ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652452

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

McLaughlin and Lemaitre (1997), in their examination of carcinization in the Anomura, rejected the traditional concept of paguroid evolution, which had consistently maintained that the lithodid crab-like body form evolved from a typical shell-dwelling hermit crab. Their hypothesis proposed just the reverse, i.e., the lithodid crab-like body form gave rise to the simple hermit crab body form through calcium loss, habitat change and consequential morphological adaptations. Their original hypothesis was based on characters derived from adult morphology, but they suggested that larval data would support their view. The megalopal and first or first- and second-crab stages of representatives of both subfamilies of the Lithodidae provide the first of such larval information. Ten species in eight genera have been examined specifically for development of abdominal tergites. These data, although preliminary in scope, unequivocally disprove the Bouvierian concept of lithodid abdominal plate development, and in so doing, lend substantial support to McLaughlin and Lemaitre's hypothesis.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652453

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

During brachyuran zoeal development, body somites, appendage setal counts and segment numbers either remain constant or show some increase. Setae and segments once gained are never lost during the zoeal phase except at metamorphosis to megalop. Changes in the relative timing of appearance of particular setae or in the expression of particular segmental articulations often coincide with abbreviated zoeal development. This study compares chaetotaxy and segmentation among three brachyuran families with differences in numbers of zoeal stages. Comparison against a reference zoeal developmental sequence (the outgroup) helped to identify some heterochronic processes such as acceleration or terminal delay of characters. Such characters may have phylogenetic significance.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652454

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Emigration and immigration of decapod larvae from estuaries depend on timing of larvae occurrence in the water column relative to the tidal, tidal amplitude and day cycles. The phase relation of these natural cycles varies with tidal regime and geographically, resulting in different time-patterns of hatching of first stage larvae and of presence of late stage larvae in the water column. Vertical migration behaviour according to phase of tide also controls transport inside estuaries. These mechanisms were investigated in a field study conducted on the northwest coast of Portugal where neap ebb tides occur during the night around the quarters of the moon. Flux of decapod larvae through one sampling station was measured during one lunar month at the Canal de Mira (Ria de Aveiro) in the spring of 1990. The sampling programme was comprised of a set of 25-h fixed station studies, separated by 25-h intervals during which no sampling took place. Plankton samples were collected with a pump every hour at three depths. Current velocity and direction at the standard depths, as well as height of the water column, were also measured every hour. Hourly instantaneous flux of larvae through a 1-m-wide vertical section of the Canal de Mira was calculated for the most abundant forms. A total number of 13 combinations of species and larval stages were analyzed, belonging to the families Atelecyclidae, Pirimelidae, Portunidae, Pilumnidae, Grapsidae, Palaemonidae, Crangonidae and Thalassinidae. Patterns of net larval flux along the lunar month could be grouped into three types. Type 1 includes first zoeas that were consistently exported to the sea. Type 2 comprises late zoeas, megalops and juveniles that were consistently imported into the estuary. First zoeas that were imported during some of the 25-h studies but were exported during the others were included in Type 3; in species of this type import periods appeared to alternate with export periods according to lunar phase. Flux of Type 1 larvae followed a semi-lunar pattern. Release activity of Type 1 zoeas took place during the night and started during neap tides around the quarters of the moon, but maximum releases occurred 3–4 h after high tide of average amplitude tides, 3–4 days after the quadratures. These observations agree with the hypothesis that hatching is timed to occur on ebb tides of the largest possible amplitude so that larvae are easily dispersed from areas with a high density of predator fishes. However, based on other observations on the Portuguese coast, it cannot be ruled out that hatching might depend on a minimum number of hours of darkness experienced by the females. Larvae included in Type 2 comprise forms that may have been retained inside the estuary for the entire larval phase, as well as one form that was imported from shelf waters. No semi-lunar pattern of import was detected in this last form. Fluctuations of net flux observed in Type 3 larvae, as well in other forms that were not included in any of the types, were more difficult to explain. These larvae were first zoeas of species belonging to different taxonomic, morphological and ecological groups and may show a diversity of adaptations to the way of life of the adults. Imports and exports of larvae depended not only on time-patterns of abundance, but also on time-patterns of larval vertical distribution. As a general rule, larval stages showed patterns of depth distribution that were consistent with vertical migration rhythmic behaviours synchronized with the tidal cycle. Though the effect was not always statistically significant, first-stage larvae were closer to the surface during ebb, especially during the night, enhancing seaward transport. On the contrary, later zoeal stages, megalops and juveniles were usually closer to the surface during flood, suggesting migration to the water column during this phase of the tide and landward transport.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652455

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The complete larval development ofBrachynotus sexdentatus(Risso, 1827) was obtained by culture in the laboratory. Five zoeal stages, megalop and first crab are described and illustrated. Larval development from hatching to megalop stage took a minimum of 17 days at 23°C. The morphological characters of the larvae ofB. sexdentatusare compared with those of the previous descriptions of plankton-collected material and other known larvae of the genusBrachynotus.Larval features of the recently redefined Varunidae are evaluated taking into account all previous larval descriptions from this family. A combination of consistent characters can be used to distinguish varunid zoeas and megalops stages from the early life stages of all other grapsoid families.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652456

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Eumedonid crabs have an unusual ecology. They are a specialized group of brachyurans, which are wholly symbiotic with echinoderms. Consequently, this taxon has received much attention from carcinologists, but consensus on the familial status of these crabs has not been reached. Eumedonids have been variously regarded as a subfamily of the Parthenopidae, as pilumnids and as a distinct family. The taxonomic position of the Eumedonidae is appraised using available first zoeal and adult characters. The validity of this family status is challenged, and the present study shows that this group of crabs cannot be distinguished from the pilumnids and therefore supports the view that the eumedonids are a subfamily of the Pilumnidae.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652457

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The complete larval development and first crab stage ofXantho pilipesA. Milne-Edwards, 1867, reared in the laboratory, are described and figured. A comparison with other larvae of the family Xanthidae, previously described:X incisus, X. poressa, Monodaeus couchiandPanopeus africanusoccurring in the Iberian Peninsula, is presented, with information on how to distinguish these species.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652458

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652459

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652460

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652451

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor