Otobothrium propecysticum Dollfus, 1969

Beveridge, Ian & Justine, Jean-Lou, 2007, Redescriptions of four species of Otobothrium Linton, 1890 (Cestoda: Trypanorhyncha), including new records from Australia, New Caledonia and Malaysia, with the description of O. parvum n. sp., Zootaxa 1587, pp. 1-25 : 11-14

Otobothrium propecysticum Dollfus, 1969

( Figs. 21–29 )

Types: syntypes, MNHN DB 16, 86-90.

Type host: Sphyrna zygaena (Linnaeus, 1758) .

Type locality: Sète, France, 27.ix.1951, coll. L. Euzet.

Site in host: spiral valve.

Material examined: From Sphyrna zygaena : 48 specimens, syntypes; from Sphyrna mokarran (Rüppell, 1837) : 8 specimens, Arafura Sea, NT, Australia ( SAM 29101).

Re-description: Based on types. Small cestodes, mature specimens 844–1598 (1217, n=10) long with 5– 8 (7, n=10) segments. Scolex craspedote, 167–247 (200, n=10) long, maximum width in region of pars bulbosa, 126–171 (148, n=10). Two bothria, wider than long, without prominent rim; pars bothrialis 111–143 (124, n=10) long; bothrial width 171–200 (187, n=8); bothrial pits tiny, c. 6 in diameter, on postero-lateral margin of bothria, in flattened specimens in middle of bothrial margin. Pars vaginalis slightly shorter than pars bothrialis, 106–141 (119, n=10) long; tentacular sheaths coiled or sinuous. Bulbs ovoid, 43–67 (58, n=10) long, 26–35 (30, n=10) wide, length: width ratio 1.67–1.42 (1.92, n=10); prebulbar organ absent; origin of retractor muscle not seen; pars post bulbosa absent.

Everted tentacles up to 130 long; with slight basal swelling; diameter at base 17–18 (17, n=3), diameter in metabasal region 10–13 (12, n=4). Armature heteroacanthous, heteromorphous, hooks hollow; hook rows begin on bothrial surface, terminate on antibothrial surface; hook files 1 and 1' separated on bothrial surface; distinct basal armature present on external surface of tentacle. Hooks 1(1') of rows 3–6 enlarged, with more slender blade and broader base; on external surface, rows 4–7 terminate with bill hooks. Metabasal armature with 6 hooks in each principal row. Hooks 1(1') large, uncinate, 10.0–12.5 (11.2, n=5) long, base 6.7–10.0 (8.0, n=5) long; hooks 2(2') erect, uncinate, 8.3–11.7 (10.3, n=5) long, base 4.2–7.5 (6.0, n=5) long; hooks 3(3') falcate, 10.0–11.7 (10.8, n=5) long, base 4.2–6.7 (5.3, n=5) long; hooks 4(4') spiniform, 4.2–6.7 (5.5, n=5) long, base 2.5–4.2 (3.5, n=5) long; hooks 5(5') slightly smaller, spiniform, 3.3–5.8 (4.7, n=5) long, base 1.7–2.5 (1.8, n=5) long; hooks 6(6') very small, spiniform, 2.5–3.3 (3.0, n=5) long, base 0.8–1.6 (1.1, n=5) long; single intercalary hook between each principal row, spiniform, 1.6–2.9 (2.5, n=5) long, base 0.8–1.3 (1.0, n=5) long.

Immature segments 522–827 (648, n=10) long, maximum width 94–174 (165, n=10); length: width ratio 3.20–4.92 (3.99, n=10); genital pores alternate irregularly; genital atrium in posterior half of segment, 196– 339 (248, n=10) from posterior end. Terminal genitalia not fully developed; in most advanced segment, vagina apparently joining cirrus within hermaphroditic sac. Testes 41–63 (50, n=10) long, 26–46 (35, n=10) wide, arranged in 2 parallel columns within segment; 7–11 (9, n=10) postovarian, 0–2 (2, n=10) postvaginal, 9–12 (11, n=10) poral anterior to genital atrium, 11–15 (13, n=10) antiporal, anterior to ovary; total number of testes 29–38 (34, n=10). Remaining genital organs not fully developed.

Remarks. Dollfus (1969) gave a very brief description of this species based on adults from Sphyrna zygaena from the Mediterranean Sea. He ( Dollfus 1969) differentiated this species from O. cysticum (Mayer, 1842) , known only from the plerocercus stage, on the position of the bothrial pits which are on the posterior margin of the bothrium in O. cysticum , but which are on the lateral margin of the bothrium in O. propecysticum . However, following examination of the 48 type specimens of O. propecysticum available, it was evident that the position of the bothrial pits was variable. The pits were on the lateral margins of the bothria in specimens which had been flattened, but were on the posterior border of the bothria of specimens which had not been excessively flattened. Consequently, it was concluded that this feature was an artefact and was not a valid distinguishing criterion for this particular species. Palm (2004) also adopted this character, finding that one specimen which he illustrated (Fig. 193e) was attributable to O. cysticum . However, this specimen is part of the type series of O. propecysticum , and is a specimen which has not been excessively flattened.

Palm (2004) was the first to identify the existence of bill-hooks on the external surface of the basal armature of O. propecysticum . He referred to "pairs of bill-hooks" while the present redescription has identified bill-hooks at the termination of hook rows 4 to 7. This feature distinguishes O. propecysticum from congeners including O. cysticum .

The new specimens reported herein are from Sphyrna mokarran from northern Australia, suggesting that the species may be widely distributed. Given the size of the host and the tiny proportions of the cestode, it may be that it has been overlooked previously and that it may prove to be more common if the spiral valves of hammer-head sharks are examined carefully for tiny cestodes.

Australia is a new locality for this species.

Figures

FIGURES 21 – 23. Otobothrium propecysticum Dollfus, 1969, based on syntypes. 21, Entire worm. 22, Scolex. 23, Premature segment. Scale bars: 0.01 mm.

FIGURES 24 – 29. Otobothrium propecysticum Dollfus, 1969, based on syntypes. Tentacular armature. 24, Metabasal armature, bothrial surface, six rows anterior to base, internal surface on left hand side. 25, Metabasal armature, external surface. 26, Metabasal armature, antibothrial surface. 27, Basal armature, bothrial surface, internal surface on right hand side. 28, Basal armature external surface. 29, Basal armature, antibothrial surface, external surface on right hand side; bill-hooks stippled. Scale-bar: 0.01 mm.