Two new species of Acanthobothrium Blanchard, 1848 (Onchobothriidae) in Narcineentemedor Jordan & Starks, 1895 (Narcinidae) from Acapulco, Guerrero, Mexico

Abstract Two species of Acanthobothrium (Onchoproteocephalidea: Onchobothriidae) are described from the spiral intestine of Narcineentemedor Jordan & Starks, 1895, in Bahía de Acapulco, Acapulco, Guerrero, Mexico. Based on the four criteria used for the identification of species of Acanthobothrium, A.soniaesp. nov. is a Category 2 species (less than 15 mm in total length with less than 50 proglottids, less than 80 testes, and with the ovary asymmetrical in shape). Acanthobothriumvidalisp. nov. is a Category 6 species (more than 15 mm in total length with more than 50 proglottids, fewer than 80 testes, and the ovary is asymmetrical). The new species differ from similar species from the Pacific Ocean by total length, the number of proglottids, diameter of the accessory sucker, the length of the cirrus sac, the number of testes per proglottid and the measurements of hooks. With the recognition of A.soniaesp. nov. and A.vidalisp. nov., 42 species of Acanthobothrium have been reported from the Pacific coast of the Americas. This is the first report of species of Acanthobothrium from a member of Narcine from Mexico and it brings the number of species reported from elasmobranchs from the Pacific Coast of Mexico to 13.


Introduction
Acanthobothrium Blanchard, 1848 is one of the richest genera within Onchoproteocephalidea (Maleki et al. 2013;Caira et al. 2017), but relatively few occurrences have been documented in Mexico. To date, the best-studied locality is the Gulf of California (Sea of Cortez; Mar de Cortés, Golfo de California) with the descriptions of 10 species (Appy and Dailey 1973;Caira and Burge 2001;Caira and Zahner 2001;Ghoshroy and Caira 2001). The only other species known from the Pacific Coast of Mexico was described from the more southern state of Jalisco (Monks et al. 1996) (see Merlo-Serna and García-Prieto 2016). More recently, A. cartagenensis Brooks & Mayes, 1980 was reported from Quintana Roo, Mexico (Caribbean) (Monks et al. 2015a) and A. marquesi was described from Campeche, Mexico (Gulf of Mexico) by Rodríguez-Ibarra et al. (2018). As part of a collaborative project to extend the knowledge of the helminth fauna of marine fishes in Mexico, rays were collected from the coastal waters off Acapulco, Guerrero, a region with few studies of the parasites of rays. There are six reports of parasites of rays from Acapulco, none for Acanthobothrium (see Merlo-Serna and García-Prieto 2016). In this paper, two new species of Acanthobothrium are described from Narcine entemedor Jordan & Starks, 1895 (Elasmobranchii: Torpediniformes: Narcinidae); one Category 2 species (Ghoshroy and Caira 2001) and one Category 6 species. The new species constitute the first records from the Southern Pacific Coast of Mexico and the first record of species of Acanthobothrium reported in Narcine entemedor from Mexico.

Systematic accounts
Etymology. The species is named in remembrance of Sonia Virginia Flores León, former player of the Pumas Club Women's Basketball Team, UNAM, daughter of Virginia León-Règagnon and Martín Ignacio Flores-Carbajal and dear friend of SM and GP-F; she will not be forgotten.
Diagnosis. Acanthobothrium soniae sp. nov. is a Category 2 species. It is small, with a range of 10-13 acraspedote proglottids. The testes are wider than long with a range of 31-47 testes per proglottid. The arms of the ovary are unequal (asymmetrical). Finally, this species also can be distinguished from similar congeners by total length, number of proglottids, diameter of accessory sucker, the length of the cirrus sac, number of testes per proglottid, and size of the hooks. Description.
Remarks. There are 42 Category 2 species (sensu Ghoshroy and Caira 2001) of Acanthobothrium that have been described worldwide. Of these, 17 species have been found in the Pacific Ocean, 14 of which are amphi-American (Table 1).
Etymology. The species is named in honor of Dr Victor Vidal Martínez (Departamento de Recursos del Mar, CINVESTAV-IPN, Merida, Yucatan, Mexico), for his contribution to our knowledge of helminths of fishes from Mexico.
Remarks. There are 14 Category 6 species of Acanthobothrium that have been described worldwide. Of these, seven species have been found in the Pacific Ocean, four of which are amphi-American (Table 2). Acanthobothrium vidali sp. nov. also is a Category 6 species, bringing the total number to 15. Category 6 species have a total length >15 mm (the length of A. vidali sp. nov. is 26.5-70.9 mm), a strobila made up of > 50 proglottids (A. vidali sp. nov. has 164-214 proglottids), number of testes per proglottids ≤ 80 (A. vidali sp. nov. has 50-76 testes per proglottid), and the arms of the ovary are asymmetrical.
As presented in Table 2, the new species can be distinguished from similar Category 6 species of Acanthobothrium that have been described from the Pacific Coast of the Americas (amphi-American species), and from others parts of Pacific Ocean by the measurementes given in Table 2. The total length of the new species (26.5-70.9 mm) is longer than that of A. aetiobatidis (Shipley, 1900) Southwell, 1925. The number of proglottids of the new species (164-214) is greater than that of A. gonzalesmugaburoi Severino & Sarmiento, 1979. The diameter of accessory sucker of the new species (75-150) is larger than that of A. obuncus (33-48) and A. soberoni (40-65). The length of the cirrus sac of the new species (125-175) is shorter than that of A. obuncus (258-322), A. aetiobatidis (200-250), and A. rodmani Fyler, Caira & Jensen, 2009 (190-234). The number   Campbell & Beverage, 2002 (17-26), and A. rodmani (17-26). Finally, the measurements of the hooks of the eight species can be found in Table 2.
The new species is the fourth species of Acanthobothrium reported from N. entemedor, preceded by A. franus and A. inbiorium (Category 5 species), and A. soniae sp. nov. (Category 2 species) described above. All species have been reported from the Pacific Coast of the Americas. Acanthobothrium vidali sp. nov. can be distinguished from these other species by number of proglottids (164-214) is greater than that of A. franus (68-141) and A. soniae sp. nov. (10-13). The total length of the lateral hook of A. vidali sp. nov. (360-465) is longer than that of A. inbiorium (95-120 µm). The length of the axial prong of the lateral hook of A. vidali sp. nov. (200-285) is longer than that of A. inbiorium (65-75 µm) (Table 3).

Discussion
To date, 190 valid species of Acanthobothrium have been reported from different regions of the world (Caira et al. 2017;Rodríguez-Ibarra et al. 2018;Franzese and Ivanov 2018). Forty species of Acanthobothrium have been described from the Pacific coast of the Americas (eleven species from USA, eleven from México, eight from Costa Rica, four from Ecuador, four from Peru, and three from Chile). With these descriptions of A. soniae sp. nov. and A. vidali sp. nov., 13 species of Acanthobothrium have been reported from the Pacific Coast of Mexico. A list of amphi-American species of Acanthobothrium from the Pacific coast, their hosts, and localities is given in Table 4.
Host specificity of most species of Acanthobothrium appears to be rather strict (Ivanov, 2005;Vardo-Zalik and Campbell 2011;Franzese and Ivanov 2018). According to the reports of species of the genus (type localities, additional localities, type host, and additional host), 82% of the species of Acanthobothrium show strict host specificity. In contrast, 33 of the 190 valid species of Acanthobothrium have been reported in more than one species of host (see the reports of Rudolphi 1819; Yoshida Table 3. Comparison of species of Acanthobothrium that have been reported from Narcine entemedor. Abbreviations: No. Number; A Base (handle) length; B Axial prong length; C Abaxial prong length; D Total hook length. Note: Information taken from the original descriptions and this study.  Table 4. Species of Acanthobothrium reported from the Pacific Ocean of the Americas (amphi-American species). ‡= Category designation obtained from Ghoshroy and Caira (2001). Category designations not included in Ghoshroy and Caira (2001) were calculated for this study using the original descriptions. Sources were as given by that author or the original descriptions used for this study.

‡
A. vargasi Marques, Brooks & Monks, 1995 -Borcéa 1935;Baer 1948;Euzet 1952;Yamaguti 1952;Young 1954;Riser 1955;Rees and Williams 1965;Goldstein 1967;Campbell 1969;Williams 1969;Carvajal-G. and Jeges-G. 1980;Rodriguez and Tantaleán-Vidaurre 1980;Brooks et al. 1981;Mayes and Brooks 1981;Escalante-A. 1986;Tantaleán-Vidaurre 1991;Marques et al. 1997a;Campbell and Beveridge 2002;Friggens and Brown 2005;Lacerda et al. 2008;and, Iannacone et al. 2011). Prior to de Carvalho and , the genus Narcine Henle, 1834 was composed of 20 species. To date, those taxa have been divided into two genera; 15 species of Narcine (tail length about equal to disc length or width) and 5 species of Narcinops de Carvalho & Last, 2016 (tail much longer tan disc length or width), this latter distributed only in Table 5. Species of Acanthobothrium reported in species of Narcine. † Data from Ghoshroy and Caira (2001); ‡ Data from Fyler and Caira (2006). Australia . No helminths have been reported from the former members of Narcine that are now assigned to Narcinops. Five valid species of Acanthobothrium have been reported worldwide from three species of Narcine (Table 5) (Subhapradha, 1955;Goldstein et al. 1969;Brooks and Mayes 1978;Marques et al. 1997b), but no species of Acanthobothrium in Narcine have been reported from Mexico (Merlo-Serna and García-Prieto 2016). In Mexico, only two species of helminth have been reported previously from Narcine: Anaporrhutum euzeti Curran, Blend & Overstreet, 2003 and Nagmia rodmani Curran, Blend & Overstreet, 2009(Curran et al. 2003Curran et al. 2009). The categorical method suggested by Ghoshroy and Caira (2001) and Fyler and Caira, (2006) was used to facilitate comparisons among the 190 valid species of Acanthobothrium. Ghoshroy and Caira (2001) proposed the categories to facilitate comparisons among taxa from the same geographic region. Because of the large number of species worldwide, it is necessary to focus only on those species from the same region that possessing the same combination of characters as the new species; thus, delimiting the comparison between similar species that could be confused with a new species and not comparing each new species to all of the 190 valid species currently described. We agree that comparisons with each species of this expanding group is unnecessary and, as the number of species increases, an exercise in futility. In agreement with previous authors, this categorical method is useful but does not reflect groupings from a rigorous phylogenetic hypothesis (i.e., is phenetic) (Campbell and Beveridge 2002;Ivanov 2005;Reyda and Caira 2006;Twohig et al. 2008;Fyler and Caira 2010;Yang et al. 2016).
Although not all species of the genus have been examined, Franzese and Ivanov (2018) suggest that the pattern of microthiches is quite uniform among species of Acanthobothrium; (i.e., all species have filitriches covering most surfaces of the worms, interspersed with gladiate spinitriches on proximal bothridial surface, scolex proper and the cephalic peduncle). Because of insufficient material, it was not possible to make a study of this species using the SEM, so we cannot provide detailed information on the microtriches.