Ultrastructure of a primitive, multinucleate, marine, cyanobacteriophagous ameba (Euhyperamoeba biospherica n. sp.) and its possible significance in the evolution of eukaryotes

Donald M. Spoon, Christopher J. Hogan, and George B. Chapman
Department of Biology, Georgetown University, Washington, D.C. 20057-1028, USA

Abstract. Samples of Euhyperamoeba biospherica n. sp., a free-living, marine, multinucleate, limax ameba of Caribbean origin (via the Biosphere 2 Ocean and a Georgetown University marine aquarium) were examined by light and transmission electron microscopy. The amebas grossly resemble two previously described species of marine, multinucleate limax amebas, Euhyperamoeba fallax and Gruberella flavescens. They differ, however, in their large size and thousands of nuclei. They also differ in containing structures that resemble bacteria more than mitochondria because of their ultrastructure and presumed division figures and because they produce rods composed of filaments or microtubules. We suggest that these amebas are more primitive than E. fallax or C. flavescens and may, therefore, contribute to our understanding of the evolution of organelles, such as mitochondria, in eukaryotic cells.

Additional key words: Bacteria, mitochondria

Rotifer look-alikes: two species of Colurella are ciliated protozoans

Paul N. Turner

Department of Biological Sciences, Wichita State University, Wichita, KS 67260, USA

Abstract. Some 19 valid species of rotifers in the genus Colurella have been described from all parts of the world, mostly from littoral or interstitial habitats of fresh and salt waters Colurella monodactylos and C. althausae, described from marine interstitial sands of the Black Sea and Caribbean, respectively, are significantly different from their congeners. Although no type specimens were deposited for either species, published drawings or photographs provide enough evidence to conclude that both of these "rotifers" are in fact ciliated protists of the family Dysteriidae, probably of the genus Dysteria.

Additional key words: protist, interstitial, benthic

Effect of age on infectivlty of cercariae of Halipegus occidualis (Digenea: Hemiuridae) to their second intermediate host

Eric J. Wetzel and Gerald W. Esch

Department of Biology, Wake Forest University, Winston-Salem, North Carolina, 27109 USA

Abstract. The effect of age on the infectivity of cercariae to their second intermediate host may limit their transmission. Individual ostracods (Cypridopsis sp.) were exposed to cercariae of the hemiurid trematode Halipegus occidualis, ranging in age from 1 to 25 days. Surviving ostracods were then examined for infection, and the number of dead hosts recorded. The number of cercariae ingested by the ostracods remained constant throughout the experiments. However, the number of mesocercariae recovered from ostracods declined significantly as the cercariae increased in age. Cercariae 25 days old were not infective to ostracods. The number of deaths among infected hosts was significantly higher than that in uninfected controls. Examination of variance to mean ratios suggested that host mortality was parasite-induced. The results indicate that the opportunity of transmission for these cercariae is considerably smaller than previously suggested.

The glandular sensory organ of Desmodoridae (Nematoda)--ultrastructure and phylogenetic implications

Monika Bauer-Nebelsick, Michael Blumer, Werner Urbancik, and Jorg A. Ott

Institut fur Zoologie, Universitat Wien, Althanstr. 14, A-1090 Vienna, Austria

Abstract. The glandular sensory organ found in representatives of all genera of Stilbonematinae (Nematoda, Desmodoridae) so far described was investigated by means of scanning and transmission electron microscopy. It is composed of one type A and one type B glandular cell, one monociliated sensory cell, and a hollow seta. Whereas the Stilbonematinae have ectosymbiotic bacteria coating the cuticle, for an outgroup comparison three non-symbiotic species belonging to three genera from the closely related subfamilies Desmodorinae and Spinniinae were chosen. In these three species the glandular sensory organ is composed of one type A glandular cell, one biciliated sensory cell, and a hollow seta. The consistent structure of a highly complex organ such as the glandular sensory organ with one type B glandular cell and one monociliated sensory cell suggests that the Stilbonematinae are monophyletic in spite of their otherwise diverse morphology.

Addttional key words: Stilbonematinae, Desmodorinae, Spiriniinae, symbiosis

New marine tardigrades from Hawaiian beach sand and phylogeny of the family Halechiniscidae

Leland W. Pollock

Department of Biology, Drew University, Madison, New Jersey 07940, USA

Abstract. Two new species of marine interstitial arthrotardigradest both members of a new genus, are described from Anahola Bay, Kauai, Hawaiian Islands. Dipodarctus n. gen. is characterized by long primary clavae situated ventral to short lateral cephalic cirri; small ovoid leg IV papillae with short terminal spines; and unequal toe-length patterns on feet IIII as compared to foot IV. Toes on foot IV are of Tanarctus-type with long medial toes, while feet I-III possess at least 3 equal, short toes. Dipodarctus borrori n. sp. has stubby, two-piece cephalic cirri; an unusual protrusible mouth cone; and outermost toe on feet I-III twice the length of remaining toes on these feet. Dipodarctus anaholiensis n. sp. has long, tapering cephalic cirri; all toes on feet l-III equal; and coarsely punctate cuticle. Dipodarctinae is erected as a new subfamily within the Halechiniscidae to include these animals. Unifying features of the subfamily include ventrally set primary clavae; short sensory papilla on leg IV; feet of legs I-III differing from foot of leg IV. Character-state polarities among the members of the subfamilies of Halechiniscidae are used to construct a cladogram in which two basic groups are distinguished primarily on the basis of toe-length patterns, claw features, and the shape of cephalic appendages.

Additional key words: Tardigrada, Heterotardigrada, Arthrotardigrada. Dipodarctinae, Dipodarctus borrori, D. anaholiensis

On the life-style and life-cycle of the luminescent polychaete Odontosyllis enopla (Annelida: Polychaeta)

Albrecht Fischer and Ursula Fischer

Zoological Institute; University of Mainz; D-55099 Mainz, Germany

Abstract. Epitokes of the syllid polychaete Odontosyllis enopla, caught during swarming and maintained in the laboratory, are described and illustrated. As they survived swarming and resumed a benthic life, sexual maturation and epitoky are reversible in this species. The hitherto unknown benthic life-style was studied in post-spawning adults and in juveniles collected from the benthos in the upper sublittoral at the site of swarming. O. enopla inhabits silk tubes fastened to hard substrates and encrusted with sand grains. The worms are carnivorous, foraging in the dark, probably on spionids. After swarming, the worms shed the swimming setae and, according to preliminary evidence, may develop a double line of dark-brown pigment across each segment. Bioluminescence is not restricted to the well-described swarming display but was observed for months after spawning as a startle response. Swimming trochophores hatch the morning after spawning and, while developing into three-segmented larvae, may continue swimming or glide on the substrate or may attach themselves to the substrate by a thread secreted from the pygidium. The lecithotrophic phase of life may last four weeks. Start of feeding and the transition to permanent benthic life have not yet been observed. The relations between Odontosyllis enopla, also called the "Bermudian fireworm," and Caribbean populations of Odontosyllis are discussed.

Additional key words: bioluminescence, epitoky, Bermuda

Spermathecae of Fabricia and Manayunkia (Sabellidae, Polychaeta)

Greg Rouse

School of Biological Sciences, Zoology A08, University of Sydney, N.S.W. 2006, Australia

Abstract. The structure of the sperm storage organs found in females of the fabriciin sabellid species Manayunkia aestuarina and Fabricia stellaris is described. In both species, adult females have a pair of prostomial spermathecae, Iying anterior and dorsal to the buccal opening, in the base of the radiolar crown. The spermathecae are epidermal structures; each ends blindly with a single opening into the surrounding water. In each spermatheca of M. aestuarina, a short duct from the narrow opening extends into the larger lumen of the ellipsoid spermathecal sac. The spermathecal cells have large nuclei and numerous dark (and electron-dense) granules. No cilia are present in any part of the spermathecae. The spermathecae are either completely empty, or contain 25-50 sperm. The spermathecae of F. stellaris are more complex than those of M. aestuarina and have three distinct regions. They closely resemble spermathecae previously described from another fabriciin, Parafabricia ventricingulata. The opening into each spermatheca leads ventrally into a ciliated chamber, or atrium, which extends posteriorly and laterally into the base of the radioles. The atrium terminates at the connecting piece which in turn leads to the heavily pigmented, but non-ciliated, sperm receptacle. The sperm receptacle is the most posterior region of each spermatheca and is dorsal to the connecting piece and atrium. Several hundred sperm can be found in each receptacle of F. stellaris. Comparing these spermathecae with those of other fabriciins, I conclude that sperm storage structures and mechanisms will provide useful characters in the systematics of the Fabriciinae.

Additional key words: Fabriciinae, reproduction, ultrastructure

Role of phylogenetic constraints in determining reproductive patterns in deep-sea invertebrates

Kevin J. Eckelbarger & Les Watling

Department of Animal, Veterinary, and Aquatic Sciences, Darling Marine Center, University of Maine, Walpole, Maine 04573, USA

Department of Oceanography, Darling Marine Center, University of Maine, Walpole, Maine 04573. USA

Abstract. The majority of deep-sea invertebrates appear to reproduce "continuously" while some species show a marked seasonal rhythm. Deep-sea habitats are not as unvarying as once believed and some areas of the deep-sea floor are subject to a variety of perturbations, including seasonal fluxes of organic matter originating from surface phytoplankton blooms. Some authors suggest that these organic pulses might activate the reproductive processes of seasonally-reproducing species while having no immediate effect on "continuous" breeders.

In this paper, we hypothesize that the different reproductive responses to organic matter can be explained by phylogenetic constraints involving interspecific differences in gonadal morphology, nutrient storage and mobilization, the mechanisms of vitellogenesis, feeding biology, digestive processes, and selective use of nutrients. Invertebrates process nutrients in different ways with some having the capacity for "fast eggproduction" while others engage in "slow egg-production." In addition, the pace of gametogenesis and the frequency of spawning will be influenced by the presence of storage tissues, which may release energy reserves to the gonads at a predetermined rate. As a result, seasonal organic fluxes to the deep-sea floor will provoke a variety of reproductive responses.

We propose three patterns that may clarify the correlation between seasonal phytodetrital pulses and seasonal reproductive patterns in some species: (I) species initiate gametogenesis immediately in response to organic input and undergo spawning soon after; (2) species spawn when seasonal pulses coincide with conditions favorable for their planktotrophic larvae; or (3) seasonal organic input initiates and synchronizes gametogenesis, producing a future spawning episode after an extended period of vitellogenesis. In those species showing seasonal reproduction, the proximate cause is the seasonal pulse of phytodetritus while the ultimate cause stems from the phylogenetic history of the organism. Reproductive periodicity of deep-sea species is generally predicted from an analysis of gamete development. Consequently, we suggest that seasonal breeders be referred to as having "synchronous gametogenesis" while socalled "continuous" breeders be referred to as having "asynchronous gametogenesis." These terms better describe the condition of the developing gametes without making inferences regarding spawning patterns. Generalizations about the potential response of groups of unrelated taxa to various environmental parameters (e.g. organic pulses) fail, because phylogenetically diverse species respond differently.