A New Caligiform Copepod (Siphonostomatoida: Dissonidae) Parasitic on Seriola Hippos From Western Australian Waters, With New Records and Morphological Variation for Dissonus Nudiventris and Dissonus Similis, and an Updated Key to the Species of Dissonus

Abstract

Dissonus hoi n. sp. is described from female and male specimens collected from the nasal cavities of a Samson Fish (Seriola hippos Günther) captured off Rottnest Island, Western Australia. Adult female D. hoi are distinguished from their congeners by possessing the following combination of characters: (1) a quadrangular genital complex, (2) ventral spines on the genital complex, (3) pair of postantennal processes, (4) a sternal furca, (5) 1-segmented abdomen, and (6) convoluted, uniseriate egg strings. New records and intraspecific morphological variation are also given for Dissonus nudiventris collected from Australia, and Dissonus similis collected from the tropical western Pacific. A key to the valid species of Dissonus is provided.

A revision of the family Dissonidae Kurtz, 1924 (Copepoda: Siphonostomatoida)

“…The new species can also readily be distinguished from D. nudiventris and D. pastinum, both of which also utilise elasmobranchs as hosts, by the presence of an ornamentation of bifid spinules on the ventral surface of the genital complex in both sexes, since D. nudiventris and D. pastinum lack such ornamentation. It differs from D. hoi in the shape and ventral ornamentation pattern of the genital complex, and in the form of the maxillule: in D. hoi the papilla carrying the three anterior setae is elongate giving the limb a bifid appearance (Tang & Kalman, 2005), whereas in the new species this papilla is a small rounded knob as in all other species. Comparisons with D. ruvetti are more difficult as this species is incompletely described (Nunes-Ruivo & Fourmanoir, 1956).…”

“…Deets & Dojiri, 1990, who figured differences between specimens), and the morphology described for D. pastinum can be encompassed within the range of D. nudiventris. Differences in the length of the tines of the sternal furca cannot be considered to be significant, given the variability already reported in the furca of D. nudiventris by Tang & Kalman (2005). The remaining difference, in the ornamentation of the maxilla, is not of sufficient magnitude to be significant at the specific level.…”

“…However, Kabata's statement that ''there are no significant differences in the details of the appendages of the two sexes'' was taken to indicate that the female antenna carried an accessory claw. Later, Tang & Kalman (2005) noted that the antenna of the female lacked the accessory claw present in males only in known Dissonus species. Unfortunately, before the publication of this correction, Deets & Dojiri (1990) used the lack of the accessory claw on the female antenna as a major distinguishing character justifying placement of their material in a new species, D. pastinum, which also occurred on a heterodontid shark.…”

“…This family also retains the biramous condition in the fourth leg, as in the Trebiidae Wilson, 1905, and the two most basal genera within the Caligidae Burmeister, 1835, Avitocaligus Boxshall & Justine, 2005 and Euryphorus Milne Edwards, 1840 (see Boxshall & Justine, 2005). The family contains just the type-genus, Dissonus , and eleven species are currently recognised (Tang & Kalman, 2005). The single male described as Dissonus sp.…”

“…The species of Dissonus are known to parasitise a wide range of fishes including both elasmobranchs and actinopterygians (Kabata, 1966;Deets & Dojiri, 1990;Tang & Kalman, 2005). All species have thus far been reported only from the Indo-Pacific, from Madagascar in the west to New Caledonia in the east.…”