Corynosoma Magdaleni in Gray Seals From the Gulf of Bothnia, With Emended Descriptions of Corynosoma Strumosum and Corynosoma Magdaleni

Abstract

Because of the likelihood that Corynosoma magdaleni Montreuil, 1958. has been confused with C. strumosum (Rudolphi, 1802) in reports of parasites from seals and to clarify its distribution in the Baltic Sea, acanthocephalans from 26 young gray seals from the southwestern Finnish archipelago (western Baltic Sea) were examined. All harbored C. semerme (Forssell. 1904). In addition to C. semerme, 12 had both C. strumosum and C. magdaleni, 3 had only C. strumosum, and 9 had only C. magdaleni. Most anatomical structures of C. strumosum are similar to, but larger than, those of C. magdaleni. The most conspicuous differences are the longer and more robust trunk of C. strumosum, the routinely longer proboscis (mean, 653 vs. 476 microm) and larger proboscis hook (mean, 69 vs. 58 microm) of C. strumosum, and the greater extent of ventral trunk spines (mean, 61 vs. 47%) in C. magdaleni. In addition, C. strumosum consistently possesses 18 longitudinal rows of proboscis hooks, whereas C. magdaleni has 17-23, with 20 being the usual number by far. In seals aged 3.6 mo, on average, C. strumosum was more prevalent and abundant than was C. magdaleni, whereas in seals of age 2.0-3.0 mo the reverse was true, with C. strumosum being nearly absent. These differences might reveal the age-dependent food habits of the very young seals. No site segregation was found between C. strumosum and C. magdaleni in the small intestine, but they clearly segregated from C. semerme, which occurred mainly in the cecum, large intestine, and rectum. All species matured equally well in gray seals, with 62, 67, and 53% of the C. magdaleni, C. strumosum, and C. semerme, respectively, comprising gravid worms (possessing eggs with fully formed acanthors).

Stability ofCorynosomapopulations with fluctuating population densities of the seal definitive host

“…C. magdaleni was not reported again until Delyamure et al (1980) found it in 3 ringed seals from the Gulf of Finland, Baltic Sea. The subsequent reports of C. magdaleni were those of C. magdaleni adults in grey seals of SW Archipelago sea between the Gulf of Bothnia and the Baltic proper (Nickol et al 2002) and cystacanths in fishes of the Bothnian Bay and from the isolated land-locked ringed seal population of Lake Saimaa in SE Finland (Sinisalo et al , 2004. The present finding of C. magdaleni in ringed seals of the Bothnian Bay confirms the status of ringed seals as a genuine definitive host of C. magdaleni in the Baltic Sea, not only in the Lake Saimaa population where C. magdaleni is the only acanthocephalan species ever found (Sinisalo et al , 2004.…”

“…Until 1982 we identified specimens as either C. strumosum (Rudolphi, 1802) Lü he, 1904, or C. semerme (Forssell, 1904) Lü he, 1905 according to Petrochenko (1956). From 1988 onwards C. magdaleni were separated from C. strumosum following the descriptions later proposed by Nickol et al (2002). The worms were preserved in 70 % ethanol and cleared in lactophenol or they were studied from fresh slides illuminated from beneath.…”

“…Throughout the 2 main study periods (1977-1982 and 1988-1999) In the latter period (1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) when C. strumosum and C. magdaleni were distinguished as separate species (see Nickol et al 2002), C. magdaleni had a slightly higher prevalence on average than C. strumosum, and its mean abundance in the 25 seals was twice as high as that of C. strumosum. When examining the ratio of C semerme to ' C. strumosum ' specimens in yearly samples, we can see that in all samples except 2 (autumn 1979 and spring 1988), C. semerme was numerically dominant.…”

“…They also suggested it is likely that C. magdaleni had been unrecognized in earlier reports of parasites from seals due to the poor description of the species and the conditions under which seals are collected, making it difficult to process acanthocephalan specimens in the conventional manner. The finding of C. magdaleni from the ringed seals in the Gulf of Finland by Delyamure et al (1980) prompted Nickol et al (2002) to consider that the Baltic ringed seal may have become a definitive host of C. magdaleni when living sympatrically with the Baltic grey seal. Nickol et al (2002) showed that both C. magdaleni and C. stumosum mature equally well in grey and ringed seals in the Finnish SW Archipelago Sea.…”

“…The finding of C. magdaleni from the ringed seals in the Gulf of Finland by Delyamure et al (1980) prompted Nickol et al (2002) to consider that the Baltic ringed seal may have become a definitive host of C. magdaleni when living sympatrically with the Baltic grey seal. Nickol et al (2002) showed that both C. magdaleni and C. stumosum mature equally well in grey and ringed seals in the Finnish SW Archipelago Sea. The third Corynosoma species, C. semerme, also matures equally well in both seal species.…”