Caulobothrium Baer, 1948

Caira, Janine N. & Jensen, Kirsten, 2021, Two new species of Caulobothrium (Cestoda: “ Tetraphyllidea ”) from the duckbill eagle ray, Aetomylaeus bovinus (Myliobatiformes: Myliobatidae), off Senegal with new insights on morphological features of the genus, Zootaxa 4903 (1), pp. 127-139 : 137-138

Caulobothrium Baer, 1948 revised

Scolex with 4 stalked bothridia; bothridia each with apical sucker, divided into loculi by multiple transverse septa; with or without longitudinal septum. Myzorhynchus absent. Cephalic peduncle variable in length. Bothridia with filitriches only; cephalic peduncle with or without small gladiate spinitriches. Strobila craspedote or acraspedote, euapolytic, apolytic or occasionally anapolytic; medial longitudinal grooves developing into tandem series of elliptical apertures posteriorly on dorsal and ventral surfaces in some. Genital pores lateral, irregularly alternating, usually at mid-level or in anterior half of proglottid. Testes numerous, 1 or 2 layers deep in cross section; post-poral testes present; post-ovarian testes present in some. Cirrus sac small; cirrus with or without armature. Ovary posterior, Hshaped in dorso-ventral view, tetralobed in cross section. Vagina opening into genital atrium anterior or at the same level as cirrus. Vitelline follicles lateral, in single or multiple lateral columns dorsally and ventrally. Uterus median, with lateral diverticula when gravid. In Myliobatidae Bonaparte and Dasyatidae Jordan. Cosmopolitan. Type species Caulobothrium longicolle ( Linton, 1890) Baer, 1948 . Additional species: C. katzi n. sp., C. multispelaeum n. sp., C. myliobatidis Carvajal, 1977 , C. opisthorchis Riser, 1955 , C. ostrowskiae Brooks, Mayes, and Thorson, 1981 , C. peduncluatum Coleman, Beveridge, and Campbell, 2019 , C. tetrascaphium Riser, 1955 , C. tobijei ( Yamaguti, 1934) Baer, 1948 , and C. uruguayense Brooks, Mayes, and Thorson, 1981 .

Prior to the present study, seven of the eight described species of Caulobothrium had been reported from six of the 11 valid species of Myliobatis Cuvier currently recognized ( Last et al. 2016). The eighth species, C. pedunculatum , was reported from one of the five species of Pastinachus ; the work of Healy et al. (2009) included an undescribed species provisionally identified as Caulobothrium n. sp. 4 from Pastinachus solocirostris Last, Manjaji, and Yearsley (as P. cf. seph en). In combination with our report of two new species from Aetomylaeus bovinus , at a minimum, this work expands the potential sources of novelty in Caulobothrium beyond the five species of Myliobatis not yet examined for this cestode genus to include the three species of Pastinachus , and six species of Aetomylaeus .

The phylogenetic trees resulting from the molecular analyses of Healy et al. (2009) placed C. multispelaeum (as Caulobothrium n. sp. 2) and C. katzi (as Caulobothrium n. sp. 3) as sister taxa robustly within a clade composed of the six other species of Caulobothrium included in their analyses. Although both species parasitize A. bovinus , this result is perplexing given the remarkably dissimilar morphologies and sizes of these two species—at 1.7–3.4 mm in TL, C. multispelaeum is essentially one of the smallest members of the genus and at 6.7–12.6 cm in TL, C. katzi is one of the largest. Yet, a similar phenomenon may exist in the bat eagle ray, Myliobatis californicus from which Riser (1955) described the small C. myliobatidis (2.5–6 mm in TL) and the giant C. tetrascaphium (over 20 cm in TL). Although molecular data are not available for these species at this time, it would be interesting to examine their phylogenetic relationships both relative to one another and their congeners in the future.

The evolutionary relationships and higher classification of the genus Caulobothrium remain uncertain. Despite its possession of bothridial stalks—a feature that characterizes members of the Rhinebothriidea—molecular phylogenetic analyses (e.g., Caira et al. 2014, 2017) place this taxon among the more than 20 genera that remain in the “ Tetraphyllidea ”. However, given the highly polyphyletic nature of the latter taxon and the essentially completely unresolved interrelationships of its various independent lineages relative to one another and to other cestode orders, the true ordinal affinities of Caulobothrium are unclear. These same uncertain phylogenetic affinities also hinder the assignment of this genus to a family at this time.

To our knowledge, the unusual, PAS-positive medial longitudinal grooves and tandem series of elliptical apertures seen throughout the dorsal and ventral surfaces of the strobila of C. multispelaeum have been observed previously in only one other group of cestodes. Koch et al. (2012; pg. 182) reported “a region of musculo-glandular tissue along midline of dorsal and ventral surfaces manifested externally as tandem series of depressions” in all three species of the lecanicephalidean genus Elicilacunonsus Koch, Jensen, and Caira, 2012 they examined. They too found these structures to be PAS positive. Observing no connection between the depressions and the internal organs of these worm, they hypothesized that these grooves may function in attachment to the mucosal surface of the host’s spiral intestine. An adhesive function for this structure is similarly possible in C. multispelaeum . However, the actual function (or functions) of these curious structures in these genera requires further investigation.