Yellow-shelled semi-slug (Parmarion martensi) is a species of animal belonging to the family Ariophantidae. It is a "semi-slug"—a mollusk that either lacks a complete shell or possesses only a very small, internal one. It is primarily nocturnal, though it may occasionally be active during the morning hours when the environment is wet, highly humid, or foggy.
P. martensi has a body length of 23.5 mm, a height of 7.3 mm, and a width of 6.4 mm. The distance from the mantle to the posterior tip is 9.6 mm, while the mantle itself measures 9.9 mm in length and 7.6 mm in width.
Its shell is reduced, extremely small, thin, and flattened; it is embedded within the body tissue and covered by the mantle, rendering it invisible from the outside. The soft body is elongated and flexible, tapering toward the tail. The skin surface is smooth and slippery, coated in a thick layer of mucus.
The head features two pairs of tentacles: a longer, upper pair of optic tentacles that function as eyes, and a shorter, lower pair of labial tentacles that serve as sensory organs for touch. Both pairs are retractable.
The radula, used for feeding, is located within the oral cavity and consists of a flexible ribbon-like structure covered in microscopic teeth. The anterior dorsal region is covered by a relatively large mantle, which protects the internal shell and vital organs. The body color is generally a dull light brown, cream, or translucent (clear). The mantle contains a pneumostome—a respiratory opening that facilitates efficient gas exchange in humid environments.
Movement is achieved via a broad, muscular foot that glides across surfaces. This ventral, muscular structure serves as the primary organ of locomotion, aided by the secretion of mucus, which plays a crucial role in reducing friction, maintaining body moisture, and providing protection against environmental threats and predators. This species exhibits a preference for various microhabitats, including leaf litter, decaying woody debris, and the damp surfaces of tree trunks. Such habitats are characterized by a high density of tree vegetation; the dense canopy cover serves to reduce the intensity of sunlight reaching the ground.
These snails are found in andosol soils within tropical mountainous and highland regions at elevations ranging from 750 to 3,000 meters, where the soil pH is 7, temperatures range from 11–25°C, humidity is 80%, and annual rainfall reaches 2,500–7,000 mm.
Due to their slow and limited movement, these animals often congregate and remain in close proximity to one another. Eggs are typically laid in clusters of 10–15. As they move, these snails secrete a mucus that is toxic to plants. They feed on leaves, stems, flowers, fruits, and other plant parts.
Shady, cool, and humid environmental conditions are essential for their activity and survival, as they help minimize the risk of losing body fluids. Temperatures between 26–30°C induce stress and slow down growth; as temperatures approach 30°C, the snails generally become inactive—entering a state of estivation—or may even die.
An atmospheric humidity level of 84.8–94% RH is highly conducive to the snails' activity. This species requires a very humid environment (above 90% RH) to prevent dehydration. They are typically active at night to avoid both dehydration and predation.
TAXON
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Subclass: Heterobranchia
Infraclass: Euthyneura
Subterclass: Tectipleura
Superorder: Eupulmonata
Order: Stylommatophora
Suborder: Helicina
Infraorder: Limacoidei
Superfamily: Helicarionoidea
Family: Ariophantidae
Subfamily: Ostracolethinae
Genus: Parmarion Fischer (1856)
Species: Parmarion martensi Simroth (1893)
VERNACULAR NAME
Chinese (simplified): 马氏盾勇螺 - 马氏褶勇螺
Chinese (traditional): 馬丁氏鼈甲蛞蝓 - 馬氏盾勇螺
English: Yellow-shelled semi-slug
Hong Kong: 馬氏盾勇螺
Indonesia: Siput janggel
Italian: Limaccia guscio giallo di Martens
Japanese: ヒラコウラベッコウガイ
Java: Janggel
Taiwan: 馬丁氏鼈甲蛞蝓
Thai: หอยลดเปลือกมาร์เทนส์
Aryo Bandoro
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