First record of a ciliate suctorian ( Ciliophora , Suctorea ) epibiont on the jellyfish Pelagia noctiluca ( Scyphozoa , Semaeostomaeida )

In the course of a survey of a specimen of the jellyfish Pelagia noctiluca (collected at Villefranche-sur-Mer, France) using scanning electron microscopy, the suctorian ciliate Trichophrya salparum was found on the jellyfish exumbrella. This ciliate species is reported for the first time on a scyphozoan jellyfish host. A redescription of this suctorian species is presented together with data on its distribution and host prevalence.


Introduction
Suctorians (class Suctorea) is a peculiar group of carnivorous or parasitic ciliates. The majority of these ciliates are commensals of various aquatic invertebrates or vertebrates (Dovgal 2002(Dovgal , 2013. A few findings of suctorians on cnidarians have been reported, but never on scyphozoan jellyfishes. For example, some representatives of genus Ephelota Wright, 1858 were found on hydroids (Yagiu 1980, Tazioli & Di Camillo 2013. As part of bioluminescence studies conducted by of one of us (PRF) a specimen of Pelagia noctiluca Forskål, 1775 was examined in a scanning electron microscope and unexpectedly revealed the presence of some 20 suctorian ciliates identified as Trichophrya salparum Entz, 1884. This is probably the first report of a suctorian ciliate from this host group. Moreover, as T. salparum rarely has been collected, we give an updated description of this species based on our finding.

Material and Methods
The suctorian specimens used in the present study were accidentally found attached to the exumbrella of a P. noctiluca (Scyphozoa, Semaeostomaeida) prepared for scanning electron microscopy. This jellyfish had a dome diameter of ~2cm and was collected at Villefranche-sur-Mer, France, in July 1995. The whole specimen was fixed in 2% glutaraldehyde in 40mM sodium cacodylate (pH = 7.4) and 0,5M sucrose before transport to Bergen, Norway. Upon arrival there, tissue blocks of the exumbrella near the marginal lappets of

Research Article
the jellyfish dome were rinsed in isotonic buffer, postosmicated, rinsed, dehydrated in ethanol and critical point dried from liquid CO 2 . After mounting on a specimen support the tissue was sputter-coated by a thin layer of gold/palladium. About 20 years later (!) the tissue was examined in a Zeiss Supra 55VP field emission scanning electron microscope operated at 5 kV with an "in-lens" secondary electron detector.
All measurements were made by a mm-ruler on paper copies of digital images at 3000 to 10000 times magnification. Diagnosis. Unloricate, unstalked suctorian ciliate. The body is somewhat hemispheric or saddle-shaped, with a large, flat base. There are two (rarely one) bundles of capitate tentacles. There are from four to 32 tentacles in each fascicle. Their diameter varied between 0.7 and 1.2 µm dependent on their degree of contraction. Tentacles are capitate with globular knobs covered by several smaller haptocyst dots. The cytoplasm is uncolored, but may contain some bright granules. The macronucleus is granular, and spherical or elongated. There are from one to three contractile vacuoles. Reproduction by multiple internal budding (Fig. 1c).
However, the first find of suctorian ciliate on tunicates probably belongs to Lachmann (1859) who mentions the species Trichophrya ascidiarum found on sea squirts of the genus Polyclinum Savigny, 1816 in the North Sea. Unfortunately, this species was not described by the author, thus the specific name Trichophrya ascidiarum Lachmann, 1859 is a nomen dubium. Tregouboff (1916) described a subspecies of T. salparum named T. salparum pyrosomae Tregouboff, 1916 (Fig. 1d). However, T. salparum is an extremely variable species thus we believed there is no reason to divide the species into subspecies. Thus, T. salparum pyrosomae Tregouboff, 1916 syn. n. is a younger synonym of T. salparum. Among the 12 species that belong to the genus Trichophrya only three, including T. salparum, have from one to two tentacle fascicles: The other two are T. angulata Dangeard, 1890, andT. brevis (Goodrich &Jahn, 1943).
However, according to Dangeard's (1890) observations T. angulata has exogenous budding thus affiliating the species to the Trichophrya is uncertain.
As for T. brevis, this species is likely to be a specific commensal of freshwater turtles. In addition, the curved or U-shaped (not rounded) macronucleus is characteristic for the latter species (Dovgal 1996(Dovgal , 2013. The T. salparum was specified by Jankowski (1967) as a type species of genus Actinobranchium Jankowski, 1967. The lack of tentacle knobs were mentioned as a main characteristic of the genus (Jankowski 1981). However, as was shown of Dovgal (2002) there is a tentacle knob in the type species, and the generic name Actinobranchium was therefore synonymized with Trichophrya.
Thus, earlier the species has been found exclusively on tunicates. The lack of finds of T. salparum on scyphozoan jellyfishes is probably due to the difficulties in discovering a small epibiont ciliate on such thick and voluminous bodies.
We found 23 specimens of T. salparum attached directly to the exumbrellar epithelium of Pelagia noctiluca on a single SEM preparation. This covered some 7.5 mm 2 of the jellyfish dome and consisted of smooth parts separated by several nematocyst warts (Fig. 2), characteristic for this species. The suctorians were exclusively found on the smooth parts where the epithelial surface was covered by densely packed irregular microridges and occasional cilia (Figs. 3 & 4). Tiny microvilli also projected from the attachment surface of the suctorian body towards the jellyfish tissue (Fig. 5).