Jørgen Lützen

MOLECULAR AND MORPHOLOGICAL EVIDENCE FOR A MONOPHYLETIC CLADE OF ASEXUALLY REPRODUCING RHIZOCEPHALA: POLYASCUS, NEW GENUS (CIRRIPEDIA)

Abstract The Rhizocephala is a group of extremely reduced parasitic crustaceans, that exclusively parasitize other Crustacea. In the family Sacculinidae, the external sac-like part (externa) of the adult parasite contains the reproductive apparatus and is attached beneath the abdomen of the host crab. Hosts with more than one externa may occur and are in most cases believed to have arisen from multiple cyprid larvae. However, in three species of the genus Sacculina, multiple externae have been shown to originate by asexual reproduction from a single parasitic cypris larva. We present a phylogenetic analysis of ten species of Sacculina and outgroups based on partial sequences from the cytochrome oxidase 1 (CO1) and the entire 18s rDNA gene. A separate parsimony analysis from the 18s rDNA and CO1 genes resulted in two trees with almost identical topologies. Both genes strongly support a monophyletic, asexually reproducing clade and fail to support a monophyletic Sacculina genus. As a consequence we have established a new genus, Polyascus, to accommodate three members of this clade which also share a number of common morphological features.

Comparative morphology and phylogeny of the family Thompsoniidae (Cirripedia, Rhizocephala, Akentrogonida), with descriptions of three new genera and seven new species

Akentrogonid rhizocephalans morphologically resembling the genus Thompsonia are revised as a result of examination of new material. The species concerned are all obligatorily colonial and have ovoid or cylindrically shaped externae with a terminal stalk and a much reduced anatomy. A numerical cladistic analysis of all Rhizocephala Akentrogonida using the Hennig 86 program leads to a redefinition of the Thompsoniidae HOeg and Rybakov, 1992. Autapomorphies for the Thompsoniidae are primarily the morphology of the attachment to the host and the total absence of a mesentery. The cladistic analysis refutes that the Thompsoniidae should have a plesiomorphic morphology and branch off very low on the rhizocephalan phylogeny. The family now comprises four genera: Pottsia gen. n. (monotypic), Diplothylacus gen. n. with two species, Thompsonia Kossmann with five species. A revived and redefined Thylacoplethus Coutière includes eight species. The genera are distinguished by the location of the spermatogenic tissue, the site where the eggs are fertilized, the presence or absence of a mantle pore and the way it is formed, the number or absence of oviducts, and the number of cuticular annuli on the stalk. All 16 species, of which six are new to science, are described when necessary, and, if possible, illustrated. A phylogeny for the redefined family is proposed. Thylacoplethus is morphologically closest to the hypothetically ancestral thompsoniid and is likely paraphyletic. The new genus Polysaccus with two species, one of them new to science, and the monotypic genus Pirusaccus Lützen resemble thompsoniids in externa morphology and in being obligatorily colonial.

BIOLOGICAL OBSERVATIONS ON HETEROSACCUS DOLLFUSI BOSCHMA (CIRRIPEDIA: RHIZOCEPHALA), A PARASITE OF CHARYBDIS LONGICOLLIS LEENE (DECAPODA: BRACHYURA), A LESSEPSIAN MIGRANT TO THE MEDITERRANEAN

ABSTRACT Since 1993, Heterosaccus dollfusi has been a very common parasite on the crab Charybdis longicollis along the Mediterranean coast of Israel. It accompanied from the Red Sea this Lessepsian migrant crab. The parasite is more common on male than female crabs, where it becomes external on hosts of many sizes shortly after a molt and undergoes characteristic growth stages. The parasite usually causes the complete loss of pleopods in both sexes and a feminine broadening of the abdomen in male crabs. Parasite survival is the same in both sexes of the host. More than one parasite per host is frequent, each probably originating from an individual cypris larva rather than from asexual budding. Hosts with single parasites outlive those with multiple infections.

Sperm dimorphism and spermatozeugmata in the commensal bivalve Pseudopythina macrophthalmensis (Galeommatoidea, Kelliidae)

Abstract The bivalve Pseudopythina macrophthalmensis (Galeommatoidea) is a commensal with the crab Macrophthalmus convexus (Ocypodidae) in Okinawa Prefecture, Japan. It is a protandric hermaphrodite which incubates the 65-µm large ova in the suprabranchial cavity. The species produces two types of sperm, which were studied with the electron microscope. The euspermatozoon has an elongate 2.8-µm-long, pointed acrosome, a slender 12- to 13-µm-long nucleus and a middlepiece containing several closely packed mitochondria arranged as a 5.5- to 6.0-µm-long sheath around the basis of the flagellum. The paraspermato- zoon is vermiform, 220-µm-long and up to 5-µm-broad. Anteriorly there is a ca 7-µm-long bullet-shaped acrosome followed by a subcylindrical 3.0- to 4.7-µm-long nucleus. Adjacent to the nucleus occurs a bundle of 26–42 40-µm-long flagella. The cytoplasm is packed with spherical lipid droplets and ovoid granules of unknown composition. Sperm of both types aggregate to form spermatozeugmata, which were found in the posterior mantle cavity or in paired seminal receptacles. Within the receptacles the euspermatozoa dissociate themselves from the spermatozeugma and become attached to the epithelial lining of the receptacle whereas the paraspermatozoa presumably disintegrate. The possible significance of the two types of sperm is discussed in the light of their presumed functions in gastropods.

Studies on the life history of Enteroxenos Bonnevie, a gastropod endoparasitic in aspidochirote holothurians

Abstract The gastropod, Enteroxenos oestergreni, an entoparasite of the holothurian Stichopus tremulus, was studied at two different depths in the Oslofjord (1965-75). 34.5-36.5 % of the host animals were infected. 82.5-85.5 % of the parasites occurred on the hosts oesophagus, 8.0-9.5 % on the stomach, the remaining ones on other viscera. 110-429 egg capsules. with a total of21 000-135 000 eggs are produced, all at one time. The population reproduces throughout the year, but each female produces only one batch of eggs in its life. Before or shortly after oviposition the parasites detach from the hosts viscera and become free in the body cavity. They are probably expelled in connexion with the annual evisceration of the host. Larval development takes about one year, spent mostly within the capsule, as the ftee life seems to be very short. At metamorphosis shell and operculum are cast off. Completion of metamorphosis in the male larva occurs on an epithelial petiole (male receptacle) in the females centr...

Thompsonia dofleini, a colonial akentrogonid rhizocephalan with dimorphic, ova- or sperm-producing, externae (Crustacea, Cirripedia)

SummarySpecimens of the blue swimming crab,Portunus pelagicus, are often infected with many thousands of externae ofThompsonia dofleini, all of which are connected through a common root system within the host crab. The species is unique in that the production of sperm cells takes place within the visceral mass of a small minority of the population of the externae. Spermatogonia are probably introduced by male cyprids into these externae when they are young, and they multiply and develop at the expense of the oocytes which rapidly disintegrate and ultimately disappear. It is assumed that the sperm cells are transferred to the ovary of the ordinary, egg-producing externae through the root system. Shortly after the eggs have been fertilized within the ovary they are transferred to the mantle cavity where they develop into cyprid larvae. The larvae become liberated when the externae drop off and the mantle wall disintegrates.

Rhizocephalans (Crustacea: Cirripedia) from Taiwan

One species of shrimp and sixteen species of brachyuran crabs are parasitized by rhizocephalans in Taiwanese waters. Ten of the crabs have never before been recorded as hosts of rhizocephalans. Eight species of rhizocephalans occur in Taiwan. Four species, Diplothylacus taiwanensis, D. calappae, Sacculina scutigera and S. docleae are new to science. The paper records the first example of simultaneous infection of the same host individual by two rhizocephalan species, and provides further evidence of successive moulting of the external mantle cuticle in several species of sacculinids.

Morphology of Pectenophilus Ornatus, New Genus, New Species, a Copepod Parasite of the Japanese Scallop Patinopecten Yessoensis

ABSTRACT Reexamination of a crustacean parasitic on the gills of the scallop Patinopecten yessoensis has revealed that it is a copepod and not, as has been claimed, a rhizocephalan. The female is without appendages and its unsegmented, 8-mm broad body presents 1 dorsal unpaired and 2 pairs of lateral peripheral bulges. A small posterodorsal birth pore leads into a capacious brood pouch which is divided into 5 compartments by lateral septa. The mouth occurs in the middle of a circular area which is fused with a conical stalked structure made up of the hosts connective tissue. The hosts ctenidial epithelium lines the exterior of the stalk as well as the parasite body. The mouth opens into a blood lacuna in the middle of the stalk, and host blood is sucked into the digestive system which, in addition to a much subdivided pharynx, comprises an esophagus and a blind midgut. The female reproductive system consists of a branched ovary, 2 short oviducts, and an unpaired seminal receptacle; cement glands are absent. The males, 1-6 per female, are enclosed within a vesicle connected with the brood pouch; they are ovoid and have minute antennules, antennae, and mandibles placed on a small cephalic prominence. Spermatophores are attached to the inside of the male vesicle from where sperm are transferred to the seminal receptacle. Eggs are incubated in the brood pouch and develop into typical copepod nauplii.

Ultrastructure of the non-germinal cells in the testes of ascidians (Urochordata) and their role in the phagocytosis of sperm

Abstract In three species of the Enterogona (Clavelina lepadiformis, Ciona intestinalis and Ascidiella aspersa) and three species of the Pleurogona (Dendrodoa grossularia, Styela clava and Molgula manhattensis) the testis was found to be invested by an epithelium separating the germ cells from the surrounding connective tissue or haemal sinuses. Each epithelial cell probably bears a single cilium, which in C. lepadiformis has a rootlet. Cilia are absent in S. clava. Lipid droplets are common and glycogen-rosettes occur in C. lepadiformis and D. grossularia. The basal plasmalemma varies from smooth to very irregular and in A. aspersa is anchored with hemidesmosomes. Except in S. clava, desmosome-like junctions occur between adjacent cells. Elimination of waste sperm following the reproductive season was observed to be undertaken by the epithelial wall cells in all species except C. lepadiformis. In C. intestinalis, D. grossularia, S. clava and M. manhattensis many of these cells detach and migrate to the interior of the testis where they continue and complete the phagocytosis of sperm. In C. lepadiformis, the non-germinal epithelium plays no role in the elimination of superfluous sperm which is probably phagocytosed, together with the rest of the body, by wandering trophocytes. Within the Urochordata the effectiveness of the testis epithelium as a blood-testis barrier varies, but is not correlated to modes of reproduction as postulated for other taxa.

SYMPATRIC THREE-SPECIES INFECTION BY SACCULINA PARASITES (CIRRIPEDIA: RHIZOCEPHALA: SACCULINIDAE) OF AN INTERTIDAL GRAPSOID CRAB

Abstract Parasitization by sacculinids (Cirripedia: Rhizocephala: Sacculinidae) induces severe modifications in morphology, behavior, and reproduction of their host crabs. To understand the mechanisms involved, it is important to have comprehensive information on their association. However, such information has been poorly available, mainly because of scarcity of distinguishing characters of sacculinids hamper identification of them. In the course of the investigation of the associations using the molecular marker (COI gene) and morphological observation to identify sacculinids, three species of Sacculina, S. confragosa, S. imberbis, and S. yatsui, were found to parasitize a single host crab, Pachygrapsus crassipes, sympatrically in a restricted area. This is the first finding for three-on-one association in a single locality.