Yamaguticestus, 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 : 1347-1348

YAMAGUTICESTUS GEN. NOV.

ZooBank registration: B380C792-EF6D-47B5-A28C- 91AE303CE3F2.

Diagnosis: Worms euapolytic, apolytic or anapolytic, acraspedote or weakly craspedote. Scolex with four bothridia; cephalic peduncle and myzorhynchus lacking; neck present. Bothridia round to oval in form, with apical sucker and single, undivided loculus. Scolex spinitriches gongylate columnar or gladiate; filitriches capilliform. Neck and strobila scutellate. Immature proglottids wider than long; mature proglottids square or longer than wide. Testes numerous, extending throughout most of proglottid; post-ovarian field absent. Vas deferens minimal. Genital pores lateral, irregularly alternating; genital atrium shallow. Cirrus sac narrowly oblong or pyriform, containing coiled cirrus; cirrus armed with spinitriches. Vagina straight or weakly sinuous, extending from ootype along midline of proglottid to anterior margin of cirrus sac, then laterally to open into genital atrium anterior to cirrus; vaginal sphincter present or absent; seminal receptacle absent. Ovary terminal or subterminal, H-shaped in frontal view, tetralobed in cross-section; ovarian margins digitiform. Vitellarium follicular; follicles in two lateral bands; each band consisting of multiple columns of follicles, extending length of proglottid, can be interrupted ventrally by terminal genitalia, not interrupted by ovary. Uterus medial, ventral, sacciform, extending from ovarian isthmus to level of cirrus sac. Excretory vessels 4, arranged in one dorsal and one ventral pair on each lateral margin of proglottid. Parasites of catsharks ( Scyliorhinidae Gill and Pentanchidae Smith ) and small squaliform sharks. Cosmopolitan.

Type species: Yamaguticestus metini sp. nov.

Additional species: Yamaguticestus longicollis (Molin, 1858) comb. nov. and Yamaguticestus squali ( Yamaguti, 1952) comb. nov.

Etymology: This genus honours Professor SatyuYamaguti for his extensive contributions to cestode systematics, which included description of the first member of this lineage known to parasitize a squaliform shark. Cestus is Latin for ‘girdle’. The gender is masculine.

Provisional name: New genus 18 of Ruhnke et al. (2017).

Remarks: Yamaguticestus differs from the 19 valid genera of the Phyllobothriidea (i.e. including Ruhnkebothrium ) as follows. Its possession of bothridia that lack facial and marginal loculi distinguishes it from Cardiobothrium , Chimaerocestos Williams & Bray, 1984 and Trilocularia Olsson, 1867 . It differs from Thysanocephalum and Ruhnkebothrium in that its bothridia are flat and oval, rather than triangular and highly folded. Its flat, oval bothridia also distinguish it from Alexandercestus Ruhnke & Workman, 2013 , Bibursibothrium , Clistobothrium Dailey & Vogelbein, 1990 , Flexibothrium , Guidus Ivanov, 2006 , Hemipristicola Cutmore, Theiss, Bennett & Cribb, 2011 and Phyllobothrium Van Beneden, 1850 , which bear bothridia that are stalked, highly folded, recurved anteriorly to form open grooves, bear a deep central cavity or are pouch-like in form. Yamaguticestus differs from Orygmatobothrium Diesing, 1863 in that its bothridia lack, rather than bear, a unique central glandulomuscular organ. Unlike those of Monorygma Diesing, 1863 and Pelichnobothrium Monticelli, 1889, the vitelline follicles of Yamaguticestus are arranged in two lateral fields, rather than in a circumcortical band. The new genus differs from Bilocularia Obersteiner, 1914 in its possession of a testicular field that extends to the anterior margin of the ovary in post-poral and anti-poral regions, rather than being limited to the region anterior to the cirrus sac. It differs from Calyptrobothrium Monticelli, 1893 in possessing, rather than lacking, a post-poral field of testes. Unlike Crossobothrium Linton, 1889 , the proglottids of Yamaguticestus bear, rather than lack, posterior laciniations. This new genus most closely resembles Scyphophyllidium Woodland, 1927 but differs in its possession of an ovary with digitiform, rather than lobulated, margins and a uterus that occupies no more than half the length of the mature proglottid, rather than extending two-thirds or more of the length of the proglottid.