Morphological variability of Dicrogaster contracta Looss, 1902 (Digenea: Haploporidae) and its proposed synonymy with D. perpusilla Looss, 1902

Abstract

Dicrogaster contracta and D. perpusilla were originally described about 100 years ago from the thicklip grey mullet Chelon labrosus. Subsequent studies have reported D. contracta in several mullet species in the Mediterranean, Azov and Caspian Seas, but D. perpusilla has never been reported again. Since previous evidence suggests that the distinguishing features between these two species are uncertain, this study provides new and additional data on the variability of morphometric and meristic characters of D. contracta in order to assess their usefulness for differentiating this species from D. perpusilla. Body measurements, egg counts and shape statistics of three sets of specimens of D. contracta from different hosts and localities were compared with similar information from previous studies, including the original descriptions of D. contracta and D. perpusilla. The results showed consistent differences between the three sets in metric measurements, egg counts and shape statistics. In addition, the values of morphometric and meristic characters of D. perpusilla fell within the range of variation recorded for D. contracta. Neither conventional body measurements, eggs counts, nor shape statistics seemed useful to distinguish D. contracta from D. perpusilla, suggesting that they represent the same species. Accordingly, the valid designation of the species should be D. perpusilla because it is the type-species of the genus. This study proposes a neotype for D. perpusilla, since no type-specimens seem to be available, and provides additional morphologic data that might be useful for diagnosis of the genus Dicrogaster.

A revision of the Haploporinae Nicoll, 1914 (Digenea: Haploporidae) from mullets (Mugilidae): Dicrogaster Looss, 1902 and Forticulcita Overstreet, 1982

“…Unfortunately, most of these are nondocumented. Sarabeev & Balbuena (2003) examined three samples of D. contracta from the NE Atlantic, Azov Sea and Spanish Mediterranean and compared the metrical data with the descriptions of this species given by other authors, as well as with the original descriptions of D. contracta and D. perpusilla of Looss (1902). They considered the two species synonymous, a decision with which we cannot agree, and selected a neotype for D. perpusilla.…”

“…Three additional species of haploporid digeneans have since been described and assigned to Dicrogaster: D. fastigata Thatcher & Sparks, 1958; fragilis Fernández Bargiela, 1987;and D. japonica Machida, 1996. With the exception of Sarabeev & Balbuena (2003), who considered the two species described by Looss (1902) as conspecific, no attempt has been made at a critical evaluation of the features distinguishing the species; this is perhaps due to their disparate distribution and the difficulties with specimen preparation (Overstreet & Curran, 2005).…”

Dicrogaster perpusilla Looss, 1902 sensu Sarabeev & Balbuena (Digenea: Haploporidae): a note of caution

“…The metrical data obtained from this voucher material indicate that juvenile and laterally mounted specimens have been used in the comparisons upon which the synonymy of D. perpusilla and D. contracta was suggested. The overall conclusion of the study is that the synonymy of D. contracta and D. perpusilla proposed by Sarabeev & Balbuena (2003) is based on questionable material. Since the neotype of D. perpusilla is unrecognisable, and a number of qualifying conditions of the ICZN in its designation were not met, the usage of the original conception of the type-species of Dicrogaster given by Looss (1902) is recommended.…”

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Sarabeev & Balbuena (2003) considered Dicrogaster perpusilla Looss, 1902 and D. contracta Looss, 1902 (Digenea: Haploporidae) synonymous. They designated a neotype for the type-species, D. perpusilla, from a sample of specimens ex Chelon labrosus off West Thurrock, UK.

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“…These features suggest that the 12 specimens of this lot may belong to Saccocoelium Looss, 1902, but the state of the material does not permit its reliable identification. The specimen designated by Sarabeev & Balbuena (2003) as the neotype of D. perpusilla represents a neogravid dorso-laterally mounted specimen and is unrecognisable. Although five of the six voucher specimens of these authors may represent Dicrogaster spp., the poor state of this material does not allow its accurate identification.…”