Lacydonia shohoensis (Annelida, Lacydoniidae) sp. nov. – a new lacydonid species from deep-sea sunken wood discovered at the Nishi-Shichito Ridge, North-western Pacific Ocean

Lacydonia Marion & Bobretsky, 1875 is the sole genus in the family Lacydoniidae Bergström, 1914. We herein describe the new species of Lacydonia shohoensis sp. nov. from 2042-m deep bottoms at Shoho Seamount of the Nishi-Shichito Ridge, the Northwest Pacific Ocean. It is most similar to L. anapaulae Rizzo et al., 2016 in having a depression on the median anterior region and lacking lateral lobes on the posterior margin of prostomium whereas it is distinguished by possessing pygidium dorsally pigmented with three reddish spots and non-pigmented pygidial lateral cirri equally elongated.

A New Species of Diaphus Associated with Seamounts of the Emperor Chain, North-Western Pacific Ocean (Teleostei: Myctophiformes: Myctophidae)

A new species, Diaphus balanovi, is described based on 35 specimens collected over the Emperor Seamount Chain in the north-western Pacific Ocean. It belongs to the D. fulgens species complex and is most similar to D. kuroshio both morphologically and genetically. Nevertheless, the new species can be distinguished from D. kuroshio by its higher gill-rakers count, large luminous scale at PLO, large Dn, somewhat higher position of SAO3, otolith shape, and larger absolute size. The CO1 mtDNA sequence of D. balanovi differs by 16 substitutions from that of D. kuroshio. Diaphus balanovi may represent a benthopelagic derivate of D. kuroshio endemic to the Emperor Seamounts.

The neuromuscular system in flatworms: serotonin and FMRFamide immunoreactivities, and musculature in Prodistomum alaskense (Digenea: Lepocreadiidae), an endemic fish parasite of the north-western Pacific

Using the immunocytochemical method and confocal scanning laser microscopy, the pioneering data are obtained on the muscle system organization and presence and localization of biogenic amine serotonin and FMRFamide-related peptides in the nervous system of trematode Prodistomum alaskense (Ward and Fillingham, 1934) Bray and Merrett, 1998 (family Lepocreadiidae). This flatworm is an intestinal parasite of endemic representatives of marine fauna of the north-western Pacific Ocean – the prowfish, Zaprora silenus Jordan, 1896 and the lumpfish, Aptocyclus ventricosus Pallas, 1769. The article provides data of scanning electron microscopy on the tegumental topography of P. alaskense. The body wall musculature of P. alaskense has three layers of muscle fibres – the outer circular, intermediate longitudinal and inner diagonal ones. The muscle system elements are well-developed in the attachment organs, digestive and reproductive systems, in the excretory sphincter. Serotonin- and FMRFamide-immunopositive neurons and neurites are found in the head ganglia, circular commissure, longitudinal nerve cords, and in the transversal connective commissures. The innervation of the oral and ventral suckers, pharynx, and the reproductive system compartments by the serotonergic and FMRFamide-immunopositive neurites is revealed. The results are discussed in connection with the published data on the presence and functional roles of the serotonin and FMRFamide-related peptides in Platyhelminthes.