Sucking of human blood by Placobdella costata (O. F. Müller, 1846) (Hirudinida: Glossiphoniidae): Case study with notes on body form

Abstract Four events of Placobdella costata sucking human blood are described. Human blood was sucked by both adult and juvenile specimens of P. costata. The feeding strategies of juveniles under parental care are presented. New data on juvenile specimens' body form are presented. Information on the potential role of mammals in dispersion and habitat preferences of leeches P. costata is considered.

The presence of both species in Europe is closely related to the appearance of turtles, their primary hosts (Bielecki et al., 2012;Moser et al., 2016;Soors et al., 2015). The Placobdella costata feeds mostly on the blood of the European pond turtle Emys orbicularis originating from North America (Bielecki et al., 2012;Sket & Trontelj, 2008). It has also been found in the Mediterranean pond turtle Mauremys leprosa (El-Mustapha et al., 2020;Romero et al., 2014), Caspian turtle Mauremys caspica (Bashirichelkasari & Yadollahvandmiandoab, 2017;Bielecki et al., 2012), and the Sicilian endemic pond turtle Emys trinacris Marrone et al., 2016). The individuals of this species are also present in regions where there are no freshwater turtles (Bielecki et al., 2012;Elliott & Tullett, 1982) and may optionally feed on the blood of birds and mammals (Bielecki et al., 2012;Elliott & Tullett, 1982;Grosser, 1996). Pawłowski (1968) claimed that leeches P. costata also attack people wading in water. Additionally, Wilkialis (1984) observed in laboratory conditions how this leech fed on human blood only in places where the skin had previously broken. Even though other species of the genus Placobdella (P. ornata, P. rugosa) are described as being capable of taking human blood (Klemm, 1991(Klemm, , 1995Moore, 1964;Moser, 1991;Sawyer, 1972Sawyer, , 1986, Mandal et al. (2018) reported the first recorded observation of glossiphoniid P. devkuntai sucking human blood.
Despite having much information about P. costata and its hosts, we do not know if only adult specimens or also young leeches collect human blood and to what extent their digestive tract is filled.
Furthermore, there has also been no documentation showing the noticeable negative (external) effects of blood sucking of these leeches on humans.
The aim of the paper is to present documented events of human blood sucking in natural conditions by adult P. costata leeches not caring for offspring and above all by young individuals in their care.
We also described the morphological features based on the parameters of the leech body form model to show that it changes during ontogenesis.

| MATERIAL S AND ME THODS
The authors describe the results of their experiences from four locations in Central and Eastern Europe ( Figure 1; Table 1). Placobdella costata (five adult and 44 juvenile specimens; Figure 2) and other species of the family Glossiphoniidae (coming from various places in Poland, some of them were described in the work of Bielecki et al., 2009) were measured based on the parameters of the body form model of leeches created by Bielecki andEpshtein (1994, 1995) ( Figure 3). The model presents the leech body on a plane, as two ellipses (that represent suckers) and trapeziums situated between them (representing anterior body part-trachelosome-2 trapeziums; posterior body part-urosome-4 trapeziums). Besides, transverse sections through the trachelosome and urosome are considered as two ellipses.
Based on 29 parameters of the morphometric description ( Figure 3), 19 body proportions indexes are as follows: • relative body length: L/D 2 = ratio of length to largest width of urosome.
• anterior sucker: C 1 1 /d 1 = ratio of horizontal diameter of sucker to trachelosome width at sucker junction; C 1 1 /D 1 = ratio of horizontal diameter of sucker to the greatest width of trachelosome; R 1 / M 1 = ratio of dorsal part of sucker to its ventral part; C 1 1 /C 1 = ratio of horizontal diameter of sucker to its vertical diameter.
• anterior body part (trachelosome): L 1 /D 1 = ratio of trachelosome length to its greatest width; D 1 /N 1 = ratio of the greatest F I G U R E 1 Place of events locationsite numbers according to the description in Table 1 trachelosome width to its greatest height; S 1 /S 2 = index describing position of the greatest width of trachelosome.
• posterior body part (urosome): L 2 /D 2 = ratio of urosome length to its greatest breadth; D 2 /N 2 = ratio of the greatest urosome width to its greatest height; K 1 /K 2 = ratio describing position of the greatest width of urosome.
• posterior sucker: C 1 1 /d 7 = ratio of horizontal diameter of sucker to urosome width at sucker junction; C 1 1 /D 2 = ratio of horizontal 16 diameter of sucker to the greatest body height; R 2 /M 2 = ratio of dorsal part of sucker to its ventral part; C 1 1 /C 2 = ratio of horizontal diameter of sucker to its vertical diameter.
• relations between urosome and trachelosome: L 2 /L 1 = ratio of urosome length to trachelosome length; D 2 /D 1 = ratio of the greatest width of urosome to the greatest width of trachelosome; N 2 /N 1 = ratio of the greatest height of urosome to the greatest height of trachelosome.
• proportions of suckers: C 2 1 /C 1 1 = ratio of horizontal diameter of posterior sucker to horizontal diameter of anterior sucker.
Similarities of the body form were found with the use of the cluster analysis (Ward's method, Manhattan distance).

| RE SULTS
In four locations in Europe, turtle leeches Placobdella costata attack-  River channel, Poland, only a single adult specimen was observed to suck human blood from the right lower limb, at the ankle in the area of the Achilles tendon.
All of the abovementioned cases of blood sucking were accom-

| Morphometric analysis
The algorithm for combining or grouping trees was chosen to interpret the similarity of the body form of 14 species from the Glossiphoniidae family and two species from the families Piscicola geometra and Erpobdella octoculata. The procedure allowed the species morphotypes to be divided into ( Figure 5)-the monotype cluster (I), in which P. geometra was found, and the polytype cluster (II) consisting of the remaining species. The latter cluster was divided into subclusters II 1 and II 2 and the latter included juvenile P. costata, and adult Hemiclepsis marginata, Theromyzon tessulatum, and P. costata. In this subcluster, adult P. costata and juvenile both T. tessulatum and P. costata and E. octoculata have the most similar body forms. It follows that P. costata minors have "tape" type body form (similar to E. octoculata) which differs from adult P. costata with a "leaf" shape (Table 2).  (Kufel, 1969), coot (Fulica atra L.) (Radkiewicz, 1972), and black stork (Ciconia nigra L.) (Matysiak, 1964). Elliott and Tullett (1982) explain the leech's presence in the British Isles because of the relationship with migrating birds whose flight routes run across continental Europe. Blood taken from bird species in laboratory conditions substantiates this thesis (Wilkialis, 1970).

| D ISCUSS I ON
In the face of the emergence of a potential source of food and physiological possibilities of obtaining it, predatory leeches take advantage of this opportunity. This gives a chance of survival to leeches and is consistent with experimental observations, which describe much wider food spectra than those that are confirmed in field observations (Esbérard et al., 2005;Wilkialis, 1970Wilkialis, , 1973Wilkialis, , 1984. Other Placobdella species are also mainly ectoparasites on turtles but are able to attack animals other than reptiles, and both verbana Carena leech, which have jaws ( Figure 4g) (Sawyer, 1986).
Placobdella costata leaves more or less rounded traces, much smaller than the medical leech, who are bright red and have three distinct grooves resulting from the action of three jaws. For some hosts, members of genus Placobdella are vectors of hemogregarine and trypanosome blood parasites (Barta & Desser, 1989;Siddall & Desser, 1990, 192a, 1992b, 1993. The confirmation of bloodsucking capacity from human by P. costata is important information in the context of human health. Like other representatives of Glossiphoniidae, adult Placobdella costata care for embryos and their young (Bielecki et al., 2012;Wilkialis, 1970). This was also visible during our observations, when adults with attached juvenile specimens attacked the legs of the researcher and first took blood, which also flowed into the wounds.
Some young leeches introduced the proboscis into these wounds and took blood (Figure 4a and b), and others including adults successfully pierced the skin. In Belarus, during two incidents, two to three adults and a "swarm" of the young were attacking. Such behavior in the care of the offspring is very helpful in the survival of young leeches.
Leeches from the family Glossiphoniidae are represented by the most numerous species (Sket & Trontelj, 2008) and have the largest number of hosts, from invertebrates to almost all vertebrates.
Various nutrition methods as well as unique care for a large number of polylecytal eggs and offspring most likely ensured their F I G U R E 5 Tree diagram for 16 leech species based on mean value of 19 body index (    Erpobdella octoculata (Linnaeus, 1758) evolutionary success (Bielecki et al., 2014;Kutschera & Wirtz, 2001).
In addition, one species of Glossiphoniidae cares for the offspring of other species in this family (Wilkialis, 1970). While breeding P.
costata and T. maculosum in one aquarium, the authors (unpublished data), similarly to Wilkialis (1970), observed the interesting phenomenon of parental care. It may be because both species feed on the blood of vertebrates (birds and reptiles, former Gadocapidae Sauropsida). While the young P. costata leeches are sucking blood, their body shape changes. The body form of leeches (Hirudinida) was developed by Bielecki and Epstein (1994) as a geometric model that contains twenty-five measurements and their nineteen proportions (features). From this model, it follows that leeches have four body forms: "cylinder," "tape," "flask-like," and "leaf," which is characteristic of leeches from the Glossiphoniidae family.
Young leeches have a different body form than adults. It is a flattened "cylinder" or "tape" (Figure 4a and b), which during blood collection changes into a deceptively body-like form ("butt") similar to leeches from the Piscicolidae family of the genus Limnotrachelobdella where it is pronounced trachelosoma and urosoma ( Figure 3) (Bielecki, 1997;Cichocka & Bielecki, 2015;Cichocka et al., 2018).
This body form probably occurs for a short period during the early ontogenesis of P. costata. Adult Placobdella costata no longer take this body form but have a "leaf" type (Bielecki, 1997;Bielecki et al., 2014;Cichocka & Bielecki, 2015). The body-flattened "cylinder" form of young P. costata leeches even before the first blood sucking corresponds to the ancestor of leeches, which sucked blood and whose body shape resembled leeches from the families Piscicolidae and Erpobdellidae (Cichocka & Bielecki, 2015;Siddall, 2002;Siddall & Burreson, 1995, 1996, 1998. In our study, the morphometic analysis proved the similarity of the body form of young P. costata and representatives of Erpobdella ( Figure 5). The eprobdellids, piscicolids, and juvenile P. costata have very similar main body parameters with only differences within the anterior sucker. Cichocka and Bielecki (2015) showed that on the leech body form model, the cladistic interpretation of leech evolution based on morphometry (LBF model) only slightly diverges from the picture of evolution based on a molecular level. In addition, these studies have shown that individual leech taxa at a family level have morphometric synapomorphy (invariants), and Glossiphoniidae have 12 of them. Such a synapomorphy in the Glossiphoniidae family is the ratio of body length to its greatest width and thickness and derivatives of these relationships (L/D 2 , L 2 /D 2 , K 1 /K 2 , N 2 /L 2 , D 2 /D 1 ). These are features related to the care of the offspring, which in P. costata are revealed already at an early stage of ontogenesis, actually at the first blood suction (Bielecki & Epstein, 1994;Bielecki et al., 1999).
We are getting more and more information about leeches' feeding relationships that tells us how this process could look from the point of view of evolutionary phenomena. It allows us to hypothesize possible future hosts. This is important especially in light of the current global environmental changes occurring, accompanied by changes in the range of species occurrence of both parasites and their hosts. Our observations regarding P. costata nutrition can also be seen as an adaptation in the absence of a preferred food base.
Moreover, the leech appears to be much more mobile than its host since it is regularly found far outside the range of turtles (Vamberger & Trontelj, 2007), which might be explained by relation with such more mobile hosts as the beaver (Castor fiber), elk (Alces alces), and waterfowl (Biegel & Grosser, 2004;van Haaren et al., 2004).
The association of leeches with beavers may explain the presence of P. costata in the Łyna River (Olsztyn, Poland), where, unlike turtles, the presence of beavers was recorded (Grzybowski & Endler, 2012 Kubova et al., 2013;Sawyer, 1986). Placobdella costata prefers places in the shallowest parts of water bodies with dense vegetation (Sapkarev, 1964), which are also suitable for feeding all of the abovementioned potential food sources, including the zone penetrated by humans (e.g., anglers). Our observations confirmed the presence of representatives of this species in the areas overgrown with submerged macrophytes, but no relationship with a specific species was found.

| CON CLUS ION
Our field observations confirm that juvenile forms of P. costata still under parental care are able to puncture the human skin and suck the blood. There was no preference for a specific place on the human limbs. We supplemented information on parental care strategies and morphological data about the body form of this species. Our analysis confirmed that the body form of leeches may change during their ontogeneses, which seems to be important in terms of species determination and classification. Based on our observations, we obtained more information about the potential role of mammals as hosts and dispersion vector of this leech. Our description, although it concerns one species, is universal and may be the basis for the consideration of broadening the spectrum of parasite hosts in the context of reducing biodiversity.

ACK N OWLED G M ENTS
Katarzyna Topolska and Łukasz Krajewski sincerely thank Mr.