What's the difference between rhachidian and rhachis?

Rhachidian

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Definition:

• (a.) Of or pertaining to the rhachis; as, the rhachidian teeth of a mollusk.

Example Sentences:

Rhachis

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Definition:

• (n.) The spine.
• (n.) The continued stem or midrib of a pinnately compound leaf, as in a rose leaf or a fern.
• (n.) The principal axis in a raceme, spike, panicle, or corymb.
• (n.) The shaft of a feather. The rhachis of the after-shaft, or plumule, is called the hyporhachis.
• (n.) The central cord in the stem of a crinoid.
• (n.) The median part of the radula of a mollusk.
• (n.) A central cord of the ovary of nematodes.

Example Sentences:

• (1) Abnormalities found in mutant feathers included decreased overall size, absence of prelumulae and prefiloplumulae feathers, an abnoramlly small rhachis with a disproportionally small medulla, thickening of the feather-sheath, and increased abundance of pulp cells.