Journal of Molluscan Studies - current issue

Embryonic and larval development of Ensis arcuatus (Jeffreys, 1865) (Bivalvia: Pharidae)

Da Costa, F., Darriba, S., Martinez-Patino, D. — 2008-04-22

The razor clam Ensis arcuatus (Jeffreys, 1865) is distributed from Norway to Spain and along the British coast, where it lives buried in sand in low intertidal and subtidal areas. This work is the first study to research the embryology and larval development of this species of razor clam, using light and scanning electron microscopy. A new method, consisting of changing water levels using tide simulations with brief dry periods, was developed to induce spawning in this species. The blastula was the first motile stage and in the gastrula stage the vitelline coat was lost. The shell field appeared in the late gastrula. The trochophore developed by about 19 h post-fertilization (hpf) (19°C). At 30 hpf the D-shaped larva showed a developed digestive system consisting of a mouth, a foregut, a digestive gland followed by an intestine and an anus. Larvae spontaneously settled after 20 days at a length of 378 µm.

Microsatellite cross-species amplification in the genus Littorina and detection of null alleles in Littorina saxatilis

Panova, M., Makinen, T., Fokin, M., Andre, C., Johannesson, K. — 2008-04-22

Microsatellite DNA is widely used as population genetic marker, but the cost of using microsatellites is high, as they usually need to be developed and optimized for each species separately. Cross-species amplification of microsatellites is therefore commonly applied to bring down the cost, but it can also involve genotyping errors. We studied cross-species amplification of microsatellites in four species of the Atlantic group of Littorina (Neritrema): L. saxatilis (Olivi, 1792), L. obtusata (Linnaeus, 1758), L. fabalis (Turton, 1825) and L. arcana Hannaford Ellis, 1978 to investigate whether markers originally developed for a more distantly related Pacific species [L. subrotundata (Carpenter, 1864)] suffered from more amplification problems than markers developed for one of the species in the Atlantic group (L. saxatilis). We also compared variation in amplification success among the species and among different regions in the NE Atlantic. Approximately half of the 12 primers developed for L. subrotundata and the seven primers developed for L. saxatilis were successfully amplified in other species of the subgenus. The success was dependent on phylogenetic distance among species within the subgenus. On the other hand, the variation in performance of the loci between geographically remote populations of the same species was as high as variation among the species. In earlier studies statistical analyses indicated that several loci showed a heterozygote deficiency due to null alleles. The presence of null alleles was confirmed by a segregation analysis of the microsatellite loci in eight half-sib families of L. saxatilis.

A review of European 'Mysella' species (Bivalvia, Montacutidae), with description of Kurtiella new genus

Gofas, S., Salas, C. — 2008-04-22

The type species of the genera Mysella Angas, 1877, Rochefortia Vélain, 1878, Rochefortula Finlay, 1927 and Altenaeum Spaink, 1972 are illustrated and discussed. A new genus Kurtiella is introduced for ‘Mysella’ bidentata (Montagu, 1803) and other European species currently placed in Mysella. These species display a unique diagnostic character state in having the cardinal platform deeply receding to house the internal ligament, along with an array of more general montacutid traits. At the species level, diagnostic characters are given for the type species K. bidentata, and for other included species K. ovata (Jeffreys, 1881), K. pellucida (Jeffreys, 1881), K. triangularis (Watson, 1897) and K. tumidula (Jeffreys, 1866), based mostly on characters of the prodissoconch and on shell outline. Montacuta simillima Smith, 1892, from St Helena, is considered a junior synonym of K. pellucida. The loss of labial palps in K. tumidula is interpreted as a further derived character, which does not conflict with the generic placement in Kurtiella.

Worth a second look: gill structure in Hemipecten forbesianus (Adams & Reeve, 1849) and taxonomic implications for the Pectinidae

Beninger, P. G., Decottignies, P. — 2008-04-22

The gill of the reef-dwelling Hemipecten forbesianus was examined using histology and scanning electron microscopy, in order to verify its reported homorhabdic state, and to provide the first detailed information on tropical pectinid gill structure. Due to the difficulty of obtaining live individuals, museum reference specimens were used for this study. The gill is heterorhabdic, and presents several notable differences compared to the larger, temperate species studied to date: (1) the small number of ordinary filaments per plica (probably associated with the very small size of these specimens), (2) the outer demibranch is approximately 15% shorter than the inner demibranch, (3) several characteristics which confer gill cohesion in other pectinid gills are absent and (4) the principal filaments are devoid of mucocytes, such that particle transport of positively-selected particles must be entirely effected in water. The apparent universality of the heterorhabdic condition within the Pectinidae leads us to recommend its use as a reliable soft-body taxonomic character at the family level. The anatomical differences between the gill of H. forbesianus and that of the larger, temperate species call for further comparison with both large and small, temperate and tropical species, in order to elucidate the effects of size and habitat on gill structure in this family.

Systematic revision of Jorunna Bergh, 1876 (Nudibranchia: Discodorididae) with a morphological phylogenetic analysis

Camacho-Garcia, Y. E., Gosliner, T. M. — 2008-04-22

The genus Jorunna is characterized by a dorsum covered with caryophyllidia, a prostate with two sections, a penis usually unarmed but occasionally armed with hooks, a copulatory spine, the presence of an accessory gland and a labial cuticle smooth or armed with jaw elements. The examination of 216 non-type specimens, 30 types, and a review of the literature show that there are 16 valid species of the genus Jorunna: J. tomentosa (Cuvier, 1804); J. funebris (Kelaart, 1859); J. pantherinaAngas, 1864; J. rubescens (Bergh, 1876); J. labialis (Eliot, 1908); J. parva (Baba, 1938); J. spazzola (Marcus, 1955); J. hartleyi (Burn, 1958); J. alisonaeMarcus, 1976; J. lemchei (Marcus, 1976); J. evansi (Eliot, 1906); J. pardusBehrens & Henderson, 1981; J.ramicolaMiller, 1996 and J. onubensis Cervera, García-Gómez & García, 1986. In addition, two new species from the Eastern Pacific are described: J. osae n. sp. and J. tempisquensis n. sp. We propose two new combinations: Jorunna parva and J. evansi. New records for the genus Jorunna are provided from Italy, Algeria, Seychelles, Madagascar, Thailand, Marshall Islands, New Caledonia, Île de la Réunion, Sudan, Papua New Guinea, Indonesia, Panama, Costa Rica, Bahamas, and Southern Mexico. We present the first preliminary phylogenetic analysis of this cryptobranch dorid genus, based on morphological anatomical data, and discuss the biogeography and evolution of several characters in this group. The phylogeny supports the hypothesis that the genus Jorunna is a monophyletic group and shows that Kentrodoris is nested within it.

Variability in the sculpture of the shell aperture of Ruthenica filograna (Rossmassler, 1836) (Gastropoda: Clausiliidae) in specimens from natural populations and from laboratory breeding

Szybiak, K., Lesniewska, M. — 2008-04-22

An analysis of variability in the sculpture of shell apertures was carried out for 1,087 specimens of Ruthenica filograna from 33 localities and for 20 laboratory-bred individuals reared from parents from a single locality. Nine patterns of aperture sculpture were distinguished. There are usually two kinds of sculpture: with one plica in the aperture being an extension of the inferior lamella, and without plicae in the aperture. Sporadically, the subcolumellar lamella may be connected with the lip of the aperture by a plica. Additional plicae occur in the aperture only rarely. All populations examined showed variations in the number and arrangement of plicae. The coefficient of variation in the number of plicae in the shell aperture ranged from 32.6% to 121.8% within localities. No consistent relationship was found between the geographical location and the shell sculpture pattern. Specimens bred in the laboratory developed shell apertures with a variety of sculptural patterns, including one present neither in the parents, nor in the population from which it came. This characteristic is probably phenotypically plastic. It cannot be used for taxonomic purposes, and it is suggested that great caution is needed before using similar characters in other species.

Population characteristics and planktonic larval stage of the New Zealand screwshell Maoricolpus roseus

Probst, T. A., Crawford, C. M. — 2008-04-22

Maoricolpus roseus is believed to have been introduced into Tasmania in the 1920s. Despite its wide distribution, dense populations and being considered successful in colonizing and altering several habitats, details of its reproduction and life cycle are not known. Specimens collected from the D'Entrecasteaux Channel (SE Tasmania) over 2 years showed sexual dimorphism with females relatively larger than males. A 1:1 sex ratio was observed and females were found carrying encapsulated larvae throughout consecutive austral summer seasons (September or October till February), with up to 70% of females carrying larvae. Larvae released from egg capsules were planktonic, all relatively well developed, and fed on microalgae, indicating that the species has planktotrophic development, and suggesting high potential for dispersal. This information is important for the development of management strategies to control this invasive species.

Molecular evidence of the evolutionary origin of a Bonin Islands endemic, Stenomelania boninensis

Miura, O., Mori, H., Nakai, S., Satake, K., Sasaki, T., Chiba, S. — 2008-04-22