Ruhnkebothrium bajaense, 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 : 1345-1347

RUHNKEBOTHRIUM BAJAENSE SP. NOV.

( FIGS 2D, E , 4 )

ZooBank registration: B2A2E247-2A00-4599-AA76- ABA973D3349E.

Description: [Based on one whole mature worm, one partial mature worm (hologenophore), and two scolices examined with SEM.] Worms euapolytic, acraspedote, 31.7 mm long; proglottids 185 in total number; maximum width at level of terminal proglottid. Scolex consisting of four bothridia, 722 long, 749–858 wide. Bothridia consisting of small, simple anterior loculus ( Fig. 4B ) and expansive, highly folded posterior loculus ( Figs 2D , 4A ), 636–753 (695 ± 52; 2; 4) long, 366–391 (384 ± 10; 2; 5) wide, sessile anteriorly, free posteriorly; anterior loculus 43–50 (N = 1) long, 58–85 (73 ± 15; 2; 4) wide. Cephalic peduncle lacking. Neck 845 long. Distal surface of anterior loculus with extremely slender gladiate spinitriches and capilliform filitriches ( Fig. 4D ); distal surface of anterior, narrow portion of posterior loculus with slender gladiate spinitriches and capilliform filitriches ( Fig. 4E, F ); distal surface of posterior loculus with slender gladiate spinitriches and capilliform filitriches ( Fig. 4G ); capilliform filitriches becoming less dense near margins of distal surfaces of posterior loculus; rim of distal surface of posterior loculus with small band of papilliform filitriches only ( Fig. 4C ). Proximal bothridial surface near rim with cyrillionate spinitriches and capilliform filitriches ( Fig. 4H ), replaced by extremely slender gladiate spinitriches and capilliform filitriches away from rim. Neck ( Fig. 4I ) and strobila with capilliform filitriches arranged in wide, flat scutes. Immature proglottids wider than long, becoming longer than wide with maturity, 180 in number. Mature proglottids five in number. Terminal proglottid 1362 long, 760 wide; length-to-width ratio 1.8:1 ( Fig. 2E ). Testes 234–257 in total number, 49–53 in number in post-poral field, 31–49 (39 ± 8; 2; 8) long, 34–53 (43 ± 7; 2; 8) wide. Vas deferens minimal, coiled medial to cirrus sac. Cirrus sac narrowly oblong (sensu Clopton, 2004), slightly curved anteriorly, 311–388 long, 76–113 wide, thin walled, containing coiled cirrus; cirrus armed with spinitriches. Genital pores irregularly alternating, 47% 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 sac. Ovary at posterior of proglottid, H-shaped in frontal view, 273 long, 408 wide, tetralobed in cross-section; ovarian margins lobulate. Vitellarium follicular; follicles somewhat irregular in shape, arranged in two lateral bands; each band consisting of multiple columns of follicles, extending throughout length of proglottid, interrupted dorsally and ventrally by terminal genitalia, not interrupted by ovary. Uterus medial, ventral, sacciform, extending from ovarian isthmus to cirrus sac; uterine duct not observed. Excretory vessels 4, arranged in one dorsal and one ventral pair on each lateral margin of proglottid.

Ty p e h o s t: S p h y r n a l e w i n i 2 o f t h e s c a l l o p e d hammerhead complex (sensu Naylor et al., 2012) ( Carcharhiniformes: Sphyrnidae ).

Type locality: Gulf of California off San Jose del Cabo, Baja California Sur, Mexico (23°02′45″N, 109°41′33″W) .

Additional locality: Gulf of California off Loreto, Baja California Sur, Mexico (25°49′52″N, 111°19′38″W) .

Site of infection: Spiral intestine.

Type material: Holotype (mature worm, CNHE no. 10662); one paratype (partial mature worm hologenophore, LRP no. 10278), two paratypes (immature worm SEM vouchers, LRP nos 10276 and 10277).

Sequence data: GenBank accession MW 419962 (BJ- 323; JW504), hologenophore LRP no. 10278.

Etymology: This species is named for its type locality in the waters off the Baja Peninsula in Mexico; the name also serves as a reminder that this species parasitizes the Pacific form of the scalloped hammerhead.

Remarks: This new species differs from its only known congener, Ru. mattisi , as follows. The genital pore of Ru. bajaense is more posterior in position in the proglottid (47% vs. 62–68% from posterior end), and its bothridia are much less folded than those of Ru. mattisi . Furthermore, it possesses cyrillionate rather than slender gladiate spinitriches near the rims of its proximal bothridial surfaces, and the scutes of its neck and strobila are wide and flat ( Fig. 4I ), rather than narrow and convex ( Fig. 3I ).

Figures

Figure 2. Line drawings of adults of Ruhnkebothrium (specimen accession numbers in parentheses). A, scolex of Ruhnkebothrium mattisi (LRP no. 10295). B, whole worm of Ru. mattisi (LRP no. 10295). C, mature proglottid of Ru. mattisi (USNM no. 1638656). D, scolex of Ruhnkebothrium bajaense (CNHE no. 10662). E, mature proglottid of Ru. bajaense (CNHE no. 10662).

Figure 3. Scanning electron micrographs of Ruhnkebothrium mattisi. A, scolex. B, detail of anterior loculi. C, distal surface of rim of posterior loculus. D, distal surface of anterior loculus. E, distal surface of anterior-most region of posterior loculus adjacent to anterior loculus. F, distal surface of posterior loculus as it expands. G, distal surface of expanded region of posterior loculus. H, proximal surface of posterior loculus. I, scutes on surface of neck.

Figure 4. Scanning electron micrographs of Ruhnkebothrium bajaense. A, scolex. B, detail of anterior loculi. C, distal surface of rim of posterior loculus. D, distal surface of anterior loculus. E, distal surface of anterior-most region of posterior loculus adjacent to anterior loculus. F, distal surface of posterior loculus as it expands. G, distal surface of expanded region of posterior loculus. H, proximal surface of posterior loculus. I, scutes on surface of neck.