BIOL 1407 Lab - Basal Animals - Porifera, Cnidaria and Ctenophora

Station 2: Parazoa - Phylum Porifera

Introduction to Phylum Porifera (Sponges)

The members of the phylum Porifera (meaning "pore bearer"), are multicellular parazoan organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly like mesohyl sandwiched between two thin layers of cells. Sponges have unspecialized cells that can transform into other types. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes.

Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Unlike other animals, they lack true tissues and organs, and have no body symmetry. The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, and leaves through a hole called the osculum. Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silicon dioxide. All sponges are sessile aquatic animals. Although there are freshwater species, the great majority are marine (saltwater) species, ranging from tidal zones to depths exceeding 8,800 m (5.5 mi).

While most of the approximately 5,000-10,000 known species feed on bacteria and other food particles in the water, some host photosynthesizing microorganisms as endosymbionts and these alliances often produce more food and oxygen than they consume. A few species of sponge that live in food poor environments have become carnivores that prey mainly on small crustaceans.

Most species use sexual reproduction, releasing sperm cells into the water to fertilize ova that in some species are released and in others are retained by the "mother". The fertilized eggs form larvae which swim off in search of places to settle. Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. A few species reproduce by budding. When conditions deteriorate, for example as temperatures drop, many freshwater species and a few marine ones produce gemmules, "survival pods" of unspecialized cells that remain dormant until conditions improve and then either form completely new sponges or recolonize the skeletons of their parents.

Scypha (also known as Grantia) is used here as a representative of the sponges. There are also a variety of sponge specimens available to show the gross anatomy of sponges. Students should know general characteristics of this phylum and additional examples of organisms in it. There are a few freshwater sponges but most are marine. Sponges are sessile animals. As adults they filter feed, pulling water in through numerous small holes (pores or ostia) on their surface and filtering out microscopic organisms before shooting the water out of larger holes (oscula) on top of their bodies.

The video is a nice introduction to sponges and their filter feeding capabilities.

Sponge biodiversity and morphotypes in 60 feet of water. Included are the yellow tube sponge, Aplysina fistularis, the purple vase sponge, Niphates digitalis, the red encrusting sponge, Spiratrella coccinea, and the gray rope sponge, Callyspongia sp. This picture was taken in the Caribbean Sea, in the Cayman Islands.

Porifera Body Symmetry

Unlike most animal organisms which exhibit some type of body symmetry, such as radial, bilateral, or spherical symmetry, most sponges are asymmetric, exhibiting no type of symmetry. There are a few species, however, that are radially symmetrical. Of all the animal phyla, Porifera are the simplest in form and most closely related to organisms from the kingdom Protista. While sponges are multicellular and their cells perform different functions, they do not form true tissues or organs .

Body Wall

Structurally, the sponge body is studded with numerous pores called ostia that lead to canals for channeling water to internal chambers. Sponges are attached at one end to a hard surface, while the opposite end, called the osculum, remains open to the aquatic surroundings. Sponge cells are arranged to form a three-layered body wall:

Pinacoderm - the outer surface layer of the body wall that is equivalent to the epidermis of higher animals. The pinacoderm consists of a single layer of flattened cells called pinacocytes. These cells are able to contract, thus reducing the size of a sponge when needed.
Mesohyl - thin middle layer that is analogous to connective tissue in higher animals. It is characterized by a jelly-like matrix with collagen, spicules, and various cells embedded within. Cells called archaeocytes found in the mesohyl are amebocytes (cells capable of movement) that can transform into other sponge cell types. These cells aid in digestion, nutrient transport, and are even capable of developing into sex cells. Other cells called sclerocytes produce skeletal elements called spicules that provide structural support.
Choanoderm - The inner layer of the body wall consisting of cells called choanocytes. These cells contain a flagellum, which is surrounded by a collar of cytoplasm at its base. Through the beating movement of the flagella, water flow is maintained and directed through the body.

Diagram of a generalized sponge body wall.

Porifera body Plan

Sponges have a particular body plan with a pore/canal system that is arranged into one of three types: asconoid, syconoid or leuconoid. Asconoid sponges have the simplest organization consisting of a porous tube shape, an osculum, and an open internal area (spongocoel) that is lined with choanocytes. Syconoid sponges are larger and more complex than asconoid sponges. They have a thicker body wall and elongated pores that form a simple canal system. Leuconoid sponges are the most complex and largest of the three types. They have an intricate canal system with several chambers lined with flagellated choanocytes that direct water flows through the chambers and eventually out the osculum.

As you are looking at Leucosolenia and Scypha (Grantia). Can you identify what body types each has?

Sponge Body Types. From left to right the water flow becomes more complex as it passes by more chaonocytes to increase the efficiency of filter feeding.

Observing an Asconoid Sponge: Leucosolenia

Leucosolenia is a genus of calcareous sponges. Species of this genus usually appear as groups of curved vases, up to 2 cm long, each ending in an osculum. The overall shape is sometimes likened to a tiny bunch of bananas. They are most often observedin tide pools, clustered around the base of seaweeds or on rocks, and occur in a variety of colours, usually rather pale. Its canal system is of asconoid type. The colony consists of few simple vase-like, cylindrical individuals each terminating in an osculum and united at their bases by irregular horizontal tubes. Leucosolenia reproduces both asexually and sexually. asexual reproduction by budding and sexual reproduction takes place by formation of gametes, i.e., ova and sperms. Lecosolenia is hermaphrodite, because both the gametes are formed in the body of same individual.

To see the body structure in more detail, obtain a whole-mount slide of Leucosolenia. Use only your scanning objective because the slide is thick and the other objectives may smash the coverslip. The body wall is closed at the base, but open at the tip, creating a vase-shaped body outline. This is a colonial species and small budding colonies may be present. Water, containing oxygen and food particles, enters a central cavity,the spongocoel, through very small pores in the body wall and exits through the osculum, the opening at the end of the body. The spongocoels of individuals in a colony may or may not be interconnected.

An example of a colony of Leucosolenia.

Leucosolenia whole mount slide

Identify the following structures

Osculum
Spongocoel

Leucosolenia whole mount (40x magnification).

Leucosolenia Diagram

Look at the diagram of Leucosolenia. Be able to identify the following structures on the diagram.

Incurrent pore
osculum
spongocoel
choanocyte
amoebocyte
spicule
porocyte

Labeled Leucosolenia diagram with a magnification of the body wall.

Lab Activity: Observing Leucosolenia

Preserved Leucosolenia (may be a plastic mount)
Prepared slide of Leucosolenia
Compound Light Microscope

Note: Handle prepared slides carefully. Glass slides can break if dropped or handled roughly.

Instructions

Exampine the preserved or mounted speciment of Leucosolenia. Look for an Osculum.
Examine the prepared slide of Leucosolenia and locate an incurrent pore along the sponge wall. Also locate spicules embedded in the wall of the sponge.
Identify the Osculum and Spongocoel.
Look for Choanocytes lining the spongocoel.
Compare the structures you observe on the preserved speciment and slide with the diagrams shown in this lab station.

Clean Up

Return the prepared slide to the slide tray.
Turn off the microscope and return it to its storage location.

Observing a Syconoid Sponge: Grantia

Grantia, also called Scypha in older texts, is a genus of marine sponges of the class Calcarea (calcareous sponges), characterized by a fingerlike body shape known as the syconoid type of structure. In the syconoid sponges, each “finger,” known as a radial canal, is perforated by many tiny pores through which water passes into a single central cavity. The water exits through an osculum, or larger opening, at the tip. Water is driven through the sponge by the beating of many hairlike cilia lining the central cavity. Grantia species grow to only about 2 or 3 cm (about 1 inch) in length.

Before looking at the cellular organization of Grantia, you are going to examine a whole specimen. Pick a specimen out of the jar below and examine the external anatomy.

Grantia, a small syconoid sponge in the Class Calcarea.

A labeled specimen of Grantia.

To view cellular organization in the body wall, obtain a slide of a longitudinal section of Grantia, a small sponge with a folded-wall (syconoid) body plan. Look at it first with the dissecting microscope to orient yourself. Note (1) how the body wall is folded, (2) the open central spongocoel and (3) possibly the osculum, depending on where the specimen was sectioned. Note how the body wall is uniform without areas specialized into organs.

Longitudinal section through Grantia (40x magnification).

Switch to your compound microscope to study the cell organization in one of the body wall folds while looking at a cross-section of Grantia. This is often a difficult slide to interpret, so be sure to fine-tune the light intensity and use the lower-power objectives for initial viewing. How many cell layers do you see between the outside and the central cavity of the spongocoel? Look at the cross-section first under 40x magnification then switch to 100x.

Be able to identify the following structures and/or regions on the slide:

Spongocoel
Incurrent canal
Radial canal
Choanocytes

Light microscope cross section through the sponge, Grantia (40x magnification).

Light microscope cross section through the outer layer of the sponge, Grantia (100x magnification).

Now that you have examined a specimen of Grantia thoroughly can you identify all of the following features on the diagram to the right?

Spongocoel
Incurrent canal
Radial canal
Choanocyte
Incurrent pore
Amoebocyte
spicule

Diagram of a cross section through Grantia similar to the microscopic image above.

Lab Activity: Observing Grantia

Preserved Grantia (may be a plastic mount)
Prepared slide of Grantia
Compound Light Microscope

Note: Handle prepared slides carefully. Glass slides can break if dropped or handled roughly.

Instructions

Exampine the preserved or mounted speciment of Grantia. Look for an Osculum.
Examine the prepared slide of Grantia and locate an incurrent pore along the Incurrent Canal. Also locate spicules embedded in the wall of the sponge.
Identify the Osculum and Spongocoel.
Look for Choanocytes lining the Radial Canal.
Compare the structures you observe on the preserved speciment and slide with the diagrams shown in this lab station.

Clean Up

Return the prepared slide to the slide tray.
Turn off the microscope and return it to its storage location.

Sponge Diversity

Class Hexactinellidae - Glass Sponges

Glass sponges of the class Hexactinellida typically live in deep sea environments and may also be found in Antarctic regions. Most hexactinellids exhibit radial symmetry and commonly appear pale with regard to color and cylindrical in form. Most are vase-shaped, tube-shaped, or basket-shaped with leuconoid body structure. Glass sponges range in size from a few centimeters in length to 3 meters (almost 10 feet) in length.

The hexactinellid skeleton is constructed of spicules composed entirely of silicates. These spicules are often arranged into a fused network that gives the appearance of a woven, basket-like structure. It is this mesh-like form that gives hexactinellids the firmness and strength required to live at depths of 25 to 8,500 meters (80–29,000 feet). Tissue-like material also containing silicates overlays the spicule structure forming thin fibers that cling to the framework. The most familiar representative of the glass sponges is the Venus' flower-basket. A number of animals use these sponges for shelter and protection including shrimp. A male and female shrimp pair will take up residence in the flower-basket house when they are young and continue to grow until they are too large to leave the confines of the sponge. When the couple reproduces young, the offspring are small enough to leave the sponge and find a new Venus' flower-basket. The relationship between the shrimp and the sponge is one of mutualism as both receive benefits. In return for protection and food provided by the sponge, the shrimp help to keep the sponge clean by removing debris from the sponge's body.

Glass sponge, a member of the Class Hexactinellidae.

Class Calcarea - Calcareous Sponges

Calcareous sponges of the class Calcarea commonly reside in tropical marine environments at more shallow regions than glass sponges. This class of sponges has fewer known species than Hexactinellida or Demospongiae with around 400 identified species. Calcareous sponges have varied shapes including tube-like, vase-like, and irregular shapes. These sponges are usually small (a few inches in height) and some are brightly colored. Calcareous sponges are characterized by a skeleton formed from calcium carbonate spicules. They are the only class to have species with asconoid, syconoid, and leuconoid forms.

Calcareous sponge, a member of the class Calcarea.

Class Demospongiae - Demosponges

Demosponges of the class Demospongiae are the most numerous of the sponges containing 90 to 95 percent of Porifera species. They are typically brightly colored and range in size from a few millimeters to several meters. Demosponges are asymmetrical forming a variety of shapes including tube-like, cup-like, and branched shapes. Like glass sponges, they have leuconoid body forms. Demosponges are characterized by skeletons with spicules composed of collagen fibers called spongin. It is the spongin that gives sponges of this class their flexibility. Some species have spicules that are composed of silicates or both spongin and silicates.

Demosponge, a member of the Class Demospongiae.

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