Scalithrium ivanovae Franzese

Franzese, Sebastian & Ivanov, Veronica A., 2021, Two new species of Scalithrium (Cestoda: Rhinebothriidea) from rajiform batoids of the Argentine Sea, Zootaxa 5005 (1), pp. 62-76: 67-72

publication ID

https://doi.org/10.11646/zootaxa.5005.1.4

publication LSID

lsid:zoobank.org:pub:48F8A874-888C-4E0C-BB65-15AF9C37D33D

DOI

http://doi.org/10.5281/zenodo.5152346

persistent identifier

http://treatment.plazi.org/id/7D528452-1CF3-4B28-B3C5-C5C4B50D0745

taxon LSID

lsid:zoobank.org:act:7D528452-1CF3-4B28-B3C5-C5C4B50D0745

treatment provided by

Plazi

scientific name

Scalithrium ivanovae Franzese
status

sp. nov.

Scalithrium ivanovae Franzese   sp. nov.

( Figs. 4B View FIGURE 4 , 5–7 View FIGURE 5 View FIGURE 6 View FIGURE 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) GoogleMaps   .

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 View FIGURE 5 ). Scolex 420–840 (600 ± 166, 12) long, composed of 4 stalked bothridia and cephalic peduncle; myzorhynchus absent ( Figs. 5C View FIGURE 5 ; 6A View FIGURE 6 ). 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 View FIGURE 5 ; 6A View FIGURE 6 ); 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 View FIGURE 4 ). 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 View FIGURE 6 ). Proximal bothridial surface with capilliform filitriches interspersed with acicular filitriches ( Fig. 6C View FIGURE 6 ). Distal bothridial surface covered by coniform spinitriches interspersed with short acicular filitriches ( Fig. 6B View FIGURE 6 ). Bothridial stalks and cephalic peduncle with short capilliform filitriches ( Fig. 6E, F View FIGURE 6 ).

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 View FIGURE 5 ). Mature proglottids covered by capilliform filitriches ( Fig. 6G View FIGURE 6 ). 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 View FIGURE 5 ), 1 layer deep in cross-section ( Fig. 7A View FIGURE 7 ). 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 View FIGURE 5 ; 7C View FIGURE 7 ). 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 View FIGURE 5 ; 7B View FIGURE 7 ), 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 View FIGURE 5 ); vaginal sphincter and seminal receptacle absent ( Figs. 5D View FIGURE 5 ; 7B View FIGURE 7 ). Ovary near posterior end of proglottid, H-shaped in dorso-ventral view ( Fig. 5B View FIGURE 5 ), tetralobed in cross-section ( Fig. 7D View FIGURE 7 ), 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 View FIGURE 5 ). 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 View FIGURE 5 ; 7B, D View FIGURE 7 ). Uterus sacciform, occupying midline of proglottid, from level of ovarian isthmus to anterior half of proglottid, without reaching anterior margin ( Fig. 5B View FIGURE 5 ). Two pairs of osmoregulatory ducts, 1 dorsal pair and 1 ventral pair; dorsal ducts narrower than ventral ducts ( Fig. 7A–D View FIGURE 7 ).

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   .