Entobdella vanbenedeni, Kearn & Whittington & Evans-Gowing, 2007

Kearn, Graham C., Whittington, Ian D. & Evans-Gowing, Richard, 2007, A revision of Entobdella Blainville in Lamarck, 1818, with special emphasis on the nominal (type) species “ Entobdella hippoglossi (Müller, 1776) Blainville, 1818 ” (Monogenea: Capsalidae: Entobdellinae) from teleost flatfishes, with descriptions of three new species and a new genus, Zootaxa 1659, pp. 1-54 : 49-50

Entobdella vanbenedeni n. sp.

( Figs. 9 – 12, 13, 15B, 17, 40)

(This taxon has been referred to throughout this paper as “ E. hippoglossi type 2”)

Type host and locality: Atlantic halibut, Hippoglossus hippoglossus (Linnaeus, 1758) ( Pleuronectiformes : Pleuronectidae ); North Atlantic Ocean. Can coexist on this host with specimens of E. hippoglossi ( Müller, 1776) Blainville, 1818 .

Site on host: Skin.

Holotype: Adult specimen from Faroe Bank ( BMNH No. 2007.4.26.10, 1 slide).

Paratype: 1 adult specimen from Faroe Bank ( BMNH No. 2007.4.26.11, 1 slide) .

Voucher specimens: 5 adult specimens from uncertain host and unknown locality of capture, Aberdeen Fish Market (see Table 1) ( BMNH Nos. 2007.4.26.12-16, 5 slides). One adult specimen from uncertain host and unknown locality (see Table 1), donated by Dr H.H. Williams ( BMNH No. 2007.4.26.17, 1 slide). Two adult specimens from uncertain host and unknown locality of capture, Aberdeen Fish Market (see Table 1) ( SAMA AHC No 29200, 2 slides) .

Etymology: The specific name acknowledges the work of P. J. Van Beneden, an outstanding parasitologist of the 19 th century. His work included anatomical studies of E. hippoglossi of exceptional quality. Moreover, he reported anatomical differences in some of his specimens which we now know indicate that the Atlantic halibut ( H. hippoglossus ) is parasitised by 2 closely related but distinct monogenean skin parasites (see Van Beneden 1858 and below).

Specimens studied: Holotype, paratype and voucher specimens as detailed above.

Description ( Fig. 40): Total body length 1.81 (1.385 – 2.223) cm (n = 10); body width 9.24 (7.8 – 11.57) mm (n = 10); haptor length and breadth, 4931 (4176 – 5896) and 4857 (3900 – 5775) respectively (n = 10); accessory sclerite length, 569 (426 – 716) (n = 17); anterior hamulus length 854 (608 – 1138) (n = 20); posterior hamulus length 139 (113 – 155) (n = 7); pharynx length and breadth 874 (650 – 1025) and 1019 (788 – 1250) respectively (n = 8); testis length and breadth, 2533 (1805 – 3429) and 1867 (1474 – 2448) respectively (n = 20). Vaginal aperture on ventral surface large, conspicuous, giving access to vaginal atrium, the wall of which has affinity for toluidine blue in resin sections ( Figs. 9 – 12). Atrium communicates with main convoluted vaginal tube via constricted opening. Convolutions of main vaginal tube arranged in tight and lengthy column. Vaginal opening surrounded by conspicuous condensed circular array of sub-tegumental fibres ( Figs. 12, 39A). Papillae on ventral surface of haptor numerous [129 (105 – 156) per mm 2 (n = 7)]; no obvious arrangement in radial rows apparent ( Fig. 40A). Papillae 20 – 95 in diameter, extending in anterior direction around and usually anterior to peduncular junction. Papillae with fleshy apical lobes not found. Eyes often absent in adults. Glands of Goto present.

Differential diagnosis: Distinguished from all other species of Entobdella , including E. hippoglossi ( Müller,1776) Blainville, 1818 , which shares the same host, the Atlantic halibut, H. hippoglossus , and E. stenolepis from the Pacific halibut ( Hippoglossus stenolepis ) by its large and conspicuous vaginal opening, surrounded by compact circular array of sub-tegumental fibres ( Fig. 12). In addition, E. vanbenedeni has large numbers of relatively small ventral haptor papillae, not arranged in obvious radial rows but extending lateral to and usually anterior to peduncular junction. Papillae of E. vanbenedeni dome-shaped, lacking prominent fleshy apical lobes like those found in E. hippoglossi . On skin of H. hippoglossus .

Comments. A taxonomic problem has been created by the discovery that the Atlantic halibut, H. hippoglossus , is parasitised by 2, closely similar, skin-parasitic entobdelline monogeneans, 1 of which is E. hippoglossi ( Müller, 1776) Blainville, 1818 (what we have called above “ E. hippoglossi type 1”) and the other a closely related but previously undescribed species (what we have called above “ E. hippoglossi type 2” and have named E. vanbenedeni n.sp.). As deduced above, Müller (1776) appears to have based his brief report on E. hippoglossi not on E. vanbenedeni . In other words Müller (1776) must be retained as the authority for E. hippoglossi and E. hippoglossi remains as the type species of the genus.

There is evidence that Van Beneden (1858) probably had specimens of E. vanbenedeni n.sp. in his collection but did not recognise them as a distinct species. First, he quotes a length range of 2.0 to 2.4 cm for his parasites. Such large specimens in our collection belong to E. vanbenedeni n. sp. Secondly, on p. 22 of Van Beneden’s account (1858), he notes that in some individuals the whole of the ventral surface of the haptor is covered with papillae and that when they are so numerous, the papillae are also small.

In the light of our discoveries it is especially interesting that Ronald (1957) came to the conclusion that Atlantic halibut, H. hippoglossus , from the east coast of Canada (Gulf of St Lawrence) were infected with 2 representatives of Entobdella . He regarded the relatively large parasites (1.3 to 2.4 cm in length) as E. hippoglossi ( Müller, 1776) Blainville, 1818 and smaller specimens (0.7 to 1.3 cm in length) as a distinct species which he named E. curvunca . According to Ronald (1957), the 2 parasites differ from each other in the shapes of the anterior and posterior hamuli (“second and third pairs of hooks” of Ronald), but there is no mention or illustration of the vagina.

The only clue to the identity of these parasites is an illustration of the haptor of E. curvunca , which shows relatively few large papillae arranged in radial rows (see Ronald 1957, his fig. 1A). These features, together with the relatively small size of “ E. curvunca ” reported by Ronald, indicate that “ E. curvunca ” is in fact E. hippoglossi ( Müller, 1776) Blainville, 1818 . The implication is that Ronald’s larger parasites are E. vanbenedeni n. sp.

These arguments support the synonymisation of Entobdella curvunca Ronald, 1957 with Entobdella hippoglossi ( Müller, 1776) Blainville, 1818 , as proposed by Klassen et al. (1989) and by Hendrix (1994). However, we were unable to detect consistent differences in the shapes of the hamuli of E. hippoglossi and E. vanbenedeni as indicated by Ronald (1957).

Schram & Haug (1988) also noted differences between specimens that they collected from the skin of halibut ( H. hippoglossus ) caught off the coast of northern Norway. In their fig. 13B they illustrate what they call a “haptor with characteristic rows of tubercles”. In this figure the “tubercles” (= papillae) appear relatively large and those lateral to the median sclerites are in radial rows, as in our E. hippoglossi ( Müller, 1776) Blainville, 1818 . In their fig. 13 A, Schram & Haug (1988) illustrate a whole animal, with the haptor enlarged in fig. 13C. They state that this haptor has “smaller tubercles, closer together than in B”. In fact the papillae are so densely packed that no radial rows are discernible. These are features of E. vanbenedeni as described here. However, Schram & Haug did not show papillae anterior to the junction of the peduncle in their figs. 13A, C and no vagina is illustrated in their fig. 13A. They regarded both of the specimens in their fig. 13 as E. hippoglossi ( Müller, 1776) Blainville, 1818 .