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Siphonophores include lots of functionally official zooids that will be homologous to free-living polyps or medusae twenty-seven (Fig. 1 ). Physalia physalis belongs to Cystonectae, an excellent clade which is aunt to all the almost every other siphonophores 8 . Inside the a lot of time-stemmed cystonects (all cystonects except for Physalia physalis) gastrozooids (giving polyps) arise given that buds about prior of your colony as they are sent for the rear from the an enthusiastic elongating stalk, if you are gonodendra (reproductive formations) appear individually across the stalk twenty eight . In most cystonects, the new gonodendra is actually compound formations, which has gonophores (smaller medusae, influence good gonad), palpons (derived gastrozooids, one lack tentacles into the cystonects), and you can nectophores 27 . P. physalis gonodendra has such zooids, along with ‘jelly polyps’ that are faster nectophores regarding not sure setting twenty-two , twenty six .
As compared to almost every other siphonophore varieties, including almost every other cystonects, Physalia physalis is peculiar when it comes to the colony organization (Figs 1 and you may ? and2). dos ). P. physalis is even the only real siphonophore varieties where in fact the gastrozooid, the primary giving zooid, doesn’t always have a tentacle to have victim just take. The sole exception to this rule is the protozooid (the first gastrozooid in order to create throughout development), which is basically a typical siphonophore gastrozooid, having a mouth area, tentacle and you may brief basigaster area 26 , 31 . Apart from the protozooid, in the P. physalis the brand new tentacle are borne to your a great pulla twenty-six . Other article authors consider either this new zooid or perhaps the connected tentacle since the good dactylozooid ten , thirteen , 21 , 30 — the phrase dactylozooid has over the years started placed on palpons various other siphonophore variety it is not currently made use of, and you will dactylozooids was official palpon-such as protective zooids in other hydrozoans 31 – 33 . To stop misunderstandings concerning homology in the zooid, i recommend that the expression dactylozooid should not be utilized, as we think about this zooid to possess developed de- novo from inside the P. physalis and is extremely unlikely homologous in order to dactylozooids in other hydrozoans (come across less than). Simultaneously, the definition of ampulla is also aren’t with the terminal vesicle of one’s tricornuate tentillum away from agalmatids 27 . We choose reviving Haeckel’s ‘tentacular palpon’ to mention to that zooid 34 , and this not simply keeps precedence, in addition to fits new probably hypothesized supply on the zooid (see below).
Cystonects was dioecious, and all sorts of the latest gonodendra inside a colony bear gonophores of simply you to definitely intercourse
Nest orientation during the siphonophores. A — prior, P — rear, D — dorsal, V — ventral, L — kept, Roentgen — right. (A) Schematic off an older colony of one’s siphonophore Nanomia bijuga. Changed to provide axes so you can an attracting regarding Nanomia bijuga from the FreyaGoetz ( signed up significantly less than CC By-SA step 3.0 ( (B) Schematic off a developing Physalia physalis larva. Attracting predicated on image from the Linda Ianniello. (C) Schematic off an older Physalia physalis nest.
Haeckel in depth two you’ll hypotheses towards supply away from tentacular palpons — the initial hypothesis, advertised by Huxley, is that they commonly zooids, but they are rather secondary diverticula on the bottom of the tentacle you to function much like ampullae inside the echinoderm tube legs 34 , thirty five . On the next hypothesis, amendment and you may subfunctionalization out of a keen ancestral gastrozooid offered rise to help you several independent zooids — an effective gastrozooid as opposed to an effective tentacle and you may an excellent tentacular palpon which have a good tentacle. Totton suggested a modification of the original hypothesis, and you will ideal your ‘ampulla’ try an excellent hypertrophied basigaster (aboral region of a gastrozooid you to definitely plays an active character during the nematogenesis) who’s got separated in the remaining portion of the gastrozooid twenty six . Yet not, i like the next theory, based on observations of your gastrozooid and you will tentacular palpon (Figs step three – 6 ; Additional clips 1 , dos ). The gastrozooid and you may tentacular palpon is borne with the separate peduncles (Figs 5A,B and you may ? and6A; 6A ; Second videos dos ), and create off collection of, independent buds (Figs 3A,B , ? ,4; cuatro ; Additional movies 1 ). Ergo, this new tentacular palpon was an effective derived gastrozooid, novel in order to Physalia physalis, who’s got an expanded tentacle, no mouth, in fact it is functionally official to own nematocyst production. The fresh new gastrozooids inside the P. physalis are also derived gastrozooids having shed tentacles and tend to be functionally formal to own serving just. The fresh subfunctionalized gastrozooid theory is additionally more parsimonious as compared to most other hypotheses, because the modification and you can subfunctionalization out-of zooids is normal within the siphonophores — palpons, her Dating including, are believed is derived, altered gastrozooids that routinely have a lesser tentacle 27 .
