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Larvalentwicklung und Metamorphose vonPhoronis psammophila (Phoronida, Tentaculata)

Larval development and metamorphosis ofPhoronis psammophila (Phoronida, Tentaculata)

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Abstract

The larval development ofPhoronis psammophila Cori is divided into 6 phases (on the basis of increasing pairs of larval tentacles); furthermore an initial and a ripe phase are distinguished. Specific aspects of the development are described: Formation and structure of larval tentacles; anlage of adult tentacles as a thickening in the larval tentacle base; late development of the metasome (larva with 4–6 tentacles); formation of the metasome pouch in the larva with 8 tentacles; enlargement of the apical plate; differentiation of the gut; differentiation of larval nephridia; formation of pigment particles in the larva with 6 tentacles (storage function of pigments and its significance for larval identification); different types of discoflagella in various regions of the body. The larval development shows the following tendencies: Improvement of locomotion; intensification of food filtration; anlage of adult organs in the larva leading to a shortening of metamorphosis duration. The larva ofP. psammophila is compared with those ofP. pallida, P. hippocrepia, andP. vancouverensis. Earlier larval determinations ofP. psammophila (e.g.Actinotrocha sabatieri, A. hatschekii) are shown to have been mistakes. Termination of the postembryonic phase (metamorphosis) can be induced experimentally by bacteria and also by cations. Pure or mixed bacteria cultures must be present at the beginning exponential growth phase. The bacteria density required is 20–94×106 bact.ml−1 for pure cultures and on the average 28×106 bact. ml−1 for mixed cultures. Metamorphosis initiation by cations can be induced with CsCl (0.06 M) and RbCl (0.035 M). Metamorphosis ofP. psammophila occurs in 6 phases: larva, ready for metamorphosis; larva, activated by bacteria or ions; evagination of the metasome diverticle, dislocation of gut; losing and swallowing of episphaere and larval tentacles; formation of the youngP. psammophila. All developmental phases are described and compared with those ofP. muelleri; imperfect metamorphosis is characterized and the youngP. psammophila compared with older stages and the adult Phoronis.

Abbreviations

am:

Analmesenterium

amp:

Ampulle

an:

Analpapille

aten:

Adulttentakel-Anlage

au:

Außenseite des Tentakels

base:

Basalkörper der Cilien

blu:

Blutkörper

cil:

Cilien

da:

Darm

dadi:

Darmdivertikel

epi:

Episphäre

epiz:

Zellen der Episphäre

fibl:

längsförmige Muskelfibrille

fibr:

ringförmige Muskelfibrille

gef:

Blutgefäß

hyp:

Hyposphäre

in:

Innenseite des Tentakels

kep:

Körperepithelzellen

lgf:

laterales Blutgefäß

llm:

linkes Lateralmesenterium

lten:

Larvaltentakel

ma:

Magen

medi:

Metasomadivertikel

mei:

innerer Teil des Metasomadivertikels

mes:

Mesocoel

met:

Metacoel

mez:

Mesodermzelle

mgf:

medianes Blutgefäß

mu:

Muskelfahne

ne:

Protonephridium

öso:

Ösophagus

om:

orales Mesenterium

pid:

Pigmentkörper der Darmdivertikel

pim:

Pigmentkörper des Metasomadivertikels

pis:

Pigmentkörper des Scheitelplatte

pit:

Pigmentkörper der Tentakel

pro:

Procoel

rlm:

rechts Lateralmesenterium

spl:

Scheitelplatte

tel:

Telotroch

telu:

Tentakellumen

tep:

Tentakelepithel

vma:

Vormagen

vme:

Ventralmesenterium

zot:

Blutgefäßzotten

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Herrmann, K. Larvalentwicklung und Metamorphose vonPhoronis psammophila (Phoronida, Tentaculata). Helgolander Wiss. Meeresunters 32, 550–581 (1979). https://doi.org/10.1007/BF02277994

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