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Biology 172L – General Biology Lab II Lab 11 Overview of Phylum Chordata

Introduction

This laboratory activity is designed to

introduce you to the characteristics and systematics of Phylum Chordata, the phylum of animals we belong to. In this lab activity you will become familiar the fundamental characteristics shared by members of the phylum as well as the distinguishing characteristics used to classify chordates into subphyla and classes. In addition, you will become introduced to the detailed anatomy of representative chordates (tunicates, lancelots, sharks, bony fish, and amphibians). Finally, you will become familiar with the vertebrate skeleton, including the homologous skeletal features that occur across a wide variety of vertebrates. Be sure to read chapter 34 (pp. 671-707) in your BIOL 172 textbook (Campbell & Reece). Also be sure to bring this texbook, your biology photographic atlas, and a hard copy of this lab description to the lab activity. GENERAL DESCRIPTION

Chordates are distinguished by possession of four fundamental features (Fig. 34.3, p. 673): (1) a cartilagionous rod, the notochord, that extends dorso-medially down the length of the body; (2) a dorsal, hollow nerve cord; (3) pharyngeal gill slits or clefts; and (4) a post-anal tail. However, in some members of the phylum, these features are only apparent during the embryonic stages as they are replaced by other structures during development. For example, in the vertebrates, the notochord is replaced by repeating bony elements called vertebrae.

The chordates are a diverse, successful collection of animals and have occupied a wide variety of habitats in aquatic, terrestrial and aerial environments. They include tunicates, lancelots, lampreys, cartilaginous fishes, bony fishes, amphibians, reptiles, birds and mammals. The vertebrates rival the arthropods in terms of their evolutionary and ecological success on our planet.

They may trace their evolutionary history to Cambrian Radiation some 530 million years ago. Representative fossils from this time period resemble small fish. Major evolutionary trends include enclosing the brain in a cranium,

efficient locomotion via two pairs of appendages, the development of a bony endoskeleton and jaws bearing teeth, and adaptations for living in the terrestrial environment. PHYLUM CHARACTERISTICS 1. bilaterally symmetric eucoelomate

deuterostomes with a complete digestive system

2. rather than possessing a spacious coelom as in the echinoderms, the coelom is filled with body organs surrounded by mesodermal peritoneum and suspended from the body wall

3. notochord, a.cartilaginous rod extending medially down the length of the body; provides flexible support against which muscles can work to provide for locomotion; the notochord is mesodermal in origin and constitutes an endoskeleton

4. dorsal hollow nerve cord typically swelling anteriorly to form a brain

5. pharyngeal gill slits each forming as an outpocketing of the pharynx and invagination of the outer surface of the animal; gills slits may be used for gas exchange and filter feeding

6. muscular postanal tail 7. segmental arrangement of body

musculature & skeleton (somites) in most 8. closed circulatory system, typically with a

muscular heart 9. some of the characteristics listed above are

exhibit in only the larval, embryonic, or juvenile stages, being absent in the adults

10. most exhibit separate sexes; limited, or no, regeneration capabilities means that few can exhibit asexual reproduction (exception = colonial tunicates)

CHORDATE SYSTEMATICS

Subphylum Urochordata

1. tunicates, sea squirts (Fig. 34.4, p. 674), and salps

2. larval stages exhibit typical chordate characteristics which are lost in the adults

3. muscles in the tail don't appear to exhibit segmentation

4. adults are usually sessile filter feeders whose pharynx is modified as a large

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basket with numerous slits 5. body surrounded by a tunic made of a

cellulose-like carbohydrate 6. some are colonial

Subphylum Cephalochordata 1. lancelots (Fig. 34.5, p. 681) 2. fish-like filter-feeding chordates exhibiting

chordate characteristics into the adult stages

3. exhibit segmental arrangement of muscle bands (somites)

4. do not have paired fins and are feeble swimmers, spending most of the time buried part way into the sand

5. circulatory system consists of blood vessels but no distinct heart

Subphylum Craniata 1. craniates (includes hagfishes and

vertebrates) 2. possess a cranium (braincase) 3. epidermis is stratified squamous

epithelium 4. exhibit high level of cephalization 5. neural crest cells (Fig. 34.7, p. 676) 6. well-developed closed circulatory system

with a chambered heart 7. possess a well-developed

excretory/osmoregulatory system (with dorsally-situated kidneys)

8. most (but not all) with hinged jaws and paired appendages in most craniates (i.e., the vertebrates)

Class Myxini i. hagfishes (Fig. 34.9, p. 677) ii. lack jaws and paired appendages iii. notochord persists into adulthood iv. skeleton is cartilaginous v. no longer considered a true

vertebrate vi. gas exchange through gills

Vertebrates a. the notochord is replaced by repeated

bony elements comprising the vertebral column in adults

b. most vertebrates with other endoskeletal components unique to vertebrates Class Cephalaspidomorphi

i. (lampreys; Fig. 34.10, p. 678) ii. lack jaws and paired appendages iii. mineralized vertebral column not

present lampreys, but cartilaginous pipe with pairs of cartilaginous projections (probably homologous with a vertebral column)

iv. notochord persists into adulthood

v. skeleton is cartilaginous vi. gas exchange through gills

Gnathostomes 1) jawed vertebrates 2) possess hinged bony jaws 3) exhibit vertebrae 4) includes jawed fishes and tetrapods

Class Chondrichthyes i. includes sharks, skates, rays, and

chimeras (Fig. 34.15, p. 681) ii. cartilaginous fishes with hinged

jaws iii. paired appendages for swimming

(pelvic and pectoral fins) iv. gas exchange through gills v. two-chambered heart vi. internal fertilization vii. lateral line system viii. digestive system with spiral valve

Class Actinopterygii (Osteichthyes) i. once classified as Class

Osteichthyes which traditionally included all bony fishes (ray-finned fishes, lung fishes, & lobe-finned; Figs. 34.16–34.18, pp. 682-683); now these are placed in separate classes: Actinopterygii, Actinistia, and Dipnoi (this treatment only deals with the former)

ii. jawed fishes with skeleton of bone (calcium phosphate)

iii. mineralized vertebral column replaces notochord in adults

iv. paired appendages for swimming (pelvic and pectoral fins) typically supported by flexible rays or rigid spines

v. gas exchange through gills in a gill chamber covered by an operculum

vi. usually exhibit external fertilization (some internal)

vii. lateral line system viii. most with lungs or swim bladder ix. two-chambered heart x. exhibited a major radiation during

the Devonian (Fig. 34.20, 685) Tetrapods

a) gnathostomes with walking legs b) almost all are air breathers (with

lungs) as adults c) arose from lobe-finned fishes (Fig.

34.40, p. 685) Class Amphibia (Figs. 34.21, p. 685, & 34.22, p. 686)

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i. includes urodeles (salamanders), anurans (frogs), & apodans (caecilians)

ii. air-breathing tetrapods with aquatic larval stages bearing gills (Fig. 34.22, p. 686)

iii. adults with lungs; some gas exchange possible through water-permeable skin

iv. three-chambered heart; usually exhibit external fertilization

v. usually lay eggs, but some bear live young

vi. eggs require moist environment Class Reptilia (Figs. 34.25-30.27, pp. 689-691)

i. includes snakes, lizards, turtles, and crocodilians

ii. air-breathing tetrapods with shelled amniotic eggs

iii. epidermal scales and waterproof skin

iv. most ectothermic poikilotherms (although dinosaurs may have been endotherms)

v. three-chambered heart (although often more efficient than that of amphibians)

vi. internal fertilization vii. ovoparity typical, but a few are

viviparous Class Aves (Figs. 34.28-34.31, pp. 692-694)

i. air-breathing tetrapods with feathers and forelimbs modified as wings (Fig. 43.28a, p. 692)

ii. endothermic iii. four-chambered heart and very

efficient gas exchange iv. hollow bones with internal

strengthening struts (Fig. 34.28b, p. 692)

v. internal fertilization vi. shelled amniotic egg (ovoparous) vii. some classification schemes

include birds in Class Reptilia Class Mammalia

i. includes platypuses, kangaroos, lions, tigers & bears etc.

ii. air-breathing tetrapods that nourish their young with secretions from mammary glands

iii. hair (homologous with reptilian scales and avian feathers)

iv. four-chambered heart v. endothermic homeotherms

vi. diaphragm ventilates the lungs vii. internal fertilization viii. amniotic egg highly modified for

live-bearing in all but the monotremes (which lay eggs)

ix. live-bearing (viviparity) in most (except the monotremes)

x. lower jaw composed of a single bone, the dentary

xi. three middle ear bones present

Procedures and Assignment

I. OVERVIEW OF PHYLUM CHORDATA 1. Examine the specimens of Phylum

Chordata on display. Pay particular attention the characteristics defining the different subphyla and classes, noting similarities, as well as differences. You do not need to report on these in your lab summary. But you should record all of your observations in your lab notebook.

2. Examine the whole mount microscope

slide of the tunicate (ascidian) swimming tadpole larva. Locate and identify its chordate features. Record your observations in your lab notebook only.

3. Examine the whole mount microscope

slide of the adult tunicate Ecteinascidia. Locate and identify the following features: tunic, incurrent siphon, excurrent siphon, atrium, pharyngeal basket, stomach, and intestine. For your lab summary, draw a labeled diagram illustrating the anatomy of a typical adult tunicate.

4. Examine the whole mount microscope

slide of the cephalochordate Amphioxus (=Branchiostoma). Locate and Identify the following features: oral tentacles, pharyngeal gill slits, dorsal nerve cord, notochord, caecum, esophagus, intestine, anus, atriopore, atrium, and segmental muscles. In order to get a better grasp of the three-dimensional anatomy of the animal, compare these observations to those made on the slide illustrating cross sections through various regions of the animal. Record your observations in your lab notebook only.

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II. Anatomy of the Dogfish Shark - Demonstration

The internal and external anatomy of the dogfish shark, Squalus acanthias, will be completed by your instructor as a class demonstration. In addition, dissected display specimens will be available for further study. 1. Examine the external anatomy of the

dogfish shark noting the following features: eye, nares (nostrils), mouth, ampullae of Lorenzini, gill slits, spiracle, anterior dorsal fin, posterior dorsal fin, caudal fin (heterocercal tail), anal fin, pectoral fins, pelvic fins (note claspers if present) and cloaca. For your lab summary, draw a labeled diagram illustrating the external anatomy of the dogfish shark.

2. Your instructor will dissect a specimen of

dogfish shark as a demonstration. Be sure you can recognize the following internal features and their respective functions: heart, gills, gill arches, gill rakers, pharynx, esophagus, stomach, intestine, spiral valve, liver, spleen, gonad (testis in male, ovary in female), kidney, and rectal gland. There is nothing from this section to include in your lab summary.

III. Anatomy of a Bony Fish – Independent

Observation 1. Examine the external anatomy of a fresh

bony fish noting the following features: mouth, eye, nares, operculum, gills, anterior dorsal fin, posterior dorsal fin, caudal fin, anal fin, pectoral fins, pelvic fins, anus, lateral line, scales. For your lab summary, draw a labeled diagram illustrating the external anatomy of the bony fish.

2. Examine the dissected display specimen

and model of a bony fish. Be sure you can recognize the following internal features and their respective functions: heart, gills, gill arches, gill rakers, pharynx, esophagus, stomach, intestine, swim bladder, liver, spleen, gonad (testis in male, ovary in female), kidney, and urinary bladder. You should compare your observations to the dissected display

specimen. There is nothing from this section to include in your lab summary. However, you should record your observations in your lab notebook.

IV. Anatomy of a Frog – Independent

Dissection 1. Examine the external anatomy of a

preserved frog specimen noting the following features: mouth, eye, nares, tympanum, forelimbs, hindlimbs, cloaca. For your lab summary, draw a labeled diagram illustrating the external anatomy of the frog.

2. Lay your frog specimen on its back and

pin down its limbs. Using a scissors and staring from the a position about 0.5 cm anterior from the cloaca, cut open the body cavity from the midline of the ventral surface. Cut all the way up past the heart to the neck, being careful not to damage the underlying organs. Cutting dorsally from the ventral midline at the start and finish of your first cut, create left and right "flaps" of the body wall that may be lifted to expose the underlying internal organs. You may pin these flaps down to hold them open. Be sure you can recognize the following internal features and their respective functions: heart, lungs, pharynx, esophagus, stomach, liver, spleen, gonad (testis in male, ovary in female; be sure to view specimens of both sexes), kidney, gall bladder, and urinary bladder. You should compare your observations to the dissected display specimen. There is nothing from this section to include in your lab summary. However, you should record your observations in your lab notebook.

V. Vertebrate Skeletons 1. Examine the skeletons of the shark, bony

fish, mudpuppy, frog, turtle, pigeon, rat, cat, and human. Note the similarities and differences among these skeletons. There is nothing from this section to include in your lab summary. However, you should record your observations in your lab notebook.

2. Tetrapod bone homologies. Be able to

recognize the following bones (when

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applicable) in all tetrapods: cranium, lower jaw (dentary or mandible), atlas, axis, vertebrae, sacrum, rib, sternum, scapula, clavicle, humerus, radius, ulna, carpals, metacarpals, phalanges, pelvis, femur, patella, tibia, fibula, tarsals, metatarsals. There is nothing from this section to include in your lab summary. However, you should record your observations in your lab notebook.

VOCABULARY stalk notochord pharyngeal gill slit postanal tail somite tunic neural crest vertebral column amniotic egg oviparous ovoviviparous viviparous endotherm ectotherm homeotherm poikilotherm cranium SYSTEMATICS TO KNOW Phylum Chordata Subphylum Urochordata Subphylum Cephalochordata Subphylum Craniata Class Myxini Vertebrates Class Cephalaspidomorphi Gnathostomes Class Chondrithyes Class Actinopterygii Tetrapods Class Amphibia Class Reptilia Class Aves Class Mammalia

Lab Summary Your lab summary should consist of the following:

1. Descriptive title.

2. Short introduction identifying main objectives of the lab activity.

3. Brief description of methods employed. 4. Results and Discussion section

including information requested in the Procedures and Assignment section above and following the appropriate protocols for presenting figures and tables in a laboratory report. Be sure to follow all of the rules from producing figures for lab reports (one figure per page). Corresponding to each figure, there should be a short paragraph that describe the significant features of the figure. Be sure to answer all questions asked throughout the Procedures and Assignment section of this lab description.

5. Short conclusion summarizing what you learned by carrying out this study.

Grassfrog: Dorsal View

Skeleton-General

Dissection

Grassfrog: Ventral View of Digestive System

Grassfrog: Ventral View of Male and Female Reproductive Systems

Lateral View of Articulated Skeleton

Skeleton

Bones VIII-Human Skeleton Entire

Bones I-Skull

Bones II-Vertebrae, Ribs & Sternum, Pelvis

Bones III-Hand and Foot

Bones IV-Clavicle, Scapula, Arm and Leg