LABORATORY 3

 

Most representatives of the phyla studied in this laboratory are aquatic organisms.  Most mollusks are marine though there are some freshwater and terrestrial gastropods (snails, slugs).  There are also a few freshwater bivalves (mussels).  The most sophisticated mollusks are the cephalopods (squids and octopods), which have developed eyes and a foot that is divided into tentacles.

 

Echinoderms and chordates are both deuterostomes meaning that the anus is the first opening of the digestive tract to form in the embryo.  Echinoderms are characterized by a spiny skin created by the dermal skeleton with calcium ossicles and the spines scattered over the surface.  Respiration occurs through dermal branchiae also on the surface, which bring the body fluids close to the surrounding seawater so that gas exchange can occur.  The radial symmetry of the adult echinoderms is secondary since the larvae and ancestral forms are bilateral.

 

The Chordates all share four characteristics, which are evident in the members at some point in their development.  These characteristics are 1) gill slits (pharyngeal pouches), 2) notochord (an elastic rod which provides some skeletal support), 3) dorsal tubular nerve chord, and 4) a post-anal tail.  Future laboratories will include well-developed chordate specimens (Campbell, Figure 34.1, p.631).  In this lab, you will concentrate on less familiar chordate members and you will be looking not only for the four chordate characteristics, but you will be comparing members of the three subphyla Urochordata, Cephalochordata, and Vertebrata.

 

PHYLUM MOLLUSCA

 

Preserved specimens:   

Observe the representative specimens of the phylum Mollusca provided for this lab.  You will be expected to identify these representatives as mollusks and to name the class of mollusks that each represents. (Campbell pp.609-612; Atlas p. 113: Know four classes in Table 7.4; Chiton Figure 7.52; and Nautilus Figure 7.58).

                      

Clam Model:         Obtain the museum jar and model of the dissected clam, a common bivalve.  Locate the following shell, mantle, foot, gills, mouth, stomach, intestine, anus, incurrent  and excurrent siphons.  What happens when a foreign particle is caught between the mantle and the shell of some molluskss

 

 

Preserved specimens:   

Observe the representative specimens of the phylum Echinodermata provided for this lab.  Be able to identify these representatives as echinoderms and to name the class to which each belongs. (Campbell pp.624-629; Atlas pp.126-129; Know the five classes in Table 7.7)

"  STARFISH (Asterias) DISSECTION:  (Work with a partner)

 

1  Obtain a starfish specimen and rise well under running water.  Place the specimen oral side down in your dissecting pan. 

 

2  Study the spine surface.  Refer to Atlas to locate components of the spiny skin:  spine, pedicellariae, and dermal branchiae (skill gills). You may use a hand lens and/or dissecting microscope.

 

3  Locate the madreporite on the aboral surface.  Identify the rays or antimeres.  Sketch the aboral side and label the bivium, trivium, and anterior ray (which is directly opposite the madreporite and is, therefore, the central ray of the trivium).

 

4  Turn the specimen over and observe the oral side.  Locate the mouth, the peristome, the ambulacral grooves, and the numerous tube feet. 

 

5  Using your scissors, remove about one-half inch of the anterior ray.  Then carefully cut through the aboral wall along each side of the ray and around the top margin of the central disc. (Recall that the stone canal connects the madreporite with the internal ring canal.  Try not to detach the madreporite from the stone canal but attempt to expose the stone canal.)

 

6  Examine the large perivisceral cavity.  It will be lined with a peritoneum and the coelom is fluid-filled (There is no closed circulatory system.)    Each ray will contain large paired pyloric caecua (caecum - singular).  Notice that the glands unite in each ray to from a common duct which empties into the pyloric stomach. 

 

7   At the base of each ray is a pair of gonads, which constitute the reproductive system.  These organisms are dieocious, but it is impossible to distinguish between the gonads.  Are these organisms sexually dimorphics 

 

8   Trace the unique water vascular system in the starfish beginning with the madreporite and ending with the tube feet.  Record this pathway in your laboratory notebook. 

 

9  Dispose of your dissected specimen in the container designated by your instructor.  Rinse and drain your dissecting pan well being careful that solid parts are not washed into the sink.  Stack the dissecting trays so that they will air dry.

PHYLUM CHORDATA

 

The phylum Chordata includes three broad groups:  the urochordates (or “tail cords”), the cephalochordates (or “head cords”), and the vertebrates (chordate with a back”bone”).  The following three slides are selected to permit you to observe a major representative of each group with the goal of observing the chordate characteristics in each.  Chapter 34 in your Campbell text includes excellent figures to assist you here.  Also consult your Atlas.

 

        Subphylum Urochordata (Tunicates)

1 Tunicate larvum – This organism is also known as a sea squirt because it can force water from the excurrent siphon  producing a “squirt.”  Why are these organisms called tunicatess  Why are these organisms urochordatess Recall that these marine organisms are sessile as adults.  The free-swimming larvum undergoes a complete and remarkable metamorphosis into this sessile adult.  Examine the slide.  Draw the organism and observe the chordate characteristics.  Refer to the diagram in your text. (The larvum on the slide will probably remind you of a tadpole.)

 

Subphylum Cephalochordata (Lancelets)

               2 Amphioxus – This organism is commonly called the lancelet because of its blade like shape.  What is the significance of taxon name cephalochordatas Lancelets spend most of their time burrowed into the mud exposing the anterior end.  They are suspension-feeders and food is trapped in mucous nets on the gill slits.  Refer to figures on page 632 of you text and page 130 of your Atlas while examining the microscope slide.  Draw the organism and label tentacles (cirri), pharynx, gill slits, notochord, dorsal tubular nerve chord, and post-anal tail.  In addition, notice the chevron-like muscle blocks called myomeres, which illustrate the segmental arrangement (metamerism) of muscle groups.  These muscle groups developed from somites (blocks of mesoderm) on each side of the notochord.  Contraction of the myomeres on either side of the flexible notochord produces movement in a sinusoidal pattern.

 

Subphylum Vertebrata

3  Ammocoetoes (sea lamprey) larvum – The lamprey is a member of the most primitive vertebrate class Agnatha.  These are the jawless fishes possessing cartilaginous skeletons.  The larvum is actually a suspension-feeder that looks very much like the adult lancelet (cephalochordata).  Observe the microscope slide and examine the specimen for the chordate characteristics and label your diagram. 

 

               Observe the adult preserved specimen of the lamprey .  Identify the anterior and posterior 

               dorsal fins, mouth, horny teeth, external gill slits, eye, and caudal fin.

Frog Dissection will be performed the week of March 1. 

Dissection of the Frog:  Rana catesbiana

 

In this part of the laboratory you will begin the dissection of the frog.  The frog is representative of lower vertebrates.  You will compare this organism and its internal structure with another vertebrate mammal -- the fetal pig -- during your laboratory next week. 

 

Amphibians were the first tetrapods.  Though there are many differences, a great deal of the knowledge gained from the study of the frog is applicable to the human body.  As you work this week on the frog and next week on the pig, think actively about similarities and differences compared with your own body.   

 

EXTERNAL FEATURES

 

These bullfrogs, Rana catesbiana, have been preserved and contain red and blue latex injected into the circulatory system for easier recognition of major vessels.  Which vessels are injected with red latex ?  An incision has been made in your specimen for this purpose.  First, observe the external features of  your specimen.  Identify the mouth, external nares, eyes, eyelids, and tympanic membrane on the head.  There are two pairs of limbs on the trunk :  the short forelimb consisting of the arm, forearm, and hand with four digits, and the muscular hindlimb consisting of a thigh, leg, and foot with five digits. Also observe the cloacal opening.  Externally, the male can be distinguished from the female by the enlarged pad on the innermost finger.

 

MOUTH CAVITY

 

Pry open the mouth and rinse if necessary.  Locate the following structures:  the maxillary teeth on the margin of the upper jaw; the vomerine teeth on the palate which are used for holding food, not for mastication, the internal nares; the Eustachian aperture opening into the auditory tube; the large transverse slit opening into the esophagus; the glottis opening into the trachea and leading to the lungs; the vocal sac apertures in the male: and the fleshy tongue.

 

GENERAL INTERNAL ANATOMY

 

Prepare to open the abdominal and thoracic cavities by raising the skin on the ventral surface and making a longitudinal cut through the skin from the pelvis to the tip of the lower jaw.  Make short transverse cuts at the anterior and posterior ends of the trunk and fold back the flaps of skin.

Before continuing, note the following muscles:  the external oblique, the pectoralis, and the rectus abdominus.  Also find the linea alba -- a white stripe that makes the position of the ventral abdominal vein.  make a longitudinal incision a little to one side of the linea alba through the body wall including the sternum, to the posterior end of the lower jaw.  Be careful not to injury the abdominal and the internal organs within the coelom. 

 

DIGESTIVE AND RELATED ORGANS

 

Using the picture in your Atlas on page 182, identify the following: the three lobes of the liver, the gall bladder, the bile duct, the esophagus, the stomach, the pylorus, the pancreas, the duodenum, the ileum, the large interstice,  the urinary bladder, the cloaca, the spleen, and the mesentery which supports the various organs.  The cloaca is a common depository for the products of the digestive, urinary, and reproductive systems.  It is seen in all vertebrates except most mammals.  Also, note the heart within the pericardium and the pair of lungs. 

 

UROGENITAL ORGANS

 

In the female frogs, note the large ovaries, the coiled oviducts, the yellow fat bodies, the kidneys, and the bilobed urinary bladder.  There may be numerous eggs contained with the ovaries. In the male, note the testes, and the fat bodies, the kidneys, and the bladder.   The testis is a small spherical organ in males which rests on the kidneys.

 

SKELETON

 

Observe the skeletons.  Compare the frog skeleton (Atlas) with the human skeleton.  Both the frog skeleton and the human skeleton are divided into the 1) axial skeleton, which consists of the skull and vertebral column and 2) the appendicular skeleton which consists of the pectoral girdles and bones of the arms and the pelvic girdle and the bones of the legs.  The vertebral column consists of 10 bones.  There is one cervical vertebrae: the atlas which articulates with the cranium.  The next seven bones are the abdominal vertebrae, then the sacrum, which is followed by the last and longest vertebral bone -- the urostyle. Locate and be able to identify these bones on the frog:

 

       

                                            

MUSCLES

 

Remove the skin from one arm and leg your specimen.  note the smooth glass appearance of the musculature which covers the skeleton.  Locate the following muscles -- first in your Atlas. 

 

       

 

 

 

CIRCULATORY SYSTEM

Using the illustrations in your Atlas, locate the following components of the circulatory system: