Prickly tube-sponge

Callyspongia crassa, commonly known as prickly tube-sponge, is a species of sponge found from the Red Sea to the Seychelles. Its wide flexible brown tube with exterior protuberances can appear as a single tube or as clusters of tubes and can reach up to 50 centimeters (20 inches) in size.^[1][2][3] Like many other sea sponges, it is primarily used for marine drugs as they have many bioactive components and properties.^[4] They also play an important role in marine reef and benthic communities, as they constantly filter water and act as habitats for smaller organisms.^[5][6] As sea sponges, they have the ability to reproduce both sexually and asexually.^[7]

The name crassa derives from the Latin word crassus meaning solid, thick, fat, or dense.^[8] Its common name, the prickly tube-sponge, comes from its physical appearance as it is a tube sponge and it is nearly completely covered in spines.^[9] It was previously named Sclerochalina crassa, but was eventually moved to the genus Callyspongia.^[2][10]

The genus Callyspongia belongs to the family Callyspongiidae. This family contains four genera: Arenosclera, Callyspongia, Dactylia, and Siphonochalina with Callyspongia being the largest and containing over 180 species.^[11] They are under the phylum Porifera, making them a sponge. Specifically, they are Demosponges, which is the most diverse class in the phylum Porifera.^[12]

The prickly tube-sponge is a large, flexible, brown, sometimes red, tube that can be found as a singular tube or as a cluster. It has been known to reach up to 50 centimeters (~20 inches) with specimens as small as 2 mm having been found, but it typically has an average diameter of 30 centimeters (~12 inches). Most of its surface is covered with spines or spine-like protrusions which tend to taper away towards the upper part of the tube.^[2][4][9]

Humans mainly use these sponges for marine drugs.^[4] Many species of sponge are used for marine drugs due to their bioactive components, many of which are used for antiseptic agents.^[4][9] Callyspongia crassa has over 20 compounds with anti-inflammatory and anti-microbial properties, among others, which contribute to its various medical uses.^{[9] [citation needed]}

Sea sponges are also of important use in the wild. They play an important role in nutrient recycling and in filtering the water^[5] which is useful for many of the reefs that they live in as clearer water makes sunlight more accessible for photosynthesizing organisms in the same area.^[13] Many sponges also serve as a habitat for a variety of other organisms. They can serve as microhabitats,^[5] with conditions different from the larger surrounding area. Tube sponges specifically, often have small fish and other inhabitants living inside of the tubes.^[6]

These sponges are native to the Red Sea. Samples have been found in the southern Red Sea off the coasts of Sudan and Eritrea^[2] and in the northern Red Sea in the Gulf of Aqaba at Eilat.^[4][9] They are known to live in marine reef and marine benthic habitats, relatively close to shore.^[2] They have been found between a depth of 1–30 m, but they are more abundant at deeper depths (15–30 m).^[4] They live in waters with high salinity and warm temperatures, with water in the Red Sea never dropping below 21 °C (70 °F).^[10]

Callyspongia crassa are filter feeders and suspension feeders, but they mainly filter feed.^[2] They filter feed because they lack true tissues and organs, so they can not have a digestive system similar to other animals.^[14][15] This sponge filter feeds by taking in water towards the base, filtering it to get the nutrients and food, and then expelling the leftover water out through the osculum.^[16] They are omnivores as their diet consists of both small plants and animals.^[3]

Sea sponges can reproduce both sexually and asexually. They often switch between the two seasonally, to best grow their populations and take up space on the reef.^[7][17]