Comprehensive Description

Background

This species can be identified as a member of the Leptoplanidae due to a combination of head tentacles, a lack of marginal eyes, and an elongated oval body shape⁶. Leptoplanids belong to the suborder Acotylea, polyclads lacking a ventral sucker⁶. Identification of species in this family is generally based on close examination of the reproductive structures⁶. Polyclads are acoelomate (lacking a coelom) and no hemal system is present. However due to the extremely dorso-ventrally flattened body of these animals the distance between the external and internal environment is always very short, therefore absorption and internal transport of gases occurs through diffusion.

Feeding and digestion

All polyclads are carnivorous, preying on a variety of small invertebrates⁶.  It is unclear which prey items this species prefers, however a North American intertidal leptoplanid flatworm, Notoplana acticola, is known to feed on limpets and acorn barnacles⁵. Invertebrate diversity is relatively low in the intertidal environment inhabited by the unidentified leptoplanid, however gastropods are numerous and these may be considered likely prey items. Polyclads have a folded, plicate pharynx which is enclosed in the pharyngeal cavity⁷. Protrusion of this pharynx out of the mouth allows the flatworm to feed on its prey. The name polyclad (poly = many, clade = branches) relates to the highly branched digestive tract of these flatworms. However, the gut is blind therefore excretion of waste occurs either through the mouth, or in the case of nitrogenous products via protonephridia or through diffusion across the body surface⁷.

Reproduction & development

Polyclads are hermaphroditic, having both male and female reproductive organs, and fertilisation takes place internally⁶. Some polyclads have elaborate mating strategies such as ‘penis fencing’⁶, but these have yet to be described in the leptoplanids and copulation is likely to take place ‘tail to tail’. The development of this species is unknown, however the development of another intertidal leptoplanid, Notoplana australis, has been thoroughly described by Anderson¹ (1977) and is summarised here: Spawning occurs throughout the year and egg masses are laid in a coiled, gelatinous string containing a single row of eggs. Hatching occurs 12-14 days after the eggs are laid. In N. australis direct development does not take place,  instead the species goes through a larval stage . The larvae resemble Götte’s larvae (a planktotrophic larval turbellarian with four ciliated lobes⁷) as opposed to Müller’s larvae (a larval turbellarian with eight ciliated lobes⁷). The larva swims actively towards light by ciliary action. After approximately three weeks the larva loses its ciliated cells, and settles on the benthos, becoming a juvenile flatworm.