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Haliclona sp. blue encrusting sponge. Scott W. Michael

[edit] The Sponges

Number of Living Species: 5,000, mostly marine, many still unidentified.

Common Characteristics: the most primitive of the multi-celled animals; sessile (not free-moving, attached to substrate); most movement of body parts too slow to be visible to naked eye; simple body plan with a system of internal water canals; body supported by spicules (small needlelike or rodlike structures embedded in the tissue). Noteworthy Behaviors: remarkable water-pumping abilities (one study showed a small sponge circulating 2,250 times its own body volume of water each day); feed on extracted microscopic particulate matter, including organic material, bacteria, various types of fine plankton; some marine sponges harbor symbiotic, photosynthetic zooxanthellae or cyanobacteria.
From: Reef Life
Denise Nielsen Tackett

[edit] The Sponges: An Introduction

By Ronald L. Shimek, Ph.D.

The sponges are a group where specific identifications of all but a few forms are impossible without examination of the internal skeletal structures. Some sponges have a defined shape and adult size, and these may often be identified from photographs. Most sponges, however, tend to grow without a defined shape or size, making them hard to describe unambiguously. Scientists who study sponges use internal structures, called spicules, to define sponge species and to assign the sponges to various groups. Spicules are mineralized internal skeletal bodies that are secreted by the sponge cells. The spicules may be either calcium carbonate or silica. And in a few cases, just to make life interesting, spicules are lacking and the sponge has a wholly proteinaceous skeleton. The spicules range in size from a few millionths of a meter to several centimeters in length. The majority are probably from 0.01 to about 0.5 mm long. There are several dozen types of spicules, and often several types are found in a given sponge. Identification of sponges to the species level often requires examination and measurement of the spicules, as well as a determination of their relative abundance. This generally involves a lot of microscopy, and requires equipment that most hobbyists lack. The bottom line: You generally can’t determine the exact species of most sponges using photographs. Be satisfied with an approximate or common name.

[edit] Calcareous Sponges

Calcareous sponges, in the Class Calcarea, have a body of spongy fibers supported by spicules made of calcium carbonate (rather than silica, as is found in the demosponges, starting on page 24). Most of the time, calcareous sponges occur in our systems accidentally; they come in on live rock or as larvae. Their maximum sizes are generally smaller than most demosponges.

Calcareous Sponges

  • Clathrina spp.
  • Leucosolenia spp.
  • Scypha spp.,
  • Sycon spp.
  • Tubular calcareous sponges

[edit] Demosponges

The sponges of most interest to aquarists are all in the Class Demospongiae. (The third sponge class, Hexactinellida, is primarily deep water and will not be found in coral reef areas or imported for aquarium use.) Demosponges are characterized by spicules made of silicon dioxide or silica. Silica is the major constituent of glass, and as you might expect, relatively few animals can metabolically utilize this material. Sponges can, however, and they use it to their advantage as a structural and defensive material. Demosponges are typically larger than calcareous ones, and may be very large indeed; some in the Antarctic are about the size of small houses.

Demosponges are found in all seas and in freshwater environments. They are typically much more structurally complex than calcareous sponges, yet most of them feed on the same sorts of micro-particulate foods. They are found in virtually all colors, but not all of them are suitable for the home aquarium. In nature, bright colors are often used to advertise to various visually based predators, such as fishes or crabs, that the bearer is distasteful or poisonous. Many beautiful sponges are exceptionally toxic and have no place in the home aquarium.

Fortunately, many others are fine, and sponges add a component of color and structure to a system that is normal to a reef, but often lacking in home aquariums. Sponges are not equally abundant or dominant on all reefs, and are much more evident and large in the Caribbean than in the Indo-Pacific. Consequently, most of our large demosponges are collected from the Caribbean. Demosponges are often purchased (rather than accidentally introduced to tanks like calcareous sponges), and it is important that several precautions be taken to ensure their continued health. Air should never be allowed to touch the surface of the sponges. Sponges are perforated by millions of microscopic canals that are used in feeding and respiration. Any air bubble getting into contact with these canals will be drawn in by capillary action and will plug the canal. This will kill the cells surrounding that bubble. These cells will rot, causing more gas, which causes more bubbles that spread outward in a gassy sphere of mortality. Eventually, the whole sponge will die. Most sponges are from areas where large bubbles never occur naturally, and they have no physiological or mechanical means to remove the bubbles from their canals. Always transfer sponges totally submerged.

[edit] Sponge Test

A curious hobbyist can confirm whether a sponge is a demosponge or a calcareous sponge by removing a sample of the sponge (about 1-2 mm) with forceps. DO NOT use your fingers. (The sponge will regenerate the damaged area.) Completely dissolve the sample in chlorine bleach. Pour off the bleach, add freshwater, and rinse the remains. You should be able to see fine, glasslike particles in the container. Add a bit of vinegar. If bubbles form, the sponge is calcareous; if not, it is a demosponge.

Excerpt from: A PocketExpert Guide to Marine Invertebrates
by Ronald L. Shimek, Ph.D.