Rhinebothrium reydai, Trevisan & Marques, 2017

Trevisan, Bruna & Marques, Fernando P. L., 2017, Species diversity of Rhinebothrium Linton, 1890 (Eucestoda: Rhinebothriidea) from Styracura (Myliobatiformes: Potamotrygonidae), including the description of a new species, Zootaxa 4300 (1), pp. 421-437 : 429

Rhinebothrium reydai n. sp., Family Rhinebothriidae , order Rhinebothriidea

( Figs. 5–8 )

Type host: Styracura schmardae (Werner) de Carvalho, Loboda & da Silva ( Myliobatiformes : Potamotrygonidae ).

Type locality: Caribbean Sea off Almirante, Bocas Del Toro Province, Panama (09°17'N, 82°20'W and 09°17'N, 82°21'W).

Site of infection: Spiral intestine.

Type specimens: MIUP CR1 (Holotype) and CRP1–CRP9 (Paratypes: 9 complete worms); MZUSP 7931a– 7931p (Paratypes: 16 complete worms), 7932 (1 SEM vouchers), and 7933a–7933d (voucher and histological sections); HWML 110076–110082 (Paratypes: 7 complete worms); LRP 9270–9276 (Paratypes: 7 complete worms).

Prevalence of infection and distribution: 45,5% (five of 11 spiral intestines), seeming to be restricted to the Caribbean coast of Panama.

Etymology: The species is named in honor of Dr. Florian B. Reyda, who took part in the sampling trip to Panama and who has contributed to the knowledge of this group of cestodes for many years.

Description. [Based on 50 mature specimens: 47 whole mounts, one worm observed with SEM, and two prepared as cross-sections]. Worms acraspedote ( Fig. 5 ), euapolytic, 2.2–7.4 mm (n = 47) long, composed of 26–68 (n = 47) proglottids. Scolex 237–376 (n = 8) in maximum width composed of four stalked and billobed bothridia constricted at center, with muscular rims ( Fig. 6 A, 7A). Bothridia 280–461 (n = 9) long by 111–202 (n = 9) wide, divided by 17–22 (n = 15) transverse septa and one medial longitudinal septum into 34–44 (n = 15) loculi; anteriormost and posterior-most loculus single. Anterior-most loculus 18–26 (n = 10) long by 29–41 (n = 10) wide. Cephalic peduncle absent. Proximal and distal surface of bothridia covered with acicular filitriches and gladiate spinitriches ( Fig. 7 C–G), except for anterior loculus with acicular filitriches only ( Fig. 7 B). Anterior portion of strobila covered with capilliform filitriches ( Fig. 7 H).

Immature proglottids wider than long, becoming as long as wide within the anterior third of the strobila (13– 30%, n = 39) thereafter, longer than wide with maturity, 19–56 (n = 47) in number ( Fig. 5 ). Terminal mature proglottids ( Fig. 6 B, D) 218–554 (n = 42) long by 67–146 (n = 43) wide, 4–14 (n = 47) in number. Some terminal proglottids with sperm-filled vas deferens and atrophied testes ( Fig. 6 B). Testes in two irregular columns, in anterior ¾ of proglottid, oval, 20–43 (n = 27) long by 17–34 (n = 27) wide, 4 (n = 47) in number ( Fig. 6 D, 8A). Cirrus sac in anterior ½ of proglottid, spherical to pyriform in shape, 33–59 (n = 39) long by 37–83 (n = 39) wide, containing coiled cirrus; cirrus armed with spinitriches ( Fig. 6 C). Genital atrium prominent. Genital pores 31–49% (n = 42) of proglottid length from anterior end, irregularly alternating. Vagina opening into genital atrium anterior to cirrus sac, thick-walled, weakly sinuous, somewhat enlarged in proximal part, with antero-medial portion adjacent to cirrus sac, both directed laterally to common genital atrium. Vaginal sphincter absent. Ovary near posterior end of proglottid, inverted A-shaped in frontal view and tetra-lobed in cross-section ( Fig. 8 B), symmetrical, 89–316 (n = 40) long by 39–79 (n = 40) wide at isthmus ( Fig. 6 B). Vitelline follicles extending length of proglottid, longer 5–15 (n = 14) than wide 4–12 (n = 14). Detached gravid proglottids and eggs not observed.

Remarks. This new taxon is unique among species of Rhinebothrium due to a combination of morphological characters, including the presence of only four testes and a single posterior-most bothridial loculus. Compared to other 11 species that share the presence of four testes, only R. chollaensis Friggens & Duszynski, 2005 possesses a single posterior-most bothridial loculus. Rhinebothrium reydai n. sp. further resembles R. chollaensis in total length (2.2–8.4 vs. 1.3–5.1, respectively), number of proglottids (26–68 vs. 32–84, respectively), and number of bothridial loculi (34–44 vs. 40–49, respectively). Both species also have similar bothridial morphology. Friggens & Duszynskii (2005) described R. chollaensis as having leaf-like bothridia with a slight constriction at the level of the stalk, which is similar to what we observed in R. reydai n. sp.. However, after examining images from the type series of R. chollaensis (Holotype [USNM 92213] and five paratypes [USNM 92213a–92214d]), we think that the constriction is more pronounced in the former, hence described as bilobed. Despite a similar morphology, R. chollaensis is apolytic whereas R. reydai n. sp. is euapolytic. Based on the type series, both species differ on the morphology of the aporal lobe of the ovary, which reaches the mid-lateral margin of the cirrus sac in R. chollaensis , whereas in R. reydai n. sp. the aporal lobe only reaches the posterior margin, since the cirrus sac takes approximately ¾ of the proglottid in width. Also, in R. reydai n. sp. the first square proglottid occurs within the anterior third of the strobila (13–30%, n = 39), whereas in the type series of R. chollaensis it occurs near the middle of the strobila (42–62%, n = 6). The morphological resemblance between these two species and their biogeographical distributions (i.e., R. chollaensis from the eastern Pacific Ocean vs. R. reydai n. sp. from the western Atlantic Ocean), might also suggest a close phylogenetic association, which has yet to be tested within the context of a phylogenetic study.

Figures

FIGURE 5. Light micrograph of the holotype of Rhinebothrium reydai n. sp. from Styracura schmardae (MIUP CR 1).

FIGURE 6. Line drawings of Rhinebothrium reydai n. sp. A. Scolex (MIUP CR 1, Holotype), B. Terminal, mature proglottid in which testes are atrophied (MZUSP 7931 b, Paratype), C. Cirrus-sac (MZUSP 7931 p, Paratype), D. Subterminal, mature proglottid (MZUSP 7931 b, Paratype).

FIGURE 7. Scanning electron micrographs of Rhinebothrium reydai n. sp. (MZUSP 7932, Paratype). A. Scolex, B. Proximal surface of anterior loculus, C. Proximal surface near centre of bothridium, D. Distal surface near centre of bothridium, E. Distal surface of transverse septa, F. Distal surface near longitudinal septum in anterior region of bothridium, G. Proximal surface in posterior region of bothridium, H. Surface of anterior portion of strobila.

FIGURE 8. Micrographs of transversal histological sections of Rhinebothrium reydai n. sp. (MZUSP 7933 a – 7933 d, Paratypes). A. Section at level of testes, B. Section at level of ovary. Abbreviations: Ed. Excretory duct, O. Ovary, T. Testis, U. Uterus, Vd. Vas deferens, Vit. Vitelline follicle.