Scalithrium ivanovae 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 ivanovae

description: Scalithrium ivanovae Franzese sp. nov.   
 ( Figs. 4B, 5–7)   
 Type host. Atlantoraja platana (Günther), La Plata skate (Rajiformes: Arhynchobatidae).   
 Type locality. San Matías Gulf, Río Negro Province, Argentina (41°11’S, 64°03’W) (host PD3-136, PD3-137, PD3-138, PD3-139).   
 Site of infection. Spiral intestine.   
 Type material. Holotype MACN-Pa 762 (entire mature worm), 14 paratypes MACN-Pa 763/1–4, 764/1–7, 765/1–3 (11 entire mature worms, 1 scolex, histological sections of 1 mature proglottid and of 1 scolex); 6 paratypes IPCAS C-897 (6 entire mature worms).   
 Prevalence of infection. 100% (4 hosts infected out of 4 examined).   
 Etymology. This species is named in memory of Dr. Verónica Adriana Ivanov, for her great contribution to the current knowledge on cestodes.   
 Description. Based on 25 specimens prepared as follows: whole mounts of 18 entire mature worms and of 1 scolex, serial sections of 1 mature proglottid and of 1 scolex, 4 worms examined with SEM. Worms euapolytic, 6.4– 16.8 mm (10.8 mm ± 3.3 mm, 7) long by 350–590 (448 ± 94, 8) wide, maximum width at level of scolex. Strobila composed of 45–72 (63 ± 9, 8) craspedote proglottids, 43–70 (60 ± 10, 6) immature, 2–3 (2 ± 0.4, 6) mature (Fig. 5A). Scolex 420–840 (600 ± 166, 12) long, composed of 4 stalked bothridia and cephalic peduncle; myzorhynchus absent (Figs. 5C; 6A). Bothridia facially loculated, 305–480 (369 ± 50, 13) long by 165–270 (208 ± 35, 11) wide. Distal bothridial surface divided by transverse septa into 12–14 (13 ± 1, 10) loculi arranged in single column (Figs. 5C; 6A); anteriormost loculus 35–50 (43 ± 6, 11) long by 53–85 (65 ± 10, 11) wide; posteriormost loculus 20–43 (29 ± 7, 7) long by 33–60 (48 ± 9, 7) 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. 4B). Bothridial stalks 48–150 (97 ± 35, 9) long by 68–250 (116 ± 55, 9) wide. Cephalic peduncle 200–535 (317 ± 118, 13) long by 80–163 (127 ± 26, 13) wide at posterior end. Apex of scolex covered by acicular filitriches (Fig. 6D). Proximal bothridial surface with capilliform filitriches interspersed with acicular filitriches (Fig. 6C). Distal bothridial surface covered by coniform spinitriches interspersed with short acicular filitriches (Fig. 6B). Bothridial stalks and cephalic peduncle with short capilliform filitriches (Fig. 6E, F).   
Immature proglottids initially wider than long, becoming longer than wide with maturity. Subterminal proglottid 435–725 (606 ± 97, 9) long by 163–238 (202 ± 30, 10) wide; velum 13–30 (21 ± 7, 8) long, covering 2–5% (3 ± 1, 8) of adjacent proglottid. Terminal mature proglottid 555– 1,050 (761 ± 146, 12) long by 168–245 (199 ± 28, 12) wide, width to length ratio 1: 3–5 (4 ± 1, 12) (Fig. 5B). Mature proglottids covered by capilliform filitriches (Fig. 6G). Testes oval, 21–32 (25 ± 3, 12) per proglottid, 23–48 (33 ± 6, 12, 60) long by 33–78 (49 ± 11, 12, 60) wide, arranged in 2 columns anterior to cirrus sac (Fig. 5B), 1 layer deep in cross-section (Fig. 7A). Cirrus sac pyriform, 84–123 (97 ± 14, 7) long by 39–64 (53 ± 9, 7) wide, containing coiled cirrus covered by spinitriches; vas deferens dorsal, entering medial margin of cirrus sac (Figs. 5D; 7C). Genital pores marginal, 29–39% (35 ± 3, 10) of proglottid length from posterior end.  
Vagina thick-walled, distal portion surrounded by darkly stained cells (Figs. 5D; 7B), 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. 5B); vaginal sphincter and seminal receptacle absent (Figs. 5D; 7B). Ovary near posterior end of proglottid, H-shaped in dorso-ventral view (Fig. 5B), tetralobed in cross-section (Fig. 7D), symmetric (60% of specimens) or asymmetric with aporal lobe longer than poral lobe (40% of specimens). Poral lobe 100–203 (150 ± 38, 8) long, aporal lobe 105–200 (154 ± 36, 8) long, 65–120 (92 ± 22, 7) wide at level of ovarian isthmus. Mehlis’ gland posterior to ovarian isthmus, 25–45 (34 ± 7, 8) in diameter (Fig. 5B). Vitelline follicles 10–25 (15 ± 4, 9, 45) long by 18–38 (24 ± 5, 9, 45) 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. 5B, D; 7B, D). Uterus sacciform, occupying midline of proglottid, from level of ovarian isthmus to anterior half of proglottid, without reaching anterior margin (Fig. 5B). Two pairs of osmoregulatory ducts, 1 dorsal pair and 1 ventral pair; dorsal ducts narrower than ventral ducts (Fig. 7A–D).  
 Remarks. Scalithrium ivanovae sp. nov. is longer than S. geminum, S. magniphallum and S. minimum (6.4–16.8 mm vs. 1.3–2.3 mm, 2.3–3.1 mm and 2–5 mm, respectively), has more loculi on the distal bothridial surface than S. filamentosum, S. minimum, S. smitii and S. trygonis (12–14 vs. 8, 11, 7 and 7–8, respectively), and fewer loculi than S. australiense, S. magniphallum, S. palombii and S. rankini (12–14 vs. 18–20, 16–18, 20–23 and 23, respectively). The absence of bilobed bothridia distinguishes S. ivanovae sp. nov. from S. bilobatum.   
 The new species also differs from S. australiense, S. geminum, S. magniphallum and S. minimum by having more testes (21–32 vs. 15–17, 9–12, 10–15 and 3–6, respectively), and from S. palombii and S. rankini by having fewer testes (21–32 vs. 82–142 and 50–55, respectively). The absence of a vaginal sphincter and seminal receptacle, along with the position of the entrance of the vas deferens into the cirrus sac, distinguish S. ivanovae sp. nov. from S. kirchneri. The microthrix pattern on the proximal bothridial surface also differs between the two new species, with coniform spinitriches only in S. kirchneri .
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 67-72, DOI: 10.11646/zootaxa.5005.1.4, http://zenodo.org/record/5141154