Ultrastructure of the tegument of the cestode Paraechinophallus japonicus (Bothriocephalidea: Echinophallidae), a parasite of the bathypelagic fish Psenopsis anomala

Abstract

Abstract. The ultrastructure of the tegument in Paraechinophallus japonicus (Bothriocephalidea: Echinophallidae), a cestode parasite of the bathypelagic fish Psenopsis anomala, was studied using scanning and transmission electron microscopy. Paraechinophallus japonicus lacks a true scolex. Four different types of microtriches have been observed on the tegumental surface of P. japonicus. Capilliform (B2.3-mm long) and blade-like spiniform (B1.4-mm long) microtriches are intermingled on the surface of the pseudoscolex. Capilliform microtriches are distinct in possessing a short base and a long electron-lucent cap. The strobila is covered with two types of microtriches, namely filiform (B2.1-mm long) and tusk-shaped microtriches (r4.5-mm long). Tusk-shaped microtriches are limited to the posterior border of each proglottid and are characterized by a short and narrow base, and a large and wide, sharply pointed, electron-dense cap. Similar tusk-shaped microtriches were previously found in members of the family Echinophallidae and may represent an autapomorphy of echinophallid cestodes, all of them being parasitic in centrolophid fish. A unified terminology of microthrix parts is proposed.Additional key words: microtriches, unified terminology, TEM, SEM, Bothriocephalidea A remarkable feature of the cestode tegument is the presence of apical structures called microtriches (Rothman 1963). Microtriches may differ in their structure, shape, size, and distribution between different species, between larvae (metacestodes) and adults, and also between regions of the tapeworm (Charles & Orr 1968;Grammeltvedt 1973;Thompson et al. 1980;MacKinnon & Burt 1983;Kuperman 1988;Caira & Ruhnke 1991; %d'a´rska´& Nebesa´rˇova1 999, 2005). Structural variations of microtriches are mostly evident on the surface of the scolex (Lumsden & Hildreth 1983;Kuperman 1988;Jones 1998;Halton 2004; Palm 2004). The morphology and distribution of microtriches of the scolex is considered to be of phylogenetic importance and represent a potentially significant taxonomic character (Richmond & Caira 1991;Caira et al. 1999; Palm 2004;Agustı´et al. 2005;Gil de Pertierra 2005).Cestodes with paired attachment organs called bothria were traditionally placed in the order Pseudophyllidea. However, recent molecular studies have shown that the order is paraphyletic and consists of two unrelated assemblages (orders): Bothriocephalidea and Diphyllobothriidea (Brabec et al. 2006;Kuchta 2007;Kuchta et al. 2008). The existence of these two groups raises the question as to their differentiation on the basis of morphological and ultrastructural characters. Therefore, the fine morphology of the tegument of Paraechinophallus japonicus YAM-AGUTI 1934, a member of the family Echinophallidae belonging to the more derived group of previous pseudophyllidean cestodes, Bothriocephalidea, was studied using transmission and scanning electron microscopy (TEM and SEM).Invertebrate Biology 127(2): 153-161. r

Ultrastructure of the scolex of Orygmatobothrium schmittii (Cestoda: Phyllobothriidea)

“…In spinitriches, the cap has been described as formed by an internal medulla and external cortex (e.g., bifid, hamulate, hastate, palmate, and pectinate spinitriches in Onchoproteocephalidea and Trypanorhyncha; Jones & Beveridge, ; Palm, Poynton, & Rutledge, ; Palm et al, ; Thompson et al, ), a massive medulla without cortex (i.e., coniform, gladiate, hamulate, hastate, palmate, pectinate, and trifid spinitriches in Bothriocephalidea, Cyclophyllidea, Diphyllidea, Diphyllobothriidea, Litobothridea, Onchoproteocephalidea, Phyllobothriidea, Tetraphyllidea, and Trypanorhyncha; e.g., Biserova, ; Biserova et al, ; Faliex, Tyler, & Euzet, ; Fyler, ; Gallagher, Caira, & Cantino, ; Hess & Guggenheim, ; Levron et al, ; McCullough & Fairweather, ; Palm, ; Thompson et al, ; Yoneva et al, ; Zd'árská, Scholz, & Nebesárová, ), or an internal medulla covered by a bilayer cortex (i.e., presumably coniform spinitriches in H. diminuta Cyclophylidea; Holy & Oaks, ). The gongylate spinitriches of O. schmittii have a well‐defined medulla and cortex, with lateral projections of the cytoplasmic membrane, adding more diversity to the internal morphology of the different spinitriches.…”

“…Gladiate spinitriches are the most common spinitriches found among tapeworms, being observed in members of Bothriocephalidea, Cyclophyllidea, Diphyllobothriidea, Lecanicephalidea, Onchoproteocephalidea, Phyllobothriidea, Rhinebothriidea, Tetraphyllidea, and Trypanorhyncha (Chervy, ; Gil de Pertierra, Incorvaia, & Arredondo, ; Ivanov, ; Koch, Jensen, & Caira, ; Pickering & Caira, ; Yoneva et al, ). Both, the external shape and the internal structure are quite similar in members of different orders (Fyler, ; Levron et al, ; McCullough & Fairweather, ; Zd'árská et al, ). Slight variations can be observed in the curvature of the baseplate and the shape of the tunic (Fyler, ; McCullough & Fairweather, ; Zd'árská et al, ).…”

“…Jones & Beveridge, 1998;Palm, Poynton, & Rutledge, 1998;Palm et al, 2000;Thompson et al, 1980), a massive medulla without cortex (i.e., coniform, gladiate, hamulate, hastate, palmate, pectinate, and trifid spinitriches in Bothriocephalidea, Cyclophyllidea, Diphyllidea, Diphyllobothriidea, Litobothridea, Onchoproteocephalidea, Phyllobothriidea, Tetraphyllidea, and Trypanorhyncha; e.g., Biserova, 1987;Biserova et al, 2016;Faliex, Tyler, & Euzet, 2000;Fyler, 2007;Gallagher, Caira, & Cantino, 2017;Hess & Guggenheim, 1977;Levron et al, 2008;McCullough & Fairweather, 1984;Palm, 2000;Thompson et al, 1980;Yoneva et al, 2017;Zd'árská, Scholz, & Nebesárová, 2004), or an internal medulla covered by a bilayer cortex (i.e., presumably coniform spinitriches in H. diminuta Cyclophylidea; Holy & Oaks, 1986).…”

Revision of the order Bothriocephalidea Kuchta, Scholz, Brabec & Bray, 2008 (Eucestoda) with amended generic diagnoses and keys to families and genera

“…Bray et al (1994) placed Glossobothrium in the Echinophallidae because they synonymised the Parabothriocephalidae with the Echinophallidae, the genus having been placed in the Parabothriocephalidae by Yamaguti (1959). However, Glossobothrium is considered here to belong to the Triaenophoridae because it possesses a lateral genital pore, the cirrus is armed with small microtriches rather than with large spines (see Levron et al, 2008a), and the posterior margin of segments is not covered with the blade-like spiniform microtriches present in most echinophallids Levron et al, 2008b).…”

Ultrastructure of microtriches on the scolex of Cyathocephalus truncatus (Cestoda: Spathe-bothriidea)

“…The terminology of individual parts of microtriches follows that proposed at the Sixth International Workshop on Cestode Systematics and Phylogeny (Smolenice, Slovakia, 15-20 June 2008), i.e. "base" corresponding to the basal part, "basal plate" representing the junctional region, and "cap" corresponding to the distal part (see also Žďárská and Nebesářová 1999, Levron et al 2008).…”