Rockacestus Caira & Bueno & Jensen 2021, GEN. NOV.

ROCKACESTUS GEN. NOV.

ZooBank registration: E44B4965-FD5A-4B87-8813- AA9CE2244938.

Diagnosis: Worms euapolytic, acraspedote or craspedote. Scolex with four bothridia; cephalic peduncle and myzorhynchus lacking; neck present. Bothridia moderately to highly folded, with apical sucker and marginal loculi. Scolex spinitriches gladiate; filitriches papilliform or acicular. Neck and strobila scutellate. Immature proglottids wider than long; mature proglottids longer than wide. Testes numerous, extending throughout most of proglottid; post-ovarian field of testes absent. Vas deferens minimal or extensive. Genital pores lateral, irregularly alternating; genital atrium shallow. Cirrus sac pyriform to elongate oval, containing coiled cirrus; cirrus armed with spinitriches. Vagina weakly sinuous, extending from ootype along midline of proglottid to anterior margin of cirrus sac, following anterior margin of cirrus to open into genital atrium anterior to cirrus; vaginal sphincter present or absent; seminal receptacle absent. Ovary terminal to subterminal in proglottid, H-shaped in frontal view, tetralobed in cross-section; ovarian margins lobulated or rarely digitiform. Vitellarium follicular; follicles in two extensive lateral bands usually converging on midline in mature proglottids; each band consisting of multiple columns of follicles, extending length of proglottid, interrupted or not by terminal genitalia; uninterrupted by ovary. Uterus medial, ventral, sacciform, extending from ovarian isthmus to cirrus sac. Excretory vessels 4, arranged in one dorsal and one ventral pair on each lateral margin of proglottid. Parasites of skates (Rajiformes). Cosmopolitan.

Type species: Rockacestus carvajali sp. nov.

Additional species: Rockacestus arctowskii (Wojciechowska, 1991) comb. nov., Rockacestus brittanicus (Williams, 1968) comb. nov., Rockacestus conchai sp. nov., Rockacestus georgiensis (Wojciechowska, 1991) comb. nov., Rockacestus piriei (Williams, 1968) comb. nov., Rockacestus radioductus (Kay, 1942) comb. nov., Rockacestus rakusai (Wojciechowska, 1991) comb. nov., Rockacestus siedleckii (Wojciechowska, 1991) comb. nov. and Rockacestus williamsi (Schmidt, 1986) comb. nov.

Provisional species: Rockacestus sp. nov. 4 ex Dipturus batis; Rockacestus sp. nov. 5 ex Amblyraja doellojuradoi; Rockacestus sp. nov. 6 ex Dipturus lamillai.

Etymology: The name Rajicestus Rocka & Laskowski, 2017 was originally established for cestodes from skates with the features of this genus. Unfortunately, Rocka & Laskowski in Rocka (2017) neither provided text differentiating the genus nor designated a type species and thus, based on the International Code of Zoological Nomenclature (ICZN, 1999; Articles 13.1 and 13.3), the name Rajicestus is unavailable. The name Rockacestus honours both Dr Anna Rocka’s earlier work on the cestodes of skates and the fact that she and her colleague were the first to recognize the distinctive nature of these skate cestodes. Cestus is Latin for ‘girdle’. The gender is masculine.

Provisional name: New genus 20 of Ruhnke et al. (2017) and Bueno (2018).

Remarks: Rockacestus differs conspicuously from all but four of the 20 valid genera of phyllobothriideans (i.e. including Ruhnkebothrium and Yamaguticestus) in its possession of marginal loculi on its bothridia. With respect to the four other genera with marginal loculi, it differs from Cardiobothrium in lacking, rather than possessing, distinct facial loculi. Unlike Chimaerocestos, the vitelline follicles of Rockacestus are distributed throughout the length of the proglottid, rather than being restricted to the posterior regions of the proglottid. It is readily distinguished from Crossobothrium in that its proglottids lack laciniations, and its neck and strobila bear, rather than lack, scutes. Rockacestus differs from the subset of species of Scyphophyllidium with marginal loculi in that its bothridia are moderately to highly folded, rather than essentially flat, and in that the spinitriches on its scolex are simple gladiate rather than serrate gladiate or gongylate columnar.

Beyond providing an appropriate generic home for the two new species described here, erection of this genus provides an appropriate generic placement for all eight species of Phyllobothrium from skates considered incertae sedis by Ruhnke et al. (2017) in the most recent revision of the Phyllobothriidea, and we hereby transfer these eight species to Rockacestus. These species parasitize a variety of skate taxa. Wojciechowska (1991) described Ro. arctowskii, Ro. georgiensis, Ro. rakusai and Ro. siedleckii from Bathyraja sp. 2, Amblyraja georgiana (Norman, 1938), Bathyraja maccaini Springer, 1971 and Bathyraja eatonii (Günther, 1876), respectively. Williams (1968) described Ro. brittanicus, Ro. piriei and Ro. williamsi (as Phyllobothrium minutum Williams, 1968) from Raja montagui Fowler, 1910, Leucoraja naevus (Müller & Henle, 1841) (as Raja naevus) and Leucoraja fullonica (Linnaeus, 1758) (as Raja fullonica), respectively. Rockacestus radioductus was described from Beringraja binoculata (Girard, 1855) (as Raja binoculata) by Kay (1942). Sequence data were generated here for three additional, putatively novel species of Rockacestus, which we have referred to provisionally as Rockacestus sp. nov. 4, Rockacestus sp. nov. 5 and Rockacestus sp. nov. 6.