Siphonophores Clovis escort integrate a great amount of functionally authoritative zooids that will be homologous so you’re able to free living polyps or medusae twenty-seven (Fig. 1 ). Physalia physalis falls under Cystonectae, a clade that’s sibling to any or all other siphonophores 8 . During the enough time-stemmed cystonects (the cystonects except for Physalia physalis) gastrozooids (feeding polyps) arise given that buds regarding the prior of one’s colony and therefore are sent on posterior of the an elongating base, while gonodendra (reproductive formations) are available by themselves along the stalk twenty-eight . In most cystonects, the latest gonodendra are substance structures, that features gonophores (reduced medusae, affect good gonad), palpons (derived gastrozooids, one to use up all your tentacles in cystonects), and you will nectophores twenty-seven . P. physalis gonodendra possess such zooids, in addition to ‘jelly polyps’ which can be reduced nectophores regarding not sure function twenty two , 26 .
As compared to other siphonophore types, also most other cystonects, Physalia physalis try odd when it comes to its nest team (Figs step one and you can ? anddos). 2 ). P. physalis is additionally really the only siphonophore variety where in fact the gastrozooid, the primary giving zooid, doesn’t have a tentacle to have prey bring. Really the only different is the protozooid (the initial gastrozooid to create during the development), that’s basically an everyday siphonophore gastrozooid, that have a mouth area, tentacle and you can short basigaster area twenty six , 31 . Besides the protozooid, when you look at the P. physalis the brand new tentacle was borne to the an effective pulla twenty-six . Most other authors reference both the brand new zooid and/or affixed tentacle because a great dactylozooid 10 , thirteen , 21 , 30 – the phrase dactylozooid have over the years started applied to palpons various other siphonophore species but is perhaps not already put, and you may dactylozooids try official palpon-instance protective zooids in other hydrozoans 29 – 33 . To prevent distress concerning homology with the zooid, we recommend that the phrase dactylozooid really should not be put, even as we look at this zooid having arisen de- novo inside the P. physalis in fact it is not likely homologous to dactylozooids in other hydrozoans (come across lower than). At the same time, the expression ampulla is even are not in the terminal vesicle of your own tricornuate tentillum out of agalmatids twenty-seven . We prefer reviving Haeckel’s ‘tentacular palpon’ to mention compared to that zooid 34 , which not merely has actually precedence, in addition to matches the new most likely hypothesized source from the zooid (find below).
Nest direction into the siphonophores. A – prior, P – rear, D – dorsal, V – ventral, L – kept, Roentgen – proper. (A) Schematic away from a mature nest of one’s siphonophore Nanomia bijuga. Modified to include axes to help you a drawing from Nanomia bijuga because of the FreyaGoetz ( licensed significantly less than CC By the-SA step 3.0 ( (B) Schematic from a developing Physalia physalis larva. Attracting according to photograph because of the Linda Ianniello. (C) Schematic off a mature Physalia physalis nest.
Haeckel detail by detail a couple of you’ll hypotheses to the source away from tentacular palpons – the original hypothesis, advertised by the Huxley, is they commonly zooids, but they are instead supplementary diverticula at the base of the tentacle you to means similarly to ampullae during the echinoderm pipe feet 34 , 35 . In the 2nd hypothesis, amendment and you may subfunctionalization off an enthusiastic ancestral gastrozooid provided increase in order to several separate zooids – a great gastrozooid instead of a tentacle and you can a great tentacular palpon that have a tentacle. Totton proposed a change in the initial theory, and you can recommended that ‘ampulla’ are a great hypertrophied basigaster (aboral area for a beneficial gastrozooid you to definitely plays an energetic role from inside the nematogenesis) who’s got separated regarding remaining portion of the gastrozooid 26 . Yet not, i favor next hypothesis, centered on observations of one’s gastrozooid and you may tentacular palpon (Figs 3 – 6 ; Supplementary movies step 1 , dos ). This new gastrozooid and tentacular palpon is actually borne into the independent peduncles (Figs 5A,B and ? and6A; 6A ; Supplementary movies 2 ), and produce off type of, independent buds (Figs 3A,B , ? ,cuatro; 4 ; Secondary video 1 ). Ergo, the latest tentacular palpon was an effective derived gastrozooid, unique so you’re able to Physalia physalis, who’s an enlarged tentacle, no mouth area, which will be functionally certified getting nematocyst manufacturing. The newest gastrozooids into the P. physalis also are derived gastrozooids with missing tentacles and so are functionally authoritative having serving only. New subfunctionalized gastrozooid hypothesis is also more parsimonious compared to the almost every other hypotheses, as modification and you may subfunctionalization of zooids is common into the siphonophores – palpons, particularly, are believed to-be derived, changed gastrozooids that normally have a reduced tentacle twenty-seven .