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huang hai de ma ding hai zhi chong ji qi you chong fa yu
Pages: 25-34
Year: Issue:  1
Journal: Oceanologia et Limnologia Sinica

Keyword:  稚虫刚毛幼虫发育口前叶图版体节黄海肛节围口节后担轮幼虫;
Abstract: 1. This paper presents the results of a study of the morphology and larval development of Spio martinensis Mesnil collected from the littoral zone of the Yellow Sea and of a comparison of it with that of the closely related Spio filicornis (O. F. Muller).2. S. martinensis is most abundantly distributed in the Yellow Sea (Tsingtao, Ya'n-tai, Dairen and Peitaiho). Judging from its geographical distribution, it can be considered as a warm-temperate species. Its density in the littoral zone of Tsingtao is 132 specimens per square meter, while its biomass is 200 gms per square meter.3. Notes on the larval development:(a) Adult worms live in soft sandy tubes in sand between low and high tide marks. The breeding season of the worm lasts from the middle to the end of May. Egg masses collected from the tubes are already in the metatrochophore stage (Pl. Ⅱ, fig. 1). Their earlier stage of development has not been observed.(b) 15 hours later, the metatrochophore is 0.20 mm long and 0.14 mm broad at the prototroch (Pl. Ⅱ, figs. 2, 3), with a darker vesicle near the centre. There is a pair of orange eyes. The prototrochal cilia lengthen, forming a ciliated bundle extending toward both the dorsal and ventral sides. The first bristle bundles have by this time appeared.30 hours later, it is 0.21 mm long and 0.14 mm wide (Pl. Ⅱ, fig. 4). There is still only one pair of eyes. The second bristle bundles have then appeared.(c) Two days later, the larvae are liberated from the egg mass, swim very actively in the culture dishes and have grown to about 0.33 mm long and 0.16 mm wide (Pl. Ⅱ, figs. 5, 6). A pair of tactile cilia is found at the anterior end of the body. Another two pairs of eyes appear. There are three pairs of orange (light-reflecting) chromato-phores. Gastrotrochs are found in the 2nd and 3rd setigers.Two days after liberation, the larva is 0.40 mm long and 0.19 mm wide (Pl. Ⅱ, figs. 7, 8). The larval setae are very long.Six days after liberation, the larva reaches the stage shown on Pl. Ⅱ, figs. 9, 10. The larva is now 0.52 mm long and 0.19 mm wide. The nuchal organ, neurotroch and ciliated pit have appeared. There are 6 pairs of chromatophores.Ten days after liberation, it is 0.67mm long and 0.20mm wide (Pl. Ⅱ, fig. 11; Pl.Ⅲ, fig. 12). The palpi appears. The gastrotrochs are present on the 3rd, 5th, 7th and 9th setigers.18 days after liberation, the larva is ready to metamorphose (Pl. Ⅲ, figs. 14, 15). In the 16-segment stage, it is 0.80 mm long and 0.20 mm wide. The palpi becomes more elongated. They are provided with orange (light-reflecting) chromatophores. The parapodial cirri, both dorsal and ventral, develop early. Two rows of obliquely orientated "bacillary glands" are formed. Nototrochs are developed on the dorsal surface of all segments from the second to the fifteenth setigers. Ventral hooded hooks are found from the 11th setiger onwards. The stomach is pigmented yellowish-green, while the other parts of the digestive canal are unpigmented.28 days after liberation, the larva reaches the young benthonic stage shown on Pl. Ⅲ, fig. 16. The larva is now 1.34 mm long and 0.24 mm wide. The chromatophores persist for a very long time, but are finally reduced. Branchiae are found in the 1st setiger and the four succeeding ones. The nuchal organs develop into the genetically typical horseshoe-shaped structure, and eventually include the nototroch in 2nd setiger.4. This species is closely related to S. filicornis, but they are different from each other as shown by a comparison of their characteristics in the following table:Characteristic featuresS. martinensis Mesnil5. filicornis (O. F. Muller)1. Nuchal organs2. Nototrochs3. Ventral hooded hooks4. Reproductive temperature5. Habitatpresenttwo rows of ciliated cells13th, tridentate16-17℃(warm-temperate species)clean medium sandabsentone row of ciliated cells10th, bidentate0-1℃ (subarctic species)muddy bottom in the Zostera or Phyllospadix region
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