A fresh look at Dinodasys mirabilis (Gastrotricha, Macrodasyida), with focus on the reproductive apparatus and sperm ultrastructure

Abstract

Adults of Dinodasys mirabilis were studied for the first time. The specimens, collected from the west coast of Sweden, were investigated alive and with electron microscopy. Sexually mature specimens attain a total length of 450-490 µm; the adhesive apparatus is made up of anterior, lateral, ventrolateral, dorsal and posterior tubes; one pair of 'cirrata' type tubes is also present. The reproductive apparatus is hermaphroditic; paired testes extend rearward from the pharyngeo-intestinal junction to 3/4 of the trunk; sperm ducts bend anteriorly at U52 and join together into a common, midventral pore at U33. Two ovaries lie along the sides of the caudal intestine, extending anteriorly from U68. Frontal organ present on the right side of the body, centred a U70; caudal organ absent; a gland organ surrounding the terminal intestine may be present but its homology with other organs in a similar position is uncertain. The spermatozoon is a filiform cell, formed by a long acrosome, a spring-like nucleus and a flagellum. The acrosome is divided into two regions: the anterior-most is thin and corkscrew-shaped, the posterior one is rectilinear; both regions are delimited by a continuous external layer of thick, dense material, that in longitudinal section appears obliquely striated and surrounds a long pile of stout, electron-dense cylinders; the nucleus contains condensed chromatin and is coiled around an elongate mitochondrion; the flagellum possesses a 9x2 + 2 axoneme devoid of striated cylinder. Within Macrodasyida, U-bend sperm ducts and the peculiar ultrastructure of the acrosome are characteristics shared by other Turbanellidae studied so far, providing a foundation for the current systematization of Dinodasys

An Integrated Morphological and Molecular Approach to the Description and Systematisation of a Novel Genus and Species of Macrodasyida (Gastrotricha)

“…Four formalin-fixed speciemens were rinsed in in 0.1 M PBS buffer, dehydrated through a graded ethanol series, critical point-dried using CO 2 , mounted on aluminium stubs, sputter-coated with gold-palladium, and observed with a Philips XL 30 scanning electron microscope [36]. …”

1. Gastrotricha

“…The morphology of the reproductive organs (male and female gonads, accessory structures such as the frontal and caudal organs, outlet ducts, gland tissues) were studied in quite a lot species of Gastrotricha at the ultrastructural level (e.g., Ruppert & Shaw 1977, Ruppert 1978a, b, 1991, Hummon 1984a-c, Kieneke et al 2008d, 2009, Guidi et al 2011, Todaro et al 2012a The study of Dactylopodola typhle revealed a reproductive system generally comparable to that of other species of the Macrodasyida (Kieneke et al 2008d). However, there are considerable differences as well.…”

“…Hence, the three resulting ground pattern hypotheses varied in some character states due to topological differences between the three phylogenetic hypotheses. It has to be stressed that the most recent studies on the anatomy and ultrastructure of the reproductive tract of Crasiella diplura (Guidi et al 2011), Dinodasys mirabilis (Todaro et al 2012a), and Megadasys sterreri were not considered at that time. Based on this procedure, the reproductive system of the common ancestor of Gastrotricha was probably composed of the components listed in the following.…”

“…Flattened epithelial linings of the entire female gonad (early oocytes plus uterus region) are described in different species that have been studied by means of TEM, e.g., Macrodasys sp. Meanwhile, they could not be found in the ovary region (e.g., Tetranchyroderma bunti: Ruppert 1978b, see Todaro et al 2012a). 1.33 C), Oregodasys (=former Platydasys) cf.…”

A new species of sublittoral marine gastrotrich, Lepidodasys ligni sp. n. (Macrodasyida, Lepidodasyidae), from the Atlantic coast of Florida

“…n., the frontal organ abuts the caudal organ; the circular muscles of the caudal organ are part of the organ itself and therefore independent of the somatic circular muscles anterior to it. How these two organs function together or separately in the uptake of allosperm or release of autosperm, repsectively, is unknown and will likely require a detailed investigation with transmission electon microscopy as has been performed for other macrodasyidan gastrotrichs (e.g., Ruppert 1978, 1991; Guidi et al 2004, 2011; Kieneke et al 2012; Todaro et al 2012). …”