| Spadellidae | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chaetognatha |
| Class: | Sagittoidea |
| Order: | Phragmophora |
| Family: | Spadellidae Tokioka, 1965 [1] |
Spadellidae is a family of sagittoideans in the order Phragmophora. Spadellidae prey on plankton and commonly reside in the epipelagic zone of the ocean. [2]
The Chaetognatha or chaetognaths are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, about 20% of the known Chaetognatha species are benthic, and can attach to algae and rocks. They are found in all marine waters, from surface tropical waters and shallow tide pools to the deep sea and polar regions. Most chaetognaths are transparent and are torpedo shaped, but some deep-sea species are orange. They range in size from 2 to 120 millimetres.
Zooplankton are the animal component of the planktonic community. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequently, they drift or are carried along by currents in the ocean, or by currents in seas, lakes or rivers.
Eukrohniidae is a family of sagittoideans in the order Phragmophora. It consists of a single genus, Eukrohnia von Ritter-Záhony, 1909.
María de los Ángeles Alvariño González, known as Ángeles Alvariño, was a Spanish fishery research biologist and oceanographer globally recognized as an authority in plankton biology. She was the first woman ever appointed as scientist aboard any British or Spanish exploration ship. She discovered 22 new species of marine animals and published over a hundred scientific books, essays, and articles. In her late career she studied the history of early marine scientific exploration.
Gnathifera is a clade of generally small spiralians characterized by complex jaws made of chitin. It comprises the phyla Gnathostomulida, Rotifera, Micrognathozoa, and Chaetognatha. It may also include the Cycliophora.
Platyhedylidae is a family of sacoglossan sea slugs, marine gastropod mollusks in the superfamily Platyhedylidae.
Dorymenia is a genus of solenogasters, a kind of shell-less, worm-like mollusk.
Rhopalaea is a genus of tunicates belonging to the family Diazonidae. The genus has a cosmopolitan distribution in warm and temperate oceans.
Parasagitta elegans, the elegant arrow worm, is a small arrow worm in the family Sagittidae, previously named Sagitta elegans
Thomas Everett Thompson PhD DSc FZS was a British malacologist and embryologist, known for his extensive studies on opisthobranch molluscs.
Heterokrohniidae is a family of sagittoideans in the order Phragmophora.
Krohnittidae is a family of chaetognaths in the order Aphragmophora. It consists of a single genus, Krohnitta von Ritter-Záhony, 1910.
Heterokrohnia is a genus of chaetognaths in the family Heterokrohniidae.
Caecosagitta macrocephala is a deep sea marine chaetognath that is distributed in meso- and bathypelagic layers. It has a very wide distribution that ranges from the Subantarctic to Subarctic Ocean. Cecosagitta macrocephalas have large heads, hence their name “macro-cephala”. Within their eyes are photoreceptive regions that allow them to catch weak light at bathypelagic depths. Along with their eyes, their gut or intestine has orange pigmentation and a luminous organ that gleams due to bioluminescence unlike some other species of Sagittidae. To be more precise, the luminescent organ is located on the ventral edge of each anterior lateral fin. It is the only member of the genus Caecosagitta, and only one of the two known species of bioluminescent chaetognath, the other being the distantly related Eukrohnia fowleri. C. macrocephala has a secreted bioluminescence that is thought to be coelenterazine based. The luciferase is highly unstable, being unable to survive a single freeze-thaw, and is rapidly inactivated at ice-cold temperatures.
Xenokrohnia is a genus of chaetognaths in the family Heterokrohniidae. It consists of one species, Xenokrohnia sorbei Casanova, 1993, which lives in a marine environment. The initial discovery was made from six specimens found in a deep-sea search in the Bay of Biscay for Spadella equidentata Casanova, 1987. A uniquely large (ventral) secretory gland, separate from other chaetognaths, defined the new genus and species. The gland, which is likely used to rid the body of digestive fluids, is probably due to the unique feeding habits of the species; these may include scavenging habits. The presence of an unusual and seemingly superfluous digestive utility is similar to Archeterokrohnia palpifera Casanova, 1986, which have a larger pair of pedipalps then what is common for chaetognaths.
Bathyspadella is a genus of chaetognaths in the family Spadellidae. The genus shares morphological similarities to Eukrohniidae and Spadellidae, although it is molecularly similar to Heterokrohniidae. The unusual position of Bathyspadella would indicate a need to revise the existing order of Phragmophora; however, that would be very difficult, as a number of genera and species exist only in small or difficult to access populations, by which it would be difficult to fully examine all related species. A review of the Chaetognatha, published after the discovery of B. oxydentata, found that the standard division of Phragmophora and Aphragmophora to be improper molecularly, noting the close morphological convergence of the Krohnittidae (Aphragmophora) and Xenokrohnia.
Calispadella is a genus of chaetognaths in the family Spadellidae. It consists of one species, Calispadella alata Casanova & Moreau, 2005. It is differentiated from other species of Spadellidae by the presence of an unusually long tail segment and a rare aspect of the lateral fins, similar to that of Paraspadella gotoi Casanova, 1990. The species is noted by the complete development of seminal vesicles in juveniles and the use of lateral fins for buoyancy in the deep-sea waters where the specimens were found. It was the first to be described exclusively in the range of deep-sea hydrothermic vents.
Hemispadella is a genus of chaetognaths in the family Spadellidae. It consists of one species, Hemispadella dauvini Casanova, 1996. The species, as the generic name implies, shares numerous, but not all, of the characteristics of Spadellidae; it shares a number of other characteristics with Heterokrohniidae. The ventral ganglion, poorly described in chaetognaths, is of similar size to the Heterokrohniidae, and the larger number of teeth, and the difference in appearance and function between the anterior and posterior teeth, are similarly characteristic. The relative tail size is similar to that of the Spadellidae, although the overall size is unprecedented among the Spadellidae. The more developed nature of transverse musculature and the basis for the lateral fins are as those of Spadellidae, as well.
Paraspadella is a genus of chaetognaths in the family Spadellidae. Paraspadella was originally considered as Spadella before a revision separated that genus into three genera: Spadella, Paraspadella, and Gephyrospadella, the last of which is now synonymised to Paraspadella. The initial division was based on previous knowledge of three groups of Spadella, in a similar manner in which Sagitta was divided into a family of genera. Paraspadella is differentiated from Spadella by the presence of disparate (digital) adhesive organs, present in the former to various degrees, but entirely absent in the latter.
Spadella is a genus of chaetognaths belonging to the family Spadellidae.
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