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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]

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]

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]