During foraging ground studies of green turtles, Chelonia mydas, at Shoalwater Bay (22°23′S, 150°15′E) in central coastal Queensland, Australia, a turtle (individual K49367) was captured on 4 July 2002 with no cloacal opening on the ventral side of its tail. The sex and maturity of the turtle was confirmed by gonad examination using laparoscopy (Limpus et al. 1994). This individual was determined to be a prepubescent, immature female with curved carapace length of 70.4 cm. Superficially, the turtle appeared healthy and to be functioning normally. The vent opened dorsally on the tail (Fig. 1). There was a gap in the vertebral column through which the cloaca passed that was identified by finger examination within the cloaca. The cloaca was very tight and muscular. Internally the reproductive system consists of a white straight oviduct that entered the anterior of the pelvic arch in a normal fashion and the ovary that contained large numbers of very small previtellogenic follicles. This is the first case of an ectopic cloaca (supracaudal vent) deformity observed out of 11,127 adult and immature green turtles that have had their tails examined during foraging area studies in Eastern Australia (Moreton Bay, Hervey Bay, Shoalwater Bay, Repulse Bay, coral reefs of the southern Great Barrier Reef and Clack Reef) during 20 years from 1983 to 2002. Likewise, this type of deformity has not been recorded among the approximately 1000 hawksbill turtles, Eretmochelys imbricata, and 1500 loggerhead turtles, Caretta caretta, examined in foraging areas of eastern Australia during the same period. The authors are unaware of any previous report of this abnormality occurring within any turtle, tortoise, or terrapin species.

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The normal appearance and position of the oviducts leading into the pelvic arch together with the normal function of the anus suggests that the condition originated during early embryogenesis before the formation of the tail bud. Normal anal positioning occurs as the caudal rudiment extends into the amnionic cavity (Stage 14; Miller 1985). This extension moves the double layered (endoderm and ectoderm) cloacal membrane from its dorsal position at the posterior of the caudal rudiment to be ventrally directed at the base of the extending tail. It appears that this did not happen. The likely scenario is that the cloacal membrane remained in place and that the extending somatic mesoderm of the tailbud was induced to develop posterior to the cloacal membrane. This presumed induction accounts for both the position of the ectopic anus and the otherwise normal shape of the tail, while not requiring radical intrusion of the developing cloacal chamber through the mesoderm of the caudal somites because the normal cloacal chamber forms in coordination with the position of the cloacal membrane (see Raynaud and Pieau 1985).

Evidence of this process was gained via palpation of the tail that demonstrated the bones did not extend on either side of the cloaca and anus; the posterior tail vertebrae were totally separated from the anterior portion of the tail. The nerve chord and peripheral nerves arising anterior to the ectopic anus would not be affected by this arrangement.

Obviously, this deformity has not had a serious impact on the survival of the turtle through its early years. At a functional level, this deformity has not impeded defecation and urinary excretion via the cloaca. However, male green turtle copulatory behavior is directed to facilitating the male's insertion into the female's cloaca from the ventral side of her tail. Therefore, with this dorsally placed ectopic cloacal opening, this female turtle will probably not be able to successfully copulate when it reaches adulthood and should be excluded from the breeding population.