Overall performance and you will Talk
Siphonophores consist of a good amount of functionally specialized zooids which might be homologous to free living polyps or medusae twenty seven (Fig. step 1 ). Physalia physalis belongs to Cystonectae, an excellent clade that’s brother to all other siphonophores 8 . In long-stemmed cystonects (every cystonects except for Physalia physalis) gastrozooids (eating polyps) develop due to the fact buds regarding prior of one’s colony and so are transmitted into the rear of the a keen elongating stem, whenever you are gonodendra (reproductive structures) arrive individually across the stalk twenty eight . In every cystonects, this new gonodendra is substance structures, that features gonophores (quicker medusae, affect an excellent gonad), palpons (derived gastrozooids, you to definitely lack tentacles in the cystonects), and nectophores twenty-seven . P. physalis gonodendra has https://datingmentor.org/tr/chatiw-inceleme/ actually this type of zooids, and additionally ‘jelly polyps’ which might be faster nectophores out of unsure function 22 , twenty-six .
Versus most other siphonophore species, also most other cystonects, Physalia physalis was unusual when it comes to their nest team (Figs step 1 and you will ? anddos). dos ). P. physalis is also really the only siphonophore variety where in actuality the gastrozooid, the main giving zooid, doesn’t always have a great tentacle for prey simply take. Really the only exception is the protozooid (the initial gastrozooid in order to create through the creativity), that is fundamentally a consistent siphonophore gastrozooid, which have a mouth area, tentacle and you can brief basigaster area 26 , 29 . Aside from the protozooid, within the P. physalis the tentacle is actually borne into the a beneficial pulla twenty six . Other authors consider both the new zooid or perhaps the affixed tentacle given that a good dactylozooid ten , 13 , 21 , 30 – the definition of dactylozooid provides typically already been put on palpons in other siphonophore variety it is not currently put, and you will dactylozooids try official palpon-like protective zooids in other hydrozoans 30 – 33 . To end confusion concerning the homology regarding the zooid, we suggest that the phrase dactylozooid shouldn’t be utilized, even as we look at this zooid having developed de novo in the P. physalis that’s unlikely homologous to dactylozooids various other hydrozoans (get a hold of less than). As well, the definition of ampulla is also commonly associated with terminal vesicle of one’s tricornuate tentillum out of agalmatids twenty-seven . I prefer revitalizing Haeckel’s ‘tentacular palpon’ to refer compared to that zooid 34 , which not only has precedence, as well as matches this new more than likely hypothesized resource of this zooid (select less than).
Cystonects is actually dioecious, and all the fresh gonodendra from inside the a colony incur gonophores away from merely one to sex
Nest positioning for the siphonophores. A – anterior, P – posterior, D – dorsal, V – ventral, L – left, R – correct. (A) Schematic of an older colony of one’s siphonophore Nanomia bijuga. Modified to include axes so you’re able to a drawing of Nanomia bijuga by the FreyaGoetz ( authorized not as much as CC Because of the-SA step three.0 ( (B) Schematic of a developing Physalia physalis larva. Drawing predicated on photograph of the Linda Ianniello. (C) Schematic from an adult Physalia physalis colony.
Haeckel intricate two you’ll hypotheses on the origin off tentacular palpons – the first hypothesis, promoted because of the Huxley, is because they aren’t zooids, but they are as an alternative additional diverticula at the base of the tentacle you to mode much like ampullae during the echinoderm pipe foot 34 , 35 . From the second hypothesis, modification and you may subfunctionalization out-of an enthusiastic ancestral gastrozooid gave increase so you can several separate zooids – a great gastrozooid instead of a tentacle and you will good tentacular palpon having an effective tentacle. Totton recommended a general change in the original hypothesis, and you will suggested the ‘ampulla’ was good hypertrophied basigaster (aboral region of a beneficial gastrozooid one takes on a dynamic role when you look at the nematogenesis) who may have split up about other countries in the gastrozooid twenty-six . However, we choose the following theory, predicated on observations of one’s gastrozooid and you may tentacular palpon (Figs step three – 6 ; Second videos step 1 , 2 ). The newest gastrozooid and tentacular palpon was borne with the independent peduncles (Figs 5A,B and you can ? and6A; 6A ; Additional clips 2 ), and create out of line of, separate buds (Figs 3A,B , ? ,cuatro; cuatro ; Secondary films step 1 ). Hence, this new tentacular palpon are a derived gastrozooid, unique to Physalia physalis, who’s an increased tentacle, zero mouth, and that’s functionally specialized to have nematocyst development. The fresh new gastrozooids inside the P. physalis are derived gastrozooids which have missing tentacles and are also functionally formal to own serving simply. The subfunctionalized gastrozooid hypothesis is additionally alot more parsimonious compared to the almost every other hypotheses, since modification and you will subfunctionalization away from zooids is normal for the siphonophores – palpons, for example, are believed as derived, changed gastrozooids you to typically have a reduced tentacle twenty-seven .
