Andrey V. Adrianov

Symmetry of priapulids (Priapulida). 1. Symmetry of adults

Priapulids possess a radial symmetry that is remarkably reflected in both external morphology and internal anatomy. It results in the appearance of 25‐radial (a number divisible by five) symmetry summarized as a combination of nonaradial, octaradial, and octaradial (9+8+8) symmetries of scalids. The radial symmetry is a secondary appearance considered as an evolutionary adaptation to a lifestyle within the three‐dimensional environment of bottom sediment. The eight anteriormost, or primary, scalids retain their particular position because of their innervation directly from the circumpharyngeal brain. As a result of a combination of the octaradial symmetry of primary scalids, pentaradial symmetry of teeth, and the 25‐radial symmetry of scalids, the initial bilateral symmetry remains characterized by the single sagittal plane. J. Morphol. 247:99–110, 2001.

Current problems in marine biodiversity studies

This paper deals with a discussion of terminology and six proposed levels of biodiversity. Recent data and estimates were used to compare species and taxonomic diversity of terrestrial, freshwater, and marine organisms. About 1.5 million terrestrial species and 320000 aquatic species are hitherto known. In spite of a long history of research, only about 280000 marine species have been discovered, of which 180000 species are invertebrates. Of 33 metazoan phyla, 31 are found in the sea, 13 of these being exclusively marine. Seventeen metazoan phyla contain freshwater species, and only 11 phyla comprise terrestrial animals. Two phyla (freshwater Micrognathozoa and terrestrial Onychophora) possess no marine species. In this paper, we review the assessment reports on marine biological diversity in coral reefs, coastal ecosystems, macrobenthos, and meiofauna. Recent data on the number of known species are listed for each metazoan phylum; the number of anticipated new species to be discovered is estimated. Deep-sea macrobenthos are believed to comprise about 25 million species; meiofauna seems to be composed of 20 to 30 million species, ten million of whom are marine nematodes. Hypotheses are discussed that can account for the high species diversity of deep-sea macrobenthos and meiofauna.

Taxonomic Study of the Kinorhyncha in Japan. III. Echinoderes sensibilis n. sp. (Kinorhyncha: Cyclorhagida) from Tanabe Bay

Abstract A new species of echinoderid kinorhynch, Echinoderes sensibilis, is described and illustrated using light and electron microscopy. The specimens were collected from masses of the red algae Corallina pilulifera growing in intertidal pools in Tanabe Bay, Honshu Island, Japan. Diagnostic characters of E. sensibilis include the presence of middorsal spines on segments 6–10; lateral spines/tubules on segments 4, 7–12; remarkable trapezium-like subventral fields of minute cuticular hairs on segments 5-12. The positions of numerous sensory spots, large sieve areas, glandular tubes and the shape of terminal tergal and sternal extensions are also diagnostic. All taxonomic characters used for this description are illustrated by SEM. Echinoderes sensibilis constitutes the fifty-eighths valid species of the genus Echinoderes and the fourteenth species described from the Pacific Ocean. This is the third representative of Pacific kinorhynchs found only in the intertidal zone and the first Pacific Echinoderes living on red macroalgae in inter-tidal pools.

Reproduction and development of common species of peanut worms (Sipuncula) from the Sea of Japan

This study deals with the reproduction and development of the most common species of peanut worms from the Sea of Japan: Thysanocardia nigra, Themiste pyroides, and Phascolosoma agassizii. Data on the time of reproduction and larval settlement and the distribution of these species in Peter the Great Bay are provided. The peculiarities of gametogenesis, spawning, and embryonic, larval, and postlarval development are described. The reproductive biology of representatives of these species from the western and eastern Pacific is examined in a comparative aspect.

Symmetry of priapulids (Priapulida). 2. Symmetry of larvae

Larvae of priapulids are characterized by radial symmetry evident from both external and internal characters of the introvert and lorica. The bilaterality appears as a result of a combination of several radial symmetries: pentaradial symmetry of the teeth, octaradial symmetry of the primary scalids, 25‐radial symmetry of scalids, biradial symmetry of the neck, and biradial and decaradial symmetry of the trunk. Internal radiality is exhibited by musculature and the circumpharyngeal nerve ring. Internal bilaterality is evident from the position of the ventral nerve cord and excretory elements. Externally, the bilaterality is determined by the position of the anal tubulus and two shortened midventral rows of scalids bordering the ventral nerve cord. The lorical elements define the biradial symmetry that is missing in adult priapulids. The radial symmetry of larvae is a secondary appearance considered an evolutionary adaptation to a lifestyle within the three‐dimensional environment of the benthic sediment. J. Morphol. 247:111–121, 2001.

A new species of Aspidiophorus (Gastrotricha, Chaetonotida) from the Russian Far East with a key to marine species of the genus

Abstract The Russian gastrotrich fauna is virtually unknown, particularly the marine fauna. In the ocean, investigations have been restricted to the White Sea, from where only three fully described species have been reported so far. In this study we describe a new species of Aspidiophorus found in a sandy sample collected from off of Vladivostok (Peter the Great Bay, Sea of Japan). Aspidiophorus oculatus n. sp. is the first marine chaetonotid gastrotrich described from Russia and the first representative of the order Chaetonotida reported from the Sea of Japan. Specimens of the new species are characterized by a body up to 147.5 µm in total length; enveloped by 57 alternating columns of 65–70 keeled, elongate scales. Pharyngeo-intestinal junction at U27; the head bears cephalion, hypostomion, pleuria and a pair of eye-spots; the furca is 20 µm long including the 12-µm long adhesive tube; the ventral interciliary field is naked, with the exception of a pair of elliptical, keeled scales occurring near the anus. Morphological differences between the new species and the other 13 marine con-generic taxa are discussed. A key to the known marine species of the world based on easily identifiable traits, visible in both living and formalin-fixed specimens is provided.

Microscopic Anatomy and Ultrastructure of Nephridium in the Sipunculan Thysanocardia nigra Ikeda, 1904 from the Sea of Japan

The microscopic anatomy and ultrastructure of nephridium have been studied in the sipunculan Thysanocardia nigra Ikeda, 1904 (Sipuncula, Sipunculidea) from the Sea of Japan using histological and electron microscopic techniques (SEM and TEM). This paper describes ultrastructural features of nephridial epithelium, muscle grid, and coelomic epithelium on the surface of the nephridium, the area of the ciliary funnel, and the “tongue.” Several types of cells were distinguished in the excretory tube of the nephridium: (1) a columnar epithelium of the excretory bunches; (2) a cubical or flattened epithelium of flask-shaped infoldings; and (3) granulocytes that migrate from the coelom to the extracellular matrix of the nephridial wall. The system of podocytes and multiciliary cells were described in the nephridial coelothelium. Two types of secretion of nephridial epithelium have been discovered: a merocrine secretion of columnar cells and an apocrine secretion of cells of the flask-shaped infoldings. Using ultrastructural data, two zones of filtration through the wall of excretory tube have been found, namely (1) the tips of flask-shaped infoldings (via the extracellular matrix and microvillary canals between the epithelial cells) and (2) areas between the flask-shaped infoldings (via the contacts of podocytes, extracellular matrix, and the basal labyrinth of the columnar cells). Unlike previously studied representatives of the genus Phascolosoma, no coelomic epithelium is present on the tips of the flask-shaped infoldings in Th. nigra. This data on the anatomy and histology allow us to conclude that the funnel only works like a gonoduct.

Spermatozeugma and sperm ultrastructure of Thysanocardia nigra, Ikeda, 1904 (Sipuncula; Sipunculidea)

Summary This study presents details of the ultrastructure of spermatozeugmata and spermatozoa of the peanut worm, Thysanocardia nigra, from the Sea of Japan. Spermatozoa are tightly packaged into unencapsulated conical bundles, spermatozeugmata, with as many as 300–350 cells comprising a single packet. Within an individual spermatozeugma, cells are aligned side by side such that head of the bundle is comprised of the heads of spermatozoa and the internal cavity of the bundle harbors numerous flagella that together form a tail for the spermatozeugma. The integrity of the packet appears to be maintained by specialized junctions between adjacent cells. The spermatozeugmata break up when discharged into the sea water. Each spermatozoon is characterized by a rounded head, consisting of the acrosome, nucleus, and midpiece. The midpiece contains mitochondria, centrioles, and some residual cytoplasm that contains dark granules. The method of “sperm packaging” and morphology of spermatozeugmata are unique to the Sipuncula. The ultrastructural modifications of spermatozeugmata are discussed as possible adaptations for the reproductive mode and unique excretory system of sipunculans.

Embryonic and larval development of the peanut worm Themiste pyroides (Sipuncula: Sipunculoidea) from the Sea of Japan

Summary Embryonic and larval development are described for the sipunculan Themiste pyroides from the Peter the Great Bay, the Sea of Japan. The eggs are 120 μm in diameter and coated by a 2 μm thick envelope, with a dense concentration of yolk. Egg cleavage is complete, spiral, and unequal. T. pyroides from the Sea of Japan is characterized by an indirect development with two pelagic larval stages—a lecithotrophic trochophore and a lecithotrophic pelagosphera that is short lived. At the blastula stage, the embryos begin to move in the near-bottom layer of water. At this stage, the embryo resembles a dense sphere with a wide ciliary band extending along its equator. The actively swimming trochophore after 3 days of development metamorphoses to a lecithotrophic pelagic larva, the pelagosphera. The pelagosphera of T. pyroides does not feed but relies on stored yolk, whose large granules are visible in the gut. At day 14, larvae finally settle on the bottom and creep peristaltically. Results of our study of the development of T. pyroides from the Sea of Japan substantially differ from the earlier published data (Rice, 1967) on development of the same species in British Columbia. The species from the East Pacific develops directly within the jelly coat, the embryo hatching from the jelly as a small, crawling worm (see Rice, 1967). These differences correlate with the differences in size of the eggs, time of breeding season and water temperature in the localities of this amphi-pacific species in the East and West Pacific.

Ultrastructural observations on spermiogenesis in the peanut worm, Themiste pyroides (Chamberlin, 1920) (Sipuncula; Sipunculidea)

Summary The process of spermiogenesis and the ultrastructure of the spermatozoa in the peanut worm, Themiste pyroides, from the Sea of Japan were observed with electron microscopy (SEM and TEM). The testes are composed of groups of spermatogonia and are covered by peritoneal cells. Clusters of spermatocytes are released from the testes into the coelomic fluid. Connected by intercellular bridges, the spermatocytes within a given cluster develop asynchronously. Proacrosomal vesicles and a flagellum appear in spermatocytes. Spermatids in the clusters retain the intercellular connections. During spermiogenesis, the acrosomal vesicle, formed by coalescence of small proacrosomal vesicles in the basal part of the spermatid, migrates to the apical part of the cell to form a conical-shaped acrosome. The basal concavity lying above the nucleus is filled with subacrosomal substance. The midpiece contains four mitochondria, two centrioles, and some residual cytoplasm with dark glycogen-like granules. A peculiar annulus structure develops around the base of the flagellum. The distal centriole has a pericentriolar complex consisting of radially oriented elements. Before the spawning process, the spermatozoa are filtered throughout the ciliary nephrostomal funnel into the excretory sac of paired nephridia where they are stored for a short time. The sperm are released into the sea water via nephridiopores. Spermatozoa remaining in the coelomic fluid after spawning are resorbed by amoebocytes. This species from Vostok Bay is characterized by a prolonged spawning period from June to early October. The reproductive strategy of T. pyroides is discussed in comparison with that of Thysanocardia nigra, the latter having a unique pattern of packaging of the spermatozoa, resulting in the formation of spermatozeugmata, as a reproductive adaptation to the very short spawning period.