(Figs. 9–13)
Specimens deposited: holotype (USNPC 103815); paratypes (USNPC 103816–103819).
Host: Rhinobatos lentiginosus Garman, 1880; Atlantic guitarfish; Rajiformes:
Rhinobatidae.
Type Locality: Gulf of Mexico at 26 16.11 ’N, 97 8.05 ’W at 9 fathoms 15.x. 94, coll. R. A. Campbell.
Site of Infection: spiral intestine.
Prevalence: 1 of 1 individual examined.
Etymology: This species is named after its host, Rhinobatos lentiginosus.
Description: Based upon measurements of 5 whole mounted specimens and 2 with SEM. Small worms 2–3.1 mm (3, n= 5) long composed of 5–7 (6, n= 5) segments; strobila acraspedote, euapolytic. Scolex proper 288–474 (347, n= 5) long by 168–304 (227, n= 5) wide, composed of 4 triloculate bothridia. Bothridia, 272–474 (347, n= 8) long by 85–140 (111, n= 8) wide; mean (BL: BW) 2.7: 1. Each of 4 bothridia free at posterior end, acuminate, covered with spinitriches over proximal surfaces and divided into three loculi by muscular septa. Anterior loculus 100– 235 (168, n= 11) long, middle loculus 45–90 (58, n= 11) long, posterior loculus 45–95 (65, n= 11) long; (A: M: P) 1: 0.35: 0.39. Apical pad 30–50 (40, n= 6) long by 65–120 (88, n= 6) wide, bearing a single accessory sucker, 10–20 (14, n= 8) long by 20–40 (29, n= 8) wide. Cephalic peduncle 288–456 (373, n= 5) long by 52–80 (65, n= 5) wide covered with spinitriches; (BL: CPL) 1: 1.2–1.6.
Hook dimensions: Hooks of similar shape; handle and prongs about equal in length. Lateral hook (n= 6): A = 35–40 (38); B= 60–100 (82); C= 80–110 (88); D= 90–135 (114); E= 110–150 (125); W= 30–40 (38). Medial hook (n= 6): A’= 30–40 (33); B’= 75–110 (87); C’= 65–100 (88); D’= 100–140 (118); E’= 95–140 (123); W’= 40–60 (45). (THL: BL) 1: 2.7 to 1: 2.8.
Strobila: Immature segments, 2–6 (4, n= 5) per worm wider than long becoming longer than wide with maturity. Mature segments, 350–570 (483, n= 3) long by 135–200 (165, n= 3) wide, 1 (1, n= 4) per worm. Genital pore opening on lateral margin, 59–69 % (63, n= 3) from posterior end of the segment; genital atrium shallow. Cirrus sac near middle of segment, subspherical in mature segments, 60–164 (142, n= 5) long by 50–108 (85, n= 5) wide, containing coiled cirrus; cirrus armed with microtriches. Testes arranged in two, single layered columns extending between ovarian lobes near ovarian isthmus to near anterior extremity of segment. Testes 22–29 (26, n= 3) in number, 5–7 (6, n= 3) preporal, 10–13 (12, n= 3) aporal, 4–6 (5, n= 3) postporal; subspherical 30–50 (37, n= 10) long by 25–40 (33, n= 10) wide. Vas deferens anteromedian, sinuous, enters cirrus sac at adnate pole. Ovary posterior, inverted -A shaped in frontal view (Fig. 12), 192–418 (272, n= 3) long, by 104–152 (132, n= 3) wide, bilobed in cross-section, lobes approximately equal in length, extending c. 75 % distance to cirrus sac from posterior end of segment; ovarian isthmus well posterior. Mehlis’ gland and ootype small, elongated, c. 15–27 long by 10–23 wide, located immediately posterior to ovarian isthmus. Vagina thick-walled, ascends along midline as sinuous tube from ootype to cirrus sac, then laterally along anterior border of cirrus sac to enter genital atrium; seminal receptacle, c. 15 in diameter, at level of ovarian isthmus; vaginal sphincter absent. Vitellarium in 2 lateral follicular columns, each column 1–2 follicles deep, extending from just posterior to ovarian isthmus to level of the most anterior testes; interrupted by cirrus sac and vagina on poral side. Uterus median, tubular, extending from ootype to near anterior extremity of segment. Excretory ducts lateral.
Remarks: Acanthobothrium lentiginosum from R. lentiginosus is a category 1 species (SFFS) and possesses ovarian lobes of approximately equal length that reach about 75 % of the distance from the posterior end of the segment to the level of the cirrus sac (Goshroy & Caira 2001). This is the first species of Acanthobothrium described from a guitarfish (Rhinobatidae) in the Atlantic Ocean and only the fifth species of Acanthobothrium reported from the genus Rhinobatos worldwide. Fyler and Caira (2004) reported finding Acanthobothrium in two species of guitarfish from Senegal but did not describe them. The Atlantic guitarfish, R. lentiginosus, is found along the east coast of North America and the Gulf of Mexico in coastal waters and in Cuba (Robins & Ray 1986; Froese & Pauly 2010). Other species of Acanthobothrium described from rhinobatids are: Acanthobothrium olseni Dailey & Mudrey, 1968, Acanthobothrium rhinobati Alexander, 1953 and Acanthobothrium robustum Alexander, 1953 all from Rhinobatos productus (Ayres); Acanthobothrium satyanarayanaroi Sarada, Lakshmi & Rao, 1993 in Glaucostegus granulatus (Cuvier); and Acanthobothrium southwelli Subhapradha, 1955 in Rhinobatos schlegelii Müller & Henle. Acanthobothrium lentiginosum can be differentiated from all of these species using the original descriptions and categorical system of Ghoshroy & Caira (2001) as follows: A. olseni belongs to category 2 in having an asymmetrical ovary, and A. lentiginosum possesses fewer testes (22–29 vs. 26–39) and a shorter cephalic peduncle (288–456 vs. 667); A. rhinobati fits categories 9 (5) due to the variable number of segments and a symmetrical ovary and is different from A. lentiginosum by larger overall size (32mm. vs. 2–3 mm) and greater numbers of segments (50 vs. 5–7) and testes (51–62 vs. 22–29); A. robustum is designated a category 4 species by possessing a symmetrical ovary, and differs in possession of 2 accessory suckers per bothridium and an accessory spur on each outer hook prong; A. satyanarayanaroi is a much larger worm (9–15 cm vs. 2–3 mm) with many segments and testes (80–90 vs. 22–29); and finally, A. lentiginosum differs from A. southwelli in the absence of postovarian testes, total number of testes (22–29 vs. 34) and number of postporal testes (4–6 vs. 13).
Acanthobothrium lentiginosum differs from other category 1 species in the western Atlantic in the following ways: from Acanthobothrium fogeli Goldstein, 1964 by the presence of postporal testes and fewer testes in total (22–29 vs. 36–54); it differs from Acanthobothrium himanturi Brooks, 1977 by its smaller size (2–3mm vs.> 3.8 mm long), fewer segments (5–7 vs. 17–26) and fewer testes (22–29 vs. 38–57); A. lentiginosum lacks a vaginal sphincter and has a more anterior genital pore (59–69 % vs. 50 %) than A. lineatum; it differs from A. lintoni in possessing fewer segments (5–7 vs. ave. 23), and fewer total testes (22–29 vs. 30–46); it possesses fewer aporal testes (10–13 vs. 17–34) and shorter ovarian lobes (192–418 vs. 620–676) than A. paulum; and A. lentiginosum is smaller (2–3 mm vs. 4.79–8.44 mm) and has fewer segments (5–7 vs. 18–30) than A. marplatense Ivanov & Campbell, 1998.
In the eastern North Atlantic and Mediterranean Sea A. lentiginosum closely resembles A. minus Tazerouti, Kechemir-Issad & Euzet, 2009 from Raja asterias Delaroche from Algeria and Acanthobothrium mathiasi Euzet, 1959 in Mustelus mustelus (Linnaeus) and M. canis from the Mediterranean Sea. Acanthobothrium lentiginosum differs from A. minu s in numerous characters including the distribution of testes (preovarian testes vs. between ovarian lobes), ovarian symmetry and extent of ovarian lobes (75 % of distance to cirrus sac vs. beyond level of cirrus sac). It differs from A. mathiasi in possessing a shorter total hook length (100–140 vs. 155–200) and fewer testes per segment (22–29 vs. 26–43). Other small species of Acanthobothrium from the eastern North Atlantic that have been reported from various hosts including rhinobatids and are <5mm total length, have similar scolex morphology and hook form and have <30 testes are: Acanthobothrium dujardinii van Beneden, 1849, Acanthobothrium edwardsi Williams, 1969 from Raja (Leucoraja) fullonica Linnaeus, Acanthobothrium quadripartitum Williams, 1968 from Raja naevus Montagu and Acanthobothrium tripartitum Williams, 1969. Despite the numerous hosts and disparate localities reported for A. dujardinii discussed by Williams (1969) it is distinct from A. lentiginosum in the possession of marginal lappets on the bothridia, as is A. edwardsi (see illustrations of Williams (1969); Figs. 21, 39,47), which also differs in having ovarian lobes that extend to the cirrus sac. Acanthobothrium lentiginosum differs from A. quadripartitum in number of testes (22–29 vs. 18), locular ratio and total hook length (90–140 vs. 80–90) and from A. tripartitum in testis number (22–29 vs. 13–16) and ovarian symmetry and form where the lobes do not reach or exceed the level of the cirrus sac as they do in A. tripartitum.
Acanthobothrium lentiginosum can be differentiated from category 1 species from the eastern Pacific as follows: it has a smaller anterior loculus (100–235 vs. 272–310), and shorter medial and lateral total hook lengths (100 –140, 90– 135 vs. 163–166, 193 – 195) than Acanthobothrium atahualpai Marques, Brooks & Barriga, 1997; it possesses fewer testes than Acanthobothrium dollyae Caira & Burge, 2001 (22–29 vs. 42–55); it possesses more testes (22–29 vs. 6–10) and has a more anterior genital pore (58–69 % vs. 10–37 %) than Acanthobothrium minisculum Marques, Brooks & Barriga, 1997; it is shorter than Acanthobothrium monski Marques, Brooks & Barriga, 1997 (2–3 vs. 3.4–7.6 mm) and possesses fewer segments (5–7 vs. 24–48); A. lentiginosum has fewer segments (5–7 v. 13 –19) and lacks the vaginal sphincter and protruding genital pore of A. nicoyaense; and it has fewer segments than Acanthobothrium royi Caira & Burge, 2001 (5–7 vs. 19–26).
In the Indo-Pacific region A. lentiginosum can be differentiated from five category 1 species by the absence of postovarian testes (Acanthobothrium foulki Reyda& Caira, 2006; Acanthobothrium marymichaelorum Twohig, Caira & Fyler, 2008; Acanthobothrium larsoni Reyda &Caira, 2006; Acanthobothrium saliki Fyler & Caira, 2006; and A. southwelli). It lacks the weak horizontal band of musculature running across the posterior loculi of Acanthobothrium asnihae Fyler & Caira, 2006 and Acanthobothrium gnomus Reyda & Caira, 2006 and it has fewer testes (22–29 vs. 44–45) than Acanthobothrium guptai Shinde & Bhagwan, 2002. Acanthobothrium lentiginosum has fewer segments than A. zainali Fyler & Caira, 2006 (5–7 vs. 19–26)
In the waters of Australia, numerous species belonging to category 1 have been described by Campbell and Beveridge (2002), Fyler & Caira (2006) and Fyler et al. (2009). A canthobothrium lentiginosum differs from each of these as follows: from Acanthobothrium bartonae Campbell & Beveridge, 2002 by bothridial shape (acuminate vs. rounded), and longer abaxial prongs (65–100 / 80–100 vs. 54–67 / 61– 65); it possesses fewer testes than Acanthobothrium clarkae Campbell & Beveridge, 2002, Acanthobothrium laurenbrownae Campbell & Beveridge, 2002, Acanthobothrium urolophi Schmidt, 1973, and Acanthobothrium pearsoni Williams, 1962 (22–29 vs. 45 –52, 31– 46, 34–41, 56– 60 respectively) but has more testes than Acanthobothrium martini Campbell & Beveridge, 2002, Acanthobothrium stevensi Campbell and Beveridge, 2002 and Acanthobothrium thomasae Campbell and Beveridge, 2002 (22–29 vs. 8 –11, 14–18, 12– 18 respectively); it lacks the vaginal sphincter and short cephalic peduncle (288–456 vs. 25–150) of Acanthobothrium mooreae Campbell & Beveridge, 2002; it lacks the very long microtriches on the cephalic peduncle and has fewer postporal testes (4–6 vs. 7–12) than Acanthobothrium odonoghuei Campbell &Beveridge, 2002; it possesses longer bothridia (240–430 vs. 170–228) and longer medial hook prongs (50–75 vs. 34–59) than Acanthobothrium rohdei Campbell & Beveridge, 2002; it has more postporal testes (4–6 vs. 0–2), fewer segments (5–7 vs. 16–23) and longer lateral abaxial hook lengths (80–110 vs. 65–75) than Acanthobothrium romanowi Fyler, Caira & Jensen, 2009; it has fewer segments (5–7 vs. 9–13) and smaller suckers (10–20 vs. 35–53) than Acanthobothrium oceanharvestae Fyler, Caira & Jensen, 2009; and it is distinct from Acanthobothrium zimmeri Fyler, Caira & Jensen, 2009 in having more postporal testes (4–6 vs. 1–2) and in lacking testes posterior to the ovarian isthmus (0 vs. 2–6).