Many centuries ago, even prior to the time of Christ, in the region of the eastern Mediterranean Sea, many men were busily engaged in a profitable occupation. Both Homer and Plato refer to this business in their writings. Daily workers left the shores to seek their livelihood in obtaining certain organisms growing on the bottom of the sea. Already in the age of Aristotle, diving suits were used for this purpose. What marine specimens furnished the incentive for such a hazardous undertaking? Certainly not the mere love of adventure could incite this dangerous employment. At dusk the returning ships offered the solution, for an observer would see the gathered treasures of the day—a harvest of sponges!
Again the age-old question arises — “Are they plants or animals?” Because of their stationary habits, their bright coloration, often green, and their branched shapes, they were considered to be members of the plant kingdom for many years. In fact, it wasn’t until the middle of the 19th century that they were correctly classified as animals, for then conclusive proof was established that their essential qualities were those belonging to the animal realm. It was discovered that the green color was due to the growth of small plants called algae, which frequently covered their surfaces, also the fact that the cell walls did not contain cellulose as is characteristic of plants aided in determining their proper classification. A further proof might be in the case of the young, for they are actively swimming larvae.
Did you ever realize that when you were using an ordinary sponge for bathing or for cleaning purposes that you were applying a skeleton of a sea animal? After the sponges have been harvested, they are buried in the warm sand or exposed to the sun until the flesh is dried and the process of decomposition is complete. Only the framework remains, and this consists of numerous bony structures called spicules. Varied and peculiar are their shapes, for some are like stars or crosses, others appear as arrows, pick-axes, spools or snow-crystals. These skeletons may be divided into three groups, depending upon the composition of their framework; some consist of lime, others of horny-like material, which still others are made of a siliceous or glassy substance.
It might be interesting to note that only two parts in every one hundred thousand parts of water are silica, and that a sponge must imbibe one ton of water to produce one ounce of siliceous spicules. Some sponges rise to the height of several feet and there is one recorded which weighs over 150 pounds after the removal of the liquid.
Sponges reproduce asexually by forming small seeds which break off and attach themselves to some object on the sea bottom, and thus a new organism begins existence. Another method of propagating the species is the sexual form of reproduction. Minute eggs are produced within the jelly-like mass of sponge tissue. Within the same sponge sperm cells are also formed and these fertilize the eggs. Then the fertilized egg is ejected from the body of the sponge and is carried by the current. After the egg reaches maturity it produces a free-swimming larvae equipped with a tail.
It was customary for the Romans to carry sponges on their long marches as a means of quenching the soldiers’ thirst. The sponge has great powers of absorption and thus could supply the necessary liquid for the trip. (In the New Testament, there are at least three references to the sponge at the time of Christ’s crucifixion). In addition, the Romans also used them to erase the errors made in writing. One example is cited of a Roman Martial who sent a poem to Caesar Augustus and accompanied it with a sponge so that he could obliterate any phrases which
would not be favorable. In those days, as well as today, sponges were used largely for bathing and cleansing.
Some species of sponges surround or engulf the shells of oysters and dissolve the entire contents. Another species known as Cliona Sulphurea has the ability to eat into hard marble, dissolving this substance as it continues to bore its way and attaches itself firmly to this foundation.
Current high prices of sponges are explainable in view of two factors. In the first place, the sponge beds have been carelessly exploited and thus the supply has unnecessarily been exhausted: and secondly, a certain fungus disease made its appearance in 1938 and within two years destroyed approximately 75 percent of all sponges off the coast of Florida and in the region of the West Indies. Fortunately, this disease disappeared just as rapidly as it came, for there is no human method of control.