Taxonomy and life history of the Acropora-eating flatworm Amakusaplana acroporae nov. sp. (Polycladida: Prosthiostomidae) |
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Authors: | K A Rawlinson J A Gillis R E Billings and E H Borneman |
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Institution: | (1) Smithsonian Marine Station, 701 Seaway Drive, Fort Pierce, FL 34949, USA;(2) Present address: Department of Genetics, Evolution and Environment, University College London, Gower Street, London, WC1E 6BT, UK;(3) Department of Physiology, Development and Neuroscience, University of Cambridge, Anatomy Building, Downing Street, Cambridge, CB2 3DY, UK;(4) 9901 Jay Lane, Bristow, VA 20136, USA;(5) Department of Biology, University of Houston, Science and Research Building II, 4800 Calhoun Rd., Houston, TX 77204, USA |
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Abstract: | Efforts to culture and conserve acroporid corals in aquaria have led to the discovery of a corallivorous polyclad flatworm
(known as AEFW – Acropora-eating flatworm), which, if not removed, can eat entire colonies. Live observations of the AEFW, whole mounts, serial histological
sections and comparison of 28S rDNA sequences with other polyclads reveal that this is a new species belonging to the family
Prosthiostomidae Lang, 1884 and previously monospecific genus Amakusaplana (Kato 1938). Amakusaplana acroporae is distinguished from Amakusaplana ohshimai by a different arrangement and number of eyes, a large seminal vesicle and dorsoventrally compressed shell gland pouch. Typical
of the genus, A. acroporae, lacks a ventral sucker and has a small notch at the midline of the anterior margin. Nematocysts and a Symbiodinium sp. of dinoflagellate from the coral are abundantly distributed in the gut and parenchyma. Individual adults lay multiple
egg batches on the coral skeleton, each egg batch has 20–26 egg capsules, and each capsule contains between 3–7 embryos. Embryonic
development takes approximately 21 days, during which time characteristics of a pelagic life stage (lobes and ciliary tufts)
develop but are lost before hatching. The hatchling is capable of swimming but settles to the benthos quickly, and no zooxanthellae
were observed in the animal at this stage. We suggest that intracapsular metamorphosis limits the dispersal potential of hatchlings
and promotes recruitment of offspring into the natal habitat. The evolutionary and ecological significance of retaining lobes
and ciliary tufts in the embryo are discussed. Camouflage, high fecundity and possible dispersal dimorphisms probably explain
how Amakusaplana acroporae can cause Acropora sp. mortality in aquaria where natural predators may be absent. |
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