Up to ten Littoraria species can occur together in a single mangrove forest in the most diverse parts of the Indo-Pacific region, as at Singapore, and discrimination of the species can be difficult. Until 1986, when the taxonomy of the group was revised, most of these similar species of mangrove periwinkles were included under the name ‘Littorina scabra’. The wide, white columella of Littoraria scabra provides one of the best means of distinguishing this species from other similar members of Littoraria, which may have a wide columella that is purplish or brown, or alternatively a much narrower columella.The most reliable character for the identification of Littoraria species is the shape of the penis in males. This is a forked structure located on the right side of the neck of the animal, and bears a single sucker-like gland and an elongate filament for transmission of sperm. In L. scabra the glandular limb is larger than that carrying the filament. It is believed that the penis is a species-recognition character that is used by the females to distinguish members of their own species, explaining why each species has a unique penial shape.A molecular phylogeny (constructed from 28S rRNA, 12S rRNA and COI gene sequences) is available for 37 of the 39 members of the genus Littoraria, and this shows that L. scabra is a member of the subgenus Littorinopsis, and within this belongs to a clade that includes L. pallescens, L. philippiana and L. angulifera.
Littoraria scabra is a marine snail belonging to the family of periwinkles (Littorinidae) and lives on mangrove trees in the tropical Indian and Pacific Oceans.The animal is edible and gathered for for food in some indigenous communities, but in general the small size, and the gritty texture of females carrying larvae, make this an unpopular shellfish.This species is not endangered at present, but is threatened by widespread destruction of mangrove forests.
Sexes are separate. During copulation the male mounts the shell of the female and inserts the penis under the lip of her shell and into the pallial oviduct. Mating may last for several hours. Sperm are transferred to the copulatory bursa, and later pass to another storage sac, the seminal receptacle, where they can survive for many months. Females spawn several thousand fertilized eggs in a short period, and retain these within the mantle cavity where they are attached in a thin layer to the folds of the reduced gills.Larvae hatch after several days as early veligers and are released simultaneously when the female descends the tree to reach the water level. Normal planktotrophic development follows, lasting an estimated 8 to 10 weeks. The length of the larval shell (protoconch) at settlement is about 0.32 to 0.42 mm. The combination of ovoviviparity and planktotrophic development is unusual in molluscs, but is characteristic of all members of the subgenus Littorinopsis. It is believed to be an adaptation to permit rapid release of larvae, thus minimising the time spent at the water surface where the female is vulnerable to aquatic predators.Females spawn probably once a month, in a lunar cycle, and at least in Queensland, Australia, the breeding season lasts throughout the year.Growth is rapid, reaching a shell length of 20 mm in about 8 months, and is slightly faster in females, giving rise to a small dimorphism in size. Males mature at about 16 mm, and females at 20 mm. Maximum lifespan is about 2 years. These data are from a population in northern Queensland.
This species is very widespread throughout the tropical regions of the Indian and western Pacific Oceans. It occurs from South Africa to the Red Sea, India, Malaysia, Australia, southern Japan, Hawaii and Polynesia.The typical habitat of L. scabra is the trunks, prop roots and lower branches of mangrove trees (mainly Rhizophora species, but also Avicennia and others), up to a height of 3m. The species avoids mangrove swamps that are very muddy or estuarine, and instead is most common on trees in relatively clear-water situations, on islands and promontories, or only on the outer seaward fringes of broad mangrove forests on continental coastlines. Where it is common, up to 20 individuals can be found on a single mangrove tree. Occasionally individuals can be found on driftwood on sandy beaches, or even on rocks in very sheltered situations.The snails graze on the surface of the bark of the mangrove trees, ingesting cork cells, fungal hyphae and diatoms.