Turbellarian black spot disease in bluespine unicornfish Naso unicornis in New Caledonia, caused by the parasitic turbellarian Piscinquilinus sp.

Abstract

Turbellarian black spot disease is described in a bluespine unicornfish Naso unicornis (Perciformes, Acanthuridae) collected from the wild off Nouméa, New Caledonia, South Pacific. Each cyst contained a whitish worm, 2 to 4 mm in length, which was able to swim freely in seawater. Cyst walls consisted of fibrous tissue with a scattering of melanocytes. Worms had 2 eyespots at the anterior end, a pharynx at the posterior end and a largely undeveloped reproductive system. They were identified as Piscinquilinus sp. (= Ichthyophaga sp.), a genostomatid turbellarian. The disease spread within 2 wk from a single infected fish to 3 other unicornfish in the same tank, in spite of copper sulphate and diluted seawater treatment; however, other fish from several families kept in the same tank were not infected, suggesting specificity of these parasites. Praziquantel injections into the infected fish eliminated the infection. Other cases of turbellarian infections are reported from 7 fish species off New Caledonia; prevalence is very low (0.3%).KEY WORDS: Black spot disease · Fish · Naso unicornis · Turbellaria · New Caledonia · Piscinquilinus · Ichthyophaga Resale or republication not permitted without written consent of the publisher

Phylogenetic relationships within Adiaphanida (phylum Platyhelminthes) and the status of the crustacean‐parasitic genus Genostoma

“…This hypothesis-perpetuated through the current classification of Piscinquilinus within the family Genostomatidae (Tyler et al 2015) -was implicitly questioned by recent ultrastructural observations of Genostoma kozloffi (Tyler & Tyler 1997;Pfisterm€ uller et al 2002). Unfortunately, corresponding ultrastructural observations, particularly of spermiogenesis, are not available for Piscinquilinus although light-microscopical observations (Syromyatnikova 1949;Justine et al 2009) demonstrate a fully ciliated epithelium without perikarya, which is much more similar to the epithelia of other "amended" Fecampiida than to the tegumental syncytium of Genostoma. Thus, while strong molecular phylogenetic evidence for the inclusion of Piscinquilinus as a member of Fecampiida has been available for over a decade (Littlewood & Olson 2001), to date the phylogenetic status of Genostoma, whether as a morphologically aberrant fecampiid, an independent acquisition of obligate parasitism within another "turbellarian" clade (e.g., Kalyptorhynchia, Prolecithophora), or as a separate lineage altogether, has remained uncertain (Fig.…”

“…Thus, for a time, it appeared that the sister‐group to Neodermata had been discovered (the so‐called “Revertospermata” hypothesis) in the form of a clade of turbellarians with a neodermatan‐type spermiogenesis, which formed all the more appealing an intermediate step on the road to Neodermata due to their own obligate parasitic habits (exclusively, however, using invertebrate definitive hosts except for the teleost‐specialist genus Piscinquilinus ; see e.g., Justine et al. ).…”

“…A still more remarkable finding came from observations of the process of spermiogenesis, which led to the realization that several genera of Fecampiida (Notentera, Urastoma, and Kronborgia) do not fuse the two characteristic platyhelminth flagellar axonemes in the disto-proximal manner of most rhabditophorans (Kornakova & Joffe 1999), instead evincing a "reversed" proximo-distal fusion similar to the members of the obligate vertebrate-parasitic Neodermata (except for Monopisthocotylea; Justine 2001). Thus, for a time, it appeared that the sister-group to Neodermata had been discovered (the so-called "Revertospermata" hypothesis) in the form of a clade of turbellarians with a neodermatan-type spermiogenesis, which formed all the more appealing an intermediate step on the road to Neodermata due to their own obligate parasitic habits (exclusively, however, using invertebrate definitive hosts except for the teleost-specialist genus Piscinquilinus; see e.g., Justine et al 2009).…”

An annotated list of fish parasites (Isopoda, Copepoda, Monogenea, Digenea, Cestoda, Nematoda) collected from Snappers and Bream (Lutjanidae, Nemipteridae, Caesionidae) in New Caledonia confirms high parasite biodiversity on coral reef fish

“…furcosus ; these were orange, abundant but with a very low prevalence, and were not studied in detail. Parasitic turbellarians are rarely found on coral reef fish [106,107]. …”

“…New, unpublished records indicated by [0]; other records: [6,24,25,45,47,58,59,71,78,79,81,87,88,107,155-166]. …”