Scalithrium kirchneri Franzese & Ivanov 2021, sp. nov.
Creators: name: Franzese, Sebastian
name: Ivanov, Veronica A.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Platyhelminthes
Cestoda
Rhinebothriidea
Rhinebothriidae
Scalithrium
Scalithrium kirchneri

description: 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).  
 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).
description: Published as part of Franzese, Sebastian & Ivanov, Veronica A., 2021, Two new species of Scalithrium (Cestoda: Rhinebothriidea) from rajiform batoids of the Argentine Sea, pp. 62-76 in Zootaxa 5005 (1) on pages 64-67, DOI: 10.11646/zootaxa.5005.1.4, http://zenodo.org/record/5141154