1) Glochid 2) Pricker 3) Prickle 4) Spine 5) Sticker 6) Thorn 1) Glochid 
The glochidium (plural glochidia) is a microscopic larval stage of some freshwater mussels, aquatic bivalve mollusks in the families Unionidae and Margaritiferidae, the river mussels and European freshwater pearl mussels. This larva form has hooks, which enable it to attach itself to fish (for example to the gills of a fish host species) for a per...
• (n.) The larva or young of the mussel, formerly thought to be a parasite upon the parent`s gills.
(from the article `bivalve`) In the freshwater Unionidae the released larva, called a glochidium, often has sharp spines projecting inward from each valve. The larva is attracted ...
Glo·chid'i·um noun ; plural Glochidia . [ New Latin , from Greek ... the point of an arrow.] (Zoology) The larva or young of the mussel, formerly thought to be a parasite upon the parent's gills. 
glochid. · the larva of a freshwater mussel of the family Unionidae that lives as a temporary parasite in the gills or on other external parts of fishes.