Trypanorhynch cestodes from elasmobranchs from the Gulf of Oman, with the description of Prochristianella garshaspi n. sp. (Eutetrarhynchidae)

A revision of the Rhoptrobothriidae (Cestoda: Tetraphyllidea)

The Rhoptrobothriidae are one of the more enigmatic families of cestodes of elasmobranchs. Opinions on the taxonomic status of the familys three original genera (i.e., Myzophyllobothrium, Rhoptrobothrium, and Myzocephalus) have varied over the 115 years since they were erected. Some authors have considered all three valid, others have considered Rhoptrobothrium to be a synonym of Myzopyllobothrium or a genus inquirendum, yet others have considered Myzocephalus to be a synonym of the phyllobothriid genus Thysanocephalum. All three genera were established for specimens collected from eagle rays off Sri Lanka. The erection of Mixophyllobothrium for two specimens from a cowtail stingray off India three decades ago added additional confusion to the situation, with some authors considering it valid and others a synonym of Myzocephalus. These disagreements stem largely from differences in interpretation of the complex morphology of the scolex of members of these genera. Furthermore, with the exception of Rhoptrobothrium comprising four species, each genus is monotypic. All but Rhoptrobothrium has not been considered in detail for nearly a century, largely because of a lack of available material. The taxonomic status of these genera is assessed here based on light and scanning electron microscopy, and molecular data generated from new material collected from eagle rays off Indonesian and Malaysian Borneo, Japan, Sri Lanka, and Viet Nam. Morphological work indicates that the genera differ largely only in the degree of folding of the four remi that extend from the cephalic peduncle. A molecular phylogeny based on sequence data for the D1D3 region of the 28S rRNA gene, which include new data for eight specimens of four species, indicates that Myzophyllobothrium, Myzocephalus, and Rhoptrobothrium are not mutually monophyletic. The latter two genera and Mixophyllobothrium are considered synonyms of Myzophyllobothrium and five species are transferred to that genus. Myzophyllobothrium okamuri n. comb. is considered a species inquirendum. Myzophyllobothrium nagasawai n. sp. is described from Aetobatus narutobiei off Japan. Myzophyllobothrium narinari n. comb. is re-described based on newly collected cestodes from the type host and locality (i.e., Aetobatus ocellatus off Sri Lanka). Despite consisting of only a single genus, the family status of the group is retained in recognition of the unusual configuration of the scolex, which bears four biloculate bothridia and four remi extending from the cephalic peduncle. The ordinal placement of the family remains uncertain, but affinities with the Phyllobothriidea, rather than Tetraphyllidea are considered.

Otobothrium muscatense n. sp. (Trypanorhyncha: Otobothriidae) from Rhabdosargus sarba (Forsskål) (Sparidae), with new locality records of larval trypanorhynchs off the Sultanate of Oman

In the evaluation of the larval trypanorhynch fauna off the Sultanate of Oman, a total of 188 bony fishes belonging to 16 species were studied, which led to the description of a new species with the establishment of new host and locality records. A new otobothriid species, Otobothrium muscatense n. sp., is described from Rhabdosargus sarba (Forsskål). Based on scolex morphology and tentacular armature, the new species closely resembles the small-sized Otobothrium Linton, 1890 species described as Otobothrium cysticum (Mayer, 1842) and O. crenacolle Linton, 1890. However, it differs from them in the basal armature by a more robust shape of the first principal and the triangular shape of the billhooks as well as by the retractor muscle originating in the posterior part of the tentacle sheath, attaching to a thickening of the tentacle sheath wall, with a muscular branch continuing and attaching at front part of the bulb. It differs from the other species of Otobothrium by size, the combination of six principal hooks and a single intercalary hook in the metabasal armature, and the plane of reflection through the tentacle surfaces. New locality records of the tentaculariids Nybelinia indica Chandra, 1986, Heteronybelinia yamagutii (Dollfus, 1960), Tentacularia coryphaenae Bosc, 1797, and Mixonybelinia lepturi Palm, 2004, together with the lacistorhynchids Pseudogrillotia multiminacantha Palm, 2004 and Callitetrarhynchus gracilis (Rudolphi, 1819), and the pseudotobothriid Parotobothrium balli (Southwell, 1929) off the Muscat region are established. Of the reported species, especially P. multiminacantha and M. lepturi occurring in Trichiurus lepturus L. further demonstrate the relatedness between the Indonesian and the northwestern Indian Ocean fauna, increasing the number of joint records between Indonesia and Omani waters to 14 species.

Two new species of Phoreiobothrium Linton, 1889 (Cestoda: Onchoproteocephalidea) off southern Iran, completing the puzzle of Phoreiobothrium faunas in Rhizoprionodon acutus species complex

It has been shown that the milk shark, Rhizoprionodon acutus (Rüppell), is probably a complex of four narrowly distributed cryptic species. To confirm this hypothesis, the oioxenous species of the onchoproteocephalid genus Phoreiobothrium Linton, 1889 was recently used to recognize each shark species of this species complex so that P. nadiae Caira and Jensen, 2015, P. swaki Caira and Jensen, 2015, and P. jahki Caira and Jensen, 2015 were described respectively from Rhizoprionodon cf. acutus 1 off Senegal, R. cf. acutus 2 off northern Australia, and R. cf. acutus 3 off Borneo. Nonetheless, the Phoreiobothrium fauna of R. acutus sensu stricto extending around the Arabian Peninsula remained unknown. In the present study, P. golchini n. sp. is described from the fourth type of this shark species complex, i.e. R. acutus sensu stricto, from the Persian Gulf. Given the oioxeny of the Phoreiobothrium species and the recent phylogeny of the milk shark species complex, if the hypothesis of the allopatric cospeciation of the members of the milk shark species complex and their cestodes is considered, it seems that scolex in Phoreiobothrium can diverge more rapidly in size and morphology than strobila. Furthermore, P. rozatii n. sp. was described from one of the members of the hardnose shark species complex, i.e. Carcharhinus macloti (Müller and Henle), in the Gulf of Oman. This study provides the first data on the occurrence of the species of Phoreiobothrium in the Persian Gulf and the Gulf of Oman.

A new genus and species of the trypanorhynch family Otobothriidae Dollfus, 1942 from the slender weasel shark Paragaleus randalli Compagno, Krupp & Carpenter (Hemigaleidae) in the Persian Gulf

A survey on the cestode fauna of Paragaleus randalli Compagno, Krupp & Carpenter in the Persian Gulf resulted in the discovery of a new trypanorhynch species of the family Otobothriidae Dollfus, 1942, the second otobothrioid species hosted by the family Hemigaleidae Hasse. The new species exhibits the closest morphological similarity to Pristiorhynchus palmi Schaeffner & Beveridge, 2013, the type- and only species of its genus. However, the new species differs from P. palmi in the position of the bothrial pits, the morphology and oncotaxy of the basal armature, the commencement of the hook files on the internal surface, a wider scolex peduncle in the pars bulbosa than in the pars vaginalis, a long neck and the presence of a lateral bothrial groove connecting the two bothrial pits to each other. The latter character is a unique trait within the Otobothrioidea Dollfus, 1942. Considering such differences, a new genus, Olgaella n. g., was erected to accommodate O. elenae n. g., n. sp. within the Otobothriidae. The evolutionary relatedness of the bothrial pits of the Otobothrioidea and the bothrial grooves of the Lacistorhynchoidea Guiart, 1927 is discussed.

Prochristianella clarkeae Beveridge, 1990 (Eutetrarhynchidae): a species complex or a species with intraspecific variation in the distribution of its tegumental microtriches?

The microthrix pattern of common forms of the trypanorhynch cestode Prochristianella clarkeae Beveridge, 1990 on which the microscopically visible microtriches almost extended to the posterior end of the scolex was described using SEM and compared to other forms for which this pattern was different. The proximal bothrial surface and the scolex peduncle of all the examined specimens were covered with palmate spinitriches and papilliform filitriches. Unlike the common specimens of P. clarkeae, on the surface of those specimens with unusual distributions of microtriches as well as those on which the microscopically visible microtriches were not observable, palmate spinitriches extended to the mid-pars vaginalis and not to the posterior end of the scolex. Statistical tests did not detect any significant difference in the measurements of the specimens possessing different microthrix patterns. Furthermore, the partial 28S rDNA confirmed that the different forms were conspecific and that P. clarkeae possesses an intraspecific variation in the distribution of palmate spinitriches. Pastinachus sephen as a new host record was also established for Prochristianella clarkeae reported for the first time from the Persian Gulf.

Dollfusiella qeshmiensis n. sp. (Cestoda: Trypanorhyncha) from the cowtail stingray Pastinachus sephen (Forsskål) in the Persian Gulf, with a key to the species of Dollfusiella Campbell & Beveridge, 1994

A new species of the genus Dollfusiella Campbell & Beveridge, 1994 is described from Pastinachus sephen (Forsskål) in the Persian Gulf. Dollfusiella qeshmiensis n. sp. is allocated to the genus Dollfusiella based on the possession of two bothria, prebulbar organs, a heteroacanthous typical armature with tightly spaced rows of hollow hooks, a basal swelling and a characteristic basal armature without prominent macrohooks. The presence of an enlarged external seminal vesicle in Dollfusiella qeshmiensis n. sp. distinguishes this species from D. michiae (Southwell, 1929), D. bareldsi (Beveridge, 1990), D. owensi (Beveridge, 1990), D. geraschmidti (Dollfus, 1974), D. angustiformis Schaeffner & Beveridge, 2013, D. hemispinosa Schaeffner & Beveridge, 2013, D. spinosa Schaeffner & Beveridge, 2013 and D. taminii Menoret & Ivanov, 2014. The new species is distinguished from the remaining species within the genus by a combination of the following morphological features: the number of testes per segment, the number of testis columns and the number of homeomorphous hooks per half spiral row in the metabasal region. In the most recent taxonomic key to the species of Dollfusiella, the presence or absence of enlarged, microscopically visible spinitriches on the scolex was used as the first distinguishing character dividing the congeners into two groups. Since the existence of visible microtriches on the scolex peduncle of D. vooremi (São Clemente & Gomes, 1989), a species so far grouped among the species lacking visible microtriches on the scolex, has been recently demonstrated, and given the fact that the presence of microscopically visible microtriches on the scolex is variable in some eutetrarhynchid species, a new key to the species of Dollfusiella is provided in which the spinitriches have been given less priority.

Two new species of Rhinebothrium (Cestoda: Rhinebothriidea) from granulated guitarfish Glaucostegusgranulatus in the Gulf of Oman

During a study of the rhinebothriideans of rays in the Gulf of Oman, two new species of Rhinebothrium Linton, 1890, Rhinebothrium kruppi sp. n. and R. persicum sp. n., were identified in Glaucostegus granulatus (Cuvier). Some significant features that distinguish R.kruppi sp. n. from R. persicum sp. n. include: scolex characteristics (hinged with 42–46 loculi vs. fusiform with 68–62 loculi), number of testes (4–5 vs. 20–27), genital pore position (61.1–76.9% of proglottid length vs. 47.2–63.3%), ovarian morphology (lobulated vs. follicular), cirrus-sac expansion (past midline of proglottid vs. limited to poral side of proglottid), vas deferens configuration (spanning posteriorly to near ovarian isthmus vs. to the level of ovarian anterior margins) and details of microthrix morphology. In addition, a combination of the aforementioned characteristics can be used to distinguish these two new species from other valid species of Rhinebothrium. These are the first species of rhinebothriidean cestodes to be described systematically from the Gulf of Oman, Iran. The two new species reported here increase the number of valid species of Rhinebothrium to 43.