Scalithrium kirchneri, Franzese & Ivanov, 2021

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 : 64-67

publication ID	https://doi.org/ 10.11646/zootaxa.5005.1.4
publication LSID	lsid:zoobank.org:pub:48F8A874-888C-4E0C-BB65-15AF9C37D33D
DOI	https://doi.org/10.5281/zenodo.5152344
persistent identifier	https://treatment.plazi.org/id/7269640A-B35A-4479-B0E6-BCB86CA051FC
taxon LSID	lsid:zoobank.org:act:7269640A-B35A-4479-B0E6-BCB86CA051FC
treatment provided by	Plazi
scientific name	Scalithrium kirchneri
status	sp. nov.

Treatment

Scalithrium kirchneri sp. nov.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 , 4A View FIGURE 4 )

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 ) GoogleMaps .

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) GoogleMaps .

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 View FIGURE 1 ). Scolex 500–1,395 (839 ± 252, 14) long, composed of 4 stalked bothridia and cephalic peduncle; myzorhynchus absent ( Figs. 1C View FIGURE 1 ; 2A View FIGURE 2 ). 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 View FIGURE 1 ; 2A View FIGURE 2 ); 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 View FIGURE 4 ). 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 View FIGURE 2 ). Proximal bothridial surface with coniform spinitriches interspersed with capilliform filitriches ( Fig. 2D View FIGURE 2 ). Distal bothridial surface covered by coniform spinitriches interspersed with acicular filitriches ( Fig. 2C View FIGURE 2 ). Bothridial stalks and cephalic peduncle with short capilliform filitriches ( Fig. 2E, F View FIGURE 2 ).

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 View FIGURE 1 ). Mature proglottids covered by capilliform filitriches ( Fig. 2G View FIGURE 2 ). 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 View FIGURE 1 ), 1 layer deep in cross-section ( Fig. 3A View FIGURE 3 ). 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 View FIGURE 1 ). 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 View FIGURE 1 ; 3B View FIGURE 3 ), 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 View FIGURE 1 ); vaginal sphincter and seminal receptacle present ( Figs. 1D View FIGURE 1 ; 3B, C View FIGURE 3 ). Ovary near posterior end of proglottid, H-shaped in dorso-ventral view ( Fig. 1B View FIGURE 1 ), tetralobed in cross-section ( Fig. 3D View FIGURE 3 ), 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 View FIGURE 1 ). 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 View FIGURE 1 ; 3B, D View FIGURE 3 ). Uterus sacciform, occupying midline of proglottid, from level of ovarian isthmus to anterior half of proglottid, without reaching anterior margin ( Fig. 1B View FIGURE 1 ). Two pairs of osmoregulatory ducts, 1 dorsal pair and 1 ventral pair; dorsal ducts narrower than ventral ducts ( Fig. 3A–D View FIGURE 3 ).

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).