The larvae of Diadema setosum (Leske, 1778) (Camarodonta: Diadematidae) from South China Sea

Abstract

Diadema setosum (Leske, 1778) develops from small isolecithal eggs with a diameter of 84 ± 3 μm. Embryonic development took about 6.5–7 h and finished when a blastula left the fertilization envelope and became a larva. At this stage, the first pigment cells had appeared. At 23 h a prism developed; at 44 h a pluteus with one pair of arms had appeared; at 45 h of development plutei had two pairs of arms. The pigment cells colour the pluteus of D. setosum dark red. When 20-day-old larvae were mechanically stimulated, they flared their arms which may be defensive behaviour. During further development, the post oral arms of plutei grew to 1900 μm or more. Metamorphosis took place at about 40–45 days. At this time, five primary ambulacral podia were visible within the larval body. The duration of metamorphosis from the moment of larval settlement until the juvenile sea urchins began to move along the bottom was 40–60 min. The diameter of the test of the newly metamorphosed juvenile sea urchins was about 500 μm.     

Foraging conditions of planktotrophic larvae of echinoderms in the southwestern part of Peter the Great Bay of the Sea of Japan

Foraging of planktotrophic larvae of echinoderm common species in the Peter the Great Bay (Sea of Japan) was estimated on the basis of distribution of phyto- and meroplankton. The diversity and abundance of phytoplankton in the studied area in summer months were shown (141 algae species; abundance—up to 743000 cells/m³; biomass—more than 2.7 g/m³ of fresh weight). It was found that in Peter the Great Bay the diet of echinoderm larvae depended on their feeding behavior, duration of their pelagic stage, and abundance and size composition of phytoplankton, included up to several micrograms of fresh algae per larva.     

Distribution, species composition, and dynamics of echinoderm larvae in an area of the Tumen River Estuary and of the Far East State Marine Reserve

Species composition, distribution, and density dynamics of echinoderm larvae were determined based on four samples taken at 28 stations in the summer-autumn season of 1997 in an area adjacent to the Tumen River Estuary and to the Far East State Marine Reserve. Larvae of nine species were recorded. The larvae ofOphiura sarsi (up to 9600 ind./m³) and ofEchinocardium cordatum (2058 ind./m³) were dominant in terms of density. The echinoderm larvae mostly appeared in the upper water layer (0–15 m). The study area can be divided into two sites based on the density and species composition of echinoderm larvae: the first to the south of Furugel'ma Island, where the density and species number were low, and the second to the north of Furugel'ma Island, where these parameters had higher values.     

Distribution of echinoderms and their larvae in the southwestern Peter the Great Bay, Sea of Japan

Based on results of processing planktonic and benthic samples collected in 1996 and 1997, a spatial distribution of echinoderms in the bottom and of their larvae in the plankton were collated for the water area of the Southern region of the Far Eastern State Biosphere Marine Reserve. Some correlation between distributions of the adult and larval sea star Asterias amurensis in July was revealed. At the same time, there was no correlation between distributions of larvae and adult individuals of the brittle star Ophiura sarsi and sea urchin Echinocardium cordatum, which are most abundant in the area. The size structure of bottom populations of the brittle stars O. sarsi and Amphiodia fissa in the studied area was assessed. The correlation coefficient between the distribution of young-of-the-year and the population density was 0.47 in O. sarsi and 0.74 in A. fissa respectively, which implied a selective settling of larvae of those species in areas inhabited by adult brittle stars. Recruitment of bottom populations from 1996 spawning was 5% in O. sarsi and 3.3% in A. fissa.     

Development of the sand dollar <Emphasis Type="Italic">Scaphechinus mirabilis</Emphasis>

Under laboratory conditions, the development of larvae of the sand dollar Scaphechinus mirabilis (Agassiz) took 28.5–29 days from fertilization to settling and the end of metamorphosis at a temperature 20°C and salinity 32.2–32.6‰ The cleavage divisions were completed in 12 hours after fertilization (AF) by the release of free swimming ciliary blastula from the egg membrane. The larvae attained pluteus I stage with one pair of arms at an age of 40 hours. In 4.5–5 days the pluteus II stage with three pairs of arms, and in 9 days the pluteus III stage with four pairs of arms were formed. On the 20–21st day AF the larvae developed a vestibule, in which the adult skeleton rudiments, spicules, plates and pedicellariae were formed on the 26–27th day AF. The size of the larvae at an age of 22.5 days was 1064.3 ± 44.7 μm. The settling of larvae was recorded on the 28–29th day of development. Most of the larvae completed their metamorphosis in 4.5–5 hours after settling.     

Fecundity of the Grass Shrimp,Pandalus kessleri (Decapoda: Pandalidae), near the Southern Kuril Islands

We determined the absolute (AIF) and relative (RIF) individual fecundity in a commercially important object, the grass shrimp, Pandalus kessleri (Decapoda: Pandalidae) near the Southern Kuril Islands. In the shrimps from Izmeny Bay (Kunashir Island) and the coastal area of the Southern Kuril Islands, the AIF equaled 192–918 (averaging 505) and 162–784 (459), respectively. In larger females, the AIF increases, reaches the maximum value, and then decreases again in the largest females. In June the AIF is smaller than in September, and in larger prawns, this difference is more pronounced. The mean large (D) and small (d) diameters of eggs equaled 1972 (1665–2400) and 1538 (1347–1900) m, respectively; the D/d ratio equaled 1.28. The mean wet weight of an egg (w) was 3.43 mg (1.986–4.9) mg. From September 1 to November 30 D and d increased from 1894 to 2088 m and from 1490 to 1567 m, respectively. The factors affecting the fecundity of grass shrimp in Izmeny Bay are discussed.     

Cell differentiation during the larval development of the ophiuroid <Emphasis Type="Italic">Amphipholis kochii</Emphasis> Lütken, 1872 (Echinodermata: Ophiuroidea)

The differentiation of the ectodermal, entodermal, and mesodermal cell lines in developing plutei of the ophiuroid Amphipholis kochii was examined using electron microscopy and the immunochemical staining technique. The ectodermal cells form the pseudostratified epithelium of the ciliary band, the flattened epithelium of the body wall, and the esophageal epithelium. The epithelium of the ciliary band consists of ciliated and mucous cells; at its base is an axonal tract formed of the processes of neurons. The serotoninergic neurons form two lateral ganglia located along the paraoral ciliary band and the posterolateral arms’ ciliary band. The prominent features of the neurons are large size, the presence of a cilium, an electron-light cytoplasm filled with microvesicles with neurotransmitters, and a large nucleus with a predominant euchromatin. The ectoderm cells (except mucous cells) are characterized by the presence of a cilium surrounded by a collar of microvilli and a thin layer of apical extracellular matrix. The entodermal cells form the digestive tract epithelium and differentiate into four cell types: type I and II cells probably function in the nutrient uptake and assimilation; type III cells perhaps secrete digestive enzymes; and myoepithelial cells that constitute the cardiac and pyloric sphincters and the anus. Sclerenchymatous cells, which are the descendants of the primary mesenchyme, form a syncytium around the developing spicules. The biomineralization process is intrasyncytial, the ophioplutei spicules retain the cytoplasmic covering throughout the period of larval development. The secondary mesenchyme gives rise to smooth muscle cells and amebocytes. Muscle cells compose the circumesophageal musculature, the cell processes of each “muscle band” seem to fuse together. At the base of the preoral band are two symmetrically located groups of muscles, viz., the anterior dilators. Amebocytes function in excretion either near the epidermis or are able to penetrate through the epidermis and excrete wastes into the external environment. The mesoderm formed by the enterocoely gives rise to three pairs of coeloms; their cells remain unspecialized during the entire period of larval development. Results of this study are compared with the micro- and neuroanatomy of the larvae of other echinoderms.     

Structure of the digestive tract of tornaria larva inEnteropneusta (Hemichordata)

The ultrastructure of the digestive tract of tornaria larva of enteropneusts was investigated. It showed that the digestive tract consists of three parts: esophagus, stomach, and intestine. The esophagus epithelium consists of two types of multiciliated epithelial cells and solitary muscle cells. Axonal tracts and neurons were found in the ventral wall of the esophagus. The cardiac sphincter contains an anterior band of strongly ciliated cells and a posterior band of cells with long vacuolized processes which partition the sphincter lumen. The stomach consists of three cell types: (1) cells with electron-opaque cytoplasm, bearing a fringed border on their apical sides; (2, 3) sparse cells with electron-light cytoplasm and different patterns of apical microvilli. Cells of the pyloric sphincter bear numerous cilia and almost no microvilli. The intestine consists of three parts. The anterior part is formed of multiciliated cells which bear the fringed border. The middle part consists of flattened cells bearing rare cilia and vast numbers of mace-like microvilli. The posterior part of the intestine is formed of cells bearing numerous cilia and few microvilli. Muscle cells were not found in either stomach or intestine epithelium. One noticed that the structure of the digestive tract of enteropneust tornaria larva differs from that of echinoid pluteus larva.