Morphology and Musculature
A. brevis has a smooth, rigid body with ventral and lateral grooves extending along the entire elongated body (Clark and Hermans, 1976).
Internally, large dorsal and ventral longitudinal muscle bands are the prominent musculature in Armandia brevis, lying directly beneath the epidermis. The ventral longitudinal muscles form two well-developed ventral bundles that shape the ridges of the ventral groove and are separated by the ventral nerve cord. The dorsal longitudinal muscle bands become thinner mid-dorsally but do not separate completely. No circular muscle fibers are found between the epidermis and longitudinal muscles, but four bands of oblique muscle occur per segment. Oblique muscle bands extend from just dorsal of the ventral nerve cord and attach to the lateral epidermis between the dorsal and ventral longitudinal muscles (Law et al., 2014).
Only two septa occur in A. brevis, just posterior to the pharynx; the remaining body cavity is undivided by septa, allowing coelomic fluids to flow freely during body movements (Law et al., 2014).
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