holdfast

n. device that holds or secures an object in place; hook; clamp; (Botany) branching or conical body that attaches seaweed or other aquatic plant to the surface; strong solid grasp

A holdfast is a root-like structure that anchors aquatic sessile organisms, such as seaweed, other sessile algae, stalked crinoids, colonial cnidarians, and sponges, to the substrate .Holdfasts vary in shape and form depending on both the species and the substrate type. The holdfasts of organisms that live in muddy substrates often have complex tangles of root-like growths, while those of organisms that live in sandy substrates are bulb-like and very flexible, such as the holdfast of sea pens, allowing the organism(s) to pull the entire body into the substrate when the holdfast is contracted. The holdfasts of organisms that live on smooth surfaces (such as the surface of a boulder) have the base of the holdfast literally glued to the surface. The organism derives no nutrients from this intimate contact with the substrate, primarily because if the organism attempted to extract nutrients enzymatically from the substrate, the substrate would be eroded away, thereby increasing the risk of falling off of the substrate.
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Noun
1. restraint that attaches to something or holds something in place
(synonym) fastener, fastening, fixing
(hypernym) restraint, constraint
(hyponym) bellyband
(derivation) adhere, hold fast, bond, bind, stick, stick to

(n.)
Something used to secure and hold in place something else, as a long fiat-headed nail, a catch a hook, a clinch, a clamp, etc.; hence, a support.
  

(n.)
A conical or branching body, by which a seaweed is attached to its support, and differing from a root in that it is not specially absorbent of moisture.
  

holdfast /'houldfɑ:st/
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