Zyxibothrium healyae, Bueno & Caira, 2023

Bueno, Veronica M. & Caira, Janine N., 2023, Phylogenetic relationships, host associations, and three new species of a poorly known group of “ tetraphyllidean ” tapeworms from elasmobranchs, Zootaxa 5254 (1), pp. 30-50 : 42-45

Zyxibothrium healyae n. sp.

( Figs. 9A–D , 10A–G )

ZooBank No. 024AF7D4-85BF-47C2-8310-4C7BF5F0151F

Type and only known host: Brochiraja spinifera (Garrick and Paul) , prickly deep-sea skate; ( Rajiformes : Arhynchobatidae Fowler ).

Type locality: Chatham Rise , New Zealand (43°08’S, 174°19’E). Site of infection: Spiral intestine. Type specimens: Holotype ( NMNZ No. W.003930 ) and two paratypes ( NMNZ Nos. W.003929 and W.003931 ); two paratypes ( LRP Nos. 9799 and 9802 ); one paratype ( USNM No. 1678896 ). Scolex prepared for SEM retained with JNC at the University of Connecticut.

Sequence data: OQ186462 (hologenophore LRP No. 9803 [CR-151-3, VB232]).

Etymology: This name honors parasitologist Claire Healy who collected the specimens of this and several other cestode species used in this study from elasmobranchs in New Zealand.

Description. Based on six complete mature worms, and one scolex observed with SEM.

Worms euapolytic, 4.6–7.4 (6.1 ± 1.1; 6) mm long, greatest width at level of scolex; 14–17 (15.1 ± 1.1; 6) proglottids per worm. Scolex consisting of four muscular bothridia and short cephalic peduncle. Scolex proper 516–978 (770.3 ± 180.6; 6) long by 504–684 (624.8 ± 71.9; 6) wide. Bothridia narrowly dolioform, 446–768 (622.8 ± 112.8; 6; 12) long by 213–341 (283.1 ± 37.6; 6; 12) wide; each divided into three facial loculi arranged in one column ( Figs. 9A , 10A ). Cephalic peduncle 77–244 (157.8 ± 71.6; 6) long by 191–338 (262.5 ± 53.8; 6) wide.

Apex of scolex ( Fig. 10B ) sparsely covered with long slender aristate gladiate spinitriches and densely packed capilliform filitriches; distal bothridial surfaces ( Fig. 10F ) densely covered with long slender aristate gladiate spinitriches interspersed with capilliform filitriches; proximal bothridial surfaces of anterior loculus ( Fig. 10C ) and middle loculus ( Fig. 10D ) densely covered with long slender aristate gladiate spinitriches interspersed with gladiate spinitriches, filitriches not observed; proximal surface of posterior loculus ( Fig. 10E ) densely covered with long slender gladiate spinitriches, filitriches not observed; cephalic peduncle ( Fig. 10G ) densely covered with large gladiate spinitriches interspersed with small gladiate spinitriches, filitriches not observed.

Proglottids slightly craspedote. Immature proglottids 12–16 (13.8 ± 1.5; 6) in number, wider than long, becoming longer than wide with maturity ( Fig. 9C ). Mature proglottids ( Fig. 9D ) 1–2 (1.3 ± 0.5; 6) in number, 1229–1601 (1435.7 ± 138.9; 6) long by 328–717 (514.5 ± 162.9; 6) wide, length:width ratio 2.1–4.5 (3 ± 0.9; 6):1; gravid proglottids not observed. Genital pores marginal, irregularly alternating, 91–94% (93 ± 1; 6) of proglottid length from posterior margin in terminal mature proglottid. Testes 24–31 (26.1 ± 2.2; 6; 7) in number, two layers deep, dorsal to cirrus sac, arranged in single dorsal field extending from mid-level of proglottid to anterior margin of proglottid, oval in frontal view, 33–77 long (50.8 ± 12.5; 6; 17) by 49–114 (71.3 ± 19.3; 6; 17) wide. Vas deferens coiled posterior to cirrus sac, extending posteriorly to the level of ovarian bridge and then anteriorly to enter cirrus sac at medial margin. Cirrus sac ( Fig. 9B ) thin-walled, pyriform, tilted posteriorly, containing coiled cirrus, 223– 384 (309.2 ± 59.9; 5) long by 162–212 (185 ± 19.7; 5) wide; cirrus armed with small spinitriches. Vagina thickwalled, weakly sinuous, extending from ootype along medial line of proglottid to level of cirrus sac, crossing cirrus sac ventrally and extending along anterior margin of cirrus sac to open into genital atrium anterior to cirrus; vaginal sphincter lacking; seminal receptacle lacking. Ovary near posterior end of proglottid, with weakly lobulated margins, H-shaped in frontal view, bilobed in cross-section, symmetrical; 157–311 (215.3 ± 66.6; 6; 7) at widest point, 319–422 (360 ± 39; 4; 8) long. Mehlis’ gland posterior to ovarian isthmus. Vitellarium follicular; follicles in two lateral bands; each band consisting of multiple columns of follicles, extending anteriorly to posterior margin of cirrus sac, converging posterior to ovary; vitelline follicles oval, 16–40 (27± 6.5; 5; 15) long by 22–43 (30.6 ± 7.6; 5; 15) wide. Uterus medial, saccate, ventral to vagina, extending anteriorly from ovarian isthmus to posterior margin of cirrus sac. Excretory vessels four, arranged in one dorsal and one ventral pair on each lateral margin of proglottid. Oncospheres not observed.

Remarks. Zyxibothrium healyae n. sp. differs from Z. kamienae and Z. duffyi most conspicuously in having three, rather than four or five, loculi on each bothridium, respectivel y. It can be further distinguished from Z. kamienae and Z. duffyi in testes number (24–31 vs. 19–24 and 32–51, respectively). It also possesses a greater number of proglottids than Z. kamienae (14–17 vs 5–8).

Figures

FIGURE 9. Line drawings of Zyxibothrium healyae n. sp. (A) Scolex (paratype, CR-76-1, NMNZ No. W.003931). (B) Detail of terminal genitalia (holotype, CR-75-2, NMNZ No. W.003930). (C) Whole worm (holotype, CR-75-2, NMNZ No. W.003930). (D) Mature proglottid (paratype, CR-75-1, LRP No. 9799).

FIGURE 10. Scanning electron micrographs of Zyxibothrium healyae n. sp. (A) Scolex, small letters indicate location of details in micrographs B–G. (B) Apex of scolex sparsely covered with long slender aristate gladiate spinitriches and densely packed capilliform filitriches. (C) Proximal surface of anterior loculus densely covered with long slender aristate gladiate spinitriches interspersed with gladiate spinitriches, filitriches not observed. (D) Proximal surface of middle loculus densely covered with long slender aristate gladiate spinitriches interspersed with gladiate spinitriches, filitriches not observed. (E) Proximal surface of posterior loculus densely covered with long slender gladiate spinitriches, filitriches not observed. (F) Distal bothridial surface densely covered with long slender aristate gladiate spinitriches interspersed with capilliform filitriches. (G) Cephalic peduncle densely covered with large gladiate spinitriches interspersed with small gladiate spinitriches, filitriches not observed.