Lab Topic 21
Protostomes I: Lophotrochozoans and Development of Complexity

 
Clade Lophotrochozoa
Phylum Ectoprocta (Bryozoa)
The image to the left is an example of a lophotrochozoan called Cristatella. The area marked is the lophophore used in filter feeding.
 
Phylum Annelida

Class Polychaeta (marine worms)

  Pictured here is Nereis, commonly called a clam worm. Note the anterior end of this polychaete, its segmented body, and the parapodia extensions used for locomotion in the image to the right.
     
Class Hirudinea (leeches)
Live leech images coming soon!
  Some leeches are used in modern medicine to aid in reattachment surgeries. Leech bites release anesthetizing, anticoagulants, and antibodies to help treat and heal wounds..
     

Class Oligochaeta (earthworms and aquatic worms)

When placed in a capillary tube, the transmitted light from a compound microscope allows one to view and study the internal organs of this animal without harm to the worm.
 
These aquatic oligochaetes, Lumbriculus variegatus, are commonly called 'California Black Worms'.
These 3 images with a black background are from Lumbriculus variegatus Biology ("Through a Looking Glass" by C. Drewes & B. Grosz)
 
 

 

Oligochaete
(Earthworm External Anatomy)

To the left is a view of the dorsal side of this earthworm. 'A' is the anterior end, B is the Clitellum, and 'C' is the posterior end of the worm. Below is an anterior ventral view.

 

How does an earthworm feed? 

What is the function of the clitellum which is a specialized region of the body wall?

 

Close up of external body wall of earthworm.
  The arrows mark the location of the setae on several body segments. What is the function of these structures? The lip-like structures indicated on the ventral surface of this animal denote the gonopores. What function do they serve?

 

Earthworm Internal Anatomy

Open Earthworm

 

Earthworm Digestive System
Arrows mark a portion of the intestine.
C denotes the crop and G denotes the gizzard
Arrow marks the pharynx
 
How is the digestive systerm in this animal similar and different from the digestive system in Porifera?
     
Earthworm Circulartory System

An earthworm has more than one heart as viewed in this image.
Is the circulartory system considered a closed or open circulatory system and why?
 
Earthworm Nephridial System -not shown at this time
What is the function of the nephridial system?
 
Earthworm Nervous System
Anterior ganglia of the nervous system
Removal of the digestive tract reveals the nerve cord on the body cavity's ventral surface.
   
Earthworm Reproductive System
This close-up view of the seminal vesicles and seminal receptacles are key to earthworm reproduction. Can you explain why? Explain what hermaphroditic means.
Earthworm Histology
The image to the left is a cross section of the earthworm at 2X. The sections highlighted are magnified below. Note the typholsole is retracted in this section.
This dorsal view of the earthworm cross section (10X) shows the dorsal blood vessel (DBV), the coelom (C) between two areas of muscle tissue (M).
This ventral view of the earthworm cross section (10X) shows the ventral blood vessel (VBV) and the ventral nerve cord (VNC)
Locate the body cavity on one of these images.
This animal has both longitudinal and circular muscle layers. Can you locate them in these images?
What are the distinguishing characteristics of animals in this phylum?

 

Clade Lophotrochozoa
Phylum Mollusca

 

Class Polyplacophora (Chitons)
Dorsal view of a chiton.
Ventral view of a chiton
Which end is anterior and which is posterior?
What characteristics would this animal have to place it in phylum mollusca?
 
Class Scaphopoda (Tusk shells)
Tusk shell
Class Gastropoda (snails, slugs, limpets, conchs, and whelks)
Snail crawling inside fish tank
Dorsal view of snail
Ventral view of snail
 

Slug
Conch

This class of gastropods is the largest in the phylum.

What is similar about these animals and what is different?

Limpet and whelk
Snail fossils of the Devonian Age ~ 400 MYA  
     
Class Bivalvia (clams, oysters, mussels, and scallops)
Freshwater bivalves
 
These native freshwater mussels were found in Iowa streams.
 Each zebra mussel pictured is about the size of a quarter. They are an invasive species that attaches to and kills native species in local waters.
     
Marine bivalves
 
This image shows a live flame scallop attached to the side of a fish tank waiting for food.
This image shows the diversity of some marine bivalves.
     
 
These bivalves have been attached by Moon Snails (Polinices lewisii). Moon snails use their radula to drill an almost perfect hole into the shell of a bivalve for extracting a tasty meal.
 

 

Class Cephalopoda (nautilus, squid, and octopus)
 
 
 
Squid head
Squid mouth
 
 
male squid
female squid
 
Class Cephalopoda (nautilus, squid, and octopus)
Image of octopus coming soon!
Nautilus shell
 
 

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Credits
Images prepared by Charlie Drewes, Linda M. Westgate, and Maria Oehler
Last update March 2008