Physalia physalis physiology: axes, cormidia, and you can zooid brands

Efficiency and you may Discussion

Siphonophores include loads of functionally specialized zooids that are homologous so you’re able to free-living polyps or medusae 27 (Fig. step 1 ). Physalia physalis falls under Cystonectae, a great clade that’s sibling to all almost every other siphonophores 8 . Inside a lot of time-stemmed cystonects (most of the cystonects except for Physalia physalis) gastrozooids (giving polyps) happen due to the fact buds throughout the anterior of one’s colony and are also transmitted towards rear because of the a keen elongating stem, whenever you are gonodendra (reproductive formations) are available on their own along the stalk twenty eight . Throughout cystonects, the brand new gonodendra is actually compound structures, which has gonophores (faster medusae, bearing a beneficial gonad), palpons (derived gastrozooids, you to run out of tentacles inside cystonects), and you may nectophores twenty-seven . P. physalis gonodendra has actually these zooids, together with ‘jelly polyps’ that will be shorter nectophores of not sure function 22 , 26 .

Compared to the most other siphonophore kinds, plus almost every other cystonects, Physalia physalis is peculiar with respect to its colony team (Figs step 1 and you can ? and2). 2 ). P. physalis is even truly the only siphonophore kinds where the gastrozooid, the primary giving zooid, doesn’t always have an excellent tentacle for prey simply take. Really the only exemption is the protozooid (the original gastrozooid to form throughout invention), which is fundamentally a consistent siphonophore gastrozooid, which have a mouth, tentacle and you can small basigaster region twenty six , 30 . Aside from the protozooid, inside P. physalis the tentacle is borne with the a great pulla twenty-six . Almost every other people refer to both the new zooid or even the affixed tentacle since an effective dactylozooid 10 , thirteen , 21 , 29 – the expression dactylozooid has over the years come used on palpons in other siphonophore types but is maybe not currently made use of, and you can dactylozooids try formal palpon-such as for instance defensive zooids various other hydrozoans 30 – 33 . To cease frustration in regards to the homology of the zooid, i advise that the definition of dactylozooid really should not be put, while we consider this to be zooid having arisen de- novo during the P. physalis in fact it is unlikely homologous so you can dactylozooids various other hydrozoans (come across below). Additionally, the term ampulla is even are not of this critical vesicle of your tricornuate tentillum out of agalmatids 27 . We choose revitalizing Haeckel’s ‘tentacular palpon’ to mention to that zooid 34 , and this just has actually precedence, and in addition fits the latest most likely hypothesized origin of zooid (come across below).

Cystonects is dioecious, and all sorts of new gonodendra in a colony happen gonophores from simply you to intercourse

Nest orientation chinalovecupid support into the siphonophores. A great – prior, P – posterior, D – dorsal, V – ventral, L – kept, R – correct. (A) Schematic from an older nest of your siphonophore Nanomia bijuga. Modified to incorporate axes to a drawing away from Nanomia bijuga of the FreyaGoetz ( licensed lower than CC By-SA 3.0 ( (B) Schematic away from a developing Physalia physalis larva. Attracting according to photograph from the Linda Ianniello. (C) Schematic out of an older Physalia physalis nest.

Haeckel outlined two possible hypotheses toward source of tentacular palpons – the initial hypothesis, advertised because of the Huxley, is they are not zooids, but they are alternatively secondary diverticula toward the base of tentacle that mode much like ampullae into the echinoderm tube foot 34 , thirty-five . From the 2nd hypothesis, amendment and you can subfunctionalization of an ancestral gastrozooid gave increase to a couple independent zooids – a beneficial gastrozooid in the place of a great tentacle and an effective tentacular palpon having good tentacle. Totton proposed a general change in the first theory, and suggested the ‘ampulla’ is actually a hypertrophied basigaster (aboral area for a gastrozooid you to performs an energetic part during the nematogenesis) having split up from the remainder of the gastrozooid twenty-six . However, i prefer the following hypothesis, based on findings of gastrozooid and you may tentacular palpon (Figs step 3 – 6 ; Secondary video 1 , dos ). The fresh new gastrozooid and you may tentacular palpon is actually borne to the separate peduncles (Figs 5A,B and you can ? and6A; 6A ; Secondary movies 2 ), and create regarding distinct, independent buds (Figs 3A,B , ? ,4; cuatro ; Supplementary video clips 1 ). Ergo, the brand new tentacular palpon try an effective derived gastrozooid, novel to help you Physalia physalis, that has an expanded tentacle, no throat, and that’s functionally authoritative to have nematocyst manufacturing. The latest gastrozooids for the P. physalis are derived gastrozooids having lost tentacles and so are functionally official to own eating only. The latest subfunctionalized gastrozooid hypothesis is also way more parsimonious as compared to other hypotheses, while the modification and you may subfunctionalization from zooids is typical into the siphonophores – palpons, such as for instance, are believed become derived, modified gastrozooids that routinely have a diminished tentacle 27 .