Balanus amphitrite DARWINの日本産品種に就て
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概要
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In the present paper the writer has enumerated eleven forms of Balanus amphitrite DARWIN as occurring in the Japanese waters, viz. communis, cirratus, poecilotheca, albicostatus, hawaiiensis, krugeri and formosanus. Of these, the last-named one formosanus seems to be a new form. These eleven forms can be divided into two groups according to their habitats. The four forms, communis, cirratus, poecilotheca and hawaiiensis, live under water at ebb tide, while the remaining three, albicostatus, krugeri and formosanus, are restricted to intertidal regions. The forms of the latter group often live in brackish water of estuaries. Moreover their habitats and distribution are much influenced by the tidal current, sea-water temperature, substratum, bottom fauna, etc. All these forms are subject to a good deal of variation in both the external and internal structures. Especially the intertidal forms, which are always submerged at ebb tide, show much conspicuous variation in regard to the surface of the compartments and the shape of the opercular valves. The diagnosis of a new from formosanus is as follows: Shell tubulo-conical, with a large rhombiform orifice. Surface of parietes usually smooth, whitish, with dark purple longitudinal stripes; no transverse stripes or patterns are found. Radii broad, purplish, with oblique summits. Scutum usually wider than long, though variable, with a short well-developed adductor ridge; interior above the adductor ridge roughened with many short callouses sometimes smooth; pit for lateral depressor muscle distinct or indistinct. Tergum rather narrow and long; interior upper portion deeply sunken, roughened with many short callouses as in scutum. Spur short, triangular in outline, obtusely pointed toward the scutal side; carinal margin of spur itself typically about twice as long as scutal margin. Crests for carinal depressor muscles 3-5 in number. Labrum with three teeth on either side of a median notch. Cirrus III with break-like teeth on frontal edge of segments of both rami. Distribution: West coast of Formosa (Rokuko-type locality; Goro; Tansui Estuary). Remarks: This Formosan form of Balanus amphitrite is closely allied to albicostatus, a subspecies common in Japan proper, but it may be distinguished from the latter by the smooth parietes and by the shape of tergum. Whether it is valid as a subspecies of Balanus amphitrite or only a local form of the subspecies albicostatus can be ascertained when a large series from various localities of Formosa and neighbourhood is examined.
- 1938-06-15