Oncodiscus sauridae Yamaguti, 1934

Kuchta, Roman, Scholz, Tomáš, Vlčková, Romana, Říha, Milan, Walter, Thorsten, Yuniar, Asri T. & Palm, Harry W., 2009, Revision of tapeworms (Cestoda: Bothriocephalidea) from lizardfish (Saurida: Synodontidae) from the Indo-Pacific region, Zootaxa 1977, pp. 55-67 : 58-61

Oncodiscus sauridae Yamaguti, 1934

Figs. 1–8 , 14–18, 21 , 24

Syns. O. fimbriatus Subhapradha, 1955 ; O. waltairensis Shinde, 1975 ; O. maharashtrae Jadhav & Shinde, 1981 ; Bothriocephalus indicus Ganapati & Rao, 1955 ; Tetrapapillocephalus magnus Protasova & Mordvinova, 1986

Type host: Saurida argyrophanes (now S. tumbil ).

Other hosts: S. longimanus , S. nebulosa (new host), S. undosquamis .

Site of infection: Scolex in the pyloric caeca or embedded in the intestinal wall, strobila in the intestinal lumen.

Type locality: Inland Sea, Tarumi-ku, Kobe, Hyōgo Prefecture, Kyūshū, Japan, Pacific Ocean.

Distribution: Indian Ocean ( India, Indonesia, Kuwait, Mozambique); Pacific Ocean ( Australia, Japan, New Caledonia).

Prevalence: In Indonesia, S. longimanus – 12%; S. tumbil – 9%; S. undosquamis – 5%. In New Caledonia, 9% of S. undosquamis were infected (J.-L. Justine – unpublished data).

References: Subhapradha (1955); Devi (1975); Khalil & Abu-Hakima (1985); Protasova & Mordvinova (1986).

Re-description: Bothriocephalidea , Bothriocephalidae . Medium-sized worms, up to 130 (90) mm long. Strobila with craspedote segments with prominent posterolateral wing-like projections, overlapping following segment ( Figs. 5 , 16, 17 ). External segmentation present, but may be incomplete (missing medially). Two pairs of longitudinal osmoregulatory canals present. Longitudinal musculature well developed, formed by numerous bundles of muscle fibres ( Fig. 7 ). Surface covered with small filiform microtriches similar in shape and size.

Scolex oval, irregularly-shaped or fan-shaped ( Figs. 1, 2, 4 , 14, 15 ), usually compressed laterally, 1,120–3,140 (1,710–4,000) long by 860–2,380 (1,360–2,190) wide. Bothria well developed, with conspicuously crenulated margins turned laterally ( Figs. 1, 2, 4 , 14, 15 ). Apical disc well developed, 310–890 (780–1,250) wide, 140–400 (160–370) high, consisting of two lateral lobes, armed with up to four irregular rows of tiny hooklets ( Figs. 2, 3 , 15, 18 , 24); hooklets easy to detach, especially in dead specimens ( Figs. 1, 4 ), 21–26 (12–24) long, with largest hooklets in second and third rows, and diminishing in size from top of lateral lobes to junction of lobes, where rows may be interrupted. Neck absent, first segments starting immediately posterior to scolex ( Figs. 1 , 15 ).

Immature segments much wider than long, 25–110 (45–165) long by 400–1,510 (230–850) wide. Mature segments wider than long, 50–810 (80–380) long by 310–1,715 (755–1,070) wide ( Fig. 5 ). Gravid segments wider than long to rectangular or, exceptionally, slightly longer than wide, 190–2000 (180–700) long by 615–1865 (985–1520) wide ( Figs. 16, 17 ).

Testes medullary, oval, 50–100 (60–100) in number per segment, 22–66 (30–61) long by 11–38 (25–50) wide, in two lateral fields, usually separated medially, continuous between segments ( Fig. 5 ). Cirrus-sac submedian, irregularly alternating, thick-walled, round or slightly oval, 70–215 (85–135) in diameter, just anterodorsal to ovary ( Figs. 5, 6, 8 ). Cirrus armed with filiform microtriches. Cirrus opening to small genital atrium lateral to median line of segment ( Fig. 7 ). Genital pore dorsal, median, slightly postequatorial ( Fig. 5 ).

Ovary transverse elongate, bilobed, lobulate, median, near posterior margin of segment, 200–630 (225–460) wide ( Figs. 5, 6 ). Vagina tubular, dorsal to ovarian bridge, arched lateral or anterolateral to cirrussac ( Figs. 5, 6 ). Vitelline follicles numerous, cortical, circumsegmental ( Fig. 7 ), oval, 13–40 (7–28) in diameter, in two lateral fields, often separated medially, reaching to posterolateral projections ( Figs. 5, 7 ). Uterine duct well developed, sinuous, ending in muscular, thick-walled uterine sac situated medially ( Figs. 5, 6 ); sac markedly enlarged in last gravid segments. Uterine pore medioventral, at distance from anterior margin of segment or almost equatorial. In some segments, pore extremely large due to collapse of wall of uterus ( Fig.

16). Eggs oval, operculate, unembryonated, 55–64 (60–63) long by 32–45 (39–42) wide, with operculum 11–20 in diameter ( Fig. 21 ).

Remarks: Oncodiscus sauridae was described by Yamaguti (1934) from Saurida argyrophanes (now S. tumbil ) and redescribed by Khalil & Abu-Hakima (1985), who collected new material and added morphological data to the original description. The total length of 9 mm was given by Yamaguti (1934) for the holotype, but this specimen measures in fact 90 mm (present study).

Besides O. sauridae , another three species of Oncodiscus , namely O. fimbriatus , O. waltairensis , and O. maharashtrae , were erected. They were differentiated mainly by the shape of the scolex, the presence or absence of a median longitudinal furrow, the presence or absence hooklets on the apical disc, the number of testes and the presence or absence of an operculum in the eggs ( Subhapradha 1955; Shinde 1975; Jadhav & Shinde 1981). However, these characters are unsuitable for species differentiation in this group of cestodes. The shape of the scolex and the presence of furrows and hooklets on the apical disc are not stable characters because they depend into a great extent on the state in which worms were fixed and on fixation procedure ( Kuchta & Scholz 2007). In dead tapeworms or in worms that have been relaxed for too long in water, the hooklets detach (one of Yamaguti’s paratypes of O. sauridae lacks hooklets on the apical disc due to tissue destruction – Fig. 1 ), the scolex shape changes and tegumental furrows may appear as a consequence of deformation of the scolex, especially when fixation by pressure between two glass slides is used (Khalil & Abu- Hakima 1985; present study).

The number of testes is variable in O. sauridae and may considerably differ even between segments of the same specimen. The maximum number of testes in O. sauridae was found to reach up to 100, which corresponds to the data from the original description ( Yamaguti 1934). Jadhav & Shinde (1981) reported as many as 350 testes in one segment of O. maharashtrae , but it is apparent that the authors confused vitelline follicles with testes. Vitelline follicles enlarge in the posterior part of the strobila and may reach a similar size compared to that of the testes in gravid segments.

Another feature which was used for species differentiation, i.e. the presence or absence of an operculum in the eggs, can easily be overlooked unless scanning electron microscopy is used ( Bray et al. 1994; Kuchta et al. 2008a; present study). Yamaguti (1934) described a median longitudinal furrow on the scolex of O. sauridae . On the basis of the absence of that structure, Subhapradha (1955) proposed O. fimbriatus . However, this structure does not represent a species-distinguishing character. Such a furrow is missing in one of the paratypes of O. sauridae and it is much less developed in other specimens of the type series. This indicates that its presence depends on the level of worm contraction or fixation procedure (S. Yamaguti strongly flattened the worms, which may have caused unnatural deformations of the scolex and strobila).

Khalil & Abu-Hakima (1985) synonymized O. fimbriatus and O. waltairensis with O. sauridae , but they considered O. maharashtrae to be a species inquirendum. This species was described from Pastinachus (Trygon) sephen (Forsskål) (Dasyatidae) from off Bombay, India. Unlike Khalil & Abu-Hakima (1985), the present authors ( Kuchta & Scholz 2007; Kuchta et al. 2008b; this study) consider O. maharasthrae to be a synonym of O. sauridae which occurred in an unusual (postcyclic or accidental) host.

All three species from India were described on the basis of only a few, apparently macerated and deformed specimens. In addition, the descriptions of the taxa from the Indian Ocean were superficial and no histological sections were made ( Ariola 1900; Subhapradha 1955; Shinde 1975; Jadhav & Shinde 1981; Protasova & Mordvinova 1984). Bothriocephalus indicus was described from Saurida tumbil . It is obvious from its morphology that the authors erroneously placed these specimens in the genus Bothriocephalus Rudolphi, 1808 , because species of this genus are devoid of a fan-shaped scolex with crenulated bothrial margins ( Ganapati & Rao 1955). In fact, B. indicus is identical in its morphology with O. sauridae (the absence of hooklets on an apical disc is apparently due to poor state of specimens studied), parasitizes the same species of fish hosts and occurs in the same region. Therefore, the synonymy of B. indicus with O. sauridae , first proposed by Kuchta & Scholz (2007), is confirmed in the present study.

Bothriocephalus sauridae was very briefly described on basis of specimens without a scolex that were collected from Saurida nebulosa off the eastern coast of Africa ( Zanzibar) ( Ariola 1900). The species was considered to be a species inquirendum ( Protasova 1977; Kuchta & Scholz 2007; present paper), but its conspecificity with O. sauridae is very probable. In the same region, O. sauridae (reported to as Tetrapapillocephalus magnus ) was found in S. undosquamis by Protasova & Mordvinova (1986).

Morphological and morphometrical examination of the specimens of Tetrapapillocephalus magnus (holotype and voucher), which are both in poor condition, shows a high similarity with O. sauridae . The taxa differ only in the absence of tiny hooklets on the apical disc in the former. However, hooklets can be easily lost during handling or when dead tapeworms are collected ( Khalil & Abu-Hakima 1985; present study).

The scolex of Tetrapapillocephalus magnus (= O. sauridae ) illustrated in the original description ( Protasova & Mordvinova 1986) belongs to another specimen, not representing the holotype as indicated ( Fig. 4 ). This immature specimen was found in Beryx splendens Lowe ; it is mounted onto the same slide with the holotype of Partitiotestis berycis Protasova & Parukhin, 1986 (GELAN 986). Numerous immature tapeworms conspecific with T. magnus were found in this host, but only one specimen was mounted (Protasova – pers. com.). Besides this report, no further data exist on the occurrence of O. sauridae in berycid fish ( Kuchta & Scholz 2007; Kuchta et al. 2008b) and it is possible that B. splendens represents an accidental or paratenic host only.

It is interesting to note that we examined some unusual material from clupeid fish ( Chirocentrus dorab ) from the Japan Sea, in the collection of Yamaguti (MPM), collected 19.vi. 1928. These specimens are conspecific with O. sauridae (also identified as Oncodiscus by Yamaguti), but this finding was never published. In addition, no other occurrence of any bothriocephalid tapeworm has been reported from this host. This finding may represent misidentification of the host, or an accidental or paratenic host.

Figures

FIGURES 1 – 8. Oncodiscus sauridae Yamaguti, 1934. 1, Scolex of paratype (MPM SY 3043); lateral view. 2, 3, Voucher (MPM SY 5616) ex Chirocentrus dorab; 2, scolex; 3, detail of hooklets. 4, Scolex of the holotype of Tetrapapillocephalus magnus (GELAN 696). 5, Schematic drawing of mature segments ex Saurida longimanus (IPCAS C- 456 / 2); vitelline follicles illustrated only in the posterior segment; ventral view. 6, Detail of mature segment ex S. tumbil (IPCAS C- 456 / 1); vitelline follicles illustrated only on the left side and testes only on right side, ventral view. 7, 8, Histological sections of gravid segments ex S. tumbil (IPCAS C- 456 / 1) at level of cirrus-sac; 7, cross-section; 8, sagittal section. Abbreviations: cs – cirrus-sac; e – eggs; lm – inner longitudinal muscles; ov – ovary; t – testes; us – uterine sac; v – vagina; vf – vitelline follicles.

FIGURES 14 – 23. Photomicrographs. 14 – 18, 21, 24, Oncodiscus sauridae Yamaguti, 1934. 14, Scolex; ex Saurida longimanus. 15, Scolex; ex S. tumbil. 16, 17, Gravid strobila; 16, Ventral view; 17, Dorsal view. 18, 24, Detail of hooklets; 18, SEM photomicrograph; 24, Photomicrograph. 21, Operculum of the egg. 19, 20, 22, 23, Penetrocephalus ganapattii (Rao, 1954). 19, 23, Gravid strobila; 19, Ventral view; 23, Dorsal view. 20, Detailed view of the envaginated cirrus. 22, Operculum of the egg.