FIGURE 4. Photomicrograph ofa stage 2b intermediate catch tentacle tip seen in cross section. Note the numerous cnidoblasts (cb) in the tentacle epithelium and gastrodermal cnidae (gc) free in the tentacle coelenteron. Scale bar is 10 @zm. FIGURE 5. Photomicrograph of a stage 2c intermediate catch tentacle tip seen in cross section. Small holotrich nematocysts (sh) are distributed at the epithelial surface and large holotrichs (lh) are recessed from the epithelial surface. The tentacle is collapsed about its coelenteron. Scale bar is 10 @m. FIGURE 6. Photomicrograph of a stage 3 intermediate catch tentacle tip seen in cross section. Small holotrichs (sh) line the epithelial surface and large holotrichs (lh) are recessed from the epithelial surface. Scale bar is 10 @m. FIGURE 7. Photomicrograph ofa mature catch tentacle tip seen in cross section. Note the numerous small holotrichs (sh) at the epithelial surface and large holotrichs (Ih) recessed from the epithelial surface. Scale bar is 10 @tm. FIGURE 8. Photomicrograph ofa regressing catch tentacle tip seen in cross section. Large holotrichs (lh) line the epithelial surface alongside small holotrichs (sh). Scale bar is 10 @m.
Note that Figures 2 through 8 are shown at the same magnification, indicating actual differences in tentacle size.
S12 G. M. WATSONAND R. N. MARISCAL
lacked cnidoblasts (Fig. 5). Feeding tentacle cmdae were rare in the 2c tentacle epithelium, but gastrodermal cnidae were often as common as in 2a and 2b tentacles.
Stage 3 intermediate catch tentacle
Stage 3 catch tentacles had many more cnidae than any of the types of tentacles discussed above (Fig. 6), because of the appearance of additional small holotrichs in these tentacles along with many large holotrichs (which had been extremely rare in stage 2 catch tentacles). The small holotrichs were distributed at the epithelial surface and the large holotrichs were recessed from the epithelial surface beneath the small holotrich cnidocytes. Feeding tentacle cnidae were extremely rare in stage 3 tentacles, as were gastrodermal cnidae. Cnidoblasts were absent from this stage. Note that the diameter of the stage 3 catch tentacle is much larger than that of the previous developmental stage (i.e., significant growth has occurred).
Mature catch tentacle
Mature catch tentacles, like stage 3 catch tentacles, were characterized by nu merous small holotrichs at the epithelial surface, followed by large holotrichs recessed from the epithelial surface (Fig. 7). However, feeding tentacle cnidae (rare in stage 3 tentacles) were absent from mature catch tentacle tips. Likewise, cnidoblasts were absent, and gastrodermal cnidae were rare in mature catch tentacles.
Regressing catch tentacle
Even though regressing catch tentacles had far fewer cnidae in their epithelium than mature catch tentacles, numerous small holotrich and large holotrich nema tocysts were present in these tentacles (Fig. 8). Note that large holotrichs were dis tributed alongside small holotrichs at the epithelial surface in regressing catch ten tacles. This holotrich distribution is in contrast with stage 3 and mature catch ten tacles, in which large holotrichs were recessed from the epithelial surface. In addition, occasional feeding tentacle cnidae were observed in the tips of regressing catch tentacles, whereas none had been present in mature catch tentacle tips. Cnidoblasts were absent and gastrodermal cnidae were rare. Note that the diameter ofthe tentacle has decreased dramatically (i.e., degrowth has occurred).