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Siphonophores integrate an abundance of functionally specialized zooids that will be homologous to help you free-living polyps otherwise medusae twenty seven (Fig. step 1 ). Physalia physalis belongs to Cystonectae, an effective clade which is cousin to all almost every other siphonophores 8 . In long-stemmed cystonects (most of the cystonects with the exception of Physalia physalis) gastrozooids (serving polyps) arise due to the fact buds about anterior of nest and generally are sent to the rear by the an elongating stem, while you are gonodendra (reproductive structures) come individually across the base 28 . In most cystonects, the fresh gonodendra is actually compound formations, which has gonophores (reduced medusae, results an effective gonad), palpons (derived gastrozooids, you to run out of tentacles into the cystonects), and nectophores twenty seven . P. physalis gonodendra keeps such zooids, together with ‘jelly polyps’ that will be shorter nectophores regarding undecided mode twenty two , 26 .
Compared to the almost every other siphonophore kinds, along with other cystonects, Physalia physalis are unusual when it comes to its nest business (Figs 1 and you will ? and2). 2 ). P. physalis is additionally the only real siphonophore varieties where in fact the gastrozooid, an important giving zooid, doesn’t have a great tentacle having sufferer capture. Truly the only exemption ‘s the protozooid (the first gastrozooid to create throughout the innovation), which is essentially a consistent siphonophore gastrozooid, which have a mouth, tentacle and you can short basigaster area twenty-six , 31 . Apart from the protozooid, when you look at the P. physalis brand new tentacle was borne towards a good pulla 26 . Other article writers make reference to possibly the zooid or the connected tentacle once the good dactylozooid ten , thirteen , 21 , 31 – the expression dactylozooid provides over the years been placed on palpons various other siphonophore types but is perhaps not currently used, and dactylozooids is specialized palpon-like defensive zooids various other hydrozoans 29 – 33 . To quit confusion regarding the homology of the zooid, i advise that the term dactylozooid really should not be put, once we think of this zooid to possess developed de novo within the P. physalis that will be unlikely homologous to help you dactylozooids various other hydrozoans (look for lower than). As well, the term ampulla is additionally commonly regarding the critical vesicle of the tricornuate tentillum out of agalmatids twenty seven . We like reviving Haeckel’s ‘tentacular palpon’ to refer to this zooid 34 , hence not merely keeps precedence, also fits brand new almost certainly hypothesized resource for the zooid (see lower than).
Cystonects try dioecious, and all sorts of this new gonodendra inside the a nest sustain gonophores regarding only you to definitely sex
Colony direction in the siphonophores. Good – anterior, P – rear, D – dorsal, V – ventral, L – kept, Roentgen – proper. (A) Schematic of an older colony of your siphonophore Nanomia bijuga. Changed to incorporate axes so you can an attracting out-of Nanomia bijuga of the FreyaGoetz ( authorized not as much as CC Of the-SA step 3.0 ( (B) Schematic out-of a developing Physalia physalis larva. Drawing centered on image because of the Linda Ianniello. (C) Schematic regarding a mature Physalia physalis colony.
Haeckel intricate one or two you can easily hypotheses toward resource away from tentacular palpons – the original hypothesis, promoted by Huxley, is that they are not zooids, however they are instead supplementary diverticula on the bottom of your own tentacle one to function much like ampullae in the echinoderm pipe base 34 , thirty five . From the second hypothesis, amendment and subfunctionalization out of an ancestral gastrozooid provided increase so you can a couple of independent zooids – a gastrozooid without an excellent tentacle and you will good tentacular palpon which have an effective tentacle. Totton proposed a general change in the original hypothesis, and you can advised the ‘ampulla’ is good hypertrophied basigaster (aboral region of an effective gastrozooid you to plays an active part during the nematogenesis) who’s got separated in the other countries in the gastrozooid twenty-six . But not, we prefer the second hypothesis, based on findings of gastrozooid and you can tentacular palpon (Figs step 3 – 6 ; Second clips step one , 2 ). The new gastrozooid and you can tentacular palpon try borne to your independent peduncles (Figs 5A,B and ? and6A; 6A ; Secondary video clips dos ), and develop of line of, separate buds (Figs 3A,B , ? ,cuatro; 4 ; Supplementary video clips 1 ). Hence, brand new tentacular palpon are a good derived gastrozooid, novel to help you Physalia physalis, who has got an increased tentacle, no lips, which can be functionally formal to possess nematocyst creation. This new gastrozooids within the P. physalis are also derived gastrozooids which have www.datingmentor.org/cs/countrymatch-recenze/ missing tentacles and generally are functionally authoritative getting serving merely. The brand new subfunctionalized gastrozooid theory is additionally so much more parsimonious as compared to other hypotheses, because modification and subfunctionalization regarding zooids is normal in siphonophores – palpons, such as for instance, are believed to-be derived, modified gastrozooids one to routinely have a diminished tentacle 27 .