. Bulletin. Natural history; Natuurlijke historie. 60 PEABODY MUSEUM BULLETIN 41. Figs. 54-56. Gastrochaena moreana Buvignier 1852, YPM 10002, Jurassic (Malm), Stramberg, Czecho- slovakia. Fig. 54. Shell valves. Upper left: lateral exterior view of right valve. Irregularity on the posterior of the shell is sediment filling the burrow. Center left: dorsal view of right valve and internal cast of left valve. Lower left: ventral view perpendicular to the plane of the pedal gape. The shell interior is partially filled with crystals of calcite. Fig. 55. Natural internal limestone casts of three bur
. Bulletin. Natural history; Natuurlijke historie. 60 PEABODY MUSEUM BULLETIN 41. Figs. 54-56. Gastrochaena moreana Buvignier 1852, YPM 10002, Jurassic (Malm), Stramberg, Czecho- slovakia. Fig. 54. Shell valves. Upper left: lateral exterior view of right valve. Irregularity on the posterior of the shell is sediment filling the burrow. Center left: dorsal view of right valve and internal cast of left valve. Lower left: ventral view perpendicular to the plane of the pedal gape. The shell interior is partially filled with crystals of calcite. Fig. 55. Natural internal limestone casts of three burrows. The burrow on the right shows the internal cast of the left valve visible in Figure 54 (left, center). The substratum is a scleractinian coral. Fig. 56. Diagrammatic reconstruction of the center burrow in Figure 55, drawn after removal of the surrounding coral substratum. The figure represents an internal cast of the burrow. The burrow was lined only near the extreme posterior of the siphonal portion (, toward the upper right, near the burrow aperture). The three scale bars are graduated in millimeters. functionally replaced by stronger comarginal shell ridges. By Pliocene time, calcified spikes were restricted to the juvenile shell (Fig. 30) or entirely lost in most species of Gastrochaena. Calcified periostracal spikes have likewise been secondarily reduced during the course of evolution of Eufistulana. Stephenson (1941) described minute spikes covering parts of the Cretaceous Eufistulana ripleyana, but these are limited to the juvenile shell or are entirely lost in the Recent Eufistulana (see below). Whereas Spengleria and Gastrochaena specialized for chemical and combined chemical and mechanical boring, respectively, certain other gastrochaenids partially or entirely abandoned the endolithic habitat for a. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these
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