The sperms of the Acoela, a group of lower worms, are filiform cells with 2 flagella incorporated into the cell body. Their axonemes can variously have 9+2, 9+1, or 9+0 patterns of microtubules; and singlet microtubules in the cell body can be arranged in axial or cortical positions. An analysis of phylogenetic relationships of acoels based on molecular characters (18S rDNA sequence data) showed that these patterns of microtubules, where known, fell into discrete monophyletic groups. To test this hypothesis, we have expanded the database of sperm characters by examining the ultrastructure of a further 10 species representing 4 acoel families. As expected, the Convolutidae fell into 2 unrelated groups: “small-bodied convolutids” (Convoluta pulchra, Prueconvoluta tigrina, Pseudaphanostoma smithrii) having 9+2 axonemes and cortical microtubules, and “large-bodied convolutids” (including Wulguru cuspidata) having 9+0 axonemes and axial microtubules. Also, as expected, a member of the Mecynostomidae (Paedomecynostomum bruneum) has 9+1 axonemes and axial microtubules. Members of a family that appears intermediate by molecular characters, the Otocelididae, significantly have a variety of patterns: axonemes with both 9+2 and 9+0 patterns (Notocelis gullmarensis) or just 9+2 (the other species), and either axial (Philocelis brueggemanni), both axial and cortical (N. gullmarensis) microtubules, or microtubules that bend between axial and cortical positions along the length of the sperm (Otocelis sandara). Members of the Dakuidae (Daku wonrimensis) also belong to this intermediate group, having 9+2 axonemes and axial microtubules, while in a fifth otocelidid (Stomatricha hochbergi), sperm characters are like those of the “large-bodied convolutids” (9+0 axonemes and axial microtubules). Characters of sperm morphology generally support the molecular hypothesis of relationships and confirm a suspected polyphyly of the families Convolutidae, Otocelididae, and Actinoposthiidae.

The problem of similarity is one of explaining the causes of striking resemblances between patterns and architectural themes that recur in organisms at various scales of biological organization. Classical explanations that have considered only the alternatives of homology and analogy overlook similarities of form that are primarily a consequence of fabrication, conveying little information about evolutionary relationships or functional role. When viewed at successively higher magnifications and when mapped onto a phylogeny, patterns of delicate cancellate microsculpture and granular microprotuberances on the surfaces of larval shells of marine gastropods fail to meet the predictions of exclusively historical or exclusively functional explanations, but are shown to be rich in fabricational information. Similar patterns suggest that early biomineralization of the initial organic shell is under weaker biological control than the processes that modulate assembly of the multi-layered, hierarchically-organized composite materials of the adult shell. Some patterns suggest remote biomineralization, without direct influence of living tissue. Scanning electron microscopy of larval shell features reveals previously undetected variation on basic themes that may have implications for the traditional disciplines of systematics, functional morphology, and fabricational morphology. The integration of the approaches of the traditional divisions of biology is required for full explanation of similarity and to generate a unified set of principles for the analysis of form in living and fossil organisms.

Anna Meyer published her first (and apparently last) scientific paper in 1913, in which she reported, in part, on the organization of the renogenital systems in the “Diotocardia” and “Monotocardia,” and the evolutionary signal present in this character suite. Meyer's phylogeny broke with conventional wisdom of her time and she reconstructed early gastropod evolution as a sequence of branching events rather than a continuous grade. Her phylogeny was ignored because it did not correspond to the well-ordered grades that came to dominate gastropod systematics for over 75 years, but her schematics of renogenital configurations have been featured in the literature for over 55 years, sometimes without citation and redrawn to show a different set of relationships. We hope that the translation of her paper from German into English ( http://www.ucmp.berkeley.edu/collections/archdut.html) will make her contribution more accessible to workers.

With few exceptions, spermatozoa-encapsulating packages in molluscs are known mostly from cephalopods and pulmonate gastropods. Among non-stylommatophoran gastropods, the marine Cerithioidea are second only to the Neritimorpha in the number of species that posess a spermatophore, but they have only rarely been found in freshwater taxa of this superfamily. We describe and compare here the sperm packages of 11 paludomid cerithioideans as part of an ongoing study on the evolution and systematics of the thalassoid (i.e., “marine-like”) endemic species flock from Lake Tanganyika. Stereomicroscopic and SEM examination revealed unexpected complexity in shape and structure of spermatophores within paludomids. In addition, we present a survey of other Cerithioidea, which revealed that spermatophores are in general structurally simple and confirmed their presence in 12 marine species (five families) and 15 limnic species (four families), including those of 10 thalassoid species for which spermatophores are described herein. Based on histological sections of the male genital tract, we hypothesize that spermatophores are formed anteriorly, wholly or in part, by the so-called spermatophore-forming organ, and which is considered a synapomorphy of the Paludomidae. In addition, we briefly discuss functional aspects inferred from morphological study of the spermatophore-forming organ, with possible implications for spermatozoan transfer and fertilization. Finally, we place the features of the spermatophores and the spermatophore-forming organ in a phylogenetic framework of cerithioidean and paludomid systematics, which suggests that the spermatophore-forming organ is a synapomorphy of Paludomidae, that a bifurcate spermatophore structure is plesiomorphic, and that the evolution of structurally complex, spiny spermatophores has occurred independently in disparate lineages within the thalassoid species flock.

Some gastropods appear to utilize a strategy for regulating testosterone levels that is atypical of such processes thus far identified in other metazoans. While most animals convert testosterone largely to polar derivatives that are readily eliminated from the organism, the mud snail Ilyanassa obsoleta converts testosterone to apolar testosterone-fatty acid esters that are retained by the organism. In the present study, we tested the hypothesis that fatty acid esterification serves to store testosterone and that stored testosterone-fatty acid ester pools vary through the reproductive cycle of the snail. This hypothesis was tested by 1) modulating total testosterone levels in individual snails and measuring the amount of the hormone stored as the fatty acid ester relative to the amount retained as free steroid and 2) measuring changes in esterified testosterone in a field population of snails during their reproductive cycle. Adult snails were experimentally manipulated to contain from ∼36-300% the level of total testosterone measured in unmanipulated individuals. The amount of testosterone-fatty acid ester present in these organisms increased in direct proportion to the level of total testosterone, while, free testosterone levels remained relatively constant. These observations suggest that free testosterone levels are regulated in the snail by fatty acid esterification/de-esterification processes. Among field sampled snails, testosterone existed predominantly in the free, non-esterified form at the onset and end of the egg laying period. At other times, the majority of testosterone was sequestered as fatty acid esters. This study provides compelling evidence that free testosterone levels in the mud snail are regulated through fatty acid esterification/de-esterification processes and this regulatory function contributes to seasonal fluctuations in free testosterone levels.

The largest extant species of the adventitious tube-building Clavagelloidea has hitherto been placed in the genus Foegia (itself formerly a subgenus of Brechites), the type species of which is the Western Australian F. novaezelandiae (Bruguière 1792). Following examinations of and comparison with F. novaezelandiae and the southern Australian F. veitchi, the latter is herein placed in its own new genus Kendrickiana.

Individuals of both F. novaezelandiae and K. veitchi are essentially amyarian in terms of adductor and pedal retractor muscles, but in the latter species the connection to the adventitious tube is located dorsally by an unique horseshoe-shaped array of muscular papillae, which are inserted into holes in the tube. K. veitchi is different from other clavagelloids too in that the siphons are capable of only limited retraction into the tube. Their extension in K. veitchi is almost exclusively by hydraulic means because the complex internal siphonal muscles seen in other species of the Clavagelloidea, and which act antagonistically with extensive blood-filled haemocoels, are vestigial. Kendrickianacan also be separated from Foegia in other anatomical respects. For example, members of the former have paired anterior suspensory muscles, and vestigial posterior pedal retractor muscles with pericardial proprioreceptors associated with them (as in Humphreyia and Dianadema), whereas the latter does not. Similarly, in Foegia there is a inuscularized pedal disc, not found in Kendrickiana. Members of F. novaezelandiae are inhabitants of intertidal hypoxic muds, whereas those of K. veitchi apparently live exclusively in subtidal sea grass beds.

The population structure and reproductive biology of a population of the spionid polychaete Pygospio elegans was studied at Drum Sands, Firth of Forth, Scotland, between March 1997 and February 1998. P. elegans was numerically dominant at the site and exhibited a population density increase through the sampling period. The population showed a seasonal pattern with two acute periods of recruitment during the year, one in spring and one in winter. Planktotrophic larvae were the only larval type produced throughout the sampling period. Larvae were released at the 3–5 setiger stage and settled at a size of 18–22 setigers. The spring recruits grew at a rate of 23 setigers per month, reaching sexual maturation size during September of the same year. The adult sex ratio was female-biased throughout the study period (mean = 2.99:l ±0.51). When fema1e:ripe male sex ratios were highest (summer and fall), the proportion of females brooding larvae decreased suggesting that sexual reproduction is seasonal. Asexual reproduction was not observed in the population of P. elegans on Drum Sands. These findings suggest that a high degree of variability is a trait of the reproductive biology of P. elegans.

Simple cupular organs similar to those described in Ciona intestinalis were observed in Corella eumyota. They consist of a macula containing the cell bodies of 20–30 primary sensory neurons whose cilia project into a dome- or finger-shaped structure, the cupula. Rather than being found in the mantle lining as in C. intestinalis, the organs were located on the atrial surface of the branchial sac. The sensory innervation was examined in whole-mount preparations using anti-tubulin immunohistochemistry. Sensory neurons in C. eumyota showed no immunoreactivity with antisera raised against gonadotropin-releasing hormone (GnRH).

A novel, elongated sense organ termed the cupular strand was found in Corella inflata. It has the same basic components as the simple type of cupular organ but consists of a single, long structure containing ∼1500 sensory cells. Located on the atrial surface of the branchial sac, it extends along the midline of the dorsal fold, from the gonoduct openings almost as far as the brain. Preparations were examined using optical and electron microscopy. Nerves and cilia were visualized by anti-tubulin immunofluorescence microscopy. It was possible to follow the sensory axons from the macula of the cupular strand to points where they joined branches of the visceral nerve, which enters a nerve root at the back of the brain.

In C. inflata the sensory cell bodies and their axons were immunoreactive not only with anti-tubulin but also with an antiserum raised against Tunicate I GnRH. There was no immunoreactivity, however, with Chicken II and catfish GnRH antisera. All three GnRH antisera labeled the dorsal strand plexus, a structure associated with production of GnRH in its role as a reproductive hormone. We concluded that the GnRH-like molecule labeled in sensory neurons differs from the form of GnRH found in the dorsal strand plexus, and may have a different function, perhaps in the neural control of ciliary activity.

The function of the cupular organs in species of Corella has not yet been investigated physiologically, but by analogy with such structures in other metazoans, cupular organs are probably hydrodynamic sensors registering local disturbances or changes in water flow through the atrial cavity.