S. Sh. Dautov

Structure and properties of hyaline spheres in holothuroid larvae

Summary The structure of the hyaline spheres (HS) in the larvae of the holothuroids Parastichopus californicus and Stichopus japonicus was examined by electron microscopy, and their sensitivity to a range of hydrolytic enzymes was tested. The HS are attached to epithelium and extend into the blastocoel. They consist primary of extracellular material but scattered cells surround them, and a few are found within matrix. Ultrastructurally, the matrix has a gel-like appearance and contains fine granules and fibrils. HS are dissolved very specifically by hyaluronidase (10 mg/ml, pH 5.4). Pronase, trypsin and papain at the same concentration damage both HS and the larval body to varying degrees. Surprisingly, HS sink when isolated from the larval body, so it is unlikely they serve as flotation devices. It seems more likely they serve as storage of structural elements utilized after metamorphosis.

Hyaline spheres in auricularia of Stichopus japonicus

Summary The hyaline spheres (HS) in auricularia of Stichopus japonicus consist of extracellular material in which solitary cells are present. This extracellular material can be stained by dyes for lipids. There are no membranes or other structural elements in HS. The cells within HS are most probably responsible for secreting the extracellular material. HS are not embryonic inductors of the ciliary rings which appear during metamorphosis. They probably store nutrients which permit larvae to complete metamorphosis successfully, but this remains to be established.

Ultrastructural Peculiarities of the Embryogenesis of the Brittle Star Amphipholis kochii (Lütken, 1972)

This paper addresses morphogenetic processes and cell differentiation during embryogenesis of the brittle star Amphipholis kochii at the ultrastructural level. The radial cleavage is not strictly determined. Embryos are covered with a thick hyaline envelope and contain numerous yolk granules and small lipid drops. Blastulae feature a thick blastoderm with extensive intercellular cavities, which are retained in the crest epithelium of late gastrulae. Embryonic cells have single cilia with long cross-striated rootlets associated with the Golgi apparatus. Depolarized cells of the primary mesenchyme with a well-developed rough endoplasmic reticulum differentiate into sclerenchyme syncytium. Gastrulation occurs by invagination. Secondary mesenchymal cells emigrate from the archenteron tip to differentiate into amebocytes, which contain a well-developed Golgi apparatus and numerous mitochondria. The endoderm is formed of cubic cells with numerous yolk granules and rare microvilli. Flattened cells of the dorsal and ventral ectoderm contain a small amount of yolk. Yolk utilization during embryogenesis occurs by intracellular lysosomal digestion with selective exocytosis of toposomes.

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) μm, 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 μm and from 1490 to 1567 μm, respectively. The factors affecting the fecundity of grass shrimp in Izmeny Bay are discussed.

Development of the sand dollar Scaphechinus mirabilis

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.

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.

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.

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.

The morphology of the apical organ and adjacent epithelium of pilidium prorecurvatum, a pelagic larva of an unknown heteronemertean (Nemertea)

The morphology of pilidia ex gr. recurvatum from Peter the Great Bay (Sea of Japan) was studied by confocal laser scanning and transmission-electron microscopy. The studied pilidium larvae differ from pilidium recurvatum in lacking a posterior ciliary ring and by the presence of a caudal tuft. On this basis, pilidiumprorecurvatum is proposed as a new name for the lavae. The apical organ of pilidium prorecurvatum is represented by a thickened epithelium, which consists of uniform columnar monociliary collar cells and is innervated by a pair of serotonergic intraepithelial neurons. The bodies of the serotonergic neurons are located outside of the apical organ, but occasional axons were found at the organ base. The rest of the pilidial epithelium is represented by flattened polygonal multiciliated cells with sparse microvilli; the bodies of two neurons lie in the helmet epithelium immediately adjacent to the apical organ. Morphologically, the apical organ of the pilidium corresponds well to that of other lophotrochozoan larvae, but their homology remains unclear.

Formation and ultrastructural organization of gonads in Oikopleura gracilis Lohmann, 1896 (Urochordata: Appendicularia)

This study deals with the formation and ultrastructural organization of the gonads in a common species of appendicularian, Oikopleura gracilis, from Peter the Great Bay. Light microscopy observations show that the gonads develop from a transparent primordium that is located in the basolateral part of the gonad cavity; the primordium increases in size in the process of development and differentiates into the testis and ovary. The testis is covered by a single layer of ultrastructurally uniform follicular epithelium and contains a population of proliferating male gonocytes. The ovary contains two types of germ line nuclei, which are large polyploid nuclei that belong to the auxiliary cells and small meiotic nuclei of the oocytes. The two nuclei types, together with a common cytoplasm, form a syncytium of the ovary, or the coenocyst. As in the dioecious Oikopleura dioica, the coenocyst of O. gracilis produces naked oocytes that are devoid of a type III follicular membrane. The coenocyst is covered by a single-layered follicular epithelium, in which two cell types can be distinguished ultrastructurally. Thus, the synchronous maturation of sex products in O. gracilis is achieved by the formation of the germ-line syncytium in the testis and the coenocyst in the ovary, which generates a large number of simultaneously ripening oocytes that are competent for fertilization.