Wataru Teshirogi

Eggshell formation in polyclads (Turbellaria)

Eggshell formation in polyclads was studied by means of transmission electron microscopy and histochemistry. Shell-forming granules (SFG) in the egg, as well as secretions of shell glands (SGS), play roles in eggshell formation. As the oocytes pass through the portion of the female tract where the shell glands open, they are surronded by a two-layered envelope of SGS. This envelope prevents the dispersion of SFGs discharged after oviposition, and its inner layer participates in eggshell formation with the SFGs. In Pseu-dostylochus sp., most SFGs consist of five parts. Similarities in staining between the parts of the SFGs and the parts of the eggshell indicate that discrete parts of the shell are derived from specific SFG components. Hardening of the eggshell and egg-plate matrix takes place through primary tanning of a sclerotin-like protein.

Analytical studies of the ultrastructure and movement of the spermatozoa of freshwater triclads

The spermatozoa in the testis of three species of triclad turbellarians showed slightly different morphologies from spermatozoa in the seminiferous tubule and ovovitelline duct, and we suggest these differences relate to maturation of the spermatozoa. Glycogen granules could be found in the flagella between the central core and the peripheral doublets of spermatozoa in the seminiferous tubule and ovovitelline duct but only rarely in spermatozoa in the testis, and connections between a third arm of the doublets and the flagellar membrane were detectable only in those spermatozoa in the ovovitelline duct and seminiferous tubule. The movement of spermatozoa also appeared to change with capacitation: spermatozoa isolated from the spermiducal vesicle swam with either the anterior process or the head leading; those within the ovovitelline duct appeared to move with the anterior process leading. The flagellum, with the so-called ‘9 + 1’ axonemal pattern, was observed to divide into nine branches toward its distal end; the central cylinder of the axoneme did not continue into the branches. An acrosome has not been observed in planarian spermatozoa. Rod-like structures and a dense mass lying in the anterior process and suspected of containing an acrosomal substance, could not be shown to produce acrosome-like proteolytic activity.

Comparative morphological studies on the visual systems in a binocular and a multi-ocular species of freshwater planarian

The visual systems of Bdellocephala brunnea Ijima & Kaburaki, a species with two eyes, and Polycelis sapporo (Ijima & Kaburaki), a species with multiple eyes, were investigated using light and electron microscopy. The eye of the binocular species consisted of 40–50 photoreceptor cells and 6–12 pigmented eyecup cells. The eye of the multi-ocular species was smaller and consisted in most specimens of one photoreceptor cell and one pigmented eyecup cell. The ultrastructure of the photoreceptor cells and of the pigmented cells was similar in the two species. Despite differences in numbers of constitutive cells, the arrangement of functional elements in the ocelli of these planarians is the same.

On the origin of neoblasts in freshwater planarians (Turbellaria)

Experiments on 1) regeneration of the cave-adapted planarian, Sphalloplana zeschi, 2) induction of sexuality in an asexual strain of Dugesia japonica japonica by feeding, and 3) culture of dissociated planarian cells, show that neoblasts originate from intestinal cells, i.e. phagocytic cells and granular clubs.

Studies on the speciation of Japanese freshwater planarian Polycelis auriculata based on the analysis of its karyotypes and constitutive proteins

Various kinds of chromosomal polymorphisms or karyotypic variations are found in the Japanese freshwater planarian Polycelis auriculata. Within this species, there are found worms whose chromosome numbers are 2n = 6, 10, 11, 12 and others, and 3x = 6 and 9. There are some which have cells with triploidy and tetraploidy complements (3x = 6 & 4x = 8), and others which have cells with triploidy and hexaploidy complements (3x = 6 & 6x = 12). These worms with such varied karyotypes are usually found in separate habitats, though occasionally they occur together. Electrophoretic analysis of the proteins extracted from the karyotipically different worms which belong to three different local populations shows some dissimilarity in the constitutive proteins according to their karyotypic differences. The results obtained suggest that this species is still in the process of speciation or chromosomal evolution.

Production of cell- and tissue-specific monoclonal antibodies in the freshwater planarian Phagocata vivida

To provide a tool for studying regeneration in planarians, we have produced monoclonal antibodies against a variety of cells and tissues of the freshwater planarian Phagocata vivida (Ijima et Kaburaki). We obtained five kinds of monoclonal antibodies specific, respectively, to 1) the excretory system, 2) nerve cells, 3) rhabdoid-forming cells and body-surface mucus, 4) gastrodermal and epidermal cells, and 5) male germ cells and epidermis.

Further survey of chromosomal polymorphisms in the freshwater planarian Polycelis auriculata

Although the chromosomal number of Polycelis (Seidlia) auriculata Ijima et Kaburaki is basically 2n = 6, this species shows remarkable chromosomal polymorphisms in different populations. Among worms collected at 30 stations in the central part of Japan’s Main Island and in Hokkaido, we found five new karyotypes, considered to be variations of tetraploidy and diploidy: 4n?fis1. + 1 = 3SM + 2A + 3T1 + 2T2 + 4M = 14, 4n?fis2.(B) = 2SM + 2A + 4T1 + 2T2 + 4M + (0-2B) = 14 - 16, 4n?fis2. + 1 = 2SM + 2A + 4T1 + 2T2 + 5M = 15, 4n?fis2.-2 = 2SM + 2A + 4T1 + 4M = 12, and 2nM- = 2SM + 2A = 4 (where SM = submetacentric; A = acrocentric; T1 and T2 = telocentric; M = metacentric; B = B-chromosome; fis1. and fis2. = occurrence of one or two centric fissions, respectively; and M- = deletion of a metacentric chromosome). These karyotypes exist singly in one individual or as various mixoploids within the same individual. No individual having only karyotype 2nM- has yet been found. This brings the total number of known karyotypes in P. auriculata to 17; these can be arranged in an order that we believe reflects their evolution.

Formation of malformed pharynx and neoplasia in the planarian Bdellocephala brunnea following treatment with a carcinogen

The effect of benzo(a)pyrene on regeneration of the pharynx in Bdellocephala brunneaIjima et Kaburaki was studied by inserting a 5-µg crystal of this carcinogen into the pharyngeal cavity of worms from which the pharynx had been extirpated 2 d previously. Multiple pharynges formed in the regenerates, and neoplasia was induced in a few cases. The malformed pharynges appeared as protrusions overlapping the anterior part of the main pharynx. Electron microscopy of the pharynx in normal, intact worms shows eight layers comprising inner and outer ciliated epithelia, muscle, and glands.

Dedifferentiation and redifferentiation of the penis of the freshwater planarian Bdellocephala brunnea

Following decapitation of Bdellocephala brunnea Ijima et Kaburaki and subsequent repeated removal of regenerating head-blastemas, the copulatory apparatus degenerated within 40–60 days. The copulatory apparatus disintegrated into cell clusters that further divided into separate neoblast-like cells that, in turn, eventually transformed into ordinary parenchymal cells by 60 days after decapitation. When the head of worms with a degenerate copulatory apparatus was allowed to regenerate by discontinuing excision of the head blastema, a new copulatory apparatus differentiated, ostensibly from the dedifferentiated cells. The neoblast-like cells appear to participate in the redifferentiation of the penis and of other parts of the copulatory apparatus.