Reproduction and rapid growth in a deep-sea
aplacophoran mollusc, Prochaetoderma yongei.
For entoprocts and small brachiopods (Novocrania anomala and Macandrevia cranium), whole-body tissue was employed; for larger brachiopods (Glottidia pyramidata, Hemithris psittacea, and Laqueus californicus), extractions focused on mantle and muscle; for the solenogaster (a.k.a neomenioid)
aplacophoran mollusc Proneomenia custodiens, unhatched juveniles were used.
Only one-third of the collected species of
Aplacophoran molluscs have been named and described even though they are an important component of the deep-sea fauna and often appear among the ten most abundant species.
Indeed, the great malacologist Johannes Thiele, with far less information than is now available, and who published over 20
aplacophoran species descriptions, concluded that
aplacophorans were not molluscs as such, but phylogenetically between annelids and molluscs and ancestral to the latter (Thiele, 1913c; Glaubrecht et al., 2005).
The observed variance to mean ratios of 10-100 for live oyster density estimates in the James River are comparable to those reported for hard clam (Mercenaria mercenaria, Fegley 2001) and
aplacophoran (Scheltema 1985) populations.
ABSTRACT Species of the neomenioid
aplacophoran genus Helicoradomenia Scheltema & Kuzirian are found only in areas of hydrothermal vents, oceanic ridges, and back-arc basins and have been collected widely in the East Pacific, Southwest Pacific, and the Triple Junction in the Indian Ocean, but not in the Atlantic.
It may very well be, however, that the ciliated cells in question are derived from the trochoblast cell lineage, as has been suggested for pericalymma larvae of protobranch bivalve and neomenioid
aplacophoran molluscs (Thompson, 1960; Zardus and Morse, 1998), and shown to be the case in the palaeonemertean Carcinoma tremaphoros (Maslakova et ah, 2004).
Most strikingly, this is exemplified in the Mollusca, where the most basal forms, the
aplacophoran taxa Neomeniomorpha and Chaetodermomorpha, constitute a vermiform appearance, while all other molluscan subgroups derive from benthic or pelagic shell-bearing taxa (Ponder and Lindberg, 2008).
This paper reports the first neuroanatomical results using immunocytochemical neural markers for a species traditionally classified as an "
aplacophoran," and offers insights into the evolution of the nervous system of vermiform shell-less molluscs.
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).
Because siboglinids are not closely related to molluscs and because of rate heterogeneity problems within the Mollusca, only a single representative (the
aplacophoran Scutopus) was used.