Anatomy Acoelomorpha

symsagittifera roscoffensis

acoelomorphs resemble flatworms in many respects, have simpler anatomy, not having gut. flatworms, have no circulatory or respiratory systems, lack excretory system. lack body cavities (acoelomate structure), hindgut or anus.

the epidermal cells of acoelomorphs unable proliferate, feature shared rhabditophoran flatworms , time considered strong evidence position of acoelomorpha within platyhelminthes. in both groups, epidermis renewed mesodermal stem cells.

the nervous system of acoelomorphs formed set of longitudinal nerve bundles beneath ciliated epidermis. close anterior end, these bundles united ring comissure, not form true brain, although hypothesized such organization precursor of cephalization of nerve system in more derived bilaterians. after decapitation, such brain (rather, cerebroid ganglion) regenerates in few weeks.

the sensory organs include statocyst and, in cases, primitive pigment-spot ocelli capable of detecting light.

acoelomorphs simultaneous hermaphrodites, have no gonads , no ducts associated female reproductive system. instead, gametes produced mesenchymal cells fill body between epidermis , digestive vacuole.