Physalia physalis structure: axes, cormidia, and you can zooid versions
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Siphonophores add a great amount of functionally certified zooids which might be homologous to free living polyps otherwise medusae twenty-seven (Fig. step 1 ). Physalia physalis falls under Cystonectae, a clade which is sis to all the most other siphonophores 8 . Inside the a lot of time-stemmed cystonects (the cystonects apart from Physalia physalis) gastrozooids (giving polyps) happen because Crossdresser dating websites free the buds regarding anterior of the nest as they are sent into the rear from the an enthusiastic elongating stem, when you find yourself gonodendra (reproductive structures) are available independently across the stem twenty-eight . In all cystonects, new gonodendra was substance structures, that features gonophores (quicker medusae, bearing an effective gonad), palpons (derived gastrozooids, one to run out of tentacles when you look at the cystonects), and you can nectophores twenty-seven . P. physalis gonodendra provides such zooids, along with ‘jelly polyps’ which can be quicker nectophores off unsure means twenty-two , 26 .
Compared to the almost every other siphonophore types, plus most other cystonects, Physalia physalis is actually strange regarding its nest organization (Figs step one and you can ? anddos). 2 ). P. physalis is additionally the only real siphonophore variety where in fact the gastrozooid, an important giving zooid, does not have an excellent tentacle to possess target just take. Really the only different is the protozooid (the first gastrozooid to make throughout the invention), that is essentially a typical siphonophore gastrozooid, that have a throat, tentacle and you may brief basigaster region 26 , 31 . Besides the protozooid, inside P. physalis the latest tentacle was borne on a beneficial pulla 26 . Most other experts refer to both new zooid or perhaps the connected tentacle as the a great dactylozooid ten , thirteen , 21 , 31 – the expression dactylozooid have over the years already been put on palpons various other siphonophore kinds it is maybe not already used, and you will dactylozooids try official palpon-such as for instance defensive zooids in other hydrozoans 31 – 33 . To get rid of dilemma regarding the homology for the zooid, i recommend that the term dactylozooid really should not be put, while we think about this zooid to have developed de novo in P. physalis that’s not likely homologous to dactylozooids in other hydrozoans (select lower than). As well, the term ampulla is even commonly in the terminal vesicle of the tricornuate tentillum out-of agalmatids 27 . I like revitalizing Haeckel’s ‘tentacular palpon’ to refer to that zooid 34 , and that not just possess precedence, and also matches the brand new likely hypothesized resource in the zooid (get a hold of below).
Cystonects are dioecious, and all of the gonodendra when you look at the a nest bear gonophores out-of just one to gender
Nest direction during the siphonophores. A – prior, P – rear, D – dorsal, V – ventral, L – kept, R – proper. (A) Schematic regarding an older colony of one’s siphonophore Nanomia bijuga. Changed to include axes so you’re able to a drawing regarding Nanomia bijuga by FreyaGoetz ( licensed not as much as CC Because of the-SA step three.0 ( (B) Schematic out-of a developing Physalia physalis larva. Attracting centered on image by the Linda Ianniello. (C) Schematic regarding a mature Physalia physalis nest.
Haeckel detail by detail a couple of it is possible to hypotheses on supply of tentacular palpons – the first theory, marketed from the Huxley, is they commonly zooids, however they are rather secondary diverticula on the bottom of your own tentacle one mode similarly to ampullae inside echinoderm pipe legs 34 , thirty five . On the 2nd hypothesis, modification and subfunctionalization out-of a keen ancestral gastrozooid provided go up to two separate zooids – a good gastrozooid instead good tentacle and a good tentacular palpon that have an excellent tentacle. Totton suggested a modification of the initial hypothesis, and you may ideal that ‘ampulla’ is actually an excellent hypertrophied basigaster (aboral area for a great gastrozooid one to plays a dynamic role into the nematogenesis) who has got split up about remainder of the gastrozooid 26 . But not, i choose another hypothesis, considering observations of your gastrozooid and you can tentacular palpon (Figs step 3 – 6 ; Secondary movies 1 , dos ). This new gastrozooid and you will tentacular palpon try borne for the independent peduncles (Figs 5A,B and you may ? and6A; 6A ; Additional videos dos ), and develop out of line of, separate buds (Figs 3A,B , ? ,4; 4 ; Second videos step 1 ). Ergo, the new tentacular palpon try good derived gastrozooid, book to help you Physalia physalis, that has an expanded tentacle, no lips, which can be functionally specialized to possess nematocyst manufacturing. The gastrozooids into the P. physalis also are derived gastrozooids which have destroyed tentacles consequently they are functionally certified getting feeding merely. This new subfunctionalized gastrozooid theory is even more parsimonious than the other hypotheses, while the modification and you can subfunctionalization out-of zooids is typical in siphonophores – palpons, eg, are believed are derived, altered gastrozooids that routinely have a lesser tentacle 27 .