRO1,5, Rogélia MARTINS2,6, Monica LANDI*,3,7 & Filipe O. COSTA4,8 1,2 DIV-RP (Modelling and Management Fishery Resources Division), Instituto Português do Mar e da Atmosfera, Av. Brasilia 1449-006 Lisboa, Portugal. E-mail: [email protected], [email protected] 3,4 CBMA (Centre of Molecular and Environmental Biology), Department of Biology, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal. E-mail: [email protected], [email protected] * corresponding author: [email protected] 5 urn:lsid:zoobank.org:author:90A98A50-327E-4648-9DCE-75709C7A2472 6 urn:lsid:zoobank.org:author:1EB6DE00-9E91-407C-B7C4-34F31F29FD88 7 urn:lsid:zoobank.org:author:6D3AC760-77F2-4CFA-B5C7-665CB07F4CEB 8 urn:lsid:zoobank.org:author:48E53CF3-71C8-403C-BECD-10B20B3C15B4 Abstract. The study of the Portuguese marine ichthyofauna has a long historical tradition, rooted back in the 18th Century. Here we present an annotated checklist of the marine fishes from Portuguese waters, including the area encompassed by the proposed extension of the Portuguese continental shelf and the Economic Exclusive Zone (EEZ). The list is based on historical literature records and taxon occurrence data obtained from natural history collections, together with new revisions and occurrences.
    [Show full text]
  • Fishes Scales & Tails Scale Types 1
    Phylum Chordata SUBPHYLUM VERTEBRATA Metameric chordates Linear series of cartilaginous or boney support (vertebrae) surrounding or replacing the notochord Expanded anterior portion of nervous system THE FISHES SCALES & TAILS SCALE TYPES 1. COSMOID (most primitive) First found on ostracaderm agnathans, thick & boney - composed of: Ganoine (enamel outer layer) Cosmine (thick under layer) Spongy bone Lamellar bone Perhaps selected for protection against eurypterids, but decreased flexibility 2. GANOID (primitive, still found on some living fish like gar) 3. PLACOID (old scale type found on the chondrichthyes) Dentine, tooth-like 4. CYCLOID (more recent scale type, found in modern osteichthyes) 5. CTENOID (most modern scale type, found in modern osteichthyes) TAILS HETEROCERCAL (primitive, still found on chondrichthyes) ABBREVIATED HETEROCERCAL (found on some primitive living fish like gar) DIPHYCERCAL (primitive, found on sarcopterygii) HOMOCERCAL (most modern, found on most modern osteichthyes) Agnatha (class) [connect the taxa] Cyclostomata (order) Placodermi Acanthodii (class) (class) Chondrichthyes (class) Osteichthyes (class) Actinopterygii (subclass) Sarcopterygii (subclass) Dipnoi (order) Crossopterygii (order) Ripidistia (suborder) Coelacanthiformes (suborder) Chondrostei (infra class) Holostei (infra class) Teleostei (infra class) CLASS AGNATHA ("without jaws") Most primitive - first fossils in Ordovician Bottom feeders, dorsal/ventral flattened Cosmoid scales (Ostracoderms) Pair of eyes + pineal eye - present in a few living fish and reptiles - regulates circadian rhythms Nine - seven gill pouches No paired appendages, medial nosril ORDER CYCLOSTOMATA (60 spp) Last living representatives - lampreys & hagfish Notochord not replaced by vertebrae Cartilaginous cranium, scaleless body Sea lamprey predaceous - horny teeth in buccal cavity & on tongue - secretes anti-coaggulant Lateral Line System No stomach or spleen 5 - 7 year life span - adults move into freshwater streams, spawn, & die.
    [Show full text]
  • Sponges Cnidarians Chordates Brachiopods Annelids Molluscs Ediacaran Arthropods 635 Cambrian PALEOZOIC PROTEROZOIC 605 Time (Mil
    © 2014 Pearson Education, Inc. 1 Sponges Cnidarians Echinoderms Chordates Brachiopods Annelids Molluscs Arthropods PROTEROZOIC PALEOZOIC Ediacaran Cambrian 635 605 575 545 515 485 0 Time (millions of years age) © 2014 Pearson Education, Inc. 2 Food particles in mucus Choanocyte Collar Flagellum Choanocyte Phagocytosis of Amoebocyte food particles Pores Spicules Water flow Amoebocytes Azure vase sponge (Callyspongia plicifera) © 2014 Pearson Education, Inc. 3 (a) Hydrozoa (b) Scyphozoa (c) Anthozoa © 2014 Pearson Education, Inc. 4 15 µm 75 µm (a) Valeria (800 mya): (b) Spiny acritarch roughly spherical, no (575 mya): about five structural defenses, times larger than soft-bodied Valeria and covered in hard spines © 2014 Pearson Education, Inc. 5 (a) Radial symmetry (b) Bilateral symmetry © 2014 Pearson Education, Inc. 6 Body cavity Body covering (from ectoderm) Tissue layer lining body cavity and suspending Digestive tract internal organs (from endoderm) (from mesoderm) © 2014 Pearson Education, Inc. 7 Porifera Metazoa Ctenophora ANCESTRAL Eumetazoa PROTIST Cnidaria Deuterostomia Hemichordata 770 million Echinodermata years ago 680 million Chordata years ago Lophotrochozoa Lophotrochozoa Platyhelminthes Bilateria Rotifera Ectoprocta Brachiopoda 670 million years ago Mollusca Ecdysozoa Annelida Nematoda Arthropoda © 2014 Pearson Education, Inc. 8 © 2014 Pearson Education, Inc. 9 Notochord Dorsal, hollow nerve cord Muscle segments Mouth Anus Post-anal tail Pharyngeal slits or clefts © 2014 Pearson Education, Inc. 10 (a) Lancelet (b) Tunicate
    [Show full text]
  • New Records of the Lancelet Branchiostoma Lanceolatum in Scottish Waters
    The Glasgow Naturalist (online 2019) Volume 27, Part 1 New records of the lancelet Branchiostoma lanceolatum in Scottish waters M. O’Reilly1, S. Nowacki1, M. Baptie1, E. Gerrie1 & M. MacKenzie2 1Scottish Environment Protection Agency, Angus Smith Building, 6 Parklands Avenue, Eurocentral, Holytown, North Lanarkshire ML1 4WQ 2Scottish Environment Protection Agency, Graesser House, Fodderty Way, Dingwall IV15 9XB 1E-mail: [email protected] ABSTRACT New records of the lancelet Branchiostoma lanceolatum from Scottish waters are presented. Most of the records originate from sublittoral monitoring around fish farms from Orkney, Shetland, the Western Isles, the Isles of Skye and Mull, but also from a distillery discharge in the Firth of Clyde and a plankton survey in the Sea of the Hebrides. Lancelets were recovered in sediment grab samples from 6 - 60 m depth. Some recent accounts of intertidal lancelets are also cited. The lancelets appear to prefer coarser sediments and in the fish farm surveys were found predominantly at reference sites, away from the immediate influence of farm deposition. INTRODUCTION The lancelet Branchiostoma lanceolatum (Pallas, 1774) is an obscure, vaguely fish-like creature, up to 8 cm long, which lives buried in sand or coarse sediments in British seas. Its body is laterally compressed, pinkish white in colour, and pointed at both ends with a lance- like tail fin (Fig. 1). There are no paired fins, nor eyes, nor even a well-defined head, and it has only a small mouth surrounded by cirri, used to filter organic matter from the surrounding water. It has a dorsal notochord and segmented muscle blocks allowing it to swim in a sinusoidal fish-like manner, but no backbone, and it is therefore classified as an invertebrate (Barnes, 2015).
    [Show full text]
  • Biology of Chordates Video Guide
    Branches on the Tree of Life DVD – CHORDATES Written and photographed by David Denning and Bruce Russell ©2005, BioMEDIA ASSOCIATES (THUMBNAIL IMAGES IN THIS GUIDE ARE FROM THE DVD PROGRAM) .. .. To many students, the phylum Chordata doesn’t seem to make much sense. It contains such apparently disparate animals as tunicates (sea squirts), lancelets, fish and humans. This program explores the evolution, structure and classification of chordates with the main goal to clarify the unity of Phylum Chordata. All chordates possess four characteristics that define the phylum, although in most species, these characteristics can only be seen during a relatively small portion of the life cycle (and this is often an embryonic or larval stage, when the animal is difficult to observe). These defining characteristics are: the notochord (dorsal stiffening rod), a hollow dorsal nerve cord; pharyngeal gills; and a post anal tail that includes the notochord and nerve cord. Subphylum Urochordata The most primitive chordates are the tunicates or sea squirts, and closely related groups such as the larvaceans (Appendicularians). In tunicates, the chordate characteristics can be observed only by examining the entire life cycle. The adult feeds using a ‘pharyngeal basket’, a type of pharyngeal gill formed into a mesh-like basket. Cilia on the gill draw water into the mouth, through the basket mesh and out the excurrent siphon. Tunicates have an unusual heart which pumps by ‘wringing out’. It also reverses direction periodically. Tunicates are usually hermaphroditic, often casting eggs and sperm directly into the sea. After fertilization, the zygote develops into a ‘tadpole larva’. This swimming larva shows the remaining three chordate characters - notochord, dorsal nerve cord and post-anal tail.
    [Show full text]
  • Class Wars: Chondrichthyes and Osteichthyes Dominance in Chesapeake Bay, 2002-2012
    Class Wars: Chondrichthyes and Osteichthyes dominance in Chesapeake Bay, 2002-2012. 01 July 2013 Introduction The objective of this analysis was to demonstrate a possible changing relationship between two Classes of fishes, Osteichthyes (the bony fishes) and Chondrichthyes (the cartilaginous fishes) in Chesapeake Bay based on 11 years of monitoring. If any changes between the two Classes appeared to be significant, either statistically or anecdotally, the data were explored further in an attempt to explain the variation. The Class Osteichthyes is characterized by having a skeleton made of bone and is comprised of the majority of fish species worldwide, while the Chondrichthyes skeleton is made of cartilage and is represented by the sharks, skates, and rays (the elasmobranch fishes) and chimaeras1. Many shark species are generally categorized as apex predators, while skates and rays and some smaller sharks can be placed into the mesopredator functional group (Myers et al., 2007). By definition, mesopredators prey upon a significant array of lower trophic groups, but also serve as the prey base for apex predators. Global demand for shark and consequential shark fishing mortality, estimated at 97 million sharks in 2010 (Worm et al., 2013), is hypothesized to have contributed to the decline of these apex predators in recent years (Baum et al., 2003 and Fowler et al., 2005), which in turn is suggested to have had a cascading effect on lower trophic levels—an increase in mesopredators and subsequent decrease in the prey base (Myers et al., 2007). According to 10 years of trawl survey monitoring of Chesapeake Bay, fish species composition of catches has shown a marked change over the years (Buchheister et al., 2013).
    [Show full text]
  • Decelerated Genome Evolution in Modern Vertebrates Revealed by Analysis of Multiple Lancelet Genomes
    ARTICLE Received 20 May 2014 | Accepted 18 Nov 2014 | Published 19 Dec 2014 DOI: 10.1038/ncomms6896 OPEN Decelerated genome evolution in modern vertebrates revealed by analysis of multiple lancelet genomes Shengfeng Huang1, Zelin Chen1, Xinyu Yan1, Ting Yu1, Guangrui Huang1, Qingyu Yan1, Pierre Antoine Pontarotti2, Hongchen Zhao1, Jie Li1, Ping Yang1, Ruihua Wang1, Rui Li1, Xin Tao1, Ting Deng1, Yiquan Wang3,4, Guang Li3,4, Qiujin Zhang5, Sisi Zhou1, Leiming You1, Shaochun Yuan1, Yonggui Fu1, Fenfang Wu1, Meiling Dong1, Shangwu Chen1 & Anlong Xu1,6 Vertebrates diverged from other chordates B500 Myr ago and experienced successful innovations and adaptations, but the genomic basis underlying vertebrate origins are not fully understood. Here we suggest, through comparison with multiple lancelet (amphioxus) genomes, that ancient vertebrates experienced high rates of protein evolution, genome rearrangement and domain shuffling and that these rates greatly slowed down after the divergence of jawed and jawless vertebrates. Compared with lancelets, modern vertebrates retain, at least relatively, less protein diversity, fewer nucleotide polymorphisms, domain combinations and conserved non-coding elements (CNE). Modern vertebrates also lost substantial transposable element (TE) diversity, whereas lancelets preserve high TE diversity that includes even the long-sought RAG transposon. Lancelets also exhibit rapid gene turnover, pervasive transcription, fastest exon shuffling in metazoans and substantial TE methylation not observed in other invertebrates. These new lancelet genome sequences provide new insights into the chordate ancestral state and the vertebrate evolution. 1 State Key Laboratory of Biocontrol, Guangdong Key Laboratory of Pharmaceutical Functional Genes, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China. 2 Evolution Biologique et Mode´lisation UMR 7353 Aix Marseille Universite´/CNRS, 3 Place Victor Hugo, 13331 Marseille, France.
    [Show full text]
  • The Absence of Sharks from Abyssal Regions of the World's Oceans
    Proc. R. Soc. B (2006) 273, 1435–1441 doi:10.1098/rspb.2005.3461 Published online 21 February 2006 The absence of sharks from abyssal regions of the world’s oceans Imants G. Priede1,*, Rainer Froese2, David M. Bailey3, Odd Aksel Bergstad4, Martin A. Collins5, Jan Erik Dyb6, Camila Henriques1, Emma G. Jones7 and Nicola King1 1University of Aberdeen, Oceanlab, Newburgh, Aberdeen AB41 6AA, UK 2Leibniz-Institut fu¨r Meereswissenschaften, IfM-GEOMAR, Du¨sternbrooker Weg 20, 24105 Kiel, Germany 3Marine Biology Research Division, Scripps Institution of Oceanography, UCSD 9500 Gilman Drive, La Jolla, CA 92093-0202, USA 4Institute of Marine Research, Flødevigen Marine Research Station, 4817 His, Norway 5British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK 6Møre Research, Section of Fisheries, PO Box 5075, 6021 Aalesund, Norway 7FRS Marine Laboratory, 375 Victoria Road, Aberdeen AB11 9DB, UK The oceanic abyss (depths greater than 3000 m), one of the largest environments on the planet, is characterized by absence of solar light, high pressures and remoteness from surface food supply necessitating special molecular, physiological, behavioural and ecological adaptations of organisms that live there. Sampling by trawl, baited hooks and cameras we show that the Chondrichthyes (sharks, rays and chimaeras) are absent from, or very rare in this region. Analysis of a global data set shows a trend of rapid disappearance of chondrichthyan species with depth when compared with bony fishes. Sharks, apparently well adapted to life at high pressures are conspicuous on slopes down to 2000 m including scavenging at food falls such as dead whales.
    [Show full text]
  • Great White Shark Carcharodon Carcharias
    Great White Shark Carcharodon carcharias Great White Sharks (Great Whites) are large predators at the top of the marine food chain. They are in the same class as all sharks and rays (Chondrichthyes) – this group is different from other fish as their skeleton is made from cartilage instead of bone. They have an average length of four to five metres, but can grow up to seven metres. Using their powerful tails to propel them, these sharks can move Bioregion resources through the water at up to 24 km per hour. Their mouths are lined with up to 300 serrated triangular teeth arranged in several rows. Diet Great Whites are able to use electroreception (the ability to detect weak electrical currents) to find and attack prey without seeing it. This can be useful in murky water or when their prey is hidden under sediment. This gives them the ability to navigate by sensing the Earth’s magnetic field. They have a strong sense of smell which is also useful in detecting prey. Contrary to some people’s beliefs, they often only attack humans to ‘sample bite’ and do not usually choose to eat human flesh, preferring marine mammals such as seals and sea lions. They are also known to feed on dolphins, octopus, squid, other sharks, rays and lobster, fish, crabs and seabirds. Breeding Great Whites have a low reproduction rate that makes it difficult for species numbers to recover. Males mature at eight to ten years and females mature at 12-18 years. Females give birth to two to ten pups once every two to three years.
    [Show full text]
  • Axial Endoskeleton of a Bony Fish
    Fish Form & Funcon Heyer Axial endoskeleton of a bony fish Fish Axial skeleton: Cranium & vertebral column • Fishes — aquatic vertebrates; axial skeleton only – Closed, single-circuit circulatory system • Class- Aganatha — jawless fishes • Class- Chondrichthyes — cartilaginous fishes Vertebra • Class- Osteichthyes — bony fishes Figure 3.02 Locomoon with an axial skeleton Fishes Class- Aganatha — jawless fishes • ~120 extant species (lampreys; hagfish) • Inner layer of mesoderm bloc becomes skeletal • Cartilaginous skeleton vertebrae • Jawless, suctorial mouth with many teeth • Outer layer becomes & protrusible toothed tongue myomere (muscle band) • Medial fin fold; No lateral (paired) fins • Proximal edge of myomere aaches to vertebrae • Distal edge of myomere projects posterio-laterally to insert into connecve ssue of skin • ... Contracon of muscle → lateral flexing body Fishes Fishes Class- Chondrichthyes — cartilaginous fishes Class- Chondrichthyes — cartilaginous fishes • Cartilaginous skeleton, but unique bone tissue present • Cartilaginous skeleton, but unique bone tissue present • Semi-rigid paired lateral fins connected across ventral body wall Subclass- Holocephali — ~ 40 spp. (chimeras) Subclass- Elasmobranchii — ~1,000 spp. (sharks; rays) • 5–7 gill slits [elasmo-branch: “strap gills”] • Protrusible upper jaw not fused to skull • Thick skin with dermal denticles Fins supprted by cartilagenous rods 1 Fish Form & Funcon Heyer Fishes Fishes Class- Chondrichthyes — cartilaginous fishes Class- Chondrichthyes — cartilaginous fishes • Cartilaginous skeleton, but unique bone tissue present Subclass- Elasmobranchii — ~1,000 spp. (sharks; rays) • Semi-rigid paired lateral fins connected across ventral body wall • Protrusible upper jaw not fused to skull CAT scan of a great white shark Lateral fins 1. Jaw opens (pectorals & pelvics) 2. Hyoid arch located ventrally springs jaw forward 3. Jaw protrudes Pelvic fins located near vent & closes 4.
    [Show full text]