Subclass POLYOPISTHOCOTYLEA

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Introduction

Sexually mature marine polyopisthocotyleans range from a few milimetres to 4 cm long in Chimaericolidae. Most species attach exclusively to the gills of their host fishes, and are sedentary. Marine Polyopishtocotylea feed on blood of host fish. Clamps for attachment develop in the haptor, usually soon after larvae settle on host gills. They grip lamellae, or other epithelial surfaces in the gill cavity, over a relatively broad area, and seldom provoke any tissue response. Clamps may be circular, muscular organs that attach by suction to flat host surfaces, or more complex structures containing many supporting skeletal elements that enable jaw-like clasping around three-dimensional surfaces of gill filaments. Worms with complex clamps tend to be more sedentary than those with clamps that act as suckers (Hayward 2005).

Clamps are supported internally by hard sclerites that vary in number and articulation. The number of clamps in most groups is fixed at three or four pairs. In a few groups (Polycliphora of Diclidophoridae; several families of Gastrocotylinea; and Microcotylinea), clamps are more numerous, ranging from tens of pairs, to over 200 pairs. However, in a given individual of such species, the clamp numbers are plastic, and depend on a combination of several factors, including worm age, water temperature and host size. in at least some cases, the size of the host (and hence gill lamellae) also determines the maximum size reached by clamps (Hayward 2005).

The haptors of most groups are symmetrical, with equal numbers of clamp pairs on both sides. Various groups depart from this basic plan in several ways. Clamps may be present in unequal numbers (e.g. Heteraxinidae), or occur all or mostly on one side (e.g. Axinidae), or be larger on one side than the other (e.g. Bicotyle (Axinidae). In several groups, some or all clamps are modified; in Anchorophoridae, for example, most or all clamps have been transformed into sclerotised anchor complexes. In a few groups, clamps numbers are reduced; for example, clamps number only two pairs in Quadrivalvia (Gastrocotylidae), and have been lost altogether in Lethacotyle (Protomicrocotylidae). Clamps may occur on pronounced stalks in some Diclidophoridae ; haptors in Hexabothriidae bear an appendix with a pair of suckers (Hayward 2005).

In Australia, 17 families are represented, comprising 49 genera.

General References

Hayward, C. 2005. Monogenea Polyopisthocotylea (ectoparastic flukes). pp. 55-63 in Rohde, K. (ed.). Marine Parasitology. Collingwood, Victoria : CSIRO Publishing 592 pp.

Hayward, C. 2005. Monogenea Polyopisthocotylea (ectoparastic flukes). pp. 55-63 in Rohde, K. (ed.). Marine Parasitology. Collingwood, Victoria : CSIRO Publishing 592 pp. [55]

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