INTRODUCTION
When surveying the animal kingdom, we find an incredible amount of diversity in structure and function. Though there are over a million described species on earth, almost all of these species are invertebrates. Invertebrates are animals that lack a backbone. We can then subdivide the invertebrates based on a few characteristics such as symmetry, tissue development, and larvae development (figure 1).
The first feature of interest in grouping is symmetry. Asymmetry means the animal, no matter what way its divided, will be identical (ex. Sponges). Radial symmetry, as in Cnidarians, means no matter what way we slice the animal longitudinally the two halves will be identical. The other phyla have bilateral symmetry, meaning these animals have a defined right and left half. These bilateral organisms are further divided based on the first opening in embryonic development being the mouth (protostomes) or Anus (deuterostomes). Of our protostomes we then divide them into Ecdysozoa or Trochozoa. Ecdysozoa have a shedable exoskeleton, and trochozoans have a larval form that is free swimming. These characteristics help us divide the highly diverse species on earth into distinct related groups.
The organisms below are all similar to each other because they are all non-coelomates. Coelomates have a body cavity that has been completely lined by the mesoderm which allows for growth of complex organs. While there is a great diversity in invertebrate organisms, there simply isn’t time in lab to address all the differences in their anatomy and physiology. However, in this lab we have highlighted some examples to begin our comparative studies of invertebrate anatomy.
ROUNDWORMS
Roundworms are in the phylum Nematoda; they have bilateral symmetry, pseudocoelom, and a complete digestive tract. Most roundworms are parasitic and take their nutrients from both plants and animals. Human consumption of undercooked foods is a common pathway to an infection of roundworms. Ascaris is a tropical intestinal parasite that when ingested burrows through the intestinal wall and makes its way to the lungs. Ascaris has both a male and female form. You can observe both forums in the preserved specimens. This will be your first dissection; it is the simplest and best to begin with. Your instructor will show you when to make you incision and how to dissect this animal.
You are looking for the following:
A male vs a female
Gonads
MOLLUSKS
Mollusks are in the phylum Mollusca. Mollusks come in many varieties including the bivalve (clam), chitons (flattened grazing marine invert.), gastropods (snails), and cephalopods (squids). All these groups share three characteristics: They have a muscular foot specialized for locomotion, visceral mass that includes the internal organs, and have a thin tissue that encloses the visceral mass called a mantle.
Examine the clam, be able to identify:
External
Hinge
Umbo
Growth ring
Exoskeleton
Internal
Heart
Kidney
Gills
Foot
Stomach
Intestine
Labial palps
Other Mollusks look quite different. One such of these groups is called the Cephalopods. these are highly adapted and, in many cases, highly intelligent group of animals that includes octopi, squid, nautili, and cuttle fish.
Examine the squid, be able to identify the following.
External
Fins
Tentacles
Beak
Eye
Mantle
Suction disks
Internal
Siphon
Stomach
Ovary
Testicle
Ink sac
heart
ANNELIDS
Annelids are in the phylum Annelida. These are considered segmented worms because the body is divided into regions called somite’s. Among the annelids are a group called oligochaetes. They share all the characteristics of Annelids except they have few bristles called setae on their body. The most well-known of the oligochaetes is the earthworm.
Examine the earth worm, be able to identify:
External
Anus
Clitellum
Mouth
Seminal groove
Internal
Brain
Pharynx
Heart’s
Esophagus
Seminal receptacles
Seminal vesicles
Crop
Gizzard
Intestine.
Septa
Dorsal blood vessel
ARTHROPODS
Arthropods are in the phylum Arthropoda. Arthropoda includes insects, arachnids, and crustaceans. They all share the same characteristics of a segmented body, exoskeleton, and jointed appendages. Insects are the most common of the arthropods; they contain three body regions, and three legs. Arachnids have four pair of legs, no antennae, and a fused head and thorax called a cephalothorax. Crustaceans have three to five pairs of legs and two pairs of antennae.
Examine the crayfish (A Crustacean), you should be able to identify:
External
Eye
Claw
Rostrum
Antenna
Mouth
Uropod
Telson
Swimmerets
Male or female
Internal
Stomach
Digestive gland (liver)
Gills
Heart
Brain
Activity Questions: These questions will be due by next lab period and uploaded into D2L from a word document.
1. Compare each phylum’s body symmetry and organization. How is shape related
to digestion, predation, and locomotion?
2. Compare the reproductive strategies of three phyla. How do the reproductive
strategies of these phyla allow them to be successful?
3. What characteristics separate the more basal phyla (e.g., Porifera) from the more
derived phyla (e.g., Chordata)?
4. Are any adaptations shared across different phyla? Explain why and how
organisms that are not related can have similar traits