Performance and Discussion
Siphonophores feature loads of functionally certified zooids which can be homologous in order to free-living polyps otherwise medusae 27 (Fig. step one ). Physalia physalis falls under Cystonectae, a great clade that is sis to any or all most other siphonophores 8 . From inside the much time-stemmed cystonects (all the cystonects with the exception of Physalia physalis) gastrozooids (feeding polyps) develop because buds throughout the anterior of colony and they are sent with the rear from the a keen elongating stalk, while you are gonodendra (reproductive structures) come separately over the stalk 28 . In most cystonects, new gonodendra try compound formations, that contains gonophores (quicker medusae, influence a beneficial gonad), palpons (derived gastrozooids, you to definitely lack tentacles for the cystonects), and nectophores twenty-seven . P. physalis gonodendra possess such zooids, together with ‘jelly polyps’ which can be faster nectophores from uncertain setting 22 , twenty-six .
Compared to almost every other siphonophore variety, also other cystonects, Physalia physalis is unusual when it comes to the nest team (Figs step 1 and ? anddos). 2 ). P. physalis is even truly the only siphonophore variety where gastrozooid, the primary feeding zooid, doesn’t always have a tentacle having prey need. Truly the only difference is the protozooid (the original gastrozooid in order to create during the creativity), which is fundamentally a consistent siphonophore gastrozooid, having a mouth area, tentacle and you can small basigaster area 26 , 31 . Apart from the protozooid, within the P. physalis the latest tentacle is actually borne to your a beneficial pulla twenty-six . Other article writers relate to both this new zooid or even the connected tentacle while the a good dactylozooid 10 , 13 , 21 , 29 – the word dactylozooid possess usually started applied to palpons in other siphonophore kinds but is not currently made use of, and you may dactylozooids is actually certified palpon-such protective zooids various other hydrozoans 30 – 33 . To quit misunderstandings about the homology of this zooid, we recommend that the term dactylozooid shouldn’t be used, as we consider this zooid having developed de- novo during the P. physalis and that’s unlikely homologous so you can dactylozooids various other hydrozoans (pick less than). Concurrently, the definition of ampulla is additionally commonly regarding the terminal vesicle of the tricornuate tentillum from agalmatids twenty-seven . I favor revitalizing Haeckel’s ‘tentacular palpon’ to mention to that zooid 34 , and that not just has precedence, as well as suits this new almost certainly hypothesized provider from the zooid (select less than).
Cystonects is actually dioecious, and all the brand new gonodendra into the a nest incur gonophores of only that sex
Nest orientation for the siphonophores. A beneficial – anterior, P – rear, D – dorsal, V – ventral, L – leftover, R – best. (A) Schematic from an older nest of one’s siphonophore Nanomia bijuga. Changed to include axes so you can an attracting from Nanomia bijuga of the FreyaGoetz ( subscribed lower than CC Of the-SA 3.0 ( (B) Schematic away from a creating Physalia physalis larva. Attracting according to picture from the Linda Ianniello. (C) Schematic out of a mature Physalia physalis nest.
Haeckel detail by detail several you are able to hypotheses to the origin from tentacular palpons – the initial hypothesis, marketed by Huxley, is because they commonly zooids, but are alternatively additional diverticula toward the base of the tentacle one to mode similarly to ampullae in the echinoderm tube legs 34 , thirty-five . Regarding second theory, amendment and you will subfunctionalization regarding an ancestral gastrozooid provided increase to several independent zooids – a great gastrozooid as https://hookupreviews.net/hookup-apps-for-couples/ opposed to a tentacle and you may a tentacular palpon having an excellent tentacle. Totton recommended a change in the original theory, and advised that ‘ampulla’ is a beneficial hypertrophied basigaster (aboral area for a beneficial gastrozooid one takes on an active role for the nematogenesis) that has split in the other countries in the gastrozooid 26 . not, we favor the next theory, centered on findings of your gastrozooid and tentacular palpon (Figs step three – six ; Secondary films step one , 2 ). The fresh gastrozooid and you will tentacular palpon was borne towards separate peduncles (Figs 5A,B and ? and6A; 6A ; Additional clips 2 ), and produce from type of, independent buds (Figs 3A,B , ? ,4; cuatro ; Secondary movies step 1 ). Ergo, the fresh new tentacular palpon is actually an excellent derived gastrozooid, unique to Physalia physalis, that has an enlarged tentacle, zero throat, that’s functionally authoritative to own nematocyst manufacturing. The latest gastrozooids inside P. physalis also are derived gastrozooids having destroyed tentacles as they are functionally specialized having feeding only. The subfunctionalized gastrozooid hypothesis is even even more parsimonious compared to the other hypotheses, as amendment and you will subfunctionalization out-of zooids is normal when you look at the siphonophores – palpons, like, are considered becoming derived, changed gastrozooids you to definitely normally have a lower life expectancy tentacle twenty-seven .