Robert B. Short

Karyotype evolution and sex chromosome differentiation in schistosomes (Trematoda, Schistosomatidae)

The morphology of C-banded metaphase chromosomes has been studied in two hermaphroditic and ten gonochoristic digenetic trematodes (schistosomes). Comparison of numbers and morphology of chromosomes indicates that the karyotype of primitive trematodes probably was composed of 10 (or 11) pairs of telocentric or subtelocentrie chromosomes, and reduction of chromosome numbers in advanced species resulted from centromeric fusion rather than elimination of chromosomes. Observation of heteromorphic chromosomes in a hermaphroditic trematode (Spirorchis) suggested a differentiation of “pre-sex” chromosomes in species ancestral to dioecious trematodes which possess distinctly differentiated sex chromosomes. Our results indicate that differentiation of Z and W chromosomes in the gonochoristic trematodes resulted from: (a) partial constitutive heterochromatinization of the W chromosome (Schistosoma mansoni and S. haematobium complexes, African schistosomes), (b) deletion of part of the W (S. japonicum and S. mekongi, Asian schistosomes), and (c) translocation of part of one sex chromosome onto another (Schistosomatium douthitti and Heterobilharzia americana, American schistosomes) with subsequent heterochromatinization of the W in H. americana.

Fine structure of possible photoreceptor in cercariae of Schistosoma mansoni.

Two structures near the anterior end of cercariae of Schistosoma mansoni are interpreted as possible photoreceptors. Each appears to be ovoid and is composed of a thin cytoplasmic wall surrounding a cavity which contains lamellae. The lamellae are extensions of modified cilia which arise from the inner wall of the cavity.

Identification of sex of schistosome larval stages

Sex of Schistosoma mansoni cercariae was identified by a C-banding technique; interphase nuclei of females exhibited W-chromatin (heterochromatin of the W chromosome) whereas those of males did not. Similar sexual dimorphism was also shown in nuclei of S. mansoni miracidia, sporocysts, and adult worms. Cercariae of the following schistosomes could not be sexed by examination of nuclei after the C-band technique: S. japonicum, S. haematobium, and Schistosomatium douthitti . The method presented was 100% accurate and relatively rapid (total time for S. mansoni cercariae: 80 min).

CONVENTIONAL GIEMSA AND C-BANDED KARYOTYPES OF SCHISTOSOMA MANSONI AND S. RODHAINI

The karyotypes of a Puerto Rican strain of Schistosoma mansoni and a Kenyan strain of S. rodhaini are similar in number of general morphology. For each species there are eight pairs of chromosomes (2n =16) which are divided into three size groups. C-banded methods revealed, in addition to centromeric heterochromatin, a large heterochromatic block in one for the No. 2 chromosomes in females but not in the other. Neither No. 2 chromosome of males possessed the heterochromatic block. This pair (2) is interpreted as the sex chromosomes, with the female being heterogametic (ZW), the male homogametic (ZZ). Differences between karyotypes of the two species occurred. These included a satellite on the No. 3 chromosome of S. mansoni and a euchromatic tip on the otherwise heterochromatic short arm of the W chromosome of this species; neither of these was present in S. rodhaini. The two species also differed in that the centromeric index of the Z of S mansoni was smaller than that of the W, whereas in S rodhaini the reverse was true. In S. mansoni the large heterochromatic block of the W chromosome was identified in prophase and interphase nuclei as well as at metaphase.

Conventional Giemsa-stained and C-banded chromosomes of seven strains of Schistosoma mansoni.

Karyotypes stained with conventional Giemsa and with a C-banding method were compared among 7 strains of Schistosoma mansoni: 2 from Puerto Rico and 1 each from St. Lucia, Brazil, Venezuela, Egypt, and Kenya. A few differences were noted in relative lengths and centromeric indexes, but overall karyotypes of all strains were similar, with 2n = 16. The W chromosome of the female of all strains had a relatively large heterochromatic block, distinguishing the female from the male karyotype.

TWO NEW SPECIES OF DICYEMENNEA (MESOZOA: DICYEMIDAE) FROM KAIKOURA, NEW ZEALAND*

Dicyemennea kaikouriensis is described from Octopus maorum and D. rostrata from Rob- sonella australis. Both hosts were collected near Kaikoura Peninsula, South Island, New Zealand. The peripheral cell number of vermiform stages of both species is typically 23. Nematogens and rhombogens of D. kaikouriensis are stocky, with relatively large calottes. Largest nematogens were about 428 to 683 , in length; largest rhombogens measured about 800 to 1,050 /,. Vermiform embryos of this species lack an abortive axial cell and reach about 90 to 100 /t at eclosion. Infusoriform larvae lack solid refringent bodies and are composed typically of 37 cells (33 somatic, 4 germinal). Nematogens and rhombogens of D. rostrata have more elongate bodies; larger specimens have expanded, disk-shaped or flowerlike cephalic enlargements which are composed of calotte and parapolar cells. Largest nematogens of this spe- cies seldom exceeded 1,500 , in length; largest rhombogens measured about 1,778 to 2,376 t, in length. Vermiform embryos have an abortive axial cell; they are sharply pointed anteriorly and reach about 175 to 270 L at eclosion. Infusoriform larvae possess solid refringent bodies and are composed typically of 39 cells (35 somatic, 4 germinal).

DICYEMA TYPOIDES SP.N. (MESOZOA: DICYEMIDAE) FROM THE NORTHERN GULF OF MEXICO.

Dicyema bilobum sp. n. is described from Octopus vulgaris collected off Pensacola, Florida, USA. This species is characterized by: nematogens and rhombogens seldom longer than 370 and 600 4, respectively; somatic cell numbers of 16, 17, and 18 (rarely 15 and 19); axial cell extending to propolars; a distinct groove separating propolar cells from metapolars in some older vermiform individuals. This is the sixth species of dicyemid reported from the eastern coast of the United States and the Gulf of Mexico. To date only five species of dicyemid mesozoans have been reported from the Atlantic and Gulf coasts of the United States: Dicyema aegira McConnaughey and Kritzler, D. typus van Beneden, D. briarei Short, D. hypercephalum Short, and D. apalachiensis Short. D. aegira and D. typus were reported from Octopus vulgaris from the east coast of Florida (McConnaughey and Kritzler, 1952) and D. aegira from the same host in the Gulf of Mexico (Short, 1957). D. hypercephalum and D. apalachiensis were reported from O. joubini from the northern Gulf of Mexico (Short, 1962) and D. briarei from O. briareus in the Florida Keys. The present paper describes a new species of Dicyema recovered from four specimens of Octopus vulgaris (mantle lengths: 11, 12, 15, 16 cm) collected in 1963 from near Pensacola, Florida. The description is based on living specimens as well as material on stained coverslip smears fixed in Bouins fixative and stained with iron hematoxylin and eosin. All drawings were made with the aid of a camera lucida. Dicyema bilobum sp. n. (Figs. 1-30) Description: Dicyema: Mature vermiform phases relatively small; majority of nematogens less than 370 /L, rhombogens usually no longer than 600 t. Lengths of ten longest nematogens observed ranged from 432 to 610 m5. Ten longest rhombogens ranged in length from 514 to 802 z. Total number of somatic cells 16, 17, and 18 (rarely 15 and 19) (Table I): 4 propolars, 4 metapolars, 6, 7, or 8 diapolars, 2 uropolars. Calotte typically orthotropal; in vermiform embryos bluntly pointed and longer than wide (Figs. 1-5), in adults more rounded anteriorly and varying from a more or less ellipsoidal to a bilobed shape in older rhombogens and occasionally nematogens (Figs. 6-10, 15-19, 2730). Calotte large and conspicuous in older vermiform individuals, occasionally as wide as or wider than rest of body. Propolars in older vermiform individuals as large or larger than metapolars. Body occasionally of uniform thickness throughout, but most often widest at the parapolars and the uropolars. Trunk cells sometimes arranged in opposed pairs, sometimes in whorls of three or otherwise. Large granules and small particles present in trunk cells of some nematogens and rhombogens, most abundant in older vermiform phases. Diapolar cells rarely tending toward a verruciform condition. Nuclei large with conspicuous nucleoli; nuclei of propolar and metapolar cells approximately equal in size; those of trunk cells variably shaped. Only occasional accessory nuclei in trunk cells of rhombogens. Anterior extent of axial cell to base of propolars, TABLE I. Somatic cell numbers of Dicyema bilobum. Phase Cell Cell Totals no. Vermiform Nematogens Rhombogens Totals embryos 15 2 2 4 16 32 25 57 17 38 7 3 48 18 34 2 10 46 9 2 2 Totals 106 36 15 157 Received for publication 5 June 1964. * This investigation was supported in part by Public Health Service Research Grant AI-04749 from the National Institute of Allergy and Infectious Diseases.

Chromosomes in parthenogenetic miracidia and embryonic cercariae of Schistosomatium douthitti.

Abstract Chromosomes of Schistosomatium douthitti have been studied in miracidial embryos derived from (1) unfertilized eggs in unisexual female mammalian infections and (2) eggs in bisexual mammalian infections. Chromosomes have also been analyzed in cercarial embryos derived from parthenogenetic miracidia. In 168 parthenogenetic miracidial embryos from unisexual mammalian infections, a haploid X set of chromosomes occurred in 160 and a diploid XX set in three; an additional five were probably diploids, although the exact chromosome constitution could not be determined. In 153 miracidial embryos from bisexual mammalian infections the following chromosome constitutions occurred: haploid X in four embryos, diploid XX in 69, diploid XY in 78, triploid XXY in one and triploid XYY in one. Chromosome analyses of cercarial embryos derived from parthenogenetic miracidia gave the following results: of 10 male infections, three were haploid X, six were normal diploid XX, and in embryos from one snail both haploid X and diploid XX cells were observed. All seven female infections were XY diploids and possessed the normal female constitution except for one which was trisomic for the smallest (7) chromosome. It is believed that haploid individuals developed from reduced eggs, and the absence of the haploid Y constitution indicates that the X chromosome is necessary for viability. Possible methods of origin of XX and XY constitutions from parthenogenetic eggs are considered briefly and it is suggested that such diploids arose as a result of meiotic irregularities.

Somatic chromosomes of Schistosoma rodhaini, S. mattheei, and S. intercalatum.

Karyotypes are reported for three African schistosomes: Schistosoma rodhaini, S. intercalatum, and S. mattheei. All have eight pairs (2n = 16) of chromosomes which comprise three distinct size groups: A, large (two pairs); B, medium (three pairs); and C, small (three pairs). Chromosomes of groups A and B are subtelocentric; those of C are more metacentric or submetacentric. These karyotypes prepared with conventional Giemsa staining are very similar to each other and to those of S. mansoni and S. haematobium. As a group, the African schistosomes studied to date exhibit clear differences in chromosome morphology from the Asian S. japonicum and S. mekongi.

DICYEMENNEA CANADENSIS N. SP. (PHYLUM DICYEMIDA) FROM BATHYPOLYPUS ARCTICUS (MOLLUSCA: CEPHALOPODA: OCTOPODA)

Dicyemennea canadensis n. sp. is described from a bathyal octopus collected off Canada in the Bay of Fundy. The dicyemid is a small species that rarely exceeds 600 μm in length. The vermiform stages are further characterized as having 17–23 peripheral cells, a conical-shaped calotte, an axial cell that extends to the base of the propoplar cells, and no abortive axial cells. Infusoriform embryos consist of 37 cells. There is 1 nucleus in each urn cell, and refringent bodies are absent. This is the first dicyemid to be described from the cephalopod Bathypolypus arcticus (Prosch, 1847), and the first dicyemid reported from Canada. In addition, it is the first species of Dicyemennea from the northwestern Atlantic Ocean to be described.