Abilities and you can Dialogue
Siphonophores feature plenty of functionally certified zooids which might be homologous to help you free living polyps otherwise medusae twenty seven (Fig. step one ). Physalia physalis is part of Cystonectae, good clade that is sis to other siphonophores 8 . In enough time-stemmed cystonects (all of the cystonects apart from Physalia physalis) gastrozooids (eating polyps) occur once the buds on the prior of your own colony and therefore are carried towards the posterior by an elongating stem, while gonodendra (reproductive formations) come by themselves over the stalk 28 . In every cystonects, the latest gonodendra is substance structures, that features gonophores (shorter medusae, results a good gonad), palpons (derived gastrozooids, that run out of tentacles in the cystonects), and nectophores 27 . P. physalis gonodendra provides these types of zooids, also ‘jelly polyps’ which might be quicker nectophores from unsure form twenty-two , twenty-six .
Compared to almost every other siphonophore varieties, plus most other cystonects, Physalia physalis try odd regarding their colony team (Figs 1 and ? anddos). 2 ). P. physalis is even the only siphonophore types where in actuality the gastrozooid, an important feeding zooid, does not have an effective tentacle to own target just take. The only difference is the protozooid (the initial gastrozooid to create during the innovation), that’s generally a frequent siphonophore gastrozooid, that have a lips, tentacle and you may quick basigaster region 26 , 29 . Besides the protozooid, when you look at the P. physalis the newest tentacle was borne towards the a great pulla 26 . Most other article writers relate to both the zooid and/or attached tentacle given that an excellent dactylozooid ten , 13 , 21 , 31 – the phrase dactylozooid provides usually started used on palpons various other siphonophore varieties it is maybe not currently put, and you can dactylozooids are certified palpon-such defensive zooids various other hydrozoans 30 – 33 . To eliminate confusion regarding homology of zooid, i suggest that the word dactylozooid really should not be utilized, as we consider this to be zooid to possess arisen de- novo within the P. physalis and is not likely homologous to dactylozooids various other hydrozoans (discover less than). As well, the phrase ampulla is even commonly regarding the critical vesicle of your own tricornuate tentillum regarding agalmatids twenty seven . I favor reviving Haeckel’s ‘tentacular palpon’ to refer compared to that zooid 34 , which not only features precedence, also fits the fresh new most likely hypothesized supply for the zooid (come across less than).
Cystonects is actually dioecious, as well as the brand new gonodendra within the a colony sustain gonophores of merely one gender
Colony direction into the siphonophores. Good – prior, P – rear, D – dorsal, V – ventral, L – kept, R – proper. (A) Schematic regarding an older nest of the siphonophore Nanomia bijuga. Modified to include axes datingmentor.org/escort/clarksville to a drawing away from Nanomia bijuga by FreyaGoetz ( signed up less than CC From the-SA 3.0 ( (B) Schematic from a developing Physalia physalis larva. Drawing considering picture of the Linda Ianniello. (C) Schematic of a mature Physalia physalis nest.
Haeckel outlined a couple possible hypotheses towards origin away from tentacular palpons – the first theory, advertised by the Huxley, is that they aren’t zooids, but are alternatively secondary diverticula on the bottom of your own tentacle one form similarly to ampullae in echinoderm tubing base 34 , thirty-five . On 2nd hypothesis, modification and you can subfunctionalization from a keen ancestral gastrozooid gave rise to help you a few separate zooids – a beneficial gastrozooid in the place of an effective tentacle and a tentacular palpon having a good tentacle. Totton proposed a change in the initial hypothesis, and you may advised that the ‘ampulla’ was a great hypertrophied basigaster (aboral area for a good gastrozooid you to plays a dynamic role into the nematogenesis) who has separated on the other countries in the gastrozooid twenty-six . However, i favor next hypothesis, centered on observations of your own gastrozooid and tentacular palpon (Figs 3 – six ; Additional video clips step one , 2 ). The newest gastrozooid and you will tentacular palpon are borne on separate peduncles (Figs 5A,B and you will ? and6A; 6A ; Secondary video clips dos ), and produce from collection of, separate buds (Figs 3A,B , ? ,cuatro; 4 ; Additional video clips step 1 ). Hence, the newest tentacular palpon was a derived gastrozooid, book in order to Physalia physalis, who has an increased tentacle, no mouth, that will be functionally formal to possess nematocyst manufacturing. The new gastrozooids inside the P. physalis are also derived gastrozooids with forgotten tentacles and so are functionally specialized to own giving only. The latest subfunctionalized gastrozooid hypothesis is additionally alot more parsimonious compared to the other hypotheses, while the modification and you can subfunctionalization off zooids is typical inside the siphonophores – palpons, eg, are believed to be derived, altered gastrozooids that typically have a lesser tentacle twenty-seven .
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