Phyla Ctenophora and Plathyhelmintes

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Lecture - Phyla Cnidaria and Ctenophora

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Lecture - Phylum Cnidaria

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Exam 1

Today students took their first exam of the semester.  Stats :

Click image for a larger view

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Labs 05 and 06 - Mollusca

In these labs students examined live and preserved specimens of the main molluscan groups.  The goal of the labs was to do a comparison of the adaptive modifications that different molluscan groups have gone trough relative to the hypothetical ancestral mollusc (HAM).  The main features  to observe were visceral mass, mantle, foot and shell.  In live snail specimens the radula was observed in action.  There were also prepared mounts to observe the radula at the microscope.

Among cephalopods, the only representative observed was a preserved specimen of a squid.

The groups considered were:

POLYPLACOPHORA (Chitons)

Representatives of Polyplacophora
(from Chilebosque forum)

Micrograph and diagram of a chiton's radula
(http://hyperaccu.com/e_06.htm - www.asnailsodyssey.com/LEARNABOUT/CHITON/chitFeed.php)

GASTROPODA (Snails, limpets, slugs)

Miscellaneous representatives of Gastropoda
Upper row: Cone, marine slug, banana slug
Lower row: Cowrie and three land snails

Micrographs of snail radulae
left; right
(for details of the anatomy of the gastropod radula click HERE)

Live specimens

Live gastropod specimens observed in the lab
Left: right after the lab session.  Right: 24 hours later

BIVALVIA (Scallops, oysters, mussles, clams)

Representatives of bivalvia
Top row: A scallop, a live scallop, a giant clam
Bottom row: A mussel, oysters, a razor clam

Some freshwater clams ("mussels") from Eastern North America
Top row: Rock Pocketbook, Plain Pocketbook, Wartyback, and Paper Pondshell
Bottom row: Elktoe, Pistolgrip, Rainbow, and Mucket
(Photos from the Illinois State Museum)

Live specimens

Freshwater clams available in the lab, most likely Spikes (Elliptio dilatata)
Top: Detail of an individual
Bottom: left, individuals "planted" in gravel; right, after allowed to wander for 24 hours

CEPHALOPODA (Octopuses, squids, cuttlefishes, nautili)

Representatives of Cephalopoda
Top: Octopus and squid
Bottom: Cuttlefish and nautilus

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Lecture - Phylum Cnidaria

Nerve nets in different cnidarian body plans
from Brusca, RC and GJ Brusca. 2003. Invertebrates (2nd edition). Sinauer.

Today we discussed the kinds of cells found in cnidarians, mainly the epitheliomuscular/nutritivemuscular and nerve cells, and their functions.

We then discussed the means of support: Hydrostatic skeleton (mainly in Scyphozoa) and hard skeletons (mainly in Anthozoa). We also discussed the main shapes in the cnidarian bauplan, the polyp and the medusa, and their role in the diversity of cnidarian life cycles.

We started discussing the biology of the cnidarian groups, with the anatomy and a little of the physiology of Scyphozoa.

Next: Hydrozoa and Cubozoa.

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Paper discussion 1 - Feeding behavior and physiology of a carnivorous sponge

The cladorhizid sponge Asbestopluma hypogea capturing small crustaceans
(from Les Bulles du Recife)
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Today in class we held a discussion on the feeding behavior and physiology of the carnivorous sponge Asbestopluma hypogea. Our discussion was specifically based on the paper

Vacelet, J. and E. Duport. 2004. Prey capture and digestion in the carnivorous sponge Asbestopluma hypogea (Porifera: Demospongiae). Zoomorphology, 123:179–190.

The discussion was largely based on aspects that the students found interesting, which for the most part were:

• Passive mechanism of hunting
• Cell changes to engulf prey
• Mode of digestion (partially extracellular)
• Speed of digestion (2-8 days depending on size of prey)
• Features in prey and sponge that allow the sponge to capture its meal
• Overall morphological changes during the digestion process

Students seemed to show a special interest for the video associated to the paper and the various SEM micrographs published by the authors.

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Lab 04 - Phyla Platyhelminthes, Rotifera, and Nematoda

Phylum Platyhelminthes (Flatworms, tapeworms, flukes)

Dugesia, a free-living platyhelminth
(from Great Lakes Water Life Photo Gallery)

Students observed live and preserved representatives of this phylum, as well as slides of whole individuals and cross sections of some of them.  The specimens available in this lab are

• Turbellaria
  
  Dugesia (planaria; live, whole mounts and cross section)
• Trematoda (flukes)
  
  • Clonorchis (human liver fluke)
    
  • Fasciola (sheep liver fluke)
    
  • Schistosoma (blood fluke)
• Cestoda (human tapeworms)
  
  • Echinococcus
    
  • Taenia 

The live planarians were used for observing phototaxis, locomotion, feeding behavior, and external anatomy.

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Phylum Rotifera ("wheel animals")

Philodina, a rotifer
(from La soledad del excéntrico)

Students made observations on live specimens of the genus Philodina. They focused on locomotion and external anatomy.

• Eurotatoria
  
  • Philodina

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Phylum Nematoda (roundworms, hokworms, pinworms, etc.)

Trichinella, a nematode
(from Science Photo Library)

Some of the most abundant metazoans on the planet.  Students observed slides of the following representatives

• Chromadorea
  
  • Ancylostoma
    
• Adenophorea
  
• Trichinella
• Secernentea
  
  • Ascaris
  • Necator

There were also displayed pictures of some nematodes of importance for humans, such as pinworms, hookworms and heartworms.

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Lecture - Phyla Porifera, Placozoa, and Cnidaria

Top: A nematocyst, before and after being discharged
Bottom: Generalized cnidarian body plan

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Today we finished our discussion of porifera by talking about their reproduction, asexual (cellular regeneration, budding, through gemmules) and sexual (internal fertilization, with zygote developing into an amphiblastula or parenchymula larva).

We closed the chapter with a brief mention of the most accepted poriferan phylogeny.

We briefly discussed the phylum Placozoa, a phylum with one species as a representative, although there is some molecular evidence suggesting there could be several species.

Finally, we started our discussion on Cnidaria.  We started with some of the general features of the phylum, in terms if diversity, habitat, and development.  It is the first phylum we consider showing symmetry, in this case radial, and true tissues, derived from two embryological layers (diploblasts)

We discussed the general body plan, with an epidermis, a gastrodermis, and a mesoglea between the two, with the gastrodermis lining a gastrovascular cavity.  We also discussed one of the defining characters of the phylum: the presence of cnidae, specialized organelles in cells called cnidocytes, with a variety of functions, but most prominently used for feeding and defense, in which case the specific cnida is called nematocyst.

Learn a little about sponge reproduction

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Lecture - Phylum Porifera

Types of canal systems in sponges: Asconoid, syconoid, and leuconoid

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Today we discussed the different canal systems in sponges, and how they allow them to  filter water in a more efficient way the more complex the canal system is. In increasing order of complexity such systems are

• Asconoid - the spongocoel is lined with choanocytes
• Syconoid - choanocytes are organized in radial canals and not exposed to the spongocoel
• Leuconoid - choanocytes are organized in interconnected chambers and the individual sponge may have multiple oscula

We also discussed what skeletal elements observed (spicules, collagen fibers, including spongin) and how they are used to classify sponges in three different groups:

• Calcarea - Sponges with calcareous spicules and no spongin (but they do have collagen fibers)
• Hexactinellida - Sponges with six-rayed siliceous spicules and no spongin (they do have collagen fibers)
• Demospongiae - Sponges with spongin and/or siliceous spicules.  Most common of all; they include the carnivorous deep sea sponges (Cladorhizidae, which lack spongin, ostia, and oscula, but have distinctive hooked siliceous spicules)

Representatives of Porifera
from left to right: Sycon quadrangulatum (Calcarea), Xestopongia sp. (Demospongiae),
and Euplectella aspergillum (Hexactinellida)

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Lab 03 - Cnidaria & Ctenophora

Miscellaneous cnidarians

Pleurobrachia, a ctenophore

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Cnidarian and Ctenophora are a phyla of animals with radial symmetry and two tissue layers, exclusively aquatic, mostly marine. Cnidarians include anemones, corals, sea jellies ("jellyfish"), and other less known groups, whereas ctenophores are the comb jellies.

Today students became familiar with the typical morphology of most of the cnidarian groups, and a little of the behavior of one of them. Only one representative of the Ctenophora was observed.

The following groups were studied

Cnidaria

• Hydrozoa
  
  • Hydroida
    
    • Hydra
      
    • Gonionemus
      
    • Pennaria
      
    • Obelia
      
    • Plumularia
  • Siphonophora
    
    • Physalia
      
    • Vellela
  • Scyphozoa
    
    • Aurelia
      
    • Cassiopea
• Anthozoa
  
  • Hexacorallia
    
    • Metridium
      
    • Acropora
      
    • Fungia
      
    • Meandrina
  • Octocorallia
    
    • Gorgonia
      
    • Renilla
      
    • Stylatula
      
    • Leptogorgia

Ctenophora

• Cydippida
  
  • Pleurobrachia

We had live individuals of the genus Hydra, which students observed under a dissecting scope.  Movement was analyzed as a response to disturbance and as response to having food available (the branchiopod crustacean, Daphnia, the water flea [incidentally the animal with the record number of genes!])

Hydra feeding on Daphnia

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Lecture Metazoan life cycles Phylum Porifera

A crustacean embryo
(http://www.flickr.com/photos/artour_a/4174414482/)

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Today we briefly mentioned the two types of life cycle that we will find in invertebrate phyla: Direct and indirect. Being indirect the most common case in the phyla that we'll cover in this course.

We discussed how developmental characters can be used to help inferring phylogenies and showed how, if looking early enough in the development of an organism, similarities across widely different metazoan phyla can be found. For instance, we talked about how the pattern of cell division after fertilization can determine two major groups of bilaterians: Protostomia and Deuterostomia.

We also started our discussion on the phylum porifera.

We talked about the basic body plan, how the choanocytes promote water movement so an entire individual can filter feed, and how non-specialized ameoboid cells, the archaeocytes can differentiate into the other cell types characteristic of this phylum (porocytes, pinacocytes, sclerocytes, choanocytes).

Next, we'll discuss the types oc canal systems found in sponges, which allow for the diversity of shapes that is found among the 7000+ (up to 15000) species of poriferans.

Basic body plan in Porifera and detail of a choanocyte and an amoebocyte

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