MORPHOGENIC MOVEMENT AND EXPERIMENTALLY INDUCED DECREASE IN NUMBER OF EMBRYONIC SEGMENTS IN THE JAPANESE HORSESHOE CRAB,TACHYPLEUS TRIDENTATUS

Chelicerata

“…The initial germ anlage commonly forms all prosomal segments (pre-cheliceral lobe, cheliceral, pedipalpal, and the four walking leg segmentsPl, Ch, Pp, L1-L4), and a differing number of opisthosomal segments are added sequentially segmentation is found in spiders, harvestmen (Juberthie 1964 ), whip scorpions (Anderson 1973 ), Amblypygi (Weygoldt 1975 ), ticks (Anderson 1973 ;Santos et al 2013b ), and pseudoscorpions (Yoshikura 1975 ). However, horseshoe crabs, scorpions and pycnogonids form only pre-cheliceral lobes and cheliceral and pedipalpal segments as well as a SAZ from their embryonic primordium, while walking leg segments and opisthosomal segments are then sequentially added from the SAZ (Anderson 1973 ;Itow and Sekiguchi 1980 ;Farley 2001 ;Brenneis et al 2011b ).…”

Induction of Secondary Embryos by Intra‐ and Interspecific Grafts of Center Cells under the blastopore in Horseshoe Crabs

“…The medial body axis of the secondary embryo was sometimes oriented in the opposite direction from that of the host embryo. This characteristic differed from that of double and triple embryos which were induced by electrocauterization and cell dissociation (8), where the posterior ends of the induced double and triple embryos faced the point where the center cells had existed. Besides, in the secondary embryos induced by grafting, the joining zone was often observed in the region between the host embryo and the secondary one (Fig.…”

“…When the cell mass is divided into two or three pieces by electrocauterization or cell dissociation, the treated embryo develops into double or triple embryos (12,8).…”

Effect of the Glutamine-Analogue "Azaserine" on Embryonic Development of the Horseshoe Crab. (azaserine/inhibition of cell growth/morphogenesis/separation of embryonic area/horseshoe crab)

“…During the morphogenic movement during stages 10 and 12, the embryonic area of the horseshoe crab lengthens posteriorly and anteriorly. The 2nd and 3rd prosomal segments are formed in the central region of elongation (6). The embryonic areas of embryos treated with azaserine were separated in the central region of elongation, and the embryos became monsters in which embryonic areas were separated mainly at the 2nd and 3rd prosomal segments.…”

“…The cells in the lateral region of the peripheral area of the germ disc migrate to the anterior area and cells move posteriorly and anteriorly along the median body axis. The 2nd and 3rd prosomal segments are formed in the central region of elongation of the embryonic area (6). The embryonic areas of embryos treated with azaserine were separated in the central region and developed into separate monsters (Fig.…”