Both the shell-less aplacophorans and the shelled chitons, also known as sea cradles, still exist today.
the team thinks that aplacophorans actually evolved from chitons by shedding their shells.
The next puzzles were two questions: Are the aplacophoran Solenogastres and Caudofoveata monophyletic or diphyletic?
ecologists, paleontologists, physiologists, phylogeneticists, and malacologists, including those who are aplacophoran taxonomists), aplacophoran taxonomic publications need as many detailed character descriptions as possible besides soft anatomy.
family Prochaetodermatidae in the North American basin, including Chevroderma N.
Aplacophoran molluscs are a small taxon with fewer than 400 described species including both neomenioids (Neomeniomorpha or Solenogastres) and the chaetoderms (Chaetodermomorpha or Caudofoveata).
Species of Helicoradomenia, the genus to which most aplacophoran vent species belong, occur on northern and southern segments and at the Galapagos Rift.
Along the molluscan line leading from the aplacophoran
to the conchiferan clades (all molluscs that arose from a shelled ancestor), the Polyplacophora (chitons) occupies an intermediate position.
The neomenioid aplacophoran
Epimenia babai from Japan is considered to have a unique larval form among neomenioid aplacophorans
in that it lacks the true test structure characteristic of neomenioid pericalymma larvae (Baba, 1938, 1940, 1951, 1999; Thompson, 1960; Nielsen, 2001).
molluscs with a narrow foot-fold in a ventral, longitudinal pedal groove and without a cuticular oral shield or mantle cavity ctenidia; midgut as a combined stomach and digestive gland; monoecius.
This appears unfounded as spikes in anomalodesmatan bivalves are secreted within the translucent layer of the periostracum, far from the contact with the mantle epithelium, whereas in aplacophorans
and polyplacophorans the sclerites are secreted directly by epithelial cells lining the cuticle internally (e.
Larval cuticles are previously unknown in gastropod larvae, although the pericalymma larvae of protobranch bivalves and neomenioid aplacophorans
have cellular tests.
2002), the test larva of neomen-ioid aplacophorans
(Thompson, 1960: Okusu, 2002), and the pericalymma of the protobranch bivalve molluscs (Gustafson and Reid, 1986; Gustafson and Lutz, 1992; Zardus and Morse, 1998), as well as the unusual larva of the sipunculid Sipuncultts nuchts (Gerould.
The late nineteenth and early twentieth centuries were especially important for the rise of systematic studies on meiobenthic molluscs, when numerous species of interstitial prosobranchs, opisthobranchs, and aplacophorans
were described (e.
, monoplacophorans, polyplacophorans, scaphopods: the lesser classes.