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Fifty years ago, it was reported that individuals of the Pacific boreal limpet Problacmaea (= Erginus) bear a penis for copulation and brood their young in the pallial cavity. These observations were based on light microscopy, but now we reveal new details of the reproductive biology of Erginus (Problacmaea) puniceus with electron microscopy. Gametogenesis is fundamentally similar to other Patellogastropoda, but there are some key differences. Oocytes develop in the ovary, dorsal to the foot in the posterior half of the body, before passing through the oviduct to the pallial cavity, where they are fertilized and brooded. Development is direct with embryos being brooded to the crawl-away juvenile stage. However, sometimes fertilization occurs internally with embryos beginning development in or near the gonad. Free sperm, which were likely autosperm (self) but could have been allosperm (cross), were found near developing oocytes in the gonad. Spermiogenesis results in the formation of an enta-quasperm with a cap-like acrosome, a bullet-shaped nucleus and spherical mitochondria in the midpiece. Copulation was not observed, but we confirm the presence of a penis with a dorsal penial groove that lies below the right cephalic tentacle in males, which is typical of functional penises of some molluscs. Males were always smaller, but intermediate-sized individuals were hermaphroditic to different extents. The largest individuals were entirely female, and their penises were smaller and often lacked the penial groove. Thus, E. (Problacmaea) puniceus appears to be a protandrous hermaphrodite, passing from male to female phase. Remnants of the testis persist into the female phase, suggesting that they are protandrous hermaphrodites with overlap, possibly allowing for self-fertilization to occur on occasion. However, the largest females lacked any testis remnants, suggesting instead that the species may be protandrous sequential hermaphrodites. [ABSTRACT FROM AUTHOR]

Adipose fins of teleost fishes have been shown to function as mechanosensory organs that respond to minute bending forces created by turbulence in fast‐flowing streams. Nonetheless, adipose fins also exist in some fishes that occupy still waters, including lanternfish (Myctophidae) in the deep sea. The authors examined adipose fin structure in northern lampfish, Stenobrachius leucopsarus, from coastal British Columbia. After fixation, embedding and sectioning of the adipose and supporting tissue, it was evident that lanternfish adipose fins are stiffened by compound actinotrichia, acting like fin rays, that would create a higher aspect ratio. The actinotrichia converge at the base of the fin in a hinge point complex that anteriorly interacts with a cartilaginous endoskeletal rod, controlled by skeletal muscles. Afferent nerves enter the fin at this point and form fine branches as they track deeper alongside actinotrichia. The authors propose that the vertical nightly migration to surface waters, as well as predator evasion within large schools, results in microturbulence. In these circumstances, the adipose fin acts as a mechanosensor providing feedback to the caudal fin, as it occurs in salmonids and catfish. [ABSTRACT FROM AUTHOR]

Eusperm and parasperm ultrastructure have been studied for the first time in the neogastropod Plicopurpura patula. Eusperm structure is typical of many Neogastropoda, in which an apical bleb characterizes the conical acrosome with subacrosomal granule; the nucleus is tubular and penetrated to its tip by basal body and axoneme; the mid-piece comprises spiral mitochondria that ensheath the axoneme but terminate at the annulus, defining the junction with the end-piece. In the proximal portion of the end-piece dense tracts of glycogen match the axoneme but these disappear distally. The parasperm is unusual in having no axonemes and no motility was observed. Eusperm do not attach to parasperm, as occurs in the similar nurse cells of Littorinimorpha, thus potential functions may be limited to some form of paternity assurance as occurs in some insects. The nucleus of the parasperm is eliminated during paraspermiogenesis, but there is considerable post-transcriptional secretion activity resulting in the production of a variety of granules, some rich in glycoproteins. A prominent paracrystalline rod accumulates in the centre of the parasperm also from Golgi-derived secretions. Preliminary evidence from proteomics suggests that this parasperm carries the heat shock protein HSP70 that could play a role in fertilization inside the female. [ABSTRACT FROM AUTHOR]

Sperm structure of the Xenacoelomorpha (Acoelomorpha plus Xenoturbellida) is updated in the light of new discoveries or new interpretations of existing data. Nemertodermatida and Acoela (Acoelomorpha) have introsperm with certain basic features in common, but all acoels lack acrosomes and usually have two flagella with unusual combinations of microtubules, whereas all nemertodermatids have small, simple acrosomes and a typical 9 + 2 flagellum. Xenoturbellida is currently considered as the sister taxon to Acoelomorpha. Xenoturbella bocki has an aquasperm that has almost nothing in common with the sperm of Acoelomorpha. We argue that the aquasperm ultrastructure of X. bocki has much in common with sperm of hemichordates and to some extent echinoderms, which was previously disputed. Molecular analyses have on the one hand supported a connection with deuterostomes but on the other hand have negated it, suggesting that the closest common ancestor of Xenacoelomorpha is either the Nephrozoa, Deuterostomia or Protostomia. Sperm structure is highly diverse among Xenacoelomorpha, with protostome-like traits in Acoelomorpha and deuterostome-like traits in Xenoturbella. Assuming Xenacoelomorph monophyly and ancestral introsperm in this taxon, however, suggests that the re-expression of the aquasperm form of Xenoturbella, involving some key changes in sperm morphology, is a secondarily derived state that could have occurred through "progenetic spermiogenesis" with the precocious development of round spermatids to maturity. [ABSTRACT FROM AUTHOR]

Gametogenesis in Chitonida is highly unusual, giving rise to eggs with elaborate, often spiny hulls and sperm with needle-like nuclear extensions and tiny acrosomes. My studies of oogenesis in a variety of chitonid families have revealed unique mechanisms of egg hull formation. Three-dimensional reconstruction of serial sections of oogenesis in the chitonidAcanthochitona garnoti(Blainville) confirms that the egg hull is formed largely by microapocrine secretions, rather than by exocytosis of Golgi vesicles. This novel process, detailed for the first time in Mollusca, bypasses the endomembrane system and releases compounds formed in the cytoplasm directly from the cell surface via budding of ‘microaposomes’. Fertilization is no less unusual. In virtually all Metazoa, except chitonids, the entire sperm enters the egg, and sperm mitochondria are digested. Typically, the centrosome that derives from the sperm centriole acts as a microtubule organizing centre, moving the two pronuclei together to form the zygote nucleus and later initiating cleavage of the embryo. However, in chitonids the sperm digest a minute pore in the egg hull that allows injection of DNA but blocks entry of sperm organelles, including the nuclear membrane. Serial sections of fertilized eggs ofMopalia muscosa(Gould) confirm that a membrane bag, abandoned on the egg surface, contains the sperm organelles. Thus, not only is there maternal inheritance of mitochondria and centrioles in Chitonida but also other sperm proteins normally associated with fertilization may be blocked from entering the egg. [ABSTRACT FROM AUTHOR]

An extensive community of organisms inhabits the common periwinkle, Littorina littorea (L., 1758), along the wave-swept rocky shores of Canada's East coast. This community, which includes both facultative and obligate endosymbionts, comprises a diverse array of species from seven animal phyla, including Annelida, Arthropoda, Gnathostomulida, Nematoda, Nemertea, and Platyhelminthes, as well as ciliates and algae. The presence of larger numbers of endosymbionts was found to correlate with specific shell characteristics of the snail host, including a wider aperture and columella, suggesting that these individuals have a larger mantle cavity relative to snails housing a small community of endosymbionts. Snails with large communities of endosymbionts were usually encrusted with coralline algae and often had trematode infections. Although L. littorea has been extensively studied since the last century, the existence of this community of organisms has passed unnoticed. The large diversity of organisms in this community suggests that these snails may provide refugia for a wide range of smaller taxa. [ABSTRACT FROM AUTHOR]

Egg hull formation during oogenesis in the chiton Callochiton dentatus does not follow the typical model of merocrine secretion involving Golgi vesicle exocytosis. Instead, microapocrine secretions are primarily responsible for egg hull formation, although merocrine secretions contribute 'areolae' and the vitelline layer. Microapocrine secretion mechanisms are poorly understood, involving a different cellular pathway than is typical. Egg hull formation in C. dentatus involves two types of microapocrine secretions released by the oocyte, one of which is described here for the first time. The plesiomorphic jelly-like egg hull of chitons, as exemplified by the eggs of members of the basal order Lepidopleurida and present also in eggs of C. dentatus (Chitonida: Callichitonidae), may have evolved solely as an oocyte secretion, whereas members of some other families in the order Chitonida form their egg hulls with considerable secretory input from the follicle cells as well. [ABSTRACT FROM AUTHOR]

Early events of fertilization are described in Chaetopleura apiculata and other selected Chitonida. C. apiculata egg hulls are elaborated into multi-branched spines with interlocking polygonal bases. Around the perimeter of each base are a series of open pores, ranging in size from 0.1-0.5 µm, which permit sperm direct access to the vitelline layer. In Callochitonidae (Chitonida) even larger pores occur in egg jelly coats, but this is considered to be the plesiomorphic condition, found also in Lepidopleurida such as Deshayesiella curvata. Other Chitonina, such as Rhyssoplax tulipa and Acanthopleura granulata, have a continuous outer dense layer that lacks pores and must be digested by penetrating sperm. Fertilization in Chitonida is unique and involves injection of chromatin into the egg via a narrow tubular nuclear extension that appears to exclude other sperm organelles, including mitochondria, centrioles, and flagellum. New evidence from studies of fertilization in Mopalia muscosa (Chitonida: Acanthochitonina) supports this hypothesis. This type of fertilization implies maternal inheritance of both mitochondria and centrioles, which is highly unusual, because in most animals one sperm centriole assists movements of pronuclei and regulates organization of the mitotic spindle. This mechanism of fertilization is defined by a series of apomorphic characters that unify the order Chitonida. [ABSTRACT FROM AUTHOR]

Presents information on a study which described the structure of the egg hull and the mechanism of fertilization of Callochiton castaneus. Comparison of Lepidopleurida and Chitonida; Methodology and results; Analysis of results.

Provides information on a study examining spermiogenesis and fertilization in the limpet Tectura testudinalis. Methodology used to conduct the study; Results of the study; Discussion on the results.

Presents a study that used single locus microsatellite DNA markers to determine the paternity of Littorina obtusata hatched from three egg masses kept in isolation in aquaria. Microsatellite loci used for paternity assessment in Littorina obtusata; Mating behavior in Littorina obtusata; Duration of copulations observed for Littorina obtusata.

Abstract: The dinoflagellate Haidadinium ichthyophilum Buckland‐Nicks, Reimchen and Garbary 1997 is an ectoparasite of the spine‐deficient, three‐spine stickleback Gasterosteus aculeatus L. Reimchen 1984, a fish endemic to Rouge Lake, Haida Gwaii. Haidadinium ichthyophilum proved difficult to assign taxonomically because its morphology and complex life cycle exhibited defining characteristics of both autotrophic and heterotrophic dinoflagellates, and was tentatively assigned to the Phytodiniales. Here, we characterized a 492 bp fragment of the small subunit ribosomal RNA (SSU rRNA) from preserved H. ichthyophilum cysts. In SSU phylogeny, H. ichthyophilum branches with the fish parasites, Piscinoodinium sp., strongly supporting the inclusion of H. ichthyophilum within the Suessiales. [ABSTRACT FROM AUTHOR]