Two new species of Scalithrium (Cestoda: Rhinebothriidea) from rajiform batoids of the Argentine Sea Author Franzese, Sebastian Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Biodiversidad y Biología Experimental, Buenos Aires, Argentina. & CONICET-Universidad de Buenos Aires, Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Buenos Aires, Argentina. Author Ivanov, Veronica A. Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Biodiversidad y Biología Experimental, Buenos Aires, Argentina. & CONICET-Universidad de Buenos Aires, Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Buenos Aires, Argentina. text Zootaxa 2021 2021-07-23 5005 1 62 76 journal article 10.11646/zootaxa.5005.1.4 1175-5326 5141154 48F8A874-888C-4E0C-BB65-15AF9C37D33D Scalithrium kirchneri sp. nov. ( Figs. 1–3 , 4A ) Type host. Rioraja agassizii (Müller & Henle) , Rio skate ( Rajiformes : Arhynchobatidae ). Type locality. Continental shelf waters off San Clemente del Tuyú , Buenos Aires Province , Argentina ( 36°12’S , 55°20’W ) (host PD5-080 , PD5-130 ) . Additional locality. Continental shelf waters off Quequén , Buenos Aires Province , Argentina ( 39°56’S , 58°20’W ) (host FMPQ-027, FMPQ-035, FMPQ-114, FMPQA-039) . Site of infection. Spiral intestine. Type material. Holotype MACN-Pa 757 (entire mature worm), 19 paratypes MACN-Pa 758/1–13, 759, 760/1– 3, 761 (12 entire mature worms, 4 scoleces, 1 strobila, histological sections of 1 mature proglottid and of 1 scolex); 8 paratypes IPCAS C-896 (8 entire mature worms). Prevalence of infection. 100% (6 hosts infected out of 6 examined). Etymology. This species is named in memory of Néstor Carlos Kirchner, former president of Argentina , for his great support to the development of national science. Description. Based on 32 specimens prepared as follows: whole mounts of 21 entire mature worms, of 4 scoleces and of 1 strobila, serial sections of 1 mature proglottid and of 1 scolex, 4 worms examined with SEM. Worms euapolytic, 4.8–13.6 mm (7.3 mm ± 3.2 mm, 12) long by 450–770 (602 ± 107, 10) wide, maximum width at level of scolex. Strobila composed of 34–66 (49 ± 13, 9) craspedote proglottids, 33–62 (47 ± 13, 9) immature, 1–5 (2 ± 1, 9) mature ( Fig. 1A ). Scolex 500–1,395 (839 ± 252, 14) long, composed of 4 stalked bothridia and cephalic peduncle; myzorhynchus absent ( Figs. 1C ; 2A ). Bothridia facially loculated, 225–550 (378 ± 100, 18) long by 143–335 (250 ± 66, 15) wide. Distal bothridial surface divided by transverse septa into 13–15 (14 ± 1, 13) loculi arranged in single column ( Figs. 1C ; 2A ); anteriormost loculus 25–73 (52 ± 13, 12) long by 45–115 (89 ± 21, 12) wide; posteriormost loculus 33–55 (44 ± 16, 2) long by 58–73 (65 ± 11, 2) wide. Distal portion of transverse septa formed by transverse muscle bundles, proximal portion formed by radial muscles with proximal fibers ending adjacent to each other and forming triangular gap ( Fig. 4A ). Bothridial stalks 98–200 (142 ± 34, 9) long by 35–85 (58 ± 17, 8) wide. Cephalic peduncle 245–1,063 (433 ± 240, 13) long by 50–120 (77 ± 18, 13) wide at posterior end. Apex of scolex covered by acicular filitriches ( Fig. 2B ). Proximal bothridial surface with coniform spinitriches interspersed with capilliform filitriches ( Fig. 2D ). Distal bothridial surface covered by coniform spinitriches interspersed with acicular filitriches ( Fig. 2C ). Bothridial stalks and cephalic peduncle with short capilliform filitriches ( Fig. 2E, F ). Immature proglottids initially wider than long, becoming longer than wide with maturity. Subterminal proglottid 330–950 (595 ± 187, 11) long by 120–195 (145 ± 22, 11) wide; velum 8–15 (13 ± 3, 9) long, covering 1–3% (2 ± 1, 9) of adjacent proglottid. Terminal mature proglottid 460–1,250 (836 ± 199, 12) long by 120–195 (149 ± 23, 12) wide, width to length ratio 1: 4–7 (6 ± 1, 12) ( Fig. 1B ). Mature proglottids covered by capilliform filitriches ( Fig. 2G ). Testes oval, 23–34 (28 ± 3, 12) per proglottid, 18–45 (28 ± 6, 10, 50) long by 30–63 (43 ± 7, 10, 50) wide, arranged in 2 columns anterior to cirrus sac ( Fig. 1B ), 1 layer deep in cross-section ( Fig. 3A ). Cirrus sac pyriform, 75–125 (98 ± 16, 11) long by 39–73 (50 ± 10, 11) wide, containing coiled cirrus covered by spinitriches; vas deferens dorsal, entering the anterior margin of cirrus sac near genital pore ( Fig. 1D ). Genital pores marginal, 29–44% (36 ± 4, 11) of proglottid length from posterior end. Vagina thick-walled, distal portion surrounded by darkly stained cells ( Figs. 1D ; 3B ), extending from ootype along midline of proglottid to anterior margin of cirrus sac, then laterally along anterior margin of cirrus sac to common genital atrium ( Fig. 1B ); vaginal sphincter and seminal receptacle present ( Figs. 1D ; 3B, C ). Ovary near posterior end of proglottid, H-shaped in dorso-ventral view ( Fig. 1B ), tetralobed in cross-section ( Fig. 3D ), symmetric, 110–283 (199 ± 55, 6, 12) long by 58–75 (68 ± 6, 6) wide at level of ovarian isthmus. Mehlis’ gland posterior to ovarian isthmus, 20–38 (30 ± 6, 6) in diameter ( Fig. 1B ). Vitelline follicles 7–20 (11 ± 3, 11, 55) long by 11–35 (20 ± 6, 11, 55) wide, in 4 total columns, 1 dorsal column and 1 ventral column on each lateral margin of proglottid, extending along entire proglottid length, interrupted ventrally by genital pore and partially interrupted dorsally and ventrally by ovary ( Figs. 1B, D ; 3B, D ). Uterus sacciform, occupying midline of proglottid, from level of ovarian isthmus to anterior half of proglottid, without reaching anterior margin ( Fig. 1B ). Two pairs of osmoregulatory ducts, 1 dorsal pair and 1 ventral pair; dorsal ducts narrower than ventral ducts ( Fig. 3A–D ). FIGURE 1. Line drawings of Scalithrium kirchneri sp. nov. from Rioraja agassizii . A. entire mature worm (holotype MACN- Pa 757); B. terminal mature proglottid (paratype MACN-Pa 758/1); C. scolex (paratype MACN-Pa 761); D. detail of terminal genitalia in a terminal mature proglottid (paratype MACN-Pa 758/1). Abbreviations: cs, cirrus sac; ov, ovary; sr, seminal receptacle; t, testes; ut, uterus; vd, vas deferens; vf, vitelline follicle; vg, vagina; vod, ventral osmoregulatory duct; vs, vaginal sphincter. FIGURE 2. Scanning electron micrographs of Scalithrium kirchneri sp. nov. from Rioraja agassizii . A. scolex, small letters indicate the location of details shown in figures 2C–F; B. surface of scolex apex; C. distal bothridial surface; D. proximal bothridial surface; E. surface of stalk; F. surface of cephalic peduncle; G. surface of terminal mature proglottid. Remarks. Scalithrium kirchneri sp. nov. is longer than Scalithrium geminum ( Marques, Brooks & Ureña, 1996 ) and Scalithrium magniphallum ( Brooks, 1977 ) (4.8–13.6 mm vs. 1.3–2.3 mm and 2.3–3.1 mm, respectively), has more loculi on the distal bothridial surface than S . filamentosum , Scalithrium minimum (Van Beneden, 1850 ) , S . smitii and Scalithrium trygonis ( Shipley & Hornell, 1906 ) (13–15 vs. 8, 11, 7 and 7–8, respectively), and fewer loculi than S . australiense , S . magniphallum , Scalithrium palombii ( Baer, 1948 ) and Scalithrium rankini ( Baer, 1948 ) (13–15 vs. 18–20, 16–18, 20–23 and 23, respectively). The absence of bilobed bothridia distinguishes S . kirchneri sp. nov. from Scalithrium bilobatum ( Young, 1955 ) . The new species also differs from S . australiense , S . geminum , S . magniphallum and S . minimum by having more testes (23–34 vs. 15–17, 9–12, 10–15 and 3–6, respectively), and from S . palombii and S . rankini by having fewer testes (23–34 vs. 82–142 and 50–55, respectively).