|Common Name(s):|| Delicate spiny sea rod||Colony Form:|| Bushy; laterally branched but usually not in one plane, to ~30 cm tall.
||Branches:|| Usually long and flexible, sometimes short relative to colony height.
||Apertures:|| Narrow, with pointed lower lip bearing sharp spine, directed upward toward branch tip.
||Color:|| Whitish, bluish-white or gray; dries dries white, yellowish-brown or tan.
||Sclerites:|| Outer layer and calices: spindles stout; calice spindles to >3 mm long, with smooth strong terminal spike. Inner layer: small 8-rayed capstans (double stars) ~0.1 mm long; some more elongated and rod-like, to 0.15 mm long, with two whorls of spines.
||Habitat:|| Moderate to deep environments; sloping rocky substrates and patch reefs, 18-128 m.
||Distribution:|| Florida Gulf Coast, West Palm Beach through the Florida Keys, Bahamas and Caribbean Sea.
||Notes:|| Similar to M. elongata, but with thinner branches, more projecting calices and deeper habitat. M. laxa spindles have single terminal spine, whereas those of M. elongata have multiple stout flattened spines along one side.
||Reference(s):|| Bayer (1961), Humann and DeLoach (2002); Sánchez and Wirshing (2005).