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The structure of te 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, lying 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 Sabellids belonging to the subfamily Fabriciinae are normally 2-4 mm in length, and can be found occurring in excess of 1.5 X 106 individuals per m2 (Lewis 1968). Such population densities are, of course, related to the reproductive mode that these sabellids show. Rouse & Fitzhugh (1994) reviewed sexual reproduction across the Sabellidae and found a range of reproductive mechanisms in the subfamily Sabellinae. However, in all fabriciin species studied to date the females brood batches of directly developing larvae. The larvae subsequently disperse by crawling out of the parental tube before building their own tubes and beginning to feed (Leidy 1883; Forsman 1956; Rasmussen 1956; Lewis 1961; Marinescu 1964; Bell 1982; Knight-Jones & Bowden 1984; Rouse & Fitzhugh 1994). How females obtain sperm to fertilize the eggs spawned into their tubes has been the subject of some speculation. A form of pseudocopulation has been postulated in Fabricia stellaris (MOLLER 1774) by Franzen (1956, 1975), but it was shown by Kahmann (1984) that transfer of sperm from male to female does not require contact between individuals. Zenkevitsch (1925) also described pseudocopulation between sexes in another fabriciin, Manayunkia baicalensis (NUSBAUM 1901). In both of these species, and in Manayunkia aestuarina (BOURNE 1883), it has been noted that females have a pair of pigmented spermathecae in the radiolar crown dorso-lateral to the buccal opening (Zenkevitsch 1925; Daly & Golding 1977; Kahmann 1984). Rouse (1992) described the ultrastructure of spermathecae in another fabriciin, Parafabricia ventricingulata FITZHUGH 1992, and in several small members of the other sabellid subfamily, the Sabellinae. The mechanisms of sperm transfer between sexes have yet to be fully elucidated in any sabellid with sperm storage by females. However, I have shown (Rouse 1995) that males of the Fabriciinae have a dorsal sperm duct that opens behind the radiolar crown. The evidence of Kahmann (1984) and the fact that no spermatophores are formed (Rouse 1995) imply release of free sperm into the water. Thus, whether or not there is a form of pseudocopulation between sexes, sperm swim through the water and somehow enter the spermathecae. In this paper I describe the structure of the spermathecae of two fabriciin species, F. stellaris and M. This content downloaded from 157.55.39.104 on Mon, 20 Jun 2016 05:53:16 UTC All use subject to http://about.jstor.org/terms Spermathecae of sabellid polychaetes aestuarina. The reasons for this study are twofold. First, the position and morphology such structures will provide additional characters for cladistic analyses of the members of the Fabriciinae (e.g., Fitzhugh 1991; Fitzhugh et al. 1994). Second, any functional analysis of the complicated reproductive process seen in the Fabriciinae requires initial morphological analysis of the structures involved.

The fine structure of the spermatozoa of two spionids is described. The spermatozoon of Prionospio cf. queenslandica is typical of an animal utilizing external fertilization, in having a subspheroidal nucleus, a midpiece composed of unmodified rounded mitochondria surrounding two centrioles and a free flagellum. The acrosome is unusual in showing bilateral symmetry. The spermatozoon of Tripolydora sp. resembles that of spionids utilizing spermatophores, in possessing an extremely elongate nucleus and midpiece. The nucleus is penetrated by the 9+2 axoneme for its entire length, linking with a single centriole at the anterior end. Platelets surround the nucleus and intermingle with the mitochondria of the midpiece, which terminates with an annulus. The acrosome shows some internal vesiculation and substructuring. Sperm structure in relation to reproductive methods is discussed and the view of external fertilization as primitive is questioned.

Acrosome reactions were induced in seminal spermatozoa of the megachiropteran Pteropus poliocephalus, the grey-headed flying fox, using the ionophore A23187 (10 microM in Tyrodes solution with 1% w/v BSA). Samples were taken at 0, 10, and 120 minutes and fixed for electron microscopy. Initial motility of approximately 70% decreased to approximately 10% over 2 hours. The first motile spermatozoa without acrosomal caps were seen after 6 minutes, and by 90 minutes approximately 60% of motile spermatozoa had completed the acrosome reaction. The first sign of the reaction (by TEM) appears to be swelling and cavitation of the acrosomal matrix within the apical and principal segments, followed or possibly accompanied by fusion and fenestration of the outer acrosomal and plasma membranes and dispersion of the matrix except from the equatorial segment. The end-product of the reaction thus conforms to that seen in other eutherian mammals. However, the reaction exposes a uniquely moulded organization of subacrosomal material ("pseudoperforatorium"), shaped like an anvil over the rostral rim of the flattened nucleus and encased by the remaining inner acrosomal membrane. This has two "lateral" spikes on each side that extend approximately to the same width as the head in the region of the equatorial segment. While these barbs could serve to stabilize or anchor the apical segment of the acrosome, their exposure following the acrosome reaction suggests some specific mechanical role in penetration of the zona pellucida or in protecting more caudal structures from abrasive damage.

1. Polychaete sperm are divisible into ect-aquasperm, ent-aquasperm, and introsperm. 2. Ect-aquasperm are the commonest type of polychaete sperm and are considered plesiomorphic for the Polychaeta. Re-evolution of ect-aquasperm (as neo-aquasperm) is, nevertheless, tentatively hypothesized for some Sabellida. 3. In terms of ultrastructural studies of sperm in the investigated polychaete families, only ect-aquasperm have been demonstrated for 16 families; only ent-aquasperm for 3 families; ect- and ent-aquasperm for 3; ect- and intro-sperm for 2; ect-, ent- and intro-sperm for 1 family; and only introsperm for 11 families but investigations can only be regarded as preliminary. To date no family is known to have ent- and intro-sperm only. Sperm ultrastructure has yet to be examined in the orders Magelonida, Psammodrilida, Cossurida, Spintherida, Sternapsida, Flabelligerida and Fauvelopsida. 4. Much variation occurs in gross morphology, ultrastructure and configuration of the several components of ect-aquasperm: acrosome, nucleus, mitochondria, and centrioles and associated anchoring apparatus. A 9 + 2 axoneme is constant. 5. Group-specific sperm structure has been demonstrated for the Nereidae (chiefly ect-aquasperm), and for introsperm of the families Histriobdellidae, Questidae; Capitellidae, Spionidae and Protodrilidae. Species-specificity of all classes of spermatozoa is well established. 6. The very small size of ect-aquasperm is correlated with production of large numbers of sperm as an adaptation to broadcast spawning. Simplicity of structure may relate more to conservation of materials than to hydrodynamics. 7. Fertilization by ent-aquasperm requires fewer eggs than in external fertilization and is accompanied by a tendency to lecithotrophy. Elongation of the nucleus and development of asymmetry are seen in several of the few known examples of ent-aquasperm. Whether modifications are related to transfer or to other features, such as lecithotrophy, is uncertain. 8. Evident multiple origins of polychaete introsperm contraindicate their value in establishing relationship between families, in contrast with their utility in groups such as decapod crustacea. 9. At the intrafamilial level polychaete introsperm have taxonomic and phylogenetic value, as seen in the Spionidae, Capitellidae, and Histriobdellidae, and are distinctive of each of these and other families. 10. At higher taxonomic levels, the ultrastructure of the sperm of the oligochaetoid Questidae distinguishes this family from euclitellates, each class of which has its own distinctive subtype of the euclitellate introsperm. 11.(ABSTRACT TRUNCATED AT 400 WORDS)

The phylogenetic position of the most speciose meiofaunal polychaete family, Nerillidae, has remained contentious. Recent hypotheses have generally focused on the fact that Nerillidae shares with Aciculata (a major polychaete subgroup) features such as compound chaetae, ventral buccal organ and short ventrolateral palps. Here we present the first phylogenetic analysis of Aciculata, together with Nerillidae, combining morphological and molecular data. We also include Aberrantidae, previously referred to or placed near to spiomorph polychaetes, but recently referred to Aciculata, possibly close to Nerillidae. The data sets of 24 terminals contain 53 morphological characters and nearly complete sequences of 18S rRNA. The sequences were analysed simultaneously with the morphological data by direct optimization in the program POY with a variety of parameter settings (costs of gaps: transversions: transitions). The various settings resulted in markedly different phylogenetic hypotheses, but on the basis of congruence (ILD) the results of two parameter settings were chosen. In all analyses, the three included nerillid species constituted a monophyletic group. Only two analyses provided fully resolved cladograms. The morphological analysis gave poor resolution and the position of the nerillids was equivocal. The two molecular-based cladograms (minimizing ILD) were also poorly resolved, but one provided a position for nerillids next to Eunice pennata and Nothria conchilega, from the subgroup Eunicida within Aciculata. The two cladograms of the combined analyses (minimizing ILD) were fully resolved and placed nerillids in a terminal position next to Aberranta sp., within a clade of eunicidan species. The study showed that the analytical conditions for the homology assignment of 18S rRNA strongly influenced the phylogenetic results. The various previous proposals on the phylogenetic position of the Nerillidae are reviewed, some of which are in accordance with the results of the present study.

Members of the conspicuous bone-eating genus, Osedax, are widely distributed on whale falls in the Pacific and Atlantic Oceans. These gutless annelids contain endosymbiotic heterotrophic bacteria in a branching root system embedded in the bones of vertebrates, whereas a trunk and anterior palps extend into the surrounding water. The unique life style within a bone environment is challenged by the high bacterial activity on, and within, the bone matrix possibly causing O2 depletion, and build-up of potentially toxic sulphide. We measured the O2 distribution around embedded Osedax and showed that the bone microenvironment is anoxic. Morphological studies showed that ventilation mechanisms in Osedax are restricted to the anterior palps, which are optimized for high O2 uptake by possessing a large surface area, large surface to volume ratio, and short diffusion distances. The blood vascular system comprises large vessels in the trunk, which facilitate an ample supply of oxygenated blood from the anterior crown to a highly vascularised root structure. Respirometry studies of O. mucofloris showed a high O2 consumption that exceeded the average O2 consumption of a broad line of resting annelids without endosymbionts. We regard this combination of features of the respiratory system of O. mucofloris as an adaptation to their unique nutrition strategy with roots embedded in anoxic bones and elevated O2 demand due to aerobic heterotrophic endosymbionts. publishedVersion