. The Biological bulletin. Biology; Zoology; Marine biology. ADAPTATIONS IN MALLEUS AND ISOGNOMON 395 The palps are relatively longer than in M. regula; the lips are similarly developed, without frilling or fusion. There is a long anal flap which assists in directing the faeces, long scroll-like pellets up to 5 mm. long. As in Malleus, all waste material in both inhalant and exhalant chambers is carried to the inner edge of the inner mantle fold and so to the posterior distal regions where it is ejected (see feathered arrows in Figure 8). Unlike M. regula, the gonad, which covers the visceral
. The Biological bulletin. Biology; Zoology; Marine biology. ADAPTATIONS IN MALLEUS AND ISOGNOMON 395 The palps are relatively longer than in M. regula; the lips are similarly developed, without frilling or fusion. There is a long anal flap which assists in directing the faeces, long scroll-like pellets up to 5 mm. long. As in Malleus, all waste material in both inhalant and exhalant chambers is carried to the inner edge of the inner mantle fold and so to the posterior distal regions where it is ejected (see feathered arrows in Figure 8). Unlike M. regula, the gonad, which covers the visceral mass, was obviously maturing although sperm was not ABR Figure 9. /. isognomon. A, B, interior views of right valves of two specimens showing stages in extension of the ligament and hinge line and of the distal region. The shells are 12 and cm. long. In the smallest animals collected the shell was 13 mm. long by 8 mm. wide and was oval rather than elongated like similar-sized M. regula. The shell is usually bluish with light-colored radiating curved rays. Young shells in dark areas tended to remain white. In some the foot was observed extended and seeking a surface for byssal attachment; when found initial threads were quickly secured. Lhitil some 30 mm. long the shells remained oval and then displayed increasing irregularities due to the confined space in which they grew and to the effects of repair. But there is increasing elongation as form changes from the initially more rounded condition. They come to assume a striking external resemblance to M. regula although the hinge line is extended posteriorly to a greater extent than in that species (cf. Figs. 1 and 9). This process of extension continues until, as shown in Figure 9B, it may attain a length double the width of the shell. At this size the mantle tissues tend to withdraw, the ligament no longer elongates and the shell only increases in Please note that these images are extracted from scanned pa
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectb, booksubjectzoology
