In contrast to vertebrates - where the brain develops from a neural tube (neurulation) - cephalopod ganglia form as individual placodes in the blastoderm of the embryo, which fuse during subsequent development (Marquis, 1989, Shigeno et al., 2001a). In addition, so-called stellate ganglia are found that innervate the mantle musculature (Messenger, 1979, Shigeno and Yamamoto, 2002, Wollesen et al., 2010, Young, 1974, Young, 1976, Young, 1977, Young, 1979). The most prominent parts of the cephalopod central nervous system are the paired, laterally situated optic lobes, which may occupy up to two thirds of the total mass of the cephalopod CNS. Thus, the cephalopod “brain” may comprise the fused cerebral, brachial, pedal, palliovisceral, and buccal ganglia of a proposed last common gastropod–cephalopod ancestor. Their CNS is believed to have evolved by fusion of paired ganglia homologous to those found in their potential sister group, the gastropods (Salvini-Plawen, 1980, Salvini-Plawen and Steiner, 1996), although recent studies show a different relationship between molluscan taxa (Kocot et al., 2011, Smith et al., 2011). Non-destructive micro-CT applications have great mapping potential when combined with other classic techniques such as histology, immunocytochemistry, and gene expression studies.Ĭephalopods exhibit a highly complex central nervous system (CNS) in protostomes as well as a diverse suite of behavioral patterns. The technique eases computer-assisted 3D-reconstructions and modeling due to the perfectly aligned, distortion-free image stacks produced by the micro-CT scans. We show that micro-CT in combination with contrast-enhancing substances, such as iodine or phosphotungstic acid, can provide detailed 3D information on the anatomy of cephalopod embryonic structures including the nervous system. We therefore focused our study on major neural ganglia during development, to assess the suitability of micro-CT as non-destructive method for ontogenetic studies. While neurodevelopmental as well as gene expression data are available for this species, basic information on its organogenesis is still lacking. As a model, we chose the Hawaiian bobtail squid Euprymna scolopes that is considered a key-organism for study of decabrachiate development.
Here, we demonstrate a state-of-the-art-technique of X-ray microtomography (micro-CT) for 3D imaging of soft-bodied organisms without mineralized structures.
Anatomy of squids serial#
Most investigations on the internal organization of soft-bodied animals such as cephalopods are based on classical serial sectioning (i.e.
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