Rhinebothrium quequense, Menoret & Ivanov, 2023

Menoret, Adriana & Ivanov, Verónica A., 2023, Cestodes of Pseudobatos horkelii (Müller and Henle) (Rhinopristiformes) including Rhinebothrium quequense n. sp. (Rhinebothriidea) and Caulobothrium pieroi n. sp. (“ Tetraphyllidea ”) from the southwestern Atlantic, Zootaxa 5361 (1), pp. 87-102 : 88-92

Rhinebothrium quequense n. sp.

urn:lsid:zoobank.org:act:77A257D0-B577-476D-A7E5-962107702A16

( Figs. 1–3 )

Type host: Pseudobatos horkelii (Müller and Henle) , Brazilian guitarfish ( Rhinopristiformes: Rhinobatidae ).

Type locality: Puerto Quequén (38°37’S; 58°53’W), Buenos Aires Province, Argentina, southwestern Atlantic .

Site of infection: spiral intestine of P. horkelii .

Prevalence of infection: 100% (n=4).

Material deposited: holotype (mature worm) MACN-Pa No. 777, 30 paratypes (25 mature worms, 2 gravid worms, and 3 detached proglottids) MACN-Pa 778/1–23, MACNPa 781/1–5, 782/1–2.

Etymology: The name of this species refers to its distribution in coastal waters off Quequén in Buenos Aires Province, Argentina, southwestern Atlantic.

Description: Based on 31 whole mounts including 25 complete worms (23 mature and 2 gravid worms), 3 incomplete worms, and 3 detached proglottids; 1 scolex observed with SEM, and cross-sections of 2 mature terminal proglottids.

Rhinebothriidae : Worms euapolytic, 3.1–7.2 (5.3 ± 1.1, n = 25) mm long, maximum width at the level of scolex, 12–27 (21 ± 3, n = 26) craspedote proglottids per worm ( Fig. 1A ). Scolex 475‒970 (662 ± 116, n = 22) long, 390‒975 (694 ± 158, n = 22) wide, composed of 4 stalked bothridia and cephalic peduncle ( Figs. 1B , 2A ). Bothridia 420–745 (600 ± 78, n = 20) long, 113–255 (203 ± 33, n = 15) wide, constricted at center, forming 2 lobes, anterior bothridial lobe slightly wider than posterior lobe, with muscular rims ( Fig. 1B ). Distal bothridial surface divided by median longitudinal septum and 21–23 (22 ± 1, n = 18) transverse septa delimiting 2 columns of 19–21 (20 ± 1, n = 18) loculi per column, lacking loculi from central constricted region, anteriormost and posteriormost loculi single, 40‒44 (41 ± 1, n = 18) total loculi per bothridium ( Figs. 1B , 2A ). Anteriormost loculus 10–16 (13 ± 2, n = 12) long, 22–37 (31 ± 4, n = 12) wide, posteriormost loculus 10–15 (12 ± 2, n = 6) long, 22–32 (27 ± 4, n = 6) wide. Bothridial stalks 107–200 (147 ± 23, n = 11) long, 67–105 (91 ± 12, n = 11) wide, attached to 31–42% (36 ± 4, n = 7) from anterior margin of bothridium. Cephalic peduncle 113–243 (167 ± 37, n = 20) long, 83‒125 (103 ± 12, n = 20) wide.

Apex of scolex proper covered with capilliform filitriches ( Fig. 2I ). Proximal bothridial surface covered with aristate gladiate spinitriches interspersed with capilliform filitriches, both increasing in size from the bothridial margin towards the stalks, then diminishing slightly in size in stalks ( Fig. 2E, F, G, K ). Distal bothridial surface covered with gladiate spinitriches interspersed with acicular filitriches on loculi; aristate gladiate spinitriches and capilliform filitriches on transverse septa and longitudinal septum ( Fig. 2B, C, H ). Cephalic peduncle and anterior portion of strobila covered with capilliform filitriches ( Fig. 2J ).

Immature proglottids 11–26 (20 ± 4, n = 26) in number, initially wider than long, becoming longer than wide with maturity ( Fig. 1A ). Mature proglottids 1–2 (n = 23) in number. Terminal mature proglottid 720‒1,375 (1,021 ± 179, n = 23) long, 130‒320 (178 ± 40, n = 23) wide, length to width ratio 3.1–9.1 (5.9 ± 1.5, n = 23): 1. Genital pores lateral, alternating irregularly, 47–58% (54 ± 3, n = 22) of proglottid length from posterior margin of proglottid; genital atrium prominent ( Fig. 1A, C ). Terminal gravid proglottid, longer than wide, 1,075 ‒1,188 (n = 2) long, 175‒240 (n = 2) wide; length to width ratio 4.5‒6.8 (n = 2): 1. Intrauterine eggs spherical with hyaline envelope, without polar filaments.

Detached gravid proglottids longer than wide, 1,560 ‒1,713 (1,648 ± 79, n = 3) long, 300‒375 (338 ± 37, n = 3) wide; length to width ratio 4.6‒5.6 (4.9 ± 0.6, n = 3): 1. Testes and vitellarium degenerate in fully gravid detached proglottids.

Testes spherical to oval, 37–75 (56 ± 9, n = 21) long, 29–53 (42 ± 7, n = 21) wide, 10–16 (12 ± 2, n = 24) in number, arranged in 2 regular columns, 1 layer deep in cross section; each column extending from near anterior margin of proglottid to anterior to cirrus sac; post-poral and post-ovarian testes absent ( Figs. 1A, C , 3A ). Cirrus sac spherical to pyriform, bent posteriorly, 100–155 (124 ± 15, n = 23) long, 40–70 (55 ± 9, n = 23) wide, containing coiled cirrus; cirrus covered with spinitriches. Vas deferens coiled anteriorly, extending from near anterior margin of cirrus sac to ovarian isthmus, then extending anteriorly to enter cirrus sac at its anterior margin ( Figs. 1C, D , 3B, D ).

Vagina thick-walled, extending from ootype along midline of proglottid to anterior margin of cirrus sac, then extending laterally along anterior margin of cirrus sac, opening into genital atrium anterior to cirrus sac ( Figs 1C, D , 3C ). Ovary lobulated, H-shaped in dorso-ventral view, tetra-lobed in cross-section, poral lobe 185–530 (387 ± 87, n = 21), aporal lobe slightly longer than poral lobe in 81% of specimens, 389–550 (389 ± 100, n = 21) long, maximum width 60–195 (108 ± 34, n = 21) ( Figs. 1C, D , 3D ). Mehlis´ gland posterior to ovarian isthmus. Vitellarium follicular; vitelline follicles spherical to oval, 13–320 (19 ± 4, n = 17) long, 7–20 (13 ± 3, n = 17) wide, in 1 dorsal and 1 ventral column on each lateral margin of proglottid lateral to testes, extending from near anterior margin of proglottid to near posterior margin of proglottid, interrupted by atrium ( Figs. 1A, C , 3A, B, C, D ). Uterus saccate, medial and ventral, extending from near margin of testicular field to near anterior to ovarian isthmus ( Figs. 1C , 3A, B, C, D ). Osmoregulatory ducts 4, 1 dorsal and 1 ventral pair on each lateral margin of proglottid ( Fig. 3A, D ).

Figures

FIGURE 1. Rhinebothrium quequense n. sp. from Pseudobatos horkelii (Müller and Henle), line drawings. A—Mature worm (holotype MACN-Pa No. 777). B—scolex (paratype MACN-Pa No. 778/1). C—Terminal proglottid (holotype MACNPa No. 777). D—Detail of the terminal genitalia of a mature proglottid (holotype MACN-Pa No. 777).

FIGURE 2. Rhinebothrium quequense n. sp. from Pseudobatos horkelii (Müller and Henle), scanning electron micrographs. A—Scolex, small letters indicate locations of detail shown in Figs. B, D and K. B—Detail of the anterior margin of bothridium including anteriomost loculi and transverse septum. C—Surface of loculus, gladiate spinitriches and acicular filitriches. D— Central constriction of bothridium. E—Proximal bothridial surface near bothridial margin, aristate gladiate spinitriches and capilliform filitriches. F—Proximal bothridial surface near stalk, large aristate gladiate spinitriches and capilliform filitriches. G—Surface of bothridial stalk, large aristate gladiate spinitriches and capilliform filitriches. H—Surface of transverse septum, aristate gladiate spinitriches and capilliform filitriches. I—Surface of apex of scolex, capilliform filitriches. J—Surface of cephalic peduncle, capilliform filitriches. K—Detail of posterior margin of bothridium, proximal surface.

FIGURE 3. Rhinebothrium quequense n. sp. from Pseudobatos horkelii (Müller and Henle), light micrographs of cross sections of a mature proglottid. A—anterior to the genital atrium. B—at the level of the genital atrium showing the cirrus sac. C—at the level of the genital atrium showing the vagina. D—anterior to the ovarian isthmus. Abbreviations: cs—cirrus sac, dod—dorsal osmoregulatory duct, ov—ovary, t—testis, ut—uterus, vd—vas deferens, vf—vitelline follicle, vg—vagina, vod—ventral osmoregulatory duct.