海底洞窟性甲殻類の系統,動物地理,生態について

抄録

Anchihaline caves refer to subterranean, water-filled passages from the sea to pools with no surface connection with the sea; such caves contain saline or brackish waters, which fluetuate with the tides. Cave environments are sometimes physicochemically similar to deep waters in terms of the presence of aphotic, oligotrophic, and oligoxic waters with no turbulance by wind and waves. Such caves are inhabited by numerous unique cavernicolous animals including sponges, polychaetes, crustaceans, and molluscs. The crustacean class Remipedia was newly established based on individuals from an anchihaline cave in the Bahamas in 1981, and, to date, accomodates 2 families, 6 genera, and 11 species from the Atlantic Ocean and the Indian Ocean. Remipedes are considered by some as the most primitive extant crustaceans because of the lack of tagmosis and homonomous metamerism in the trunk, which has up to 38 free segrments. Other cave-dwelling crustaceans include maxillipodans such as copepods, tantulocaridans, ostracods, cirripeds, and facetotectans; malacostracans such as phyllocaridans, thermosbaenaceans, mysidaceans, isopods, amphipods, and decapods. The Facetotecta (nauplius y) is first recorded from a lava tube in the Canary Islands in this review. Among these some are endemic to caves, while others are widely distributed inside and outside the caves. Many marine troglobionts are regarded as Tethyan relicts in consideration of their present distribution patterns. Some of them are closely related to deep-sea taxa. Both types may have originated from shallow water ancestors after the Middle Tertiary Period. The existance of cavernicolous crustaceans in the Mediterranean Sea suggests that their ancestors may have survived even through the Messinian Salinity Crisis. Phylogenetic studies on cavernicolous copepods suggest that these might have independently colonized caves many times in geological history. Most of troglobitic crustaceans exhibit troglomorphies such as reduced body pigment and eyes. The number of eggs per clutch tends to be fewer in trogrlobionts than in their shallow-water relatives. Some cavernicolous crustaceans show direct development and specialized feeding modes. We hope studies on stygobionts will be developed also in Japan because there are many anchihaline caves in the Ryukyu Islands, southern Japan, where we may be able to discover unknown and phylogenetically important taxa.