Cephalopod head parts are among the most complex occurring in all invertebrates. Hypotheses for the evolutionary process require a drastic body-plan transition in relation to the life-style changes from benthos to active nekton. Determining these transitions, however, has been elusive because of scarcity of fossil records of soft tissues and lack of some of the early developmental stages of the basal species. Here we report the first embryological evidence in the nautiloid cephalopod Nautilus pompilius for the morphological development of the head complex by a unique assembly of multiple archetypical molluscan body parts. Using a specialized aquarium system, we successfully obtained a series of developmental stages that enabled us to test previous controversial scenarios. Our results demonstrate that the embryonic organs exhibit body plans that are primarily bilateral and antero-posteriorly elongated at stereotyped positions. The distinct cephalic compartment, foot, brain cords, mantle, and shell resemble the body plans of monoplacophorans and basal gastropods. The numerous digital tentacles of Nautilus develop from simple serial and spatially-patterned bud-like anlagen along the anterior-posterior axis, indicating that origins of digital tentacles or arms of all other cephalopods develop not from the head but from the foot. In middle and late embryos, the primary body plans largely change to those of juveniles or adults, and finally form a "head" complex assembled by anlagen of the foot, cephalic hood, collar, hyponome (funnel), and the foot-derived epidermal covers. We suggest that extensions of the collar-funnel compartment and free epidermal folds derived from multiple topological foot regions may play an important role in forming the head complex, which is thought to be an important feature during the body plan transition.

Sperm maturation is the development of spermatozoa from nonfunctional gametes to mature spermatozoa fully capable of vigorous motility and fertilization.1-4) Under conditions of cultivation, male Japanese eel

In polyandrous mating systems, sperm competition and cryptic female choice (CFC) are well recognized as postcopulatory evolutionary forces. However, it remains challenging to separate CFC from sperm competition and to estimate how much CFC influences insemination success because those processes usually occur inside the female's body. The Japanese pygmy squid, Idiosepius paradoxus, is an ideal species in which to separate CFC from sperm competition because sperm transfer by the male and sperm displacement by the female can be observed directly at an external location on the female's body. Here, we counted the number of spermatangia transferred to, removed from, and remaining on the female body during single copulation episodes. We measured behavioral and morphological characteristics of the male, such as duration of copulation and body size. Although males with larger body size and longer copulation time were capable of transferring larger amounts of sperm, females preferentially eliminated sperm from males with larger body size and shorter copulation time by spermatangia removal; thus, CFC could attenuate sperm precedence by larger males, whereas it reinforces sperm precedence by males with longer copulation time. Genetic paternity analysis revealed that fertilisation success for each male was correlated with remaining sperm volume that is adjusted by females after copulation.

1In the Japanese pygmy squid Idiosepius paradoxus, females often pick up 2 the spermatangium using their mouth (buccal mass) after copulation. To examine

We verified whether telomere length shortens with age in the loggerhead sea turtle (Caretta caretta) by measuring telomere lengths (relative telomere to single copy gene [T/S] ratios) in whole blood and epidermis from 20 captive individuals with a real-time PCR method. There was no significant correlation between age and relative T/S ratios in blood. Although the correlation between age and relative T/S ratios in epidermis was not significant, older turtles had smaller relative T/S ratios in epidermis. It was thus demonstrated that telomere length in epidermis could be a useful age estimator for sea turtles. Relative age information obtained with this simple, rapid, non-invasive technique may help to advance our understanding of the ecology of endangered sea turtles. This is the first publication on age-related changes in telomere length among chelonians.

To examine the mechanism of sperm storage in Idiosepius paradoxus, here we describe aspects of the mating behavior of I. paradoxus and the morphology of the spermatozoa and the seminal receptacle after copulation. The seminal receptacle is located in the ventral portion of the buccal membrane surrounding the buccal mass, and opens inside the buccal membrane. It branches into approximately six sacs, similar in appearance to a bunch of bananas, and its wall consists of cuboidal ciliated epithelial cells (with oval nuclei) surrounded by a connective tissue. Multiple vacuoles are distributed in the bottom region of each sac. These histological and morphological characteristics differ from previous reports for loliginid squids and cuttlefish. In all except one receptacle observed in this study, sperm were stored near the bottom of each sac, and each sperm was facing the sac bottom. We observed spermatozoa in the entrance of the seminal receptacle in only one squid. These results suggest that spermatozoa were actively moving, and that sperm actively swam to the seminal receptacle. The volume of sperm in the seminal receptacles of the squid that had copulated eight times was the same as that in the squid that had copulated 29 times, which suggests that the seminal receptacle was filled after approximately eight copulation events. A squid that had copulated nine times retained a significant number of sperm in the seminal receptacle after spawning, suggesting that all of the sperm in the receptacle was not depleted after one spawning event.

No abstract

1Females can express mate (or fertilisation) preferences after copulation. In the 2 Japanese pygmy squid, Idiosepius paradoxus, in which males do not show any 3 conspicuous pre-copulatory displays, the females remove the spermatangia 4 attached to their bodies after copulation. In this study, we observed pre-and 5 post-copulatory behaviours and analysed which variables associated with 6 copulation were correlated with spermatangia removal. When females mated with 7 larger males or copulation lasted longer female squid elongated their buccal mass 8 after copulation and removed more spermatangia. We also investigated the effects 9 of spermatangia removal on the retained spermatangia to predict whether cryptic