In mature adults this underlying pattern may become obscured or lost entirely, especially in mid-body segments XI–XXII ( Figure 2A,B). With further maturation these may become broadly confluent anteriorly and posteriorly, but they remain centred at the same ordinal locations as the respective patches of the hatchling. multilineata, widen into irregular cream-coloured expanses on either side of the mid-line ( Figure 2C). During growth and development these same patches in P. In hatchlings, these white patches are invariably centred at the midline at segments VIa3 (nuchal), IXa2 (pre-genital), XIIa2 (genital), XV/XVI (mid-crop), XVIII/XIX (pre-intestine) and XXIIa1 (anal), respectively ( Figure 11 and Figure 12). parasitica invariable display six white pigment patches ( Figure 10, wp) not discretely evident in the adult of this species. Interestingly, in the current study a similar aggregation of annectant cells occurs in the eyes of P. Of possible taxonomic significance, however, such a median annectant lobe was not present in P. parasitica in that it appears not to be present in all specimens from Illinois nor from the Outer Banks. This possibly unique annectant lobe is not diagnostic of P. Finally, at least one specimen from the Outer Banks displayed what appears to be a similar median lobe ( Figure 4, mac). 4) without comment from a specimen from Massachusetts. A very similar annectant lobe had been illustrated earlier by Whitman (fig. ‘Very frequently, but apparently not invariably’, a median lobe of salivary tissue links the two posterior salivary glands. Moore was first to describe a peculiar-overlooked feature of the salivary complex of P. No significant differences between species were noted in the female reproductive system. In both species the seminal vesicle joins the vas deferens just anterior to level of g. XI), consistently more anterior than the much less swollen seminal vesicles of P. parasitica is at level of the atrium (i.e., behind g. The apparent juncture between the ejaculatory duct and seminal vesicle in P. parasitica are particularly prominent and swollen ( Figure 4, sv), and typically observable through the ventral tegument ( Figure 3A). multilineata the ejaculatory duct is longer and joins the seminal vesicle at about the level of g. In one mature specimen (PP-1) the ejaculatory duct extends a little more anterior, to X/XI. parasitica the narrow, tubular ejaculatory duct is confined to segment XI and joins the seminal vesicle at about level of the atrium (PP-4a). multilineata are noted in the various dissections, but owing to the physiologically plastic nature of these structures taxonomic significance requires further scrutiny. Differences between the male anatomy of P. Why do the two American turtle leech species coexist rather than reduce competition by partitioning their food supply? Morphological differences are interpreted as reflecting interspecific competition, a phenomenon not found in their Palaearctic counterpart. parasitica, the first example of character displacement in the Hirudinea. rugosa clade, but tubercle suppression in P. A morphologically significant observation is that developmental divergence results in tubercle prominence in P. An unexpected finding is that hatchlings of both species are very difficult to distinguish. This paper addresses morphological differences between them. rugosa clade commonly coexist and feed on the same turtle species without host preference. These two tuberculated forms are recognised herein as a clade and treated as a single ‘species’ for comparative purposes. The latter species is morphologically indistinguishable from P. rugosa, which geographically overlap in eastern USA and southern Canada. American Placobdella which feed on turtles are represented predominantly by two common species, P. costata is the only representative in the Palaearctic region. The genus Placobdella (Glossiphoniidae) has a centre of species concentration in North America.
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