Rockacestus conchai, 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 : 1357-1359

ROCKACESTUS CONCHAI SP. NOV.

( FIGS 8F–K , 9 )

ZooBank registration: A1AA7903-EA81-4CEB-BE94- 1F1A1B8D713B.

Description (Based on five whole mature worms, and three scolices examined with SEM.) Worms euapolytic, craspedote, 9.9–16.9 (12.9 ± 3; 5) mm long; proglottids 64–105 (81 ± 17; 5) in total number; maximum width at level of scolex. Scolex consisting of four bothridia ( Figs 8F , 9A ), 1122–1775 (1306 ± 265; 5) wide. Bothridia highly folded ( Fig. 8G ), with apical sucker and single loculus, 478–624 (559 ± 76; 3; 4) long, 600– 830 (699 ± 96; 3; 4) wide when folded, sessile anteriorly, free posteriorly; loculus with marginal loculi; apical sucker 81–135 (111 ± 18; 4; 12) long, 96–140 (121 ± 12; 5; 13) wide. Cephalic peduncle lacking. Neck 5.1–7.4 (5.8 ± 1; 5) mm long. Distal surface of apical sucker ( Fig. 8H ) and anterior portions of loculus ( Fig. 8I ) with aciculuar filitriches; distal surface of loculus with sparsely arranged lingulate spinitriches and acicular filitriches ( Fig. 8J ). Proximal bothridial surface with acicular filitriches. Neck ( Fig. 8K ) and strobila with capilliform filitriches arranged in wide scutes. Immature proglottids wider than long, becoming longer than wide with maturity ( Fig. 9B ), 63–101 (78 ± 16; 5) in number. Mature proglottids becoming longer than wide posteriorly ( Fig. 9C, D ), one to three (2.4 ± 0.9; 5) in number. Terminal proglottid 987–1580 (1270 ± 275; 5) long, 368–540 (462 ± 77; 5) wide, lengthto-width ratio 2.3–3 (2.7 ± 0.3; 5):1. Testes 51–73 (61 ± 9; 4; 4) in total number, ten to 14 (12 ± 2; 4; 4) in number in post-poral field, 35–55 (43 ± 5; 5; 20) long, 60–90 (76 ± 8; 5; 20) wide. Vas deferens extensive, coiled medial to cirrus sac. Cirrus sac oval, 209–358 (281 ± 57; 5) long, 113–164 (143 ± 21; 5) wide, thin walled, containing coiled cirrus; cirrus armed with spinitriches. Genital pores irregularly alternating, 66–75% (69 ± 3; 5) 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, 252–445 (325 ± 77; 5) long, 167–266 (214 ± 49; 4) wide, tetralobed in cross-section; ovarian margins lobulated. Vitellarium follicular; follicles arranged in two lateral bands that converge medially; each band consisting of multiple columns of follicles, extending throughout length of proglottid, interrupted partly or completely 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: White-dotted skate, Bathyraja albomaculata (Norman, 1937) ( Rajiformes : Arhynchobatidae Fowler ).

Type locality: Atlantic Ocean off the Falkland Islands (48°39′10.8″S, 60°44′42.6″W) .

Additional localities: Atlantic Ocean off the Falkland Islands (49°38′49.8″S, 59°50′43.2″W) .

Site of infection: Spiral intestine.

Type material: Holotype (mature worm, NHMUK no. 2020.12.17.1); two paratypes (mature worms, USNM nos 1638654 and 1638655); two paratypes (mature worms, LRP nos 10293 and 10294), three paratypes (immature worm SEM vouchers, LRP nos 10279–10281).

Sequence data: GenBank accession MW 419959 , hologenophore (FA-70, KW1011) LRP no. 10324.

Etymology: This species is named for elasmobranch biologist Francisco Concha, in recognition of his appreciation of cestode taxonomy as evidenced by his collection of the type material of this species from the Falkland Islands.

Remarks: Rockacestus conchai is smaller in total length (9.9–16.9 vs. 170, 70–170, 50, 26–58, 50–140, 36–62 and 90 mm) and has fewer testes (73 vs. 100, 140–190, 150, 100 or more, 120–165, 85–105 and 80–100) than Ro. brittanicus , Ro. georgiensis, Ro. piriei, Ro. radioductus, Ro. rakusai, Ro. siedleckii and Ro. williamsi , respectively. The bothridia of Ro. conchai are conspicuously more delicate and folded than those of the remaining two species (i.e. Ro. arctowskii and Ro. carvajali ). It can be distinguished further from Ro. arctowskii in possessing a smaller apical sucker (81–135 long by 96–140 vs. 212–250 in diameter) and from Ro. carvajali in lacking, rather than possessing, a posterior depression bounded by circular band of muscle fibres.

Figures

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.

Figure 9. Line drawings of adult of Rockacestus conchai (specimen accession numbers in parentheses). A, scolex (USNM no. 1638654), posterior portions of right two bothridia incomplete. B, whole worm (NHMUK no. 2020.12.17.1). C, subterminal mature proglottid (NHMUK no. 2020.12.17.1), with vitelline follicles not shown posterior to dashed line. D, terminal mature proglottid (NHMUK no. 2020.12.17.1.).