Redescription of Rhadinorhynchus ornatus (Acanthocephala: Rhadinorhynchidae) from Skipjack Tuna, Katsuwonus pelamis, Collected in the Pacific Ocean off South America, with Special Reference to New Morphological Features

Abstract

Adults of Rhadinorhynchus ornatus Van Cleave, 1918 were collected from the small intestine of skipjack tuna, Katsuwonus pelamis (Linnaeus), in the high seas of the Pacific Ocean off the west coast of South America (new parasite locality record) and described using optical microscopy and a scanning electron microscope (SEM). Our specimens were somewhat comparable to those described from North America and Japan, but had more trunk spines. Definitive differences between the length and thickness of each of the dorsal and ventral proboscis hooks are noted for the first time, with most ventral middle hooks being relatively shorter and more robust than dorsal middle hooks. The SEM documented, for the first time, the different surface topography of the tegument in the proboscis, the neck, and in 3 trunk regions; the presence of microtrichs in the mid- and posterior trunk regions; the elevated base of trunk spines; the circular arrangement of basal proboscis hooks; the different morphology of all dorsal and ventral proboscis hooks and the striations of their surface; the ribbed surface topography of eggs; the elevated slit-like female gonopore; and the rimmed edge of the bursa. The presence of microtrichs on the tegumental surface is further supported by transmission electron microscopy studies. This is the first report of microtrichs in any species of Acanthocephala and the second report of striations in proboscis hooks. The geographical distribution of R. ornatus appears to correspond, at least in part, to that of its epipelagic primary host, K. pelamis, throughout the world in waters ranging in temperature from 14.7 to 30 C.

SEM studies on acanthocephalan parasite, Echinorhynchus veli infecting the fish Synaptura orientalis (Bl & Sch, 1801)

“…In Tenuiproboscis sp (Sanil et al 2011) observed a progressively decreasing size of hooks from anterior to posterior region, but the posterior most row of spines was larger. As in most acanthocephalan species, hook surface is smooth in E. veli in contrast to surface striations in Porrorchis indicus (Abd-El-Moaty and Taeleb, 2011), Dentitruneus truttae (Dezfuli et al 2008) and Rhadinorhynchus ornatus (Amin et al 2009). Dezfuli et al (2008) speculated that the striations may help effective attachment to the host intestinal wall.…”

“…The trunk epidermis in E. veli has micropores and microtriches increasing the surface area of nutrient absorption. There are both micropores and microtriches in some acanthocephalans (Amin et al 2009). Microtrichus are highly specialised microvilli covering the entire surface of the tegument of cestodes and some acanthocephalans.…”

New Features ofNeoechinorhynchus(Neoechinorhynchus)dimorphospinus(Acanthocephala: Neoechinorhynchidae) from Recent Collections in the Arabian Gulf Using SEM, with Notes on Histopathology

“…In addition to their present reporting in N. dimorphospinus (Eoacanthocephala: Neoechinorhynchidae), ribbed hooks have also been reported in 3 other species in 2 other families of Palaeacanthocephala: Dentitruncus truttae Sinzar, 1955 (Illiosentidae), Rhadinorhynchus ornatus Van Cleave, 1918 (Rhadinorhynchidae), and Leptorhynchoides polycristatus Amin, Heckmann, Halajian, El-Naggar, Tavakol, 2013 (Rhadinorhynchidae). Dezfuli et al (2008) and Amin et al (2009) suggested that such hook striations may provide a more effective attachment to the host's intestine. The striations of the hooks of D. truttae appeared as small dents on the outer periphery of the hooks' outer striped layer (Dezfuli et al, 2008).…”

“…10). These peripheral canals are continuous with canalicular crypts, which appear to constitute a huge increase in external surface area and which are also implicated in nutrient uptake (see Whitfield 1979 andAmin et al 2009 for a discussion of this topic). Accordingly, it would appear that nutrient uptake is similar along the length of the trunk and not variably performed in different regions of the trunk as has been shown for both Acanthocephalus lucii (Müller, 1776) Lühe, 1911, and Acanthocephalus ranae (Schrank, 1788) Lühe, 1911, by Amin et al (2011) and Heckmann et al (2011), respectively.…”

Expanded description ofNeoechinorhynchus (Hebesoma) manubrianus(Acanthocephala: Neoechinorhynchidae) from marine fish in Halong Bay, Vietnam

“…10). See Amin et al (2009) for implications to differential absorption. The terminal position of the crescent-shaped female gonopore (Fig.…”