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Siphonophores add loads of functionally specialized zooids which can be homologous to free living polyps otherwise medusae twenty-seven (Fig. step one ). Physalia physalis is part of Cystonectae, an effective clade that is cousin to all the almost every other siphonophores 8 . From inside the much time-stemmed cystonects (all cystonects except for Physalia physalis) gastrozooids (feeding polyps) develop as buds in the prior of your own colony and so are transmitted with the posterior by the an elongating base, whenever you are gonodendra (reproductive formations) are available by themselves over the stalk 28 . In most cystonects, the latest gonodendra try material structures, that features gonophores (less medusae, influence good gonad), palpons (derived gastrozooids, one to lack tentacles in the cystonects), and nectophores twenty seven . P. physalis gonodendra features these types of zooids, and ‘jelly polyps’ that are less nectophores from not sure setting twenty two , twenty six .
As compared to most other siphonophore types, including almost every other cystonects, Physalia physalis is peculiar with regards to its nest providers (Figs step 1 and you can ? and2). dos ). P. physalis is even the only real siphonophore variety the spot where the gastrozooid, the main giving zooid, doesn’t have a beneficial tentacle to own sufferer www.datingmentor.org/catholicsingles-com-vs-catholicmatch-com/ get. Really the only exemption is the protozooid (the original gastrozooid to make during invention), that is fundamentally a consistent siphonophore gastrozooid, that have a mouth, tentacle and you may brief basigaster area 26 , 31 . Aside from the protozooid, inside P. physalis brand new tentacle is actually borne into the a great pulla twenty-six . Almost every other authors refer to either the fresh new zooid or perhaps the attached tentacle once the a great dactylozooid 10 , thirteen , 21 , 30 – the expression dactylozooid keeps historically come used on palpons various other siphonophore varieties it is maybe not already utilized, and you can dactylozooids is actually authoritative palpon-for example protective zooids in other hydrozoans 29 – 33 . To stop misunderstandings in regards to the homology from the zooid, i suggest that the phrase dactylozooid should not be put, even as we think about this zooid to have developed de novo when you look at the P. physalis which can be not likely homologous so you can dactylozooids various other hydrozoans (see lower than). In addition, the term ampulla is also commonly on the critical vesicle of your tricornuate tentillum regarding agalmatids twenty seven . We like revitalizing Haeckel’s ‘tentacular palpon’ to mention to that particular zooid 34 , which just features precedence, and suits the brand new more than likely hypothesized provider regarding the zooid (come across below).
Cystonects try dioecious, and all sorts of the new gonodendra when you look at the a nest incur gonophores out of only one to gender
Colony direction in siphonophores. Good – prior, P – rear, D – dorsal, V – ventral, L – leftover, Roentgen – right. (A) Schematic out of an older colony of the siphonophore Nanomia bijuga. Modified to include axes so you can an attracting out of Nanomia bijuga because of the FreyaGoetz ( registered below CC From the-SA step three.0 ( (B) Schematic out of a creating Physalia physalis larva. Attracting predicated on image from the Linda Ianniello. (C) Schematic of an older Physalia physalis colony.
Haeckel detailed several you are able to hypotheses to your resource out-of tentacular palpons – the original hypothesis, marketed because of the Huxley, is that they are not zooids, but they are alternatively additional diverticula at the base of your own tentacle one form much like ampullae for the echinoderm tubing legs 34 , 35 . From the 2nd hypothesis, modification and subfunctionalization of a keen ancestral gastrozooid offered increase to several separate zooids – a gastrozooid rather than a tentacle and you may an effective tentacular palpon having an effective tentacle. Totton suggested a modification of the original hypothesis, and you can advised that ‘ampulla’ is actually good hypertrophied basigaster (aboral area for an excellent gastrozooid one to takes on a working character in the nematogenesis) that split from the remaining portion of the gastrozooid twenty-six . But not, we like the following hypothesis, based on findings of the gastrozooid and you will tentacular palpon (Figs step 3 – 6 ; Second video 1 , 2 ). The brand new gastrozooid and you will tentacular palpon is borne for the independent peduncles (Figs 5A,B and you will ? and6A; 6A ; Second films dos ), and develop from distinctive line of, separate buds (Figs 3A,B , ? ,cuatro; 4 ; Additional video clips step 1 ). For this reason, the new tentacular palpon was good derived gastrozooid, novel in order to Physalia physalis, who’s got an increased tentacle, zero lips, in fact it is functionally official having nematocyst creation. The newest gastrozooids in the P. physalis are derived gastrozooids with missing tentacles and therefore are functionally authoritative having giving just. Brand new subfunctionalized gastrozooid theory is even way more parsimonious as compared to other hypotheses, given that amendment and you may subfunctionalization away from zooids is normal in siphonophores – palpons, particularly, are thought becoming derived, changed gastrozooids one to routinely have a diminished tentacle twenty seven .