The Monogenean Which Lost Its Clamps

Abstract

Ectoparasites face a daily challenge: to remain attached to their hosts. Polyopisthocotylean monogeneans usually attach to the surface of fish gills using highly specialized structures, the sclerotized clamps. In the original description of the protomicrocotylid species Lethacotyle fijiensis, described 60 years ago, the clamps were considered to be absent but few specimens were available and this observation was later questioned. In addition, genera within the family Protomicrocotylidae have either clamps of the “gastrocotylid” or the “microcotylid” types; this puzzled systematists because these clamp types are characteristic of distinct, major groups. Discovery of another, new, species of the genus Lethacotyle, has allowed us to explore the nature of the attachment structures in protomicrocotylids. Lethacotyle vera n. sp. is described from the gills of the carangid Caranx papuensis off New Caledonia. It is distinguished from Lethacotyle fijiensis, the only other species of the genus, by the length of the male copulatory spines. Sequences of 28S rDNA were used to build a tree, in which Lethacotyle vera grouped with other protomicrocotylids. The identity of the host fish was confirmed with COI barcodes. We observed that protomicrocotylids have specialized structures associated with their attachment organ, such as lateral flaps and transverse striations, which are not known in other monogeneans. We thus hypothesized that the clamps in protomicrocotylids were sequentially lost during evolution, coinciding with the development of other attachment structures. To test the hypothesis, we calculated the surfaces of clamps and body in 120 species of gastrocotylinean monogeneans, based on published descriptions. The ratio of clamp surface: body surface was the lowest in protomicrocotylids. We conclude that clamps in protomicrocotylids are vestigial organs, and that occurrence of “gastrocotylid” and simpler “microcotylid” clamps within the same family are steps in an evolutionary sequence, leading to the absence of these attributes in species of Lethacotyle.

Towards the resolution of the Microcotyle erythrini species complex: description of Microcotyle isyebi n. sp. (Monogenea, Microcotylidae) from Boops boops (Teleostei, Sparidae) off the Algerian coast

“…To ensure that hosts and monogenean were labelled with respect of host-parasites relationships, we followed a precise protocol (Ayadi et al 2017;Bouguerche et al 2019;Justine et al 2013). One specimen of Microcotyle sp.…”

A new species of Microcotyle (Monogenea: Microcotylidae) from Scorpaena notata (Teleostei: Scorpaenidae) in the Mediterranean Sea

“…complete traceability. For 3 individual S. notata and 3 H. dactylopterus, a tissue sample of the fish was taken and one monogenean was extracted; the monogenean was cut in two halves, the posterior half being processed for molecules and the anterior being kept for morphological assessment and preparation of a voucher slide [18].…”

No vagina, one vagina, or multiple vaginae? An integrative study ofPseudaxine trachuri(Monogenea, Gastrocotylidae) leads to a better understanding of the systematics ofPseudaxineand related genera

“…Considering that in a single species, P. trachuri , we found specimens with and without what look like “multiple lateral vaginae”, we believe that the taxa mentioned above, and probably others, should be re-examined, preferably using both morphology and molecular information. More generally, we stress the importance of integrative taxonomy [ 21 ] for the taxonomy of parasites, including correct identification of hosts using both morphology and molecular analysis as in the present work and recent studies [ 5 , 8 – 10 , 43 ] and, whenever possible, deposition of hosts in curated collections [ 12 , 36 , 39 , 42 ].…”

“…To ensure that hosts and parasites were labelled with respect to their host-parasites relationships, we followed recent works dealing with description of new species of Monogenea by using barcoding [ 5 , 8 – 10 , 43 ]. For each host fish from which monogeneans were collected, a tissue sample from the gill was taken.…”