Abstract
The nereidid annelid Platynereis dumerilii emerged as a well-understood model organism. P. dumerilii and P. massiliensis are sister taxa, which are morphologically indistinguishable as adults. Interestingly, they exhibit highly contrasting life-histories: while P. dumerilii is a gonochorostic species with planktonic feeding larvae, P. massiliensis is a protandric hermaphrodite with lecitotrophic semi-direct -development in brood tubes. Using light microscopy and immunohistochemical methods coupled with confocal laser scanning microscopy, we describe the development of P. massiliensis. Musculature was stained with phalloidin-rhodamine. FMRFamide, acetylated α-tubulin, and serotonin were targeted by antibodies for the staining of neuronal structures. Additionally, eye development was investigated with the specific 22C10-antibody. The development of P. massiliensis is characterized by the absence of a free-swimming stage, a late development of food uptake, and the presence of a large amount of yolk even in late juvenile stages. Most notably, early juvenile stages already exhibit an organization of several organ systems that resembles those of adults. Larval characters present in the free-swimming feeding larvae of P. dumerilii, as e.g. the apical organ and larval eyes, are absent and regarded to be lost in developing stages of P. massiliensis. Many of the differences found in the development of these two species can be described in the context of heterochronic changes. We strongly advocate expanding evolutionary developmental studies from the well-established model annelid P. dumerilii to the closely related P. massiliensis to study the evolutionary conservation and divergence of genetic pathways involved in developmental processes.
Highlights
The vast majority of bilaterian animals are classified into three large clades: Deuterostomia, Ecdysozoa and Lophotrochozoa
General development of Platynereis massiliensis Because of the unknown duration since fertilization, we established a staging system for the juveniles according to morphological characteristics: stage 0: spherical, prototroch developed, rich in yolk, no visible chaetigers stage 1: 3 chaetigers, spherical, rich in yolk, remnants of prototroch visible stage 2: 3 chaetigers, very large amount of yolk at the vegetal pole, spherical, absence of prototroch stage 3: 3 chaetigers, elliptic body shape, development of mouth opening stage 4: 3-5 chaetigers, yolk almost consumed, antennae start to develop stage 5: 5-8 chaetigers, antennae and palps fully developed stage 6: 8-11 chaetigers, adult body shape stage 7: 11-15 chaetigers, adult body shape
Platynereis massiliensis was once considered as an atokous form of P. dumerilii and it was Hauenschild (1951)
Summary
The vast majority of bilaterian animals are classified into three large clades: Deuterostomia, Ecdysozoa and Lophotrochozoa. Especially in the last decade the annelid Platynereis dumerilii emerged as a well-understood model species (Fischer and Dorresteijn, 2004; Fischer et al, 2010; Simakov et al, 2013). Evolutionary developmental studies on Platynereis dumerilii provided important insights into the evolution of segmentation, vision and the nervous system in Bilateria (Prud’homme et al, 2003; Arendt et al, 2004; Denes et al, 2007; Tessmar-Raible et al, 2007; Jekely et al, 2008; Dray et al, 2010; Tomer et al, 2010). In the case of Platynereis, a comparison of P. dumerilii and P. massiliensis would be ideal to describe and understand temporal shifts leading to different early development styles and morphology. By comparing the development of P. massiliensis and P. dumerilii we are able to describe changes in the timing of events in musculature, nervous system and eye development
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