Structure and development of Lobatostoma manteri sp.nov. (Trematoda: Aspidogastrea) from the Great Barrier Reef, Australia

Abstract

Lobatostoma manteri sp.nov. is described. It differs from other species of this genus in the number of marginal alveoli (usually 56–62), the location of the testis near the posterior end and the large size of the cirrus pouch. Mature worms occur in the intestine of the fish Trachinotus blochi. Eggs containing fully developed larvae are laid. The eggs are eaten by snails and hatch in the stomach. Larvae have an oral sucker, pharynx, simple caecum, ventro-terminal acetabulum, two dorsal excretory bladder cells in front of the acetabulum, and a caudal appendage. They migrate into the digestive gland and differentiate to pre-adults with fully developed genital organs and the full number of alveoli on the adhesive disk; young spermatozoa and egg cells develop but do not mature. Pre-adults have a minimum number of 8500 sensory papillae on the surface. The worms are usually found in a cavity formed by enlargement of the main duct and one or more (?) side ducts of the digestive gland near the stomach in Cerithium moniliferum, or in the stomach and main ducts of the digestive gland of Peristernia australiensis. They may creep from the ducts into the stomach and back into the ducts. Fish become infected by eating snails. Worms from fish die soon after transfer into sea water but can be kept alive for up to 13 days in frog's Ringer solution or dilute sea water (1:5), in which they lay eggs containing larvae infective to snails. Worms from snails remain alive in sea water, dilute sea water, frog's Ringer or Tyrode solution. Eggs of worms from single infections have the haploid chromosome number of 7; there is normally no self-fertilization and development does not reach the blastula stage. The life-cycle of Lobatostoma manteri is the simplest two-host cycle of trematodes known. Reasons are given why it must be considered the most primitive one, of a type from which digenean life-cycles have evolved.