''Iotrochota birotulata'', commonly known as the green finger sponge, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

sea sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

in the family

Iotrochotidae Iotrochotidae is a family of sponges belonging to the order Poecilosclerida Poecilosclerida is an order of the demosponge class. It is the most speciose demosponge order with over 2200 species (World Porifera Database). It contains about 25 re ...

. It is found in shallow waters in the Caribbean Sea.

Description

The green finger sponge usually has upright or sprawling cylindrical branches that occasionally divide. The branches are about in diameter and can grow to in length. Young individuals and some large specimens have an encrusting habit. They grow over the surface of a rock in a layer a few millimetres thick with occasional short chimney-like outgrowths. Other individuals have a number of vertical tubes, each with a large opening called an

osculum The osculum (plural "oscula") is an excretory structure in the living sponge, a large opening to the outside through which the current of water exits after passing through the spongocoel. Wastes diffuse into the water and the water is pumped thr ...

at the end. These variations in growth habit led to the belief that several different species of sponge were involved. However, specimens growing in reef caves often have an encrusting base with a central, finger-like cluster of branches, so it is now believed that the different forms are a single species, perhaps differing in structure because of different environmental conditions. In the branched form, the osculi are found on the upper side of the branches and may be slightly raised above the surrounding tissue. The consistency of the sponge is soft but resilient, and when squeezed, it exudes a purple fluid. The general colour of the sponge is purplish black but there is often a layer of bright green cells on the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...

. These have

dendritic Dendrite derives from the Greek word "dendron" meaning ( "tree-like"), and may refer to: Biology *Dendrite, a branched projection of a neuron *Dendrite (non-neuronal), branching projections of certain skin cells and immune cells Physical * Dendr ...

patterns on the surface and cover sub-surface canals which lead to the osculi.

Distribution and habitat

The green finger sponge is found in the Caribbean Sea at depths varying from . Its range includes the West Indies, the Bahamas, southern Florida, Venezuela and northern Brazil, but it is absent from Bermuda. It inhabits

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock out ...

s, the deeper water outside the reef crests and the underside and surfaces of rocks in shallow bays.

Biology

The golden zoanthid (''Parazoanthus swiftii''), a

colonial Colonial or The Colonial may refer to: * Colonial, of, relating to, or characteristic of a colony or colony (biology) Architecture * American colonial architecture * French Colonial * Spanish Colonial architecture Automobiles * Colonial (1920 au ...

coral, is often found twined round the sponge in a

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

relationship. The polyps look like small

sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

s and contain toxins which deter

predatory Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

fish from eating the sponge. The coral benefits from the increased volume of food particles its polyps can capture as water is drawn through fine pores into the sponge.

References

{{Taxonbar, from=Q1892902 Poecilosclerida Sponges described in 1877