LAB: Morphology and Invertebrates I

OVERVIEW

In this lab you willlearn various anatomical terms and study several representative animals of four invertebrate phyla. These organisms differ in some aspects, but each, to some extent engages in food gathering, digestion, excretion, responsiveness to the environment, gas exchange and reproduction. Inorder to examine the anatomy and physiology of various organisms you will need to build a vocabulary of terms that refer to body planes, sections and relative location. The section on morphological terms should help. Fill out the Comparative Anatomy Chart as you complete each activity. You will add to this table of information for the next few weeks.

OBJECTIVES

Before doing this lab you should understand:

  • Phylogenic tree
  • Body symmetry, Germ layers and gastrulation

After doing this lab you should be able to:

  • Identify the ways in which major invertebrate phyla solve problems of living in a freshwater, marine, or terrestrial environment. Think of locomotion, body support, protection, food acquisition, osmoregulation and water balance.
  • Describe the various body plans of organisms and relate them to the ecology of organisms
  • Recognize features, which distinguish animals from different phyla
  • Discuss the similarities and differences in the organ systems of the phyla examined
  • Define and discuss: radial and bilateral symmetry, cephalization, and open vs. closed circulatory systems
  • Compare modes of locomotion
  • Be familiar with examples of various members of these phyla

Morphology

Know the following anatomical terms. See the figures below.

  1. Descriptive Terms:

Dorsal:describing the back portion of a structure

Ventral:describing the lower surface of a structure

Medial:describing the mid region of an organism

Lateral:the sides, right and left

Anterior:the head end, or the part, which moves forward

Posterior:the tail end of the animal

Distal:away from the main mass of the body (e.g., the fingers)

Proximal: near the main mass of the body (e.g., shoulder, thigh)

Peripheral:on or near the surface

Superficial:on or near the surface

Central:toward the middle of the body

Oral:the surface on which the mouth is located

Aboral:the surface opposite from that containing the mouth

Cranial:towards the head

Caudal:towards the tailLateral View of frog embryo

Questions: (can be answered at the end of lab)

  1. Define the two types of body symmetry.
  2. If you were to divide animals from both types of symmetry, how would the number of possible planes of symmetry compare between the two types of body plans?

In a bilaterally symmetric organism such as a fish, various axes and planes are designated for orientation and reference, as follows. Try to imagine these planes and axes in relation to the human body.

Anteroposterior/longitudinal axis – a line extending from the head to the tail,not necessarily dividing

the body in half

Dorsiventral axis – a line running across the body from the dorsal to the ventral side

Transverse axis – a line running across the body from side to side

Sagittal/median plane – this plane is vertical and passes through the exact midline of the body, it

includes both anteroposterior and dorsivental axies

Transverse plane – any cross section through the body which includes transverse and dorsiventral axes.

Frontal plane – any plane, which includes transverse and anteroposterior axies.

Sample Sagittal Sections:

The sagittal plane is a vertical plane through the longitudinal axis dividing the body into left and right portions. If the animal is bisected straight down the midline, the section is called a "midsagittal" section (see section 1). If the animal is sectioned away from and lateral to the midline, the section is referred to as "parasagittal" (see sections 2 and 3).

Section1

Section 2

Section 3

Sample Transverse Sections:

The transverse plane is a plane perpendicular to the longitudinal axis. It divides the body crosswise into cranial and caudal portions. A transverse section is also called a "cross section".

Dissecting Technique: The detailed procedures of dissection are best learned through experience, but the following principles will serve as a useful guide.

  1. Dissection does not mean cutting an animal to pieces, but rather exposing bodily structures with the least possible damage. A minimal number of incisions should be made – only for the purpose of separating parts so they may be seen more easily.
  2. Do not cut a structure unless you know what it is and if you should cut it. When cutting, make clean, neat cuts.
  3. Most organisms are bilaterally symmetrical. There fore you can dissect one side, while leaving the organs on the other side intact
  4. In manipulating body organs and searching for specific structures, always use the blunt probe or forceps. Do not use a scissor, a scalpel, or pins because the sharp point damages organs and tissues. Be careful not to destroy structures embedded in fat or connective tissue.
  5. Keep your preparation moist by regularly applying water/
  6. When finished with your dissection properly dispose of the organism. Clean and dry the dissecting pan and equipment

EXERCISE1: Observing Living Organisms

Hydra [CNIDARIAN]

  • Obtain a specimen and place on your dissecting microscope
  • Using low and intermediate powers make a diagram of your specimen. Label with as many parts as you are familiar with
  • Observe how the Hydra moves
  • Identify and label the stalk-like body and basal disk by which it attaches. Note the many tentacles surrounding the mouth.

3. Are the tentacles hollow or solid?

  • You may see swellings or out growths on the body. These are buds, a form a asexual reproduction. Many Cnidarians are capable of both sexual and asexual reproduction. Hydra produce young asexually by mitotic cell division, which produces a miniature copy of the polyp attached to its body.
  • Use a pipet to add a daphnia and observe feeding behavior.

Planaria [ PLATYHELMINTHES]

  • Transfer a specimen to a clean observation dish. Describe how it moves.

4. Does it use muscular contractions, cilia or another method?

  • Add a very small piece of boiled egg. Observe how it finds its food.
  • Make a diagram of your specimen. And label as many parts as you can. Label thehead, mouth, eyes
  • Dim the illumination of your scope until the specimen is just visible.
  • Shine a light at the anterior endof the specimen.

5. Write your observations.

  • Now shine a light at the posterior end of your specimen.

6. How does it respond?

Lubricus [ANNELIDA]

  • Examine the living earthworms on display. Make an observation of how it moves. Can you see individual segments contract and expand? Use a magnifying glass to look closer.

7. How does the mouth differ from the anus?

  • Place the worm on your hand. Can you feel the setae? (if not try your cheek!)
  • Make an external diagram of your worm and label as many parts as you can.

8. How many segments are there until you reach the Clitellum?

9. How many setae are there for each segment?

10. How does the anus differ from the mouth?

  • Locate the dark streak running the length of the body. This is the dorsal blood vessel.

Questions:

11. What are some of the key differences in locomotion between these three phyla? Based on your observations of movement only which phyla seems more advanced?

EXERCISE 2: Prepared Slides

HYDRA -

  1. Examine a slide of a longitudinal section of Hydra using intermediate and high power objectives
  2. Locate the following in your specimen, mouth/anus; gastrovascular cavity; tentacles; basal disc, and if they exist in slide Bud, testis, ovaries.
  3. Diagram your specimen and label as much as you can. Use higher magnification to distinguish the germ layers.
  4. How many cell layers are there?
  5. Look closely at the cells in the basal disc. How does their appearance differ from the cells of the body epidermis?
  6. Examine the cross section of the Hydra. Diagram and label the characteristic features that identify this organism as a Eumetazoa (True Tissue organism)

Hydra belong to the phylum Cnidaria, so called because the posses specialized cells, cnidocytes, which contain stinging organelles. Name at least one other organism that has similar features, that you would classify as a Cnidaria.

Based on your observations of Hydra, make a brief statement explaining what evidence you saw that would support the following:

Although Cnidarians lack organs they do possess true tissue as exemplified by their primitive nervous system.

PANARIAN –

  1. Examine a whole mount slide of a planarian
  2. Identify the pharynx, the large tubular structure in the central region of the body. Where is the mouth situated in relation to the pharynx?
  3. Identify the eyespots. These are light sensitive areas on the head, but do not form actual images. Add to your live specimen drawing any new features that you see.
  4. Examine a cross section slide. Each slide has three sections relative to the pharynx: i) anterior, ii) transverse, iii) posterior.
  5. Make a detailed study of a section posterior to the pharynx. Use the 40X objective to make a drawing. Label the regions that identify this organism as an acoelomate.

LUMBRICUS –

Obtain a slide containing several sections through the intestinal region of the earthworm. Study first under low power, for orientation; then use higher magnification to make out details.

  1. Make a detailed sketch.
  2. Using the reference figure as a guide,identify the dorsal and ventral side of your sketch.
  3. Identify and label the following: coelom, epidermis (ectoderm) muscles (mesoderm), digestive track (endoderm), setae (bristles)
  4. What do you notice that identifies this organism as a coelomate?

EXERCISE 3: Phylum Annelida Dissection

The Phylum Annelida contains about 15,000 species. In contrast to cnidarians and Platyhelminthes, annelids possess a true coelomic cavity. This cavity will be readily visible when you look at a cross section of the worm. This body cavity is filled with a fluid, which when acted upon by muscles forms a hydralic skeleton. Annelids, unlike Cnidarians or Platyhelminthes posses a complete digestive system. Since annelids have both a mouth and an anus, the digestive system forms a tube within the body of the worm (as opposed to a gatrovascular cavity) Annelids also show an increased complexity in both the development of organ systems and the degree of cephalization.

**Review the morphology descriptive term section before proceeding with the following dissection**

Proceedure:

  1. Obtain a dead worm. Place the worm in your hand and examine the dorsal and ventral surfaces. Locate the clitellum
  2. Use scissors to make a lateral incision on the dorsal surface about 1 cm posterior to the clitellum.
  3. Cut through the dorsal body wall in the median line to the anterior end. Be sure to lift up on the scissors as you cut so that you don’t cut any internal organs [Your technique is worth 5 pts.]
  4. Place worm, dorsal blood vessel up, so that it is parallel to the long edge of the dissecting pan. Pin down the body starting at the posterior end of your cut, near the clitellum, and work anteriorly. Place pin so that the angle distally.
  5. Use a squirt bottle filled with Ringer’s solution (osmotically correct aqueous solution) to gently wash away any internal debris.
  6. Use a beaker to grab about 400 mL of Ringer’s solution and completely immerse your dissection.
  7. Use a dissecting microscope or hand lens to and make a detail diagram of your specimen.
  8. Show your diagram to the instructor and you will receive an Earthworm Internal Structure Reference card. Locate and label your diagram with the following structures using the card as reference.
  9. Use a sharp scalpel to cut through two adjoining segments from the posterior of the earthworm. This will produce a cross section which can be placed on a microscope slide and examined under a 2X or 3X magnification.
  10. Diagram your cross section and using the Earthworm Internal Structure Reference card locate and label your diagram with as many structures as you can.

Exercise 3 Questions: Use the following vocabulary to complete the descriptive paragraphs below:

gastrointestional tract / Septa / esophagus / somites / nephridia / gizzard
hearts / pharynx / cerebral ganglia / coelom / intestine / Crop
Blood vessels / hemoglobin / nerve cord / seminal vessicals

The a)______(G.I.), or alimentary tract, is a long tube, which runs the length of the body. The, b)______are dark, ring-like structures that encircle the G.I. tube. Light colored reproductive organs, c) ______, are also arranged around the anterior part of the G.I. tract. Notice thed)______, the prominent body space between the GI tract and body wall. It is lined with peritoneum, which is derived embryological from the mesodermal germ layer. e)______separate the segments also known asf)______. The digestive system begins with the g)______which forms an expansion in somites3-5; note the pharyngeal muscles associated with it. The h)______which follows the pharynx, is long and slender, and extends through somites 7-14. It is covered by parts of the reproductive system. The i)______, a large, thin-walled sac, is then followed by the j)______, which has thick walls and connects to the k)______which is a thin-walled tube extending to the anus.

Earthworms possess a closed circulatory system. The blood fluid is always contained within l)______. The dorsal blood vessel and the ring-like hearts, contract rhythmically to pump blood through the system of closed blood vessels. The respiratory pigment m)______is present, dissolved within the blood (earthworms lack red blood cells). Note the “brain”, or n)______are located dorsally in somite 3. From these dorsal ganglia, connections encircle the pharynx to enter the first of a series of ventral ganglia, which make up the o)______. (to see the nerve cord carefully pull the pharynx and a short section of digestive tract aside. Except at the anterior and posterior ends of the worm, each somite contains a pair of p)______which remove waste by siphoning it out of the body.