. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GASTRULATION IN A HYDROZOAN 33. FIGURE 18. Cross-section through the blastopore region of an 8-h embryo. Microvilli and cilia of migrating cells extend into the space of the blastopore (B). N, nucleus of cell in region of the blastopore. X6700. direction to form a young planula (Figs. 7-9, 12-15). The 10-h planula is ca. 350 long, 180 /urn wide in the anterior region, 170 ^m wide in the mid region, and 120 ^um wide in the tail (Fig. 15). By 10 h the planula has a distinct anterior end and posterior end. The blastopore is loc
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GASTRULATION IN A HYDROZOAN 33. FIGURE 18. Cross-section through the blastopore region of an 8-h embryo. Microvilli and cilia of migrating cells extend into the space of the blastopore (B). N, nucleus of cell in region of the blastopore. X6700. direction to form a young planula (Figs. 7-9, 12-15). The 10-h planula is ca. 350 long, 180 /urn wide in the anterior region, 170 ^m wide in the mid region, and 120 ^um wide in the tail (Fig. 15). By 10 h the planula has a distinct anterior end and posterior end. The blastopore is located at the posterior pole of the planula and will soon close (Figs. 14, 15). No gastrovascular cavity or mouth is found in the planula at any stage of its development. The 10-h planula will elongate to form a mature planula (24-96 h old depending on temperature) which will attach via its anterior end to a substrate and undergo metamorphosis. DISCUSSION Within the Cnidaria the processes of gastrulation are numerous and vary widely from species to species (Tardent, 1978). Among the anthozoans gastrulation has been reported to occur via either invagination, delamination, multipolar ingression, or a combination of invagination and polar ingression (Tardent, 1978). In scyphozoans gastrulation may occur via invagination, polar ingression, multipolar ingression, or invagination plus polar immigration (Tardent, 1978). In hydrozoans examples of gastrulation by polar ingression, multipolar ingression, and delamination have been reported. However, until now no examples of invagination have been documented (Jagersten, 1972; Tardent, 1978). Jagersten (1972) provided a brief overview of gastrulation in the cnidarians and stated that within the phylum a connection existed between the mode of gastrulation and whether the formed larva was lecithotrophic or planktotrophic. In species which gastrulate via either delamination, multipolar ingression, or unipolar ingression, the. Please note that t
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