Ultrastructure of spermiogenesis and the spermatozoon of Macracanthorhynchus hirudinaceus (Pallas, 1781) (Acanthocephala: Archiacanthocephala), a parasite of the wild boar Sus scrofa

The present paper describes the ultrastructure of spermiogenesis and the spermatozoon of Macracanthorhynchus hirudinaceus, an acanthocephalan parasite of the wild boar Sus scrofa. At the beginning of spermatogenesis, spermatocytes exhibit synaptonemal complexes and 2 centrioles. In the spermatid, only 1 centriole remains, generating a flagellum with a 9+2 pattern. Another ultrastructural feature observed during the spermiogenesis of M. hirudinaceus is the condensation of the chromatin, forming a "honeycomb" structure in the old spermatid and a homogeneous, electron-dense structure in the spermatozoon. The mature spermatozoon of M. hirudinaceus presents a reversed anatomy, as has been described previously in other species of the Acanthocephala. The spermatozoon is divided into 2 parts: an axoneme, and a nucleocytoplasmic derivative. The spermatozoon flagellum exhibits a 9+2 or 9+0 pattern. The process of spermiogenesis and the ultrastructural organization of the spermatozoon of M. hirudinaceus are compared with available data regarding other acanthocephalan species.     

Fine structure of anterior terminus of apical sense organ in Macracanthorhynchus hirudinaceus (Acanthocephala)

The apex of the proboscis of Macracanthorhynchus hirudinaceus is crowned by a cone-shaped projection with a small opening in its center. The bottom of this opening is the anterior terminus of the apical sensory organ. When viewed in transverse section, the anterior terminus of this organ appears as a series of distinct layers that encircle a central cone enclosing a complex arrangement of nerves and a sensory support cell duct. Four membrane-defined layers encircle the cone area. The outermost glycocalyx is morphologically identical with that described on the metasoma. The second layer, or tegument, is similar in appearance to that observed on the trunk except for the greater abundance of keratinlike bundles throughout. These bundles are also organized into a loose network along the inner tegumental membrane. The third layer, a latticework of fine filaments containing few organelles, has an erratic boundary that occasionally extends into layer 4. The area adjacent to the inner and outer boundary contains numerous vesicles. Layer 4 has 2 distinct zones. The outer contains filaments arranged as in circular muscle; whereas, the medial lacks such filaments but consists of a finely grained matrix. Radiating throughout both zones are numerous osmiophilic bundles of fibers. The cone at this level contains 8 branches of the apical sensory nerves that interdigitate with the duct from the sensory support cell. Numerous filaments and vesicles are associated with this complex.     

The complete mitochondrial genome sequence of Oncicola luehei (Acanthocephala: Archiacanthocephala) and its phylogenetic position within Syndermata

In the present study, we determined the complete mitochondrial genome sequence of Oncicola luehei (14,281bp), the first archiacanthocephalan representative and the second complete sequence from the phylum Acanthocephala. The complete genome contains 36 genes including 12 protein coding genes, 22 transfer RNA (tRNA) genes and 2 ribosomal RNA genes (rrnL and rrnS) as reported for other syndermatan species. All genes are encoded on the same strand. The overall nucleotide composition of O. luehei mtDNA is 37.7% T, 29.6% G, 22.5% A, and 10.2% C. The overall A+T content (60.2%) is much lower, compared to other syndermatan species reported so far, due to the high frequency (18.3%) of valine encoded by GTN in its protein-coding genes. Results from phylogenetic analyses of amino acid sequences for 10 protein-coding genes from 41 representatives of major metazoan groups including O. luehei supported monophyly of the phylum Acanthocephala and of the clade Syndermata (Acanthocephala+Rotifera), and the paraphyly of the clade Eurotatoria (classes Bdelloidea+Monogononta from phylum Rotifera). Considering the position of the acanthocephalan species within Syndermata, it is inferred that obligatory parasitism characteristic of acanthocephalans was acquired after the common ancestor of acanthocephalans diverged from its sister group, Bdelloidea. Additional comparison of complete mtDNA sequences from unsampled acanthocephalan lineages, especially classes Polyacanthocephala and Eoacanthocephala, is required to test if mtDNA provides reliable information for the evolutionary relationships and pattern of life history diversification found in the syndermatan groups.     

The nervous system in the praesoma of Echinorhynchus salmonis (Acanthocephala: Echinorhynchidae)

Based on light microscopic observations, nerve pathways are described for the first time in the praesoma of a species of the Echinorhynchidae. The pathways are described for 18 nerves, 8 paired and 2 single, which originate from the cerebral ganglion and a post-ganglionic cell and terminate in the body wall musculature and the proboscis. The location of two commissures formed by these nerves is also described.     

Ultrastructure of the spermatid and spermatozoon of Macracanthorhynchus hirudinaceus.

The ultrastructure of the spermatid and spermatozoon of Macracanthorhynchus hirudinaceus (Archiacanthocephala) was studied by means of transmission electron microscopy. The flagellum and nucleus in the spermatid gradually expanded simultaneously. The karyoplasma of the spermatid transformed into dense inclusions and a multibarrel structure, which were also found in the spermatozoan body. The multibarrel structure was located close to the flagellum and consisted of many irregular microtubes. The flagellum of the developing spermatozoon was observed in a concavity of the spermatid nucleus. The microtubule arrangement of the flagellum was "9 + 2". No mitochondria or acrosome were observed in spermatozoa.     

A morphological study of the nervous system of the praesoma of Octospinifer macilentus (Acanthocephala: Noechinorhynchidae)

The nerve pathways in the praesoma are described for the first time for a member of the genus Octospinifer. Eleven nerves, five paired, and one single, are traced from the cerebral ganglion to their associations with the musculature of the body wall, neck sense organs, and the musculature of the proboscis wall and the invertor muscles of the proboscis. The structure and location of the Stützzelle (support cell) and its association with the neck sense organs are described. A comparison with the nervous system in the praesoma of Noechinorhynchus and Paulisentis is discussed.     

Organisation of the praesoma in Acanthocephalus anguillae (Acanthocephala, Palaeacanthocephala) with special reference to the muscular system

The organisation of the praesoma in the parasite Acanthocephalus anguillae was studied on the light and electron microscopic level, with emphasis on the morphology of the musculature. The study was compiled to add new data to the ground pattern of the Acanthocephala for analysis of the phylogenetic relationships within the Gnathifera. In A. anguillae the praesomal epidermis and lemnisci form a coherent syncytium, separated from the epidermis of the trunk. Hooks are seen to be derivatives of the subepidermal basal lamina and are covered by the praesomal epidermis. The praesomal circular body wall musculature forms a network of anastomosing muscle fibres that lines the proboscis; a praesomal longitudinal body wall musculature does not exist. The truncal circular and longitudinal body wall musculature rise up to the praesomal proboscis. The unpaired proboscis retractor, consisting of longitudinal circomyar fibres, forms an outer and an inner concentric tube; the latter extends through the entire praesoma and penetrates the receptacle wall. The sack-like receptacle is surrounded by a receptacle constrictor. The nervous system of the praesoma consists of a prominent cerebral ganglion, three nerves which extend anteriorly, ramify and end within the praesomal musculature, and two strong lateral posterior nerves. A. anguillae lacks an apical organ, lateral organs and a support cell. Many of the features present in the praesoma of A. anguillae can be assumed as ground-pattern characteristics of the Acanthocephala. Accepted: 22 January 2001     

A morphological study of the anterior nervous system of the praesoma of Neoechinorhynchus cylindratus (Acanthocephala: Neoechinorhynchidae)

The nerve pathways in the praesoma, based on light microscopy of serial transverse, sagittal, and longitudinal sections stained with Ehrlich's acid hematoxylin are described for the first time for a memeber of Neoechinorhynchus. The route from the cerebral ganglion to the musculature and sense organs of the proboscis and body wall for 11 nerves, five pair and one single, the presence and structure of the Stutzzelle (support cell) and its association with the neck sense organs are described. A comparison with the nervous system in the praesoma of Paulisentis fractus is discussed.     

A morphological study of the nervous system of the praesoma of Paulisentis fractus (Acanthocephala: Neoechinorhynchidae)

The nerve pathways in the praesoma are described for a member of the class Eoacanthocephala for the first time. Eleven nerves, five paired and one single, are traced from the cerebral ganglion to their associations with the musculature of the body wall, neck sense organs, and the musculature of the proboscis wall and the invertor muscles of the proboscis. The structure and location of the stutzzelle and series of nerve endings in the hypodermis of the body wall and at the apex of the proboscis are described.     

The morphology of the intrinsic tongue musculature in snakes (Reptilia,ophidia): Functional and phylogenetic implications

Tongue musculature in 24 genera of snakes was examined histologically. In all snakes, the tongue is composed of a few main groups of muscles. The M. hyoglossus is a paired bundle in the center of the tongue. The posterior regions of the tongue possess musculature that surrounds these bundles and is responsible for protrusion. Anterior tongue regions contain hyoglossal bundles, dorsal longitudinal muscle bundles and vertical and transverse bundles, which are perpendicular to the long axis of the tongue. The interaction of the longitudinal with the vertical and horizontal muscles is responsible for bending during tongue flicking. Despite general similarities, distinct patterns of intrinsic tongue musculature characterize each infraorder of snakes. The Henophidia are primitive; the Scolecophidia and Caenophidia are each distinguished by derived characters. These derived characters support hypotheses that these latter taxa are each monophyletic. Cylindrophis (Anilioidea) is in some characters intermediate between Booidea and Colubroidea. The condition in the Booidea resembles the lizard condition; however, no synapomorphies of tongue musculature confirm a relationship with any specific lizard family. Although the pattern of colubroids appears to be the most biomechanically specialized, as yet no behavioral or performance feature has been identified to distinguish them from other snakes.     

The spermatozoon of the Echiniscidae (Tardigrada,Heterotardigrada) and its phylogenetic significance

The spermatozoon ultrastructure of four species of moss-dwelling Heterotardigrada belonging to four genera of Echiniscidae, namely Pseudechiniscus juanitae, Echiniscus duboisi, Novechiniscus armadilloides and Antechiniscus parvisentus, was investigated. In all species, the testicular male gamete is similar in morphology and in length. The spermatozoon is made up of a long head, consisting of a cylindrical acrosome and an oval or rod-shaped nuclear region which contains a nucleus with osmiophilic and electron-dense chromatin, and a tapering tail, with a "9+2" axoneme. An elongated sack-like structure originates from the posterior part of the head, extending beyond the main axis of the cell and running parallel to the tail. It consists of two parallel tubular regions which sometimes form a strict double helix and contain two voluminous, "free" mitochondria with unmodified cristae. In addition, a voluminous vesicle is present laterally to the centriole or between the end of the nucleus and the beginning of the mitochondria, limited by two cytomembranes and filled with electron-lucent and granular material. The male gametes representative of these moss-dwelling Echiniscidae are very similar to the spermatozoa of the marine Echiniscoididae Echiniscoides sigismundi. This close similarity emphasises that habitat changes have had little influence on the organisation of the sperm cell representative of Echiniscoidea. Spermatozoon characters which could be useful for phylogenetic studies on Tardigrada are discussed.