Rockacestus carvajali, Caira & Bueno & Jensen, 2021

Caira, Janine N., Bueno, Veronica & Jensen, Kirsten, 2021, Emerging global novelty in phyllobothriidean tapeworms (Cestoda: Phyllobothriidea) from sharks and skates (Elasmobranchii), Zoological Journal of the Linnean Society 193, pp. 1336-1363 : 1354-1357

ROCKACESTUS CARVAJALI SP. NOV.

( FIGS 7 , 8A–E )

ZooBank registration: C1BE31F7-1E16-4A24-920B- E42B5796066E.

Description (Based on two whole mature worms, three whole immature worms, and three scolices examined with SEM.) Worms euapolytic, craspedote, 13.1–14.5 mm long; proglottids 75–81 in total number; maximum width at level of scolex. Scolex consisting of four bothridia, 546–903 (774 ± 165; 4) long, 900– 1146 (1049 ± 104; 5) wide. Bothridia folded ( Figs 7A , 8A ), with apical sucker and single loculus, 406–648 (509 ± 104; 4; 7) long, 378–753 (552 ± 134; 4; 7) wide when folded, sessile anteriorly, free posteriorly; loculus with marginal loculi and posterior depression bounded by circular band of muscle fibres ( Fig. 7B ); apical sucker 84–155 (118 ± 21; 5; 15) long, 85–154 (116 ± 21; 5; 16) wide; posterior depression 126–214 (156 ± 36; 3; 7) long, 132–199 (165 ± 30; 3; 7) wide. Cephalic peduncle lacking. Neck 5.2–6.7 mm long. Distal surface of apical sucker and anterior portions of loculus with papilliform filitriches ( Fig. 8B ); distal surface of posterior depression with lingulate spinitriches and papilliform filitriches ( Fig. 8C ). Proximal bothridial surface with papilliform filitriches ( Fig. 8D ). Neck ( Fig. 8E ) and strobila with capilliform filitriches arranged in wide scutes. Immature proglottids wider than long, becoming longer than wide with maturity, 71–76 in number ( Fig. 7C ). Mature proglottids wider than long ( Fig. 7D ), becoming longer than wide posteriorly ( Fig. 7E ), four or five in number. Terminal proglottid 1143–1424 long, 537–540 wide, length-to-width ratio 2.1–2.6:1. Testes 46–55 (50 ± 4; 4; 4) in total number, nine to 12 (10 ± 1; 4; 4) in number in post-poral field, 38–53 (47 ± 5; 2; 6) long, 64–83 (74 ± 8; 2; 6) wide. Vas deferens coiled medial to cirrus sac. Cirrus sac oval, 302 long, 132 wide, thin walled, containing coiled cirrus; cirrus armed with spinitriches. Genital pores irregularly alternating, 73–79% of proglottid length from posterior end; genital atrium shallow. Vagina weakly sinuous, extending from ootype along midline of proglottid to anterior margin of cirrus sac, then laterally along anterior margin of cirrus sac to open into common genital atrium anterior to cirrus. Ovary at or near posterior margin of proglottid, H-shaped in frontal view, 344–406 long, 182–252 (217 ± 50; 4) wide, tetralobed in cross-section; ovarian margins lobulate. Vitellarium follicular; follicles arranged in two lateral bands that converge medially; each band consisting of multiple columns of follicles, extending throughout length of proglottid, partly or fully interrupted by terminal genitalia, uninterrupted by ovary; follicles highly variable in form. Excretory vessels 4, arranged in one dorsal and one ventral pair on each lateral margin of proglottid. Gravid proglottids not observed.

Type host: Yellownose skate, Dipturus chilensis (Guichenot, 1848) ( Rajiformes : Rajidae de Blainville ).

Type locality: Pacific Ocean off Puñihuil on the island of Chiloé, Chile (41°55′43″S, 74°02′16″W) .

Additional locality: Pacific Ocean off Niebla, Los Rios, Chile (39°51′S, 73°24′W) .

Site of infection: Spiral intestine.

Type material: Holotype (mature worm, MNHNCL no. PLAT-15023); two paratypes (one mature worm, USNM no. 1638652; one immature worm, USNM no. 1638653); two paratypes (immature worms, LRP nos 9770 and 9771), three paratypes (mature worm SEM vouchers, LRP nos 9773–9775).

Sequence data: GenBank accession MW 419973 , hologenophore (CHL-76-5; VB136) LRP no. 8913.

Etymology: This species is named for Chilean parasitologist Dr Juan Carvajal, without whose assistance with the logistics, our fieldwork in Chile, which led to collection of the type material of this species, would not have been possible.

Remarks: Rockacestus carvajali is the smallest member of the genus, with a total length of 13.1– 14.5 (vs. 15–33, 170, 60–170, 50, 26–58, 50–140, 36–62 and 90 mm in Ro. arctowskii , Ro. brittanicus, Ro. georgiensis, Ro. piriei, Ro. radioductus, Ro. rakusai, Ro. siedleckii and Ro. williamsi , respectively). It further differs from all of these species except Ro. georgiensis and Ro. piriei in possessing bothridia that are highly, rather than moderately, folded. It possesses fewer testes per proglottid than both of the latter species (47 vs. 140–190 and 150, respectively).

Figures

Figure 7. Line drawings of adult of Rockacestus carvajali (specimen accession numbers in parentheses). A, scolex (LRP no. 9770). B, detail of single bothridium (MNHNCL no. PLAT-15023). C, whole worm (MNHNCL no. PLAT-15023). D, subterminal mature proglottid (MNHNCL no. PLAT-15023). E, terminal mature proglottid (MNHNCL no. PLAT-15023).

Figure 8. Scanning electron micrographs of Rockacestus. A, scolex of Rockacestus carvajali. B, distal surface of bothridium of Ro. carvajali. C, distal surface of posterior depression of bothridium of Ro. carvajali. D, proximal surface of bothridium of Ro. carvajali. E, scutes on surface of neck of Ro. carvajali. F, scolex of Rockacestus conchai. G, bothridium of Ro. conchai. H, distal surface of apical sucker of Ro. conchai. I, distal surface of anterior region of loculus of Ro. conchai. J, distal surface of remainder of bothridium of Ro. conchai. K, scutes on surface of neck of Ro. conchai.