The Company of Biologists LimitedActa Medica Okayama0022-0949205222002Hatching controlled by the circatidal clock, and the role of the medulla terminalis in the optic peduncle of the eyestalk, in an estuarine crab Sesarma haematocheir34873504ENMasayukiSaigusaEmbryos attached to the female crab Sesarma
haematocheir hatch synchronously within 1 h. Hatching is also synchronized near the time of the expected nocturnal high tide. These events are governed by a single circatidal clock (or pacemaker) in the female crab. The present
study examined the role of the optic peduncle of the eyestalk on hatching and hatching synchrony. Surgery was performed either from the tip of the eyestalk [to remove the region of the optic peduncle from the compound eye–retina complex to the medulla interna (MI)] or from a small triangle 'window' opened on the eyestalk exoskeleton [to create lesions on the medulla
terminalis (MT) of the optic peduncle]. Neither hatching nor hatching synchrony was affected by removal of the region of the optic peduncle from the compound eye–retina complex to the MI: the circatidal rhythm also remained. Removal of the MI probably caused damage to the sinus gland and the bundle of axons running from the sinus gland to the X organ. Nevertheless, maintenance of
highly synchronized hatching indicates that the X
organ–sinus gland system is not related to hatching. Hatching and hatching synchrony were not affected by dorsal-half cuts of the MT: the timing of hatching was not affected either. By contrast, transverse and ventral-half cuts of the MT caused severe damage to most females;
hatching of many females was suppressed, while hatching of some females was either periodic, at intervals of approximately 24 h, or arrhythmic for a few days. The bundle of neuronal axons is tangled in the MT, and the axons inducing hatching pass through the ventral half of
the MT. Complete incision of these axon bundles may have suppressed hatching. Incomplete incision of the axon bundle or partial damage to the neurons may have caused periodic or arrhythmic patterns of hatching. There are
two possible roles for MT in hatching. One possibility is that neurons in the MT only induce hatching under the control of the circatidal pacemaker located in a site
somewhere other than the optic peduncle. Another
possibility is that the circatidal pacemaker is actually present in the MT. The second possibility seems more plausible. Each embryo has a special 48–49.5 h developmental program for hatching. This program could be initiated by the circatidal pacemaker in the female, and
hatching synchrony may also be enhanced by the same pacemaker.No potential conflict of interest relevant to this article was reported.Acta Medica Okayama20742004Purification and cDNA cloning of the ovigerous-hair stripping substance (OHSS) contained in the hatch water of an estuarine crab Sesarma haematocheir 621632ENOlegGusevHidekiIkedaTetsushiOkochiJae MinLeeMasatsuguHatakeyamaChiyokoKobayashiKiyokazuAgataHidenoriYamadaMasayukiSaigusa<p>The egg attachment system of an estuarine crab
Sesarma haematocheir is formed on the maternal
ovigerous hairs just after egg laying, and slips off these
hairs just after hatching. The stripping is caused by an
active factor that we call OHSS (ovigerous-hair stripping
substance), which is released by the embryo upon
hatching. OHSS was purified, and its active form had a
molecular mass of 25·kDa. The cDNA of OHSS cloned
from an embryonic cDNA library was 1759·bp long,
encoding 492 amino acids in a single open reading frame
(ORF). The C-terminal part of the predicted protein was
composed of a trypsin-like serine protease domain, with
homology to counterparts in other animals of 33–38%.
The predicted protein (54.7·kDa) secreted as a zymogen
may be cleaved post-translationally, separating the Cterminal
from the N-terminal region. The OHSS gene was
expressed in the embryo at least 2 weeks before hatching.
Expression was also detected in the zoea larva 1 day after
hatching and in the brain of the female. However, it was
not detected in the muscle, hepatopancreas or ovigerous
seta of the female. Ultrastructural analysis indicated that
the material investing maternal ovigerous hair, i.e. the
outermost layer (E1) of the egg case, is attached at the
special sites (attachment sites) arranged at intervals of
130–160·nm on the hair. It is suggested that OHSS acts
specifically at these sites, lysing the bond with the coat,
thus disposing of the embryo attachment system. This
enables the female to prepare the next clutch of embryos
without ecdysis.</p>
No potential conflict of interest relevant to this article was reported.岡山実験動物研究会Acta Medica Okayama61988海産生物における実験動物化について思うこと3337ENMasayukiSaigusaNo potential conflict of interest relevant to this article was reported.岡山実験動物研究会Acta Medica Okayama91992瀬戸内の森と林―自然林の生育とその生態的機能を考える―612ENMasayukiSaigusaNo potential conflict of interest relevant to this article was reported.岡山大学理学部地球科学教室Acta Medica Okayama1340-7414912002西表島船浦湾におけるマングローブ干潟の堆積環境 ―堆積物と生物遺骸の保存状況について―918ENHiroyukiAzumaMasayukiSaigusaHiroshiFukudaThe distribution of conch shell contained in clastic sediments in the mangrove swamps in the Funaura Bay, Iriomote Island, Okinawa Prefecture was studied. The sediments in the mangrove swamp are mainly composed of up to 90% sands. The sand clasts are inferred to be derived from the sandstone of Miocene Yaeyama Group. The conch shells are richer in the muddy fraction than the sandy fraction. Many Terebralia palustris inhabit the mangrove swamp. However few dead shells were also observed in the sediments. Effect of selective transportation hermit crabs is considered to be the cause of this distribution.No potential conflict of interest relevant to this article was reported.