In lieu of an abstract, here is a brief excerpt of the content:

Chaetognaths are among the most abundant constituents of the marine zooplankton community. They represent around 10% of both the zooplankton numerical abundance and biomass in the world oceans (Bone, Kapp, and Pierrot-Bults 1991). Most species of chaetognaths are oceanic and cosmopolitan in distribution, while some are relegated to coastal estuarine-oceanic margins, although often in large numbers owing to the greater plankton productivity in those areas. Chaetognaths are holoplanktonic , developing directly from egg to adult during their life in the water column. Many species of Chaetognatha are epipelagic, but some undergo extensive vertical migrations and can be collected as part of the meso- or bathypelagic planktonic fauna. A few uncommon genera are benthic (i.e., Spadella, Paraspadella, Bathyspadella), and some others are exclusively deep-living (e.g., Hemispadella, Heterokrohnia) (Casanova, 1986, 1994, 1996, 1999). The new genus Calispadella was described recently as the first chaetognath recorded in a hydrothermal vent field (Casanova and Moreau 2005). Chaetognaths are active, raptorial predators that consume a significant percentage of zooplankton standing stock in coastal environments (Feigenbaum and Maris 1984). They prey heavily on copepods and fish larvae (Alvariño 1985, Saito and Kiørboe 2001); however, the hypothesis that chaetognaths can affect the recruitment of fishes at early stages (Alvariño1985) is not conclusive and has been under discussion for decades (Khulman 1977, Feigenbaum and Maris 1984). Some species of Chaetognatha have been regarded as zoogeographic or hydrographic indicators in different oceanic regions (Bieri 1959, Alvariño 1968, 1977, Brinton, Fleminger, and Siegel-Causey 1986). Chaetognath Studies in the Gulf of Mexico The earliest taxonomic accounts on the Chaetognatha of the Gulf of Mexico (GMx) were focused on the northern half of the Gulf, along the Florida coast (Pierce 1951). In the Fishery Bulletin 89, Pierce (1954) recorded 9 species of 6 genera of Chaetognatha; the material was collected at 2 fully oceanic sites in the northern half of the GMx basin. It is noteworthy to mention that the only Gulf record of Eukrohnia hamata, published by Pierce (1954), probably refers to another species, either E. bathypelagica Alvariño, 1962, or E. bathyantarctica 1165 69 Planktonic Chaetognatha of the Gulf of Mexico Rosa Ma. Hernández-Flores, Jerry A. McLelland, and Eduardo Suárez-Morales  Chaetognatha. After Hyman 1959. 1166 ~ Planktonic Chaetognatha with no intermediate taxonomic levels. Tokioka (1965) and Casanova (1985) proposed changes to the traditional classification scheme based on the analysis of previously unevaluated morphological characters (see Casanova 1999). Based on these criteria, the phylum Chaetognatha was then divided into 2 classes: Archisagittoidea, which contains a fossil form, and the Sagittoidea, a group including all present-day chaetognaths. This taxon has 2 orders, the Phragmophora, with a transverse muscle wall in the trunk, and the Aphragmophora, devoid of this character. In this new scheme, the formerly overloaded genus Sagitta was partitioned into 11 genera; currently, this genus contains only a few species. Overall, the new classification has been controversial, and not all specialists agree in using it; some of them state that there is no phylogenetical evidence supporting such changes (see Ghirardelli 1997). It is recognized that there are up to 115 species of Chaetognatha currently known in the world oceans (Bieri 1991, Pierrot-Bults 1996, Casanova 1999). Many species, up to 26, have been described recently by Russian researchers (Kasatkina 2001, 2002, 2003a, b, Kasatkina and Selivanova 2003a, b, Kasatkina and Sergeev 2004) from different areas of the North Pacific. Descriptions of all these species are in the Russian language , and their taxonomical status has yet to be resolved; if proved valid, the number of chaetognath species would increase to more than 140 wordwide. The species of Chaetognatha are contained in 15 genera, some of which are monotypic (i.e., Bathyspadella, Pterosagitta, Bathybelos , Xenokrohnia) and others (e.g., Archeterokrohnia, Eukrohnia, Krohnitta, Krohnitella) have only a few species each. Recently described new genera include Pseudeukrohnia , Calispadella, Protokrohnitella, and Protoeukrohnia ) (Kasatkina 1998, 2003a, Casanova and Moureau David, 1958, both described several years later. Eukrohnia hamata (Möbius, 1875) is common only in bipolar, deepwater regions, especially in the North Atlantic. It is considered unlikely that this species occurs in the Gulf of Mexico (see McLelland 1989a, b). Later on, the works by Tokioka (1955), Owre (1960), Pierce (1962), Fagetti (1968), and Owre (1973) contributed important additions to the knowledge of the chaetognath fauna of the Gulf. In the 1980s, the works by McLelland (1984, 1989a, b), McLelland and Perry (1989), and Maidana and Mostajo (1980), who added relevant data including new...

Share