アサリのヤドリガニのゾイア期に就いて

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The pea-crab Pinnotheres latissimus B?URGER occurs frequently in Hakata Bay living commensalistic with a pullet, PaNhia (Tapes) philippinarum. Berried crabs are to be found in summer, the zenith of the season falling in July. The eggs are of apricot orange colour, changing to cream yellow when ready to hatch out. Early eggs measure 0.33 mm in diameter, late eggs 0.42 mm. Berried crabs taken out from bivalves were reared in fingerbowis containing some seawater and sand. Pre-zoea hatched out from the eggs would still remain on the abdomen of the mother crab. Pre-zoea : 1.15 mm long; antennules and antennae rudimentary, abdomen with 5 segments plus telson ; telson with 3 lobes of the F1-type. Pre-zoea cast the embryonic cuticle and become first zoea. First zoea : 1.2 mm long. At first it comes up to the surface of water, then in one day or two it descends to the bottom curling up its body in the shape of a ball. Carapace rounded, without spines, antenna rudimentary stumps of the D-type; first and second maxillipeds with 4 swimming hairs on the exopodites, endopodites with 5 and 2 joints respectively; abdomen with 5 segments plus telson, second and third segments with lateral knobs. Second zoea have all the features similar to those of t h e first zoea, except the differentiated mouth parts. Hair formula : 3-4?n, 4, 3-0. The following 4 characters are observed as stable: I. Spines totally absent. 2. Antenna of the D-type. 3. Telson of the F,-type. 4. Hair formula: 3-4?n, 4, 3-0. Comparing these points in all the species of Pinnotheres hitherto reported one can find that they all have antenna of the D-type and telsons of the F,-type. Thus Pinnotheres is distinguished from the other genera only by two characters of the antenna and telson. The other two stable features of zoea serve to distinguish the species inside the genus Pinnotheres.1. 博多灣のアサリに共棲するヤドリガニ Pinnotheres latissimus B?URGER のゾイアを觀察した。2. 抱卵の雌は博多灘に於いて6月乃至9月に互つて見られるが7月に最も多い。3. 前期ゾイアは孵化後も尚母體の腹部に止まつてゐる。4. 前期ゾイアの甲殼は不定形をなし, 第1・第2觸角は明かでなく, 腹部は5節と尾節とから成り, 尾節は特殊のF1型をなす。5. 第1期ゾイアは趨光性を有する。腹部を曲げて球形となり下層に沈む。甲殼は棘を有せず圓形である。第2觸角はD型をなす。腹部は前期ゾイアと同樣に5節と尾節とからなり, 第2及び第3環節の側方に瘤状突起を生ずる。6. 第2期ゾイアは第1期ゾイアと殆ど同じ形状をなすがロ器の分化が著しい。毛式: 3-4-n, 4, 3-0 7. 各ゾイア期を通じて安定した形質は次ぎの4つである。(i) 甲殼に棘が全くない (ii) 第2觸角はD型 (iii) 尾節はF1型 (iv) 毛式: 3-4-n, 4, 3-0. 8. 今迄に報告された Pinnotheres 屬各種のゾイアに就いて7に掲げた形質を比較すると此屬のゾイアは第2觸角D型と尾節F1型とが共通であるが故に兩者によつて他屬と區別し得る。從つて種の區別は甲殼の棘と毛式とに依つてなされる。
九州帝國大學農學部の論文
1935-07-00

著者

三宅貞祥
日本甲殻類学会

アサリのヤドリガニのゾイア期に就いて

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