SEA SPONGES

WHAT IS A SEA SPONGE?
Although sea sponges may look like plants, they are the simplest of multi-cellular animals. Sea sponges are bottom-dwelling invertebrate creatures that are primarily marine, however there are a small number of sponge species that can live and survive in freshwater regions. The scientific term for sponges is Porifera, which literally means "pore-bearing". The surface of a sea sponge is made up of thousands of tiny pores, called ostia. These pores lead internally to a system of canals, whose main functions are collecting nutrients and oxygen, and disposing waste and carbon dioxide.


CHARACTERISTICS THAT DEFINE A SEA SPONGE
1. No definite symmetry
2. Body is multicellular but there are no tissues and no organs
3. Most to all adults are sessile
4. Can reproduce both sexually and asexually
5. No nervous system
6. Lives in aquatic environments, mostly marine
7. All are filter feeders
8. Often have a skeleton composed of spicules
9. Cells surround a water filled space though there is no true body cavity


CLASSIFICATION
Sea sponges are classified under the Kingdom Animalia and the Phylum Porifera. Sponges are classified into three taxonomic classes based on the chemical composition of their skeletons:
Calcarea: calcerous sponges; skelteon composed of calcium carbonate; considered the most primative group of sea sponges; include asonoid, syconoid and leuconoid body forms (see ANATOMY)
Demospongiae: horn sponges (ie. bath sponges); skeleton composed of protein fibers; include only leuconoid body forms
Hexactinellida: glass sponges; skeleton composed of silicon dioxide; include only leuconoid body forms
Besides the three afforementioned classes, there is one other class of sea sponges that has not yet been mentioned, sclerospongiae. This class is not considered a taxonomic class of sponges though it still exists. Sclerospongiae includes all coralline or tropical reef sponges.

ANATOMY

A sea sponge's body primarily consists of spicules and spongin. Spicules are needle shaped fiberlike structures that act as the sponge's skeleton. Spongin is a protein that helps provide body support. In some instances the spongin will combine with the spicules to provied support, in other times the spongin works alone.

Sea sponges have three different body plans: asconoid, syconoid and leuconoid. Asconoid sponges are tube shaped and perforated by spores. The opening of the tube, called the osculum, leads to the spongocoel, the inner region of the tube. The spongocoel holds the collar cells. Syconoid sponges tend to be larger in size than asconoids and have a tubular body with a single osculum. The syconoid body wall is thicker and the penetrating pores are longer, forming a system of simple canals lined by collar cells. The collar cells' flagella work to force water into the spongocoel and out through the osculum. Leuconoid sea sponges are the largest and most complex. These sponges consist of masses of tissue penetrated by numerous canals, all of which lead to a number of smaller chambers lined with flagellated collar cells. Water moves through the canals, into the chambers, and out through the central canal and osculum.



THE SKELETON
The "skeleton" of a sea sponge is made up of tiny needlelike splinters called spicules. Spicules consist of a mesh of protein called spongin. Many sea sponges can only be identified by the microscopic examination of the skeleton. Because of this, indentification from photographs can become very difficult.

PYSIOLOGY

All sponges lack the complex organs and true tissues needed to form the excretory, circular, digestive and respiratory systems. All the nutrients a sea sponge needs are carried via water. The nutrients diffuse through the sponges' pore cells and are then expelled through the sponge’s osculum. The osculum is capable of propelling metabolic waste at a relatively high velocity for large distances away from the sponge. Sea sponges also rely on water currents to carry out basic circulation, digestion and respiration.

FEEDING

Sea sponges are filter feeders and mainly diet on tiny, floating organic particles known as plankton. When in the need of food, sponges depend on a system of pores, called ostia, and canals through which water passes. To better understand why the canals are important and how they aid in sponge feeding, it is key to first know the makeup of the canals, how they work and their main functions.

Within the canals of sea sponges, tubelike chambers are lined with specialized cells called choanocytes, or collar cells. Each collar cell has a sticky, funnel shaped collar and a hairlike whip called a flagellum. The collar cell serves two important purposes. First, the sticky collar works as a filter to strain out the smallest food items found in the water, such as plankton and individual bacteria. After a collar cell collects enough nutrients, another type of cell called an amoebocyte will transfer the food to other cells within the sponge. Second, the back and forth beating of the flagella drives water into the canals. The water makes collecting nutriends and oxygen possible, and carbon dioxide and waste easy to remove. The forces water through the sponge work to keep the animal alive and healthy.

REPRODUCTION

Most sea sponges are generally hermaphrodites, meaning they are both male and female, though they can only be one gender at a time. When sponges procreate, they can either reproduce by means of sexual or asexual reproduction.

SEXUAL REPRODUCTION
The process of sexual reproduction between sea sponges occurs in the mesohyl, an acellular gel layer that is the innermost layer of the sponges body. After developing gametes, the "male" sponge will release its sperm into its canals. The sperm is pumped out of the sponge and into the surrounding water by the osculum. Once in the water the sperm cells are then taken into the pore systems of neighbour "female" sponges similarily to how food particles would be. Once inside a female sponge the gametes are collected by collar cells. These cells, also known as choanocytes, then proceed to shed their collars. This process transforms the collar cells into specialized amoeba-like cells which transfter the sperm from the mesohyl to the eggs located in the ovocyte, a cell generating ova. In the majority of sea sponges, the fertilized egg will then develop into a blastula. In some species the blastula will be released into the water directly after fertilization, where in others release is delayed and some development will first take place within the parent sponge. Upon release, the larvae may either settle immediately and grow into an adult spong, or may act planktonically for a few days. The next time the sponges reproduce, they may change sexual roles.


ASEXUAL REPRODUCTION
When reproducing asexually, sea sponges form buds which are also known as gemmules. External buds are formed when fragments of a sea sponge's body are broken off by water currents and carried to other locations. There the buds begin to grow into clones, or genetically identical sponges, of their parents. Some species will produce buds internally rather than externally. These buds are made to survive in extremely unfavorable conditions and this may result in the death of the parent sponge.

HABITAT

Sponges are extremely versatile creatures and they can be found on numerous surfaces, depths, and water environments. Around the globe, sponges have been spotted on surfaces ranging from the intertidal zone to depths more than 8,500 metres. Although sponge species are largely marine, sponges continue to adapt to fresh water surroundings. Approximately 150 species are currently recorded as freshwater animals. Due to sponges worldwide distribution, many species differ in their limits and ranges in depth for survival. However, in warmer waters it appears that sponges thrive and are much greater in abundance. Sponges also tend to live in quiet waters to minimize any agitated sediment from clogging their pores. This can easily result in harming the animal’s ability to feed and continuing its existence.

MOVEMENT

Most assortments of adult sponges are sessile and are commonly fastened to surfaces. Often one can spot these animals on hard exteriors such as rocks on the ocean floor. Some however are competent in creating a root-like base and can attach itself to soft sediment. Although not all Poriferan have been recorded to do so, many species have been recognized in their ability to move at extremely slow speeds. Commonly, sponges tend to rely on water currents for movement.

Being sessile creatures can come with its advantages and it can danger the animal substantially. Less energy is spent on movement, and resources are spent on growth and reproduction. Sessile tide pool organisms take advantage of the movement of the water around them and the water brings food, oxygen, and gametes from other animals. Strong holding mechanisms help them avoid being swept away by the tide, which can allow the animal to adapt to its environment well. As for the dangers of being sessile, predators can easily approach and attack porifera which often contributes to shortages in sponge population.

RESPONSE AND ADAPTATIONS TO THE ENVIRONMENT

ADAPTATIONS
Poriferans are well adapted to their environments and have dense structures that aid them in harsh conditions. For instance, sponges must be able to control the high volume of water diffusing through them each day and they achieve this through constricting their pores for easy management. By monitoring the amount of water flow through their structures filter detritus particles resourcefully.

Often sponges are able to emit a toxic substance into their environments as means of protection. These toxic substances are also useful in ensuring space for a sponge to cultivate. As marine life progresses, sponges are finding more and more competition in finding a suitable niche. However, symbiotic relationships between Poriferans and other sponges also continue to emerge. One can easily find relationships between sponges, algae, and bacteria in which sponges supply protection as the symbiont provides food. The toxins released by the sponge (as mentioned earlier) can also provide a solid shield of defense for the organisms within the symbiotic relationship.


RESPONSE
Sea sponges do not have senses and cannot taste, see, hear, smell or feel (touch), and because sea sponges do not have nerves, they cannot actively respond to their surrounding environment. To protect themselves from predators, sea sponges rely on their spicules. The sharp, needle-like spicules work to make digestion hard and uncomfortable for their attackers.

COMPARISON TO OTHER PHYLA

Sponges themselves are really distinctive creatures and share few similarities with organisms in other phyla. They are the only invertebrates to be asymmetrical and along with cnidarians they are only classified on the tissue level of organization. In fact, although cnidarians are dissimilar in appearance, they share many characteristics with porifera. Both are sessile at one point in their life cycles, which also is diplontic. Porifera are one of the oldest animal ancestors, which also leads us to believe that they evolved much earlier than other invertebrates. These animals truly are remarkable and have evidently managed to distinguish themselves immensely form other invertebrates regarding characteristics, adaptations, as well as behaviour.

FAMOUS SEA SPONGES

TUBE SPONGE
Callyspongia vaginalis
The tube sponge is one of the most common varietes of sea sponge found on the reef. Tube sponges are distinguishable by its long tube-shaped growths. These sea sponges range from purple to blue, gray and gray-green in colour. Tube sponges are one of the few reef invertebrates that are blue in colour.


VASE SPONGE
Ircinia campana
Vase Sponges are a common species typically found in the Caribbean off the east coast of Florida. These sea sponges have a large bell shaped and a deep central cavity. Vase sponges can grow up to 2 feet wide and 3 feet high. They range in colour from purple to red and brown, and are known to make their homes on rocks near the sandy bottom of the ocean.

YELLOW SPONGE
Cleona celata
This poriferan is normally a small species commonly found throughout the Pacific coastal waters of the United States. Yellow sponges can be found growing in small colonies and range in colour from orange to bright yellow. This sea sponge can most often be found encrusting rocks on the reef face.


RED TREE SPONGE
Haliclona compressa
This bright red sponge species is very common throughout the Caribbean Sea. Red Tree Sponges typically grow to be about 8 inches tall. These sea sponges are realtively easy to take care of and keep in a home aquarium environment with a moderate water flow and dim light.

COMMON SEA SQUIRT
Didemnum molle
This species of sea squirt is very common on the reef, and is usually found in deep water. These sea sponges can be found encrusting the rocks in large colonies, and are known to have a leathery baglike body with a white and gray of brown spotted exterior, and a bright green interior.


PAINTED TURNICATE
Clavelina Picta
Tunicates are very similar to sea squirts. Like most sea sponges, they take water in through the osculum, filter out the nutrients, then expel the water through another opening. Painted turnicates are approximately ¾ inches long and usually grow in colonies. They vary in colours such as translucent red, purple and yellow.

DID YOU KNOW. . . . .

Here are 10 interesting facts you may not know about sea sponges!

1. Because sea sponge cells are not linked in a tissue, the cells can be separated and put back together. Some species, such as the freshwater sponge Ephydatia fluviatilis can be pushed through a sieve, and if given enough time, the individual cells will come together again to form a new sponge! These are the only animals that can put themselves back together again if broken into pieces.

2. Sea sponges are believed to have comprised more than half the biomass of marine reefs!

3. One of the first drugs used for treating cancer, cytosine arabinoside was isolated from a sea sponge!

4. Sponges are remarkable pumping "machines". A sponge the size of a gallon milk container is capable of pumping enough water to fill a residential small size swimming pool within one day!

5. Within a sponge, it is possible to find 16 000 other animals!

6. The largest sponge ever measured, a Monorapuhs sponge, was approximately 10 feet wide!

7. Sponges sometimes live on the backs of hermit crabs and act as a type of shell!

8. Ancient Greeks used sea sponges to pad their helmets and leg armor!

9. When Mitch Sogin, a biologist at the Marine Biology Lab at Woods Hole, compared the genetic blueprint of a sponge with those of other animals, he discovered that all animals with more than one cell are based on a sponge’s genetic blueprint.

10. Sea sponges produce potent chemicals to defend themselves against other animals that try to overgrow, poison, infect or eat them.

GLOSSARY

ACELLULAR: not made up or divided by cells
AMOEBOCYTE: cells with pseudopods, located in teh mesohyl; used in processing food, distributing nutrients to other cells and for other functions

BENTHAL: relating to or happening under a body of water on the bottom
BLASTULA: an early stage of embryonic development in animals; produced by cleavage of a fertalized ovum and consisting fo a spherical layer of cells surrounding a fluid-filled cavity

CALCEREA: calcerous sponges; skeleton composed of calcium carbonate
CHOANOCYTES: cells lining the interior body walls of sponges; also known as collar cells

DEMOSPONGIAE: horn sponges (ie. bath sponges); skeleton composed of protein fibers
DIPLONTIC LIFE CYCLE: organism is diploid as an adult

GEMMULE: a bud or fragment produced during the asexual reproduction of sponges

HERMAPHRODITE: an organism possessing both male and female reproductive organs
HEXACTINELLIDA: glass sponges; skeleton composed of silicon dioxide

INTERTIDAL ZONE: the area in marine aquatic environments between the low and high tide marks
INVERTEBRATE: an animal without a backbone

MESOHYL: an acellular gel layer that makes up the innermost layer of a sponge's body

OSCULUM: a large hole at the top of a sponge that expels water and wastes
OSTIA: surface pores on a sponge
OVOCYTE: a cell found in sponges that produces ova

PLANKTON: a diverse group of minute animals and plants that freely drift in water
PORIFERA: the scientific name for sea sponges; means "pore-bearing"

SPICULES: the small needle-like skeletal parts of sponges
SPONGIN: the organic matter composing the skeleton of sponges

WORKS CITED

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Stevely, John and Don Sweat. Sponge History. University of Florida: IFAS Extension.
http://edis.ifas.ufl.edu/SG045