Stillabothrium Healy 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 : 4-6

Stillabothrium Healy et Reyda gen. n.

ZooBank number for genus:

urn:lsid:zoobank.org:act:B2B660B1-E30D-4208-935E-F89C06A2D16D

Diagnosis: Rhinebothriidea . Worms euapolytic, small. Scolex consisting of scolex proper and 4 bothridia; cephalic peduncle absent; short germinative zone present; apical organ absent. Bothridia stalked, consisting of anterior and posterior regions with distinctly different arrangement of loculi and septa; bothridial margins with thin rim. Anterior region with horizontally oriented loculi (i.e. loculi wider than long) with two ( Figs. 2B , 4B ) or more ( Figs. 6B , 8B , 10B , 12B , 15 ) complete transverse septa, with ( Figs. 2B , 4B ) or without ( Figs. 6B , 8B , 10B , 12B , 15 ) single partial medial longitudinal septum. Posterior region lacking medial longitudinal septum, divided into odd number of vertically oriented loculi (i.e. loculi longer than wide) by even number of nonmedial longitudinal septa; nonmedial longitudinal septa all incomplete ( Figs. 6B , 8B , 10B , 12B , 15 ) or a combination of incomplete and complete ( Figs. 2B , 4B ); incomplete nonmedial longitudinal septa either abut posteriormost transverse septum of anterior region of bothridia ( Figs. 2B , 4B , 10B ,), or overlap one or more posteriormost transverse septa ( Figs. 6B , 8B , 12B , 15 ). Lateral margins of posterior region of bothridium divided into additional loculi by marginally ( Figs. 2B , 4B ) or diagonally ( Figs. 6B , 15 ) oriented septa in some species.

Longitudinal septa of posterior region appear as ridges in section ( Fig. 13 ) with proximal and distal portions different; proximal portion of septa formed by underlying bothridial wall, consisting of radial muscles oriented with proximal ends of fibres adjacent to each other; distal portion of septa formed by separate muscle bundle; proximal and distal portions of septa separated by triangular gap.

Testes numerous, arranged in two columns, one layer deep in cross section, restricted to pre-poral region of proglottid. Cirrus sac extending medially to or past midline of proglottid. Cirrus spinitriches present. Vas deferens extending posteriorly to ovarian isthmus, entering cirrus sac at anterior margin. Vagina opening anterior to cirrus sac; vaginal sphincter absent. Ovary H-shaped in dorsoventral view, tetralobed in cross section. Vitellarium follicular; follicles in 2 lateral bands; bands interrupted by terminal genitalia and usually also by ovary. Uterus saccate, medial, extending from posterior margin of proglottid or ovarian isthmus, anteriorly to near anterior margin of proglottid. Parasites of batoid elasmobranchs ( Rhinobatidae , Zanobatidae and Dasyatidae ); Indo-Pacific and coastal Afro-tropics.

I n f o r m a l s y n o n y m s: Rhinebothriinae New genus 3 Healy et al. (2009), Caira et al. (2014), Ruhnke et al. (2015), and Marques and Caira (2016).

T y p e s p e c i e s: Stillabothrium ashleyae sp. n.

A d d i t i o n a l s p e c i e s: Stillabothrium amuletum ( Butler, 1987) comb. n.; Stillabothrium cadenati ( Euzet, 1954) comb. n.; Stillabothrium campbelli sp. n.; Stillabothrium davidcynthiaorum sp. n.; Stillabothrium hyphantoseptum sp. n.; Stillabothrium jeanfortiae sp. n.

E t y m o l o g y: From the Latin ‘stilla’, meaning drop, for the teardrop shape of the bothridia of species the genus.

Remarks. Stillabothrium gen. n. is generally consistent with the diagnosis of the order Rhinebothriidea as given by Healy et al. (2009): Species of Stillabothrium possess facially loculated bothridia borne on stalks and possess a vas deferens that enters the cirrus sac at the anterior, rather than the medial, margin. Stillabothrium can be distinguished from all rhinebothriidean genera except Escherbothrium Berman and Brooks, 1994 , Phormobothrium Alexander, 1963 and Tritaphros Lönnberg, 1889 in its possession of bothridia that are fully facially loculate, with posterior loculi that are longer than wide. Stillabothrium differs from Phormobothrium and Tritaphros in lacking an apical organ on the scolex. Stillabothrium is most similar to Escherbothrium , but Stillabothrium can be distinguished from the latter genus in lacking a medial longitudinal septum in the posterior region of the bothridium, thereby possessing an odd number of loculi. In Escherbothrium , the posterior region of the bothridium includes a short medial longitudinal septum (see fig. 6 in Berman and Brooks 1994) and an even number of loculi. In addition, Escherbothrium was described as possessing an apical sucker and rounded protrusions on its distal bothridial surfaces (see both in fig. 8 in Berman and Brooks 1994). Conversely, in Stillabothrium the feature on the anteriormost portion of the bothridium is considered to be a loculus, rather than a sucker, and no rounded protrusions were observed on the scolex of any surfaces of any of the six species of Stillabothrium examined with SEM in this study. Based on the recent designation of families within Rhinebothriidea by Ruhnke et al. (2015), Stillabothrium belongs to family Escherbothriidae Ruhnke, Caira et Cox, 2015 .

Species of Stillabothrium have appeared in previous works under different temporary names. The genus was first recognised by Healy (2006) in her dissertation, under a preliminary name which, as recommended by Article 8 of the ICZN (1999), she disclaimed. In addition to providing preliminary morphological characterisation of species, Healy (2006) included partial 28S rDNA sequence data for eight species of Stillabothrium . Subsequently, four molecular phylogenetic studies ( Healy et al. 2009, Caira et al. 2014, Ruhnke et al. 2015, Marques and Caira 2016) have included the sequence data originally generated by Healy (2006). Each study, which refers to Stillabothrium as ‘Rhinebothriinae New genus 3’, supported recognition of those eight species as an independent, novel, genus.

Figures

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. 4. Line drawings of Stillabothrium davidcynthiaorum sp. n. from Himantura heterura (Bleeker). A – whole worm (LRP 9046); B – scolex (holotype, MZUM [P] 2016.9 [H]); C – terminal proglottid (LRP 9046).

Fig. 6. Line drawings of Stillabothrium campbelli sp. n. from Himantura cf. pastinacoides. A – whole worm (holotype; MZUM [P] 2016.11 [H]); B – scolex (LRP 9066); C – terminal proglottid (LRP 9067).

Fig. 8. Line drawings of Stillabothrium hyphantoseptum sp. n. from Pastinachus solocirostris Last, Manjaji et Yearsley. A – whole worm (holotype; MZUM [P] 2016.13 [H]); B – scolex (LRP 9092); C – terminal proglottid (LRP 9088).

Fig. 10. Line drawings of Stillabothrium jeanfortiae sp. n. from Himantura australis Last, White et Naylor. A – whole worm (holotype; QM G235198); B – scolex (LRP 9123); C – terminal proglottid (holotype; QM 235198).

Fig. 12. Line drawings of Stillabothrium cadenati comb. n. from Zanobatus schoenleinii (Müller et Henle). A – whole worm (LRP 9135); B – bothridium (LRP 9134); C – terminal proglottid (LRP 9136).

Fig. 15. Line drawing of bothridium of the holotype (QM GL4621) of Stillabothrium amuletum (Butler, 1987) comb. n. from Glaucostegus typus [Anonymous (Bennett)].

Fig. 13. Histological sections through bothridium of Stillabothrium cadenati (Euzet, 1954) comb. n. from Zanobatus schoenleinii (Müller et Henle). Arrows indicate divisions between proximal and distal portions of transverse septa. Abbreviations: ATS – an- teriormost transverse septum; IV – intestinal villus; RM – radial musculature; RTS – reduced transverse septum; SM – septal mus- culature; ST – stalk; TM – transverse muscle bundle.