Order Spirophorida

ypically with spherical growth form, with tetraxonid and monaxonid megascleres (triaenes, huge oxeas) in radiate pattern; protriaenes and anatriaenes most common and often protrude from surface; monocrepidial desmas may be present; microscleres contorted microspined sigmaspires, an apomorphy for the group. Reproduction is oviparous without a larval stage, or viviparous with production of young adults within parent.