An argument for multiple origins of the metatroch was its formation by cells of the second quartet in the caenogastropod Crepidula fomicata (Hejnol et al., 2007; Henry et al., 2007), in contrast to its formation by cells of the third quartet in the annelid
Polygordius (Woltereck, 1904); but the metatroch of the caenogastropod Ilyanassa obsoleta is formed by cells of both the second and third quartet (Gharbiah et al., 2013).
Los taxa cuya abundancia fue notablemente mayor al incluir la fraccion [mayor que o igual a] 500 [micron]m y 1 mm, respecto de la abundancia obtenida al incluir solo la fraccion de tamano [mayor que o igual a] 1 mm fueron los anelidos Aricidea catherinae (72%), Polygordius sp.
Los taxa cuya abundancia fue notablemente mayor al incluir la fraccion [mayor que o igual a] 500 [micron]m y <1 mm, respecto de la abundancia obtenida al incluir solo la fraccion de tamano [mayor que o igual a]1 mm fueron el anelido Polygordius sp.
In primitive annelids like Podarke (Treadwell 1901), and
Polygordius (Woltereck 1904), the first two cleavages are equal, but D quadrant specification presumably does not occur by specifying 3D, but does occur one cleavage cycle later by specifying one of the fourth quartet cells.
The larval nervous system of
Polygordius lacteus Schneider 1868 (Polygordiidae.
Annelida: Capitela "capitata" sp.; Diopatra viridis Kinberg 1865; Eunice sp.; Halosydnella australis (Kinberg, 1855); Lumbrineridae species indet.; Neanthes succinea (Frey & Leuckart, 1847); Nereidae species indet.; Ophelidae species indet.; Orbiniidae species indet.; Phyllochaetopterus socialis Claparede, 187O; Polonoidae species indet.;
Polygordius appendiculatus Frainpont, 1887; Procerastea halleziana Malaquin, 1893(2); Serpulidae species indet.; Syllis sp.; Terebridae species indet.
These findings suggest that the secondary ciliated band in the veliger is not homologous to the metatroch found in the trochophore larva of other spiralians, such as the annelid
Polygordius lacteits (reportedly derived from 3c and 3d; Wollereck.
For another example, the endolarva of
Polygordius appendiculatus develops the segmented body as an elaborate folded pouch within the highly inflated larval hyposphere, rather than adding segments progressively to the posterior of the post-trochal region (Woltereck, 1902; Okada, 1970; ironically, this unusual larva is the original inspiration for the trochophore concept--see Rouse, 1999).
The other extreme, with highly specialized larval types with larval organs shed during a cataclysmic metamorphosis, is well known--for example, from the nemertine pilidium larva and the larva of the annelid
Polygordius. The differences in feeding biology may be, for instance, between planktotro-phy or macrophagy and between lecithotrophy or active feeding.
Beitrage zur praktischen Analyse der
Polygordius Entwicklung nach dem "Nordsee"-und "Mittelmeer"-Typus.
Die metamorphose yon
Polygordius appendiculatus (Polychaeta, Archiannelida): Induction und ablauf.
The larval nervous system of
Polygordius lacteus Scheinder, 1868 (Polygordiidae, Polychaeta): immunocytochemical data.