Chaetal arrangement and chaetogenesis of hooded hooks in Lumbrineris (Scoletoma) fragilis and Lumbrineris tetraura (Eunicida,Annelida)

As the structure and arrangement of chaetae are highly specific for annelid species and higher taxonomic entities, we assume that rather conservative information guarantees formation of specific chaetae. Each chaeta of an annelid is formed within an ectodermal invagination, and the modulation of the apical microvilli pattern of the basalmost cell of this invagination determines the structure of the chaeta. Any hypothesis of the homology of chaetae could thus be tested by examining the process of chaetal formation. Investigations into the ultrastructure and formation of hooded hooks in different capitellids and spionids revealed that these chaetae can be homologized. The hood of each of their hooded hooks is formed by elongation of two rings of microvilli peripheral to the chaetal anlage, which give rise to the inner and outer layers of the hood. The hood layers are well separated and surround an empty space. Superficially similar hooded hooks are described for certain Eunicida. Presently available cladistic analyses suggest that the hooded hooks of eunicidans evolved independently of those in Capitellidae and Spionidae. Compared with the latter two families, we therefore expected to find differences in chaetogenesis of the hooded hooks in the eunicids Lumbrineris (Scoletoma) fragilis and Lumbrineris tetraura (Lumbrineridae). This was the case. In these eunicidans, the hood was formed by the bisected apical wall of the chaetoblast right after the mid‐apical section of the chaeta had been sunk deeply into the chaetoblast during its formation. The apical wall generated a brush of microvilli that preformed the hood. Because the microvilli of the hood showed some accelerated differentiation, they soon merged with those of the slowly growing setal shaft to form the broad manubrium of the hooded hook in lumbrinerids. Our study confirms the predicted differences in chaetogenesis of the superficially similar hooded hooks of capitellids and spionids compared with those of eunicids.     

Review of the Capitellidae (Annelida, Polychaeta) from the Eastern Tropical Pacific region, with notes on selected species

The main objective of this work is to contribute to the taxonomic knowledge of the species of Capitellidae reported for the Eastern Tropical Pacific. This catalogue includes the original name of each species, new names, synonymies, type localities, the museum or institution where the type material is deposited, revision of the material reported for the region by different authors, new examined material, previous reports from other regions of the world, and comments on systematics and distributions. The catalogue lists 43 species in 19 genera. Of these, 6 species were erroneously recorded for the region (Decamastus gracilis Hartman, 1963; Decamastus nudus Thomassin, 1970; Mastobranchus variabilis Edwing, 1984; Notomastus aberans Day, 1957; Notomastus americanus Day, 1973; Notomastus latericeus Sars, 1851) and 5 species are found here to be questionable records for the Eastern Tropical Pacific (Capitella capitata (Fabricius, 1780); Dasybranchus glabrus Moore, 1909; Decamastus lumbricoides Grube, 1878; Notomastus lineatus Claparède, 1870 and Notomastus tenuis Moore, 1909).     

Intertidal recruitment and feeding in relation to optimal utilization of nursery areas by juvenile English sole (Parophrys vetulus: Pleuronectidae)

Synopsis Juvenile Parophrys vetulus 19–102 mm were collected on an intertidal flat in Humboldt Bay during 1976–1977. Recently metamorphosed fish that fed almost exclusively on harpacticoid copepods and other epibenthic crustaceans were found in large numbers during spring and early summer. A feeding transition occurred among fish 50–65 mm in length, and infaunal polychaetes were the dominant prey of fish greater than 65 mm. Increases in the feeding niche width and average size of prey items, as well as a decrease in the number of prey items per stomach, accompanied growth.The disappearance of English sole from intertidal areas in early fall at an average size of 82 mm and their subsequent residence in subtidal channels until a size of 140 mm suggest a size-depth segregation within the nursery ground. The advantages of such a distribution are discussed in terms of optimal foraging and reduction of intra- and interspecific competition.