Editing Endoskeleton (section)

=== Sponges===
The poriferan "skeleton" consists of mesh-like network of microscopic [[sponge spicule|spicule]]s. The soft [[connective tissue]]s of sponges are composed of gelatinous [[mesohyl]] reinforced by fibrous [[spongin]], forming a [[composite material|composite]] [[matrix (biology)|matrix]] that has decent [[tensile strength]] but severely lacks the [[stiffness|rigidity]] needed to resist [[deformation (engineering)|deformation]] from [[ocean current]]s. The spicules act as [[structural element]]s that add much needed [[compressive strength|compressive]] and [[shear strength]]s that help maintain the sponge's shape (which is needed to ensure optimal [[filter feeding]]), much like the [[aggregate (composite)|aggregate]]s and [[rebar#Stirrups|rebar stirrup]]s within [[reinforced concrete]]. Sponges can have spicules made of [[calcium carbonate]] ([[calcite]] or [[aragonite]]) or more commonly [[silica]], which separate sponges into two main [[clade]]s, [[calcareous sponge]]s ([[class (biology)|class]] [[Calcarea]]) and [[siliceous sponge]]s, the latter being the dominant extant clade with two classes [[Demospongiae]] ([[common sponge]]s) and [[Hexactinellida]] ([[glass sponge]]s). There are however species (such as [[Spongia officinalis|bath sponge]] and [[Spongilla lacustris|lake sponge]]) that have no or severely reduced spicules, which gives them an overall soft "spongy" structure.

Deep-sea demosponges from the family [[Cladorhizidae]] have evolved a unique [[carnivorous]] survival strategy, by having tiny [[grappling hook]]-like spicules ([[microsclere]]s) that extends outwards like [[bur]]s to snag and trap passing-by aquatic animals such as small fish and [[crustacean]]s. As sponges don't have dedicated [[digestive system]]s, these predatory sponges rely on [[symbiotic]] organisms such as [[scale worm]]s and [[microbe]]s to help digest the seized prey and release [[nutrient]]s that can then be absorbed by the sponges' cells.