spicule

(noun)

a sharp, needle-like piece

Related Terms

Examples of spicule in the following topics:

  • Phylum Porifera

    • Sponges lack true tissues, have no body symmetry, and are sessile; types are classified based on presence and composition of spicules.
    • The presence and composition of spicules and spongin are the differentiating characteristics between the classes of sponges .
    • Hemoscleromorpha sponges tend to be massive or encrusting in form and have a very simple structure with very little variation in spicule form (all spicules tend to be very small).
    • Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silica.
    • Sponges are classified based on the presence and types of spicules they contain.

  • Embryonic and Fetal Bone Formation

    • The first step in the process is the formation of bone spicules which eventually fuse with each other and become trabeculae.
    • Much like spicules, the increasing growth of trabeculae result in interconnection and this network is called woven bone.
    • These aggregates of bony matrix are called bone spicules.
    • Separate mesenchymal cells differentiate into osteoblasts, which line up along the surface of the spicule and secrete more osteoid, which increases the size of the spicule.
    • During the formation of bone spicules, cytoplasmic processes from osteoblasts interconnect.

  • Sponge Communities

    • Hexactinellids, or "glassy" sponges, are characterized by a rigid framework of spicules made of silica.
    • Hexasterophoran sponges have spicules called hexactines that have six rays set at right angles.
    • Orders within hexasterophora are classified by how tightly the spicules interlock with Lyssanctinosan spicules less tightly interlocked than those of Hexactinosan sponges.
    • Hexactinosan sponges have a rigid scaffolding of "fused" spicules that persists after the death of the sponge.
    • The tendrils of new sponges wrap around spicules of older, deceased sponges.

  • Pre-Cambrian Animal Life

    • They are believed to show the existence of hard body parts and spicules that extended 20–40 cm from the main body (estimated about 5 cm long).

  • Development of the Skeleton

    • As the osteogenetic fibers grow out to the periphery they continue to calcify, and give rise to fresh bone spicules.

  • Types of Skeletal Systems

    • An example of a primitive endoskeletal structure is the spicule of sponges.

  • Bone Remodeling and Repair

    • Some bone spicules may also appear at this point.

  • Morphology of Sponges

    • Some of these more-specific cell types include collencytes and lophocytes, which produce the collagen-like protein to maintain the mesohyl; sclerocytes, which produce spicules in some sponges; and spongocytes, which produce the protein spongin in the majority of sponges.

  • Physiological Processes in Sponges

    • In gemmules, an inner layer of amoebocytes is surrounded by a layer of collagen (spongin) that may be reinforced by spicules.

  • Phylum Nematoda

    • Specialized structures at the tail of the male keep him in place while he deposits sperm with copulatory spicules.