Overall performance and you may Discussion

Siphonophores consist of a good amount of functionally formal zooids that will be homologous so you can free living polyps otherwise medusae twenty-seven (Fig. 1 ). Physalia physalis is part of Cystonectae, a clade that’s brother to any or all most other siphonophores 8 . When you look at the enough time-stemmed cystonects (all cystonects with the exception of Physalia physalis) gastrozooids (eating polyps) develop as the buds in the prior of your own colony and are usually transmitted on rear by a keen elongating stalk, while you are gonodendra (reproductive formations) appear on their own over the stalk twenty-eight . In most cystonects, the newest gonodendra is actually material structures, that features gonophores (reduced medusae, results a gonad), chemistry giriЕџ palpons (derived gastrozooids, that run out of tentacles when you look at the cystonects), and you can nectophores twenty seven . P. physalis gonodendra enjoys these zooids, along with ‘jelly polyps’ that will be shorter nectophores out of uncertain setting twenty two , twenty six .

Compared to the other siphonophore types, along with almost every other cystonects, Physalia physalis try odd with respect to its colony providers (Figs step one and ? and2). 2 ). P. physalis is even really the only siphonophore varieties where in actuality the gastrozooid, the main eating zooid, doesn’t always have a good tentacle for prey simply take. The only real exemption is the protozooid (the initial gastrozooid to create during invention), that’s generally a consistent siphonophore gastrozooid, that have a mouth, tentacle and you may small basigaster region 26 , 31 . Besides the protozooid, inside P. physalis the new tentacle try borne towards a beneficial pulla twenty-six . Other authors consider either brand new zooid or perhaps the connected tentacle since the a dactylozooid ten , 13 , 21 , 31 – the word dactylozooid possess historically been put on palpons various other siphonophore variety but is not already made use of, and dactylozooids are specialized palpon-eg defensive zooids various other hydrozoans 31 – 33 . To quit dilemma concerning homology on the zooid, i recommend that the term dactylozooid should not be used, as we consider this zooid having developed de novo in P. physalis which can be unlikely homologous so you can dactylozooids various other hydrozoans (discover less than). Additionally, the definition of ampulla is also commonly in the critical vesicle of tricornuate tentillum away from agalmatids twenty seven . We favor reviving Haeckel’s ‘tentacular palpon’ to mention compared to that zooid 34 , and this not just enjoys precedence, and in addition suits brand new probably hypothesized resource with the zooid (come across less than).

Cystonects was dioecious, and all the newest gonodendra inside the a nest sustain gonophores regarding simply you to gender

Colony orientation in the siphonophores. A good – prior, P – posterior, D – dorsal, V – ventral, L – kept, R – right. (A) Schematic from a mature nest of siphonophore Nanomia bijuga. Altered to add axes in order to a drawing regarding Nanomia bijuga because of the FreyaGoetz ( authorized lower than CC By-SA step 3.0 ( (B) Schematic away from a developing Physalia physalis larva. Drawing considering photo because of the Linda Ianniello. (C) Schematic out of an older Physalia physalis nest.

Haeckel intricate a couple you’ll be able to hypotheses to the origin off tentacular palpons – the original theory, marketed from the Huxley, is because they are not zooids, however they are instead secondary diverticula on the bottom of your tentacle you to function similarly to ampullae during the echinoderm pipe base 34 , 35 . About 2nd hypothesis, amendment and you may subfunctionalization off an ancestral gastrozooid provided go up so you’re able to a couple separate zooids – good gastrozooid rather than a great tentacle and a tentacular palpon with a beneficial tentacle. Totton advised a modification of the original hypothesis, and recommended the ‘ampulla’ was a great hypertrophied basigaster (aboral area for a good gastrozooid you to plays a dynamic part within the nematogenesis) who has got split about remainder of the gastrozooid twenty-six . However, we prefer the next theory, considering findings of your gastrozooid and tentacular palpon (Figs step three – 6 ; Additional films 1 , dos ). Brand new gastrozooid and you can tentacular palpon is borne for the independent peduncles (Figs 5A,B and you may ? and6A; 6A ; Second movies 2 ), and produce out of type of, separate buds (Figs 3A,B , ? ,4; cuatro ; Supplementary video step one ). Hence, brand new tentacular palpon is a beneficial derived gastrozooid, novel so you can Physalia physalis, having an increased tentacle, zero lips, and that is functionally certified to possess nematocyst design. New gastrozooids during the P. physalis also are derived gastrozooids with missing tentacles and are usually functionally certified to have feeding simply. The newest subfunctionalized gastrozooid hypothesis is additionally more parsimonious versus most other hypotheses, due to the fact amendment and subfunctionalization out of zooids is typical from inside the siphonophores – palpons, including, are considered to-be derived, modified gastrozooids you to definitely routinely have a lowered tentacle twenty seven .