Computed Microtomography (Micro-CT) in the Anatomical Study and Identification of Solenogastres (Mollusca)

Abstract

Solenogastres are vermiform marine molluscs characterised by an aculiferous mantle, a longitudinal ventral pedal groove and a terminal or subterminal pallial cavity. Their classification is based in part on the type of mantle sclerites, but identification to even the family level generally requires the study of internal anatomical characters. Taxonomically important internal characters include those related to radular structure, the type of ventrolateral glandular organs of the pharynx and the reproductive system, among others. In order to study their internal anatomical organisation, according to the classical reconstruction method, serial histological sections of specimens are made, from which the 2D internal anatomy of the specimen can be reconstructed manually. However, this is a time-consuming technique that results in destruction of the specimen. Computed microtomography or micro-CT is a non-destructive technique based on the measurement of the attenuation of X-rays as they pass through a specimen. Micro-CT is faster than histology for studying internal anatomy and it is non-destructive, meaning that specimens may be used for e.g., DNA extraction or retained as intact vouchers. In this paper, the utility of micro-CT for studying taxonomically important internal anatomical structures was assessed. Results of the 3D anatomical study of the soft parts of four specimens of three species using micro-CT are presented: Proneomenia sluiteriHubrecht, 1880, Dorymenia menchuescribanaeGarcía-Álvarez et al., 2000 and Anamenia gorgonophilaKowalevsky, 1880. Micro-CT enabled detailed study of most taxonomically important anatomical characters, precise measurements of structures, and observation of the relative position of organs from a variety of angles. However, it was not possible to observe the radula and some details of the ventral foregut organs could not be discerned. Despite these limitations, results of this study highlight micro-CT as a valuable tool to compliment histology in the study of solenogaster anatomy and in non-destructively identifying animals to the family and even genus-level.

Aplacophoran traits in the late Ordovician septemchitonid polyplacophorans

“…Probably this exemplifies a change from relying on a protective function of dorsal shell to the passive defense against predators with its long spine array. These highly important findings do not help in explaining the origin of the ventral furrow in the extant solenogasters, generally believed to hide a rudiment of the foot (e.g., Haszprunar & Wanninger, 2000; Kocot et al, 2019; Martínez‐Sanjuán et al, 2022; Scheltema et al, 2012).…”

Four new Solenogastres (Mollusca, Aplacophora) from the South China Sea and paraphyly of Proneomeniidae Simroth, 1893

“…Micro-computed tomography is a promising technique for advancing aplacophoran taxonomy as this is a non-destructive method that can be used to obtain data on internal anatomy and three-dimensional (3-D) reconstructions. High levels of detail can be obtained for many anatomical structures but this is costly and advances in this technique are still required to improve the resolution needed to study small animals (Martínez-Sanjuán et al 2022). In the same way, 3-D reconstructions based on histology (e.g.…”