Microscleres

Microscleres are small skeletal spicules found in many sponges (Porifera). They complement the larger megascleres that form the main framework of the sponge skeleton. Microscleres are typically microscopic to sub-microscopic in size and occur in a wide variety of shapes, including star-like, spherical, needle-like, and other complex forms. Their composition follows the sponge’s mineral pattern: siliceous microscleres in most siliceous sponges and calcareous microscleres in calcareous sponges, though some groups may have mixed mineralogy.

Role and distribution: Microscleres are embedded throughout the mesohyl and often interact with megascleres to reinforce the skeletal network. They contribute to the texture and surface ornamentation of the sponge and can influence mechanical properties and predator deterrence. Because microscleres are highly variable among species, they are frequently used in sponge taxonomy and systematics alongside megascleres.

Development and taxonomy notes: Microscleres are produced by specialized sclerocytes during sponge growth. Variation in microsclere form and presence is used to distinguish species, genera, or higher taxa in many groups, particularly among demosponges and hexactinellids. In some taxa, the microscleres provide essential diagnostic characters when megascleres are less informative.

Summary: Microscleres are a diverse class of small spicules that, together with megascleres, build a sponge’s skeleton. Their morphology, mineralogy, and distribution within the tissue make them important for function, ecology, and taxonomic identification across sponge lineages.