Aim  To determine the origin and diversification of monachine seals using a phylogenetic framework. Methods  Molecular sequence data from three mitochondrial genes (cyt b, ND1 and 12S), and one nuclear marker (an intron from the α‐lactalbumin gene) were examined from all extant species of monachine seals. Maximum likelihood and partitioned Bayesian inference were used to analyse separate and combined (mitochondrial + nuclear) data sets. Divergence times were estimated from the resultant phylogeny using nonparametric rate smoothing as implemented by the program r8s. Results  Mirounga, Monachus and the Lobodontini form three well‐supported clades within a monophyletic Monachinae. Lobodontini + Mirounga form a clade sister to Monachus. Molecular divergence dates indicate that the first split within the Monachinae (Lobodontini + Mirounga clade and Monachus) occurred between 11.8 and 13.8 Ma and Mirounga, Monachus and the Lobodontini originated 2.7–3.4, 9.1–10.8 and 10.0–11.6 Ma, respectively. Main conclusions  Two main clades exist within Monachinae, Monachus and Lobodontini + Mirounga. Monachus, a warm water clade, originated in the North Atlantic and maintained the temperate water affinities of their ancestors as they diversified in the subtropic regions of the Northern Hemisphere. The cold‐water clade, Lobodontini + Mirounga, dispersed southward to the cooler climates of the Southern Hemisphere. The Lobodontini continued south until reaching the Antarctic region where they diversified into the present‐day fauna. Mirounga shows an anti‐tropical distribution either reflective of a once cosmopolitan range that was separated by warming waters in the tropics or of transequatorial dispersal.

Five new species of Acanthobothrium (Tetraphyllidea: Onchobothriidae) are described from the spiral intestine of the Freshwater whipray, Himantura chaophraya, in the Kinabatangan River in Malaysian Borneo. Based on criteria set forth in a previous categorization scheme for species of Acanthobothrium, these consist of 3 Category 1 species, Acanthobothrium asnihae n. sp., Acanthobothrium saliki n. sp., and Acanthobothrium zainali n. sp.; a Category 8 species, Acanthobothrium etini n. sp.; and a Category 2 species, Acanthobothrium masnihae n. sp.. Acanthobothrium asnihae n. sp. differs from all Category 1 species in its possession of a horizontal band of weak musculature that divides the posterior loculus in half. Among Category 1 species, A. saliki n. sp. differs from all but Acanthobothrium southwelli in its possession of postovarian testes. It differs from A. southwelli in its possession of fewer testes and a greater number of proglottids. Acanthobothrium zainali n. sp. differs from the 25 other Category 1 species in a combination of overall size, muscular pad and hook shape, arrangement and number of testes, ovary configuration in cross section, position of ovarian isthmus, and genital pore position. Acanthobothrium etini n. sp. is distinguished from all 5 other Category 8 species in its lack of testes from the proglottid antiporal and postporal regions and in testis number. Acanthobothrium masnihae n. sp. differs from the 35 other Category 2 species in its possession of fewer testes, postporal testes, or a greater number of proglottids. A key to Acanthobothrium species parasitizing H. chayophraya is presented. This represents the first report of Acanthobothrium from freshwater stingrays belonging to a family other than the Potamotrygonidae.

Spiral intestines of 12 specimens of the dwarf whipray, Himantura walga, collected from Malaysian Borneo in 2002 and 2003, were examined for cestodes. These yielded a new species of Acanthobothrium (Tetraphyllidea) and a new species of Echinobothrium (Diphyllidea), both of which are described. Acanthobothrium marymichaelorum n. sp. is a category 1 species. It differs from all but 4 of its category 1 congeners in its possession of postovarian testes. It also differs from these 4 species in its possession of fewer testes, shorter length, fewer proglottids, and/or shorter posterior loculus. Echinobothrium minutamicum n. sp. differs from its congeners in its possession of outer hooks in the dorsal and ventral rostellar groups that are trifid; it is also the smallest member of its genus. The spiral intestine of H. walga consisted of 12 mucosal chambers. Most (89%) of the 35 specimens of E. minutamicum n. sp. for which chamber data were generated were found in chambers 2-4. In contrast, the 57 specimens of A. marymichaelorum n. sp. occurred throughout chambers 5-12, with 86% in chambers 6-10. The modes of attachment of both cestode species were similar, i.e., both embedded their scolex within the lumen of a mucosal crypt with the hooks and/or spines penetrating the lamina propria. Both also eroded the epithelial lining of the crypts and caused modest expansion of crypt diameter. Although the configuration of the mucosal surface may explain sites in which both species were able to attach, it does not explain their absence from other regions; histological sections and scanning electron microscopy showed the mucosal surface to be similar in configuration throughout the length of the spiral intestine. The cestode fauna of H. walga also included at least 1 species of rhinebothriine, 2 lecanicephalidean species, a trypanorhynch species, and 1-2 additional new species of Acanthobothrium. However, formal description of these species must await the collection of additional material, mature material, and/or the erection of the new genera. It is of note that the fauna of the dwarf whipray consists of a suite of unusually small taxa. Although the cestode genera reported here are generally consistent with those reported from other Himantura species, they are completely inconsistent with previous records from H. walga (as Trygon walga) in Sri Lanka. This suggests that either the original host identifications are suspect or that differences exist in the faunas of H. walga between these 2 localities.

A recent major revision of the elasmobranchs of Australia, which expanded the described fauna from 190 to 307 species, has serious implications for our understanding of the host associations of parasites of Australian elasmobranchs. Most importantly, it questions the identities of the host records for many parasite species. This study focuses on cestodes of the tetraphyllidean genus Acanthobothrium parasitising Rhynchobatus, a batoid genus, the Australian elements of which have recently been revised. Four new cestode species are described from Rhynchobatus laevis (Bloch & Schneider, 1801) from the Northern Territory, Australia. These species differ from their ~160 congeners in several morphological respects. They differ conspicuously from their four Australian congeners also hosted by a Rhynchobatus species, all four of which (i.e. Acanthobothrium bartonae Campbell & Beveridge, 2002, Acanthobothrium gibsoni Campbell & Beveridge, 2002, Acanthobothrium lasti Campbell & Beveridge, 2002 and Acanthobothrium rhynchobatidis Subhapradha, 1955) were reported from Rhynchobatus djiddensis (Forsskål, 1775), a batoid species no longer considered to occur in Australian waters. This suggests that one or both of the other Australian members of Rhynchobatus (i.e. R. australiae Whitley, 1939 and R. palpebratus Compagno & Last, 2008) are likely candidates as hosts for one or more of the latter four species. With respect to the relationships among congeners parasitising the same host species, phylogenetic analyses of sequence data of the D1–D3 region of 28S rDNA for three of the four new cestode species support previous work suggesting that congeners parasitising the same host species are not each other’s closest relatives. This study also serves to emphasise the importance of careful scrutiny of host identities, particularly in systems such as this, in which host taxonomy is under active revision.

Abstract:Five new species of Acanthobothrium van Beneden, 1850 from the spiral intestine of a specimen of an unusual species of Himantura from the Arafura Sea off northern Australia are described. Acanthobothrium oceanharvestae sp. n. is one of 26 category 1 species (sensu Ghoshroy and Caira 2001) lacking post-ovarian testes; it differs from these in total length, number of proglottids, number of testes, cirrus sac size and details of the terminal genitalia. Acanthobothrium popi sp. n. is unique among category 2 species in its possession of post-ovarian testes. Acanthobothrium rodmani sp. n. is a category 6 species distinct from all congeners in the dense blade-like spinitriches on the distal surfaces of its anterior-most bothridial loculi and conspicuously tapered posterior bothridial margins, which are reflexed anteriorly. Acanthobothrium romanowi sp. n. differs from most other category 1 species in that its genital pore is distinctly posterior. It differs from the remaining category 1 species in size, testis number, cephalic peduncle microthrix form, proglottid shape, and bothridial loculus dimensions. Acanthobothrium zimmeri sp. n. is among the six category 1 species with post-ovarian testes. It differs from these species in total length, ovary shape, number of proglottids and testes and vas deferens extent. This brings the number of Acanthobothrium species with post-ovarian testes to 10, all of which are Indo-Pacific in distribution, and 7 of which parasitize Himantura species. A key to the five new species parasitizing Himantura sp. is provided. Sequence data for the D1-D3 region of 28S rDNA for the five new species and two congeners parasitizing other Himantura species shows no intraspecific variation. Analysis of these and comparable data for two species available in GenBank (Acanthobothrium parviuncinatum and Acanthobothrium sp. 1) showed an interspecific variation of 0.7-11.3% among species pairs. Bayesian, Likelihood and Parsimony phylogenetic analyses of these data for these nine species indicate that the five new species parasitizing Himantura sp. are generally not each others' closest relatives.