Cydippida
| Cydippida | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Comb jellyfish Mertensia ovum |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Cydippida | ||||||||||||
| Lesson , 1843 | ||||||||||||
| Familys | ||||||||||||
|
As cydippida is called an ecologically important and diverse order of comb jellies (Ctenophora) from the class Tentaculata . Cydippida such as the sea gooseberry ( Pleurobrachia pileus ) are in many ways the "typical" rib jellyfish and combine many characteristics that may be considered original within the group. Since the group is probably not monophyletic, i.e. does not include all descendants of their last common ancestor, the systematics predominant today, cladistics , does not recognize the group as a taxon .
construction
Most species have a spherical to slightly oval appearance and are, if at all, compressed in the plane of the tentacles , that is, the pharyngeal body axis lying perpendicular to the line connecting the two well-developed tentacle sheaths is shortened.
All species have well-developed comb ribs; Unlike in other jellyfish orders, the individual comb platelets are not connected to each other by flagellum canals - the signal from the statocyst is apparently transmitted solely through the serial overturning of the platelets and the resulting water currents - comparable to the domino effect .
The food caught by the long tentacles passes through the mouth into the muscular throat, where it is broken down by the release of digestive enzymes and finally passed on to the centrally located stomach.
From there, on the side remote from the mouth, an aboral canal leads out, which is divided into four short anal canals, two of which end blind and two in anal pores. Two paragastric channels run parallel to the flat sides of the gullet, one tentacle channel each runs to the attachment of the tentacles in the tentacle sheaths and supplies them with nutrients. In addition, there are four transversal canals that run vertically in all "cardinal directions" away from the body axis and divide again outwards in a Y-shape. They open into the meridional canals running below the ridges, which, like the paragastric canals, run out blindly.
The musculature is smooth like in all other comb jellyfish, only in Euplokamis dunlapae there are striated muscles, which in this species enable an explosive unrolling of the tentils when touched by prey.
Distribution, habitat and locomotion
Cydippida species are distributed worldwide and live free-swimming in the sea as part of the macrozooplankton , both on the high seas and near the coast.
They use their comb ribs for locomotion, but mostly allow themselves to be drifted passively in ocean currents, which can result in large groups of individuals.
nutrition
Like most comb jellyfish, the Cydippida feed on various plankton, especially cnidarians , crabs , but also small fish . All species use their tentacles to catch prey, which are pulled through the water like a drift net. As soon as a prey comes into contact with these and sticks to the transverse threads, the tentils, which are occupied by adhesive bodies, the colloblasts , the corresponding tentacle is shortened by muscle action and pulls the prey forward towards the mouth. At the same time, the comb jelly reverses the direction of impact of two suitable rows of combs so that it turns towards the tentacle section with the captured prey until it touches the mouth so that it can be swallowed. Because of the turning maneuver, this method is also known as "spin capture" and is only efficient for larger prey.
The species of the genus Haeckelia take over the nettle cells , then known as kleptocnids , from their prey prey - a circumstance which, until it was discovered, led to confusion among zoologists for a long time, since the occurrence of nettle cells in corticosteroid jellyfish is mistaken for a close relationship the originators of these cells, the cnidarians.
A species from the genus Lampea presumably lives parasitically on sea squirts (Ascidiacea) by attaching itself to them with the everted pharynx lining.
Reproduction
All Cydippida reproduce sexually. Although they are hermaphrodites , meaning that they have both male and female gonads, self-fertilization is apparently rather rare.
Tribal history
Unlike the other groups of jellyfish, the order fossil is known from finds from the geological age of the Devonian , which were found in fine-grained shale from the Hunsrück . There are two species, Archaeocydippida hunsrueckiana and Paleoctenophora brasseli . However, they cannot be assigned to any modern family.
Comparison with the other cider jellyfish taxa shows that the order appears to have preserved a large number of original features. The embryological development of all other comb jellyfish via a Cydippea stage, which looks like a miniature version of a Cydippida comb jellyfish, even if the adult animals have a strongly modified physique, as in the Platyctenida, indicates the relatively small morphological divergence of the Cydippida from the putative common ancestor of all comb jellyfish. From this, however, according to the systematics prevailing today, the cladistics , the question arises as to which common, newly established characteristics connect the Cydippida at all - without such synapomorphies the group cannot count as a natural unit.
Preliminary results of both morphological and molecular genetic studies indicate that the Cydippida may be a polyphyletic taxon, i.e. a completely arbitrary grouping of species with the exception of characteristics inherited from the common ancestor of the comb jellyfish have nothing in common.
If these results are confirmed, the classification of the fossil species in the order Cydippida would be largely irrelevant and would only mean that they were representatives of the stem line of the corticoid jellyfish - it would no longer be possible to deduce that they belong to a modern group within the cortical jellyfish.
Systematics
A total of ten families with more than sixty species are distinguished within the order:
- The family Ctenillidae is monotypic, so it contains only one species, Ctenella aurantia . It was only discovered in 1993.
- The Euplokamidae family includes five species in a genus Euplokamis . The only species of rib jellyfish with striated muscles, which is used for the explosive unrolling of the rolled-up tentils, belongs here.
- The Haeckeliidae family includes five species in two genera, Haeckelia and Tinerfe .
- The family Bathyctenidae with the species Bathyctena chuni is again monotypical .
- The Lampeidae family includes three species in one genus, Lampea , including the only parasitic comb jellyfish.
- The Mertensiidae family comprises ten species in four genera, including the common and eponymous genus Mertensia .
- The family Pleurobrachiidae is the most species-rich Cydippida taxon and comprises twenty-nine species in seven genera, including the sea gooseberry ( Pleurobrachia pileus ).
- The monotypic family Dryodoridae with the species Dryodora glandiformis was not described until the 1990s .
- The family Cryptocodidae was also first described in the 1990s and includes only one species with Cryptocoda gerlachi .
- In May 2020, the Vampyroctenidae family was introduced with Vampyroctena delmarvensis as the only species.
The specified numbers of species should only be viewed as a guide, as many species names are probably synonyms.
In addition to the families listed, there are six previously unassigned genera and several undescribed species, including the "Red Tortuga", which does not yet have a scientific name.
literature
- Mackie, GO, Mills, CE, Singla, CL, Structure and function of the prehensile tentilla of Euplokamis ( Ctenophora, Cydippida ), Zoomorphology, 107 , 1988, p. 319
- Mills, CE, Miller, RL, Ingestion of a medusa ( Aegina citrea ) by the nematocyst-containing ctenophore Haeckelia rura (formerly Euchlora rubra ): Phylogenetic Implications , Journal of Marine Biology, 78 , 1984, p. 215
- Tamm, S. L, Moss, AG, Unilateral ciliary reversal and motor responses during prey capture by the ctenophore Pleurobrachia, Journal of Experimental Biology, 114 , 1985, p. 443
Web links
Individual evidence
- ↑ James P. Townsend, Michael G. Tassia, Alejandro Damian-Serrano, Nathan V. Whelan, Kenneth M. Halanych, and Alison M. Sweeney. 2020. A Mesopelagic Ctenophore representing A New Family, with Notes on Family-level Taxonomy in Ctenophora: Vampyroctena delmarvensis gen. Nov. sp. nov. (Vampyroctenidae, fam. Nov.). Marine biodiversity. 50: 34. DOI: 10.1007 / s12526-020-01049-9
