Morphological and molecular data for species of Lecithaster Lühe, 1901 and Hysterolecithoides Yamaguti, 1934 (Digenea: Lecithasteridae) from fish of East Asia and phylogenetic relationships within the Hemiuroidea Looss, 1899

Four representatives of the genus Lecithaster and one representative of the genus Hysterolecithoides were found during investigation of the trematode fauna of fish species in Vietnamese, Japanese and eastern coastal waters of the Russian Far East. Based on morphometric data, adult trematodes from Vietnamese Strongylura strongylura and Russian Acanthogobius flavimanus were identified as Lecithaster confusus, trematodes from Vietnamese Hemirhamphus marginatus as L. sayori and from osmerid fishes as L. salmonis. Further, a single specimen of Lecithaster sp. and representatives of Hysterolecithoides epinepheli were found in Vietnamese Siganus fuscescens. Morphological and molecular data, including 18S ribosomal DNA (rDNA) V4 fragment, 28S rDNA D1-D3 fragment, internal transcribed spacers (ITS) and a mitochondrial COI gene fragment were analysed for Lecithaster spp. The results revealed that L. sayori and L. salmonis are not synonyms of L. stellatus and L. gibbosus, respectively, but that Hysterolecithoides frontilatus and H. guangdongensis are junior synonyms of H. epinepheli. The 28S-rDNA-based phylogenetic tree of Hemiuroidea showed a distinct position for the genus Lecithaster with internal differentiation into three subclades, including L. confusus, L. sayori and Lecithaster sp. within the first subclade, L. mugilis and L. sudzuhensis within the second subclade and L. salmonis and L. gibbosus within the third subclade. Bayesian phylogenetic reconstructions of Hemiuroidea showed four clades for members of Hemiuridae and Lecithasteridae. The first clade consisted of Hemiuridae representatives and the second clade represented the genus Lecithaster. The third clade included genera Aponurus and Lecithophyllum (Lecithasteridae) and the fourth clade combined members of lecithasterid Quadrifoliovariinae and Hysterolecithinae and hemiurid Opisthadeninae and Bunocotylidae with high statistical support.

Comparison of the Visual Capabilities of an Amphibious and an Aquatic Goby That Inhabit Tidal Mudflats

The mudskipper Periophthalmus modestus and the yellowfin goby Acanthogobius flavimanus are gobiid teleosts that both inhabit the intertidal mudflats in estuaries. While P. modestus has an amphibious lifestyle and forages on the exposed mudflat during low tide, the aquatic A. flavimanus can be found at the same mudflat at high tide. This study primarily aimed to elucidate the differential adaptations of these organisms to their respective habitats by comparing visual capacities and motor control in orienting behavior during prey capture. Analyses of retinal ganglion cell topography demonstrated that both species possess an area in the dorsotemporal region of the retina, indicating high acuity in the lower frontal visual field. Additionally, P. modestus has a minor area in the nasal portion of the retina near the optic disc. The horizontally extended specialized area in P. modestus possibly reflects the need for optimized horizontal sight on the exposed mudflat. Behavioral experiments to determine postural and eye direction control when orienting toward the object of interest revealed that these species direct their visual axes to the target situated below eye level just before a rapid approach toward it. A characteristic feature of the orienting behavior of P. modestus was that they aimed at the target by using the specialized retinal area by rotating the eye and lifting the head before jumping to attack the target located above eye level. This behavior could be an adaptation to a terrestrial feeding habitat in which buoyancy is irrelevant. This study provides insights into the adaptive mechanisms of gobiid species and the evolutionary changes enabling them to forage on land.