Stillabothrium ashleyae Willsey et Reyda, 2016

Reyda, Florian B., Healy, Claire J., Haslach, Andrew R., Ruhnke, Timothy R., Aprill, Tara L., Bergman, Michael P., Daigler, Andrew L., Dedrick, Elsie A., Delgado, Illari, Forti, Kathryn S., Herzog, Kaylee S., Russell, Rebecca S. & Willsey, Danielle D., 2016, A new genus of rhinebothriidean cestodes from batoid elasmobranchs, with the description of five new species and two new combinations, Folia Parasitologica (038) 63 (38), pp. 1-28 : 6-8

Stillabothrium ashleyae Willsey et Reyda sp. n.

Figs. 1–3 , 16A

ZooBank number for species:

urn:lsid:zoobank.org:act:B316EE69-A04B-4A09-9AB5-658752FDC431

Description (based on whole mounts of 25 complete mature worms and 14 free proglottids, cross sections of 2 strobila, longitudinal sections of 1 scolex, and 3 scoleces prepared for SEM): Worms ( Fig. 2A ) euapolytic, acraspedote, 1.11–2.78 mm (1.66 ± 0.39; n = 23) long, greatest width 353–590 (455 ± 70; n = 24) at level of scolex; 6–10 (7.7. ± 1; n = 25) proglottids per worm. Cephalic peduncle lacking; darkly staining germinative zone 17–217 (54 ± 37; n = 24) long.

Scolex ( Fig. 2B ) consisting of scolex proper bearing 4 stalked bothridia. Stalks 46–164 (76 ± 31; n = 13) long by 53–100 (75 ± 17; n = 13) wide, attached slightly posterior to middle of bothridia. Bothridia ( Fig. 2B ) varying in shape with degree of contraction, from shallowly-deltoid ( Fig. 3A ) to deeply-deltoid ( Fig. 3B ), facially loculated, 140–227 (175 ± 26; n = 20) long by 190–334 (270 ± 44; n = 24) wide; bothridial margins with thin rim. Anterior region of bothridia ( Fig. 2B ) with 3 (n = 18) horizontally oriented loculi (i.e. loculi wider than long) with 2 complete transverse septa and one partial medial longitudinal septum. Anteriormost loculus 30–46 (39 ± 5; n = 15) long by 41–72 (59 ± 11; n = 18) wide. Posterior region of bothridia with 8 (n = 21) nonmedial longitudinal septa dividing bothridia into 9 primary loculi longer than wide; outermost primary loculi on each side subdivided by 3, or occasionally 2 (2.94 ± 0.2; n = 16) relatively short marginal septa into 3–4 small subloculi; longitudinal septa of posterior region not overlapping transverse septa of anterior region.

Loculi ( Fig. 3D ) and septa of distal bothridial surfaces bearing capilliform filitriches and coniform spinitriches. Proximal bothridial rim ( Fig. 3E ) bearing capilliform filitriches greater in length than those on distal bothridial surfaces ( Fig. 3D ). Proximal bothridial surfaces ( Fig. 3E,F ) away from rim bearing acicular filitriches and coniform spinitriches. Isolated cilia observed on proximal bothridial surfaces. Bothridial stalks ( Fig. 3G ) and strobila ( Fig. 3H ) bearing capilliform filitriches only.

Strobila with 2–4 (3.2 ± 0.8; n = 25) proglottids wider than long followed by 3–7 (4.5 ± 1; n = 25) proglottids longer than wide. Strobila widest at terminal proglottid; terminal proglottid 320–880 (591 ± 125; n = 25) long by 68–150 (101 ± 20; n = 24) wide; genital pore located 35–46% (40 ± 3; n = 25) of proglottid length from proglottid posterior margin. Immature proglottids 4–9 (6.4 ± 1.2; n = 25) in number. Mature proglottids 1–2 (1.2 ± 0.4; n = 25) in number, including 0–1 (0.3 ± 0.5; n = 25) vas deferens-mature proglottids.

Testes in mature proglottids 18–27 (22 ± 2; n = 25) in total number, 1 layer deep in cross section ( Fig. 2D ), arranged in 2 columns ( Fig. 2C ); columns extending from anterior margin of proglottid to anterior margin of cirrus sac, 19–37 (25 ± 4; n = 24) long by 20–45 (31 ± 6; n = 22) wide. Vas deferens coiled, entering anterior margin of cirrus sac, extending from level of ovarian isthmus to overlap posteriormost testes ( Fig. 2C ). Cirrus sac thin-walled, oval, extending medially to near midline of proglottid; cirrus sac in terminal mature proglottid 26–42 (33 ± 5; n = 17) long by 26–47 (32 ± 6; n = 17) wide; cirrus sac in vas deferens-mature proglottids 28–38 (34 ± 4; n = 8) long by 36–50 (43 ± 5; n = 8) wide. Cirrus spinitriches present.

Vagina ( Fig. 2C ) thick-walled, weakly sinuous, somewhat overlapping anterior margin of cirrus sac ( Fig. 16A ), extending along midline of proglottid from ootype region to anterior margin of cirrus sac, then laterally to open into genital atrium anterior to cirrus sac; vaginal sphincter absent. Seminal receptacle present. Ovary near posterior end of proglottid, H-shaped in frontal view, tetralobed in cross section ( Fig. 2E ); ovarian lobes asymmetrical; poral and aporal ovarian lobes in terminal mature proglottids 80–215 (161 ± 33; n = 16) and 85–220 (163 ± 34; n = 16) long, respectively. Poral and aporal ovarian lobes in vas deferens-mature proglottids 146–265 (194 ± 47; n = 7) and 141–282 (190 ± 51; n = 7) long, respectively. Maximum width of ovary 35–96 (56 ± 17; n = 17). Ovarian isthmus at or anterior to midpoint of ovary; poral lobe of ovary stopping 26–63 (41 ± 12; n = 23) short of genital pore. Mehlis’ gland well posterior to ovarian isthmus, 19–35 (26 ± 5; n = 21) long by 14–30 (18 ± 4; n = 21) wide. Vitellarium follicular; vitelline follicles arranged in 1 dorsal and 1 ventral column on each side of proglottid; columns extending from anterior to posterior margin of proglottid, interrupted by terminal genitalia, and mostly interrupted by ovary ( Fig. 2C ). Uterus ventral, sacciform, extending from near isthmus of ovary to near anterior margin of proglottid.

Free proglottids with greatly expanded vas deferens and atrophied testes, 521–919 (724 ± 136; n = 12) long by 134–202 (165 ± 21; n = 12) wide. Free gravid proglottids 750 (n = 1) long by 210–280 (245 ± 50; n = 2) wide; unembryonated eggs oval, without filaments, 14–17 (15 ± 1; n = 6; from same proglottid) long.

T y p e h o s t: Dasyatis biasa (Last, White et Naylor) ( Myliobatiformes : Dasyatidae ).

A d d i t i o n a l h o s t: None.

Ty p e l o c a l i t y: South China Sea off Mukah (02°53'52''N; 112°05'44''E), Sarawak, Malaysian Borneo (BO-477) .

A d d i t i o n a l l o c a l i t i e s: Java Sea off Selakau (01°03'31''N; 108°58'26''E) , West Kalimantan, Indonesian Borneo (KA-182, KA-184) . Java Sea off Sukadana (01°14'33''S; 109°57'00''E) , West Kalimantan, Indonesian Borneo (KA-378) .

S i t e o f i n f e c t i o n: Spiral intestine.

Ty p e m a t e r i a l: Holotype MZUM (P) No. 2016.6 (H). Paratypes: IPCAS No. C-737; LRP Nos. 8992–8994; 9005–9037 (including molecular vouchers, cross sections and SEM specimens); MZB Nos. Ca197–Ca199; MZUM (P) Nos. 2016.7 (P)–2016.8 (P); SBC No. P-00069; USNM Nos. 1420453– 1420460.

E t y m o l o g y: This species is named in honour of Ashley Willsey Attoma, sister of D.D. Willsey, for her support of her sister’s studies.

Remarks. Stillabothrium ashleyae sp. n. is the type and first described species of the genus. The distribution of S. ashleyae includes both the Malaysian and Indonesian portions of the island of Borneo. Stillabothrium ashleyae appears to be highly host specific, as it was only encountered in specimens of D. biasa . It was not found parasitising any of the multiple other species of dasyatids (e.g. Dasyatis Rafinesque and Himantura Müller et Henle ) examined during our survey work. We note that specimens with a morphology similar to S. ashleyae were found in D. zugei (VN-23, VN-34) from Vietnam. However, preliminary molecular and morphological data suggest that the specimens from Vietnam represent a distinct species of Stillabothrium that awaits formal study and description.

Three specimens of S. ashleyae were included in the phylogenetic analysis ( Fig. 1 , Table 1 ).

Figures

Fig. 1. Phylogram based on Bayesian analysis of 1084 bp region of D1–D3 28S rDNA. Numbers above branches indicate Bayesian posterior probabilities, numbers below indicate Bootstrap percentage values, based on 1000 replicates. Scale indicates expected num- ber of substitutions per site. Diagrammatic line drawings of fully opened bothridia of the seven described species mapped onto the clades representing those respective species. Host species information in Table 1.

Fig. 2. Line drawings of Stillabothrium ashleyae sp. n. from Dasyatis biasa (Last, White et Naylor). A – whole worm (holotype; MZUM [P] 2016.6 [H]); B – scolex (LRP 9011); C – terminal proglottid (LRP 9010) with position of sections labeled (uterus not shown); D – section of mature proglottid at level of testes (LRP 9037); E – section of mature proglottid posterior to ovarian bridge (LRP 9030).

Fig. 3. Scanning electron micrographs of Stillabothrium ashleyae sp. n. from Dasyatis biasa (Last, White et Naylor). A–C – scoleces, letters indicate locations of other SEMs; D – distal bothridial surface at anterior loculus; E – proximal bothridial surface and rim, letter indicates location of F; F – proximal bothridial surface; G – stalk; H – strobila.

Fig. 16. Light micrographs of terminal genitalia of Stillabothrium species, each with genital pore oriented left. A – Stillabothrium ashleyae sp. n. from Dasyatis biasa (Last, White et Naylor); B – Stillabothrium davidcynthiaorum sp. n. from Himantura gerrardi (Gray); C – Stillabothrium campbelli sp. n. from Himantura cf. pastinacoides; D – Stillabothrium hyphantoseptum sp. n. from Pastinachus solocirostris Last, Manjaji et Yearsley; E – Stillabothrium jeanfortiae sp. n. from Himantura australis Last, White et Naylor; F – Stillabothrium cadenati comb. n. from Zanobatus schoenleinii (Müller et Henle).