Glossary
Glossary terms beginning with: M
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- madrepores
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Small perforations usually confined to genital plate 2 which mark the external opening to the water vascular system. These are also known as hydropores.
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- madreporite plate
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The genital plate that lies at the apex of interambulacral zone 2 and which is pierced by madrepores. It is usually the largest of the genital plates.
- mamelon
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A rounded, ball-like articulation surface forming the top of a tubercle and the bearing surface on which the spine rests. The mamelon may be perforate (with a central pit) or imperforate (as in this picture).
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- marginal (fasciole)
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A fasciole band that runs around the ambitus of the test, passing beneath the periproct at the posterior.
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- membranous gaps
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Large gaps between plates of the corona that are filled with soft-tissue membranes in life. These are found only in the echinothurioids.
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- meridoplacous
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An interambulacral plating arrangement in which the first (primordial) plate (red) is followed by a single sternal plate (2b: green). The second sternal plate (2a: green) is paired with the first episternal plate (3b: blue)
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- meridosternous
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A meridoplacous plastron.
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- metaplacous
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An interambulacral plating arrangement in which the sternal plates (purple) as well as the basicoronal plate (red) are arranged uniserially.
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- metasternous (plastron)
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A metaplacous plastron
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- microcanal system
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A system of fine, interconnected pore-space immediately beneath the outer plate surface (present in certain clypeasteroids and best observed in slightly abraided tests).
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- miliary granule
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A microscopic knob-like projection from the plate surface that lacks a distinct mamelon but which supports a fine stalked pedicellaria or tiny spinelet.
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- milled ring
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A small flange near the base of the spine marking the distalmost limit of muscle attachment onto the spine base.
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- monobasal (disc)
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An apical disc with five ocular plates but only one genital plate (G2). This genital plate dominates.
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- monocyclic (disc)
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An apical disc in which all of the ocular plates are in contact with the periproct, and separate adjacent genital plates.
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