Phoreiobothrium swaki, Caira, J. N. & Jensen, K., 2015

Caira, J. N. & Jensen, K., 2015, Insights on the identities of sharks of the Rhizoprionodon acutus (Elasmobranchii: Carcharhiniformes) species complex based on three new species of Phoreiobothrium (Cestoda: Onchoproteocephalidea), Zootaxa 4059 (2), pp. 335-350 : 342-345

Phoreiobothrium swaki n. sp.

( Figs. 5 , 6 )

Type host. Rhizoprionodon cf. acutus 2 (sensu Naylor et al. 2012b) ( Carcharhiniformes , Carcharhinidae ).

Type locality. Gulf of Carpentaria off Weipa, Queensland, Australia (12°35'11"S, 141°42'34"E).

Additional localities. Fog Bay off Dundee Beach, Timor Sea, Northern Territory, Australia (12°45'33"S, 130°21'7"E).

Date of collection (holotype). 18 May 2004.

Type material. Holotype (QM No. G235021; whole mount of immature worm) and 1 paratype (QM No. G235020; whole mount of immature worm); 2 paratypes ( USNM Nos. 1283357–1283358; whole mounts of 2 immature worms); 2 paratypes (LRP Nos. 8754–8755; whole mount of immature worm, and whole-mounted SEM strobilar voucher). Scolex examined with SEM retained at the University of Kansas.

Site of infection. Spiral intestine.

Etymology. This species honors Stephen (Swak) Baer who through a series of fortuitous circumstances now also has a tapeworm to call his very own.

Description. (Based on 5 whole mounts of immature worms, and 1 immature worm prepared for SEM with its strobilar voucher). Worms 4.2–4.9 (4.4 ± 0.3; 5) mm long, euapolytic or possibly hyperapolytic, greatest width 245–279 (264 ± 15; 4) at level of posterior proglottid; 22–39 (32 ± 7; 5) proglottids per worm. Scolex consisting of scolex proper bearing 4 rectangular bothridia and cephalic peduncle, 183–205 (194 ± 9; 4) wide at level of hooks. Bothridia 139–196 (175 ± 18; 8; 4) long by 96–118 (105 ± 8; 7; 4); each bearing anterior muscular pad in form of loculus, 1 pair of hooks, and post-hook region divided into subequal anterior and posterior loculi. Muscular pad 28–45 (36 ± 6; 9; 5) long, anterior margin without papillae. Anterior loculus conspicuously longer than posterior loculus, 117–145 (138 ± 10; 6; 4) long, posterior margin of anterior loculus bearing few papillae-like projections; posterior loculus horizontally oblong in form, 25–32 (27 ± 2; 8; 4) long, subdivided into 11–13 (13 ± 0.8; 6; 3) subloculi; subloculi 5–10 (8 ± 1; 13; 4) wide, approximately equal in length throughout posterior loculus; boundary between anterior and posterior loculus with double septum ( Figure 6 B). Hooks tri-pronged, each with blunt talon embedded in musculature of scolex; prongs unequal in length, hollow, covered with thin layer of tissue; accessory piece between hook bases absent. Lateral hook measurements: A 30–51 (41 ± 8; 6; 5), B 36–48 (43 ± 5; 6; 5), C 26–34 (31 ± 3; 6; 5), D 36–66 (53 ± 11; 6; 5), E 17–25 (22 ± 3; 6; 5), F 12–19 (15 ± 3; 6; 5); medial hook measurements: A' 34–56 (48 ± 7; 7; 5), B' 38–58 (48 ± 8; 7; 5), C' 31–39 (35 ± 3; 7; 5), D' 44–71 (59 ± 10; 7; 5), E' 16–26 (21 ± 4; 7; 5), F' 10–19 (14 ± 3; 7; 5); lateral and medial hooks approximately equal in length. Cephalic peduncle 439–1,838 (1,160 ± 501; 5) long, with inconspicuous posterior margin.

Apex of scolex proper, muscular pad and distal bothridial surfaces ( Figure 6 F) covered with papilliform filitriches only. Proximal bothridial surfaces covered with papilliform filitriches and sparsely arranged, small gladiate spinitriches ( Figure 6 E). Cephalic peduncle covered with acicular filitriches and large gladiate spinitriches ( Figure 6 D). Strobila covered with capilliform filitriches and sparsely arranged large gladiate spinitriches decreasing in density posteriorly.

Proglottids acraspedote. Immature proglottids 22–39 (32 ± 7; 5) in number, initially wider than long, becoming longer than wide with maturity; posterior-most immature proglottid 330–712 (473 ± 147; 5) long by 245–279 (264 ± 15; 4) wide. Mature and gravid proglottids not observed. Testes 55–68 (62 ± 5; 7; 4) in number, of these 4–7 (6 ± 1; 7; 4) in postvaginal poral field, elongate oval to round, 12–28 (17 ± 5; 15; 5) long by 20–55 (34 ± 10; 15; 5) wide, 1 layer deep in cross section, extending from anterior of proglottid to anterior margin of ovary, in 4–6 irregular columns anterior to cirrus sac. Vas deferens minimal, coiling at antero-medial margin of cirrus sac, entering cirrus sac at its antero-medial margin. Cirrus sac oblong, 89–107 (99 ± 8; 5) long by 24–31 (27 ± 3; 5) wide, containing coiled cirrus; cirrus armed with spinitriches. Genital pores marginal, irregular alternating, 46–52 (49 ± 3; 5) % of proglottid length from posterior end. Vagina weakly sinuous, extending along midline of proglottid from ootype region to anterior margin of cirrus sac, then laterally along anterior margin of cirrus sac, opening into common genital atrium anterior to cirrus sac. Ovary near posterior margin of proglottid, H-shaped in frontal view, bilobed in cross section, lobulated, essentially symmetrical, 115–221 (151 ± 43; 5) long by 159–181 (165 ± 11; 4) wide. Mehlis’ gland posterior to ovarian isthmus. Vitellarium follicular, in 2 lateral bands; each band consisting of 1 dorsal and 1 ventral column of follicles, extending from near anterior margin of proglottid to posterior margin, interrupted by cirrus sac on dorsal side, uninterrupted by ovary. Uterus ventral, medial, extending from ootype to stop 3–4 testis-lengths short of anterior margin of testicular field. Excretory ducts in 2 lateral pairs. Eggs not observed.

Remarks. Phoreiobothrium swaki n. sp. is easily distinguished from P. anticaporum in the position of its genital pores which are located approximately at the middle, rather than at the extreme anterior portion of the proglottids (46–57 vs. 85–95% of proglottid length from posterior end). Unlike the basal prongs of the hooks of P. exceptum , P. lewinensis and P. purinsensis , which are extremely reduced, those of this new species are well developed. Its possession of tri-pronged, rather than bi-pronged, hooks readily distinguishes it from P. manirei . Phoreiobothrium swaki n. sp. has a greater number of testes (53–68 vs. 36–49) than P. perilocrocodilus , and also lacks the 4–5 small, muscular papillae on the anterior margin of muscular pad seen in the latter species. This new species is a much smaller worm than P. blissorum , P. l a s i u m, P. pectinatum and P. robertsoni (3.2–4.9 mm vs. 13– 18.9, 11–25.6, 11–30 and 8.1–11.9 mm in total length, respectively). Its abaxial prongs are much less recurved than those of P. tiburonis , and whereas fully mature proglottids were never seen on the strobila of this new species, P. tiburonis bears 1–3 mature proglottids on the strobila—in fact, in their original description of this species Cheung et al. (1982) reported that in some cases gravid proglottids were retained on the strobila. With respect to the two other species found in members of the R. acutus complex, P. swaki n. sp. differs from P. j a hk i in that, rather than bearing a posterior loculus that is shallowly obovoid and thus medial subloculi that are substantially longer than the lateral subloculi, the posterior loculus of the new species bears subloculi of approximately the same length throughout. Unlike P. nadiae , which exhibits 1–3 mature proglottids on the strobila, mature proglottids of P. s w a k i n. sp. were not observed on any of the six worms examined. Moreover, P. s w ak i n. sp. possesses narrower bothridia (96–148 vs. 163–193) and a shorter anterior loculus (117–157 vs. 194–232) than P. nadiae .

Figures

FIGURE 5. Line drawings of Phoreiobothrium swaki n. sp. A. Scolex (QM No. G 235021). B. Hooks (USNM No. 1283357). C. Whole worm (QM No. G 235021). D. Terminal, immature proglottid (QM No. G 235021).

FIGURE 6. Scanning electron micrographs of Phoreiobothrium swaki n. sp. A. Scolex, small letters indicate locations of Figures 6 D – F. B. Subloculi. C. Pre-hook region and hooks. D. Microtriches on cephalic peduncle. E. Microtriches on proximal bothridal surface. F. Microtriches on distal bothridal surface.