Complex epidermal organs of Phascolion (Sipuncula): insights into the evolution of bimodal secretory cells in annelids. (2nd June 2014)

• Record Type: Journal Article
• Authors: Müller, Carsten H.G.; Hylleberg, Jørgen; Michalik, Peter
• Is Part Of: Acta zoologica. Volume 96:Number 3(2015:Jul.)
• Page Start: 343
• Page End: 374
• Publication Date: 2014-06-02
• Subjects: Zoology -- Periodicals; 590
• DOI: 10.1111/azo.12082
• Languages: English
• ISSNs: 0001-7272

Abstract

<abstract abstract-type="main" id="azo12082-abs-0001"> <title>Abstract</title> <p>The epidermal organs of an undescribed <italic>Phascolion</italic> species from the Balearic Islands were investigated using SEM, TEM, LM, CLSM and μCT methods. We found axial receptor cells confirming the previously assumed sensory function of epidermal organs. Our analyses also revealed six types of secretory cells. Some secretory cells types are capable of secreting filamentous and amorphous secretion in two different ways simultaneously (bimodal secretion). The high diversity of cell types, the complex pattern of acinar units, and the absence of a common gland pore make epidermal organs of <italic>Phascolion</italic> unique amongst sipunculans (<italic>Phascolion</italic> type). Our reconstruction of the evolution of the epidermal organs of Sipuncula revealed that <italic>Phascolion</italic>‐type epidermal organs may have derived from either <italic>Golfingia‐, Sipunculus‐ or Phascolosoma‐</italic>type epidermal organs. The oldest known sipunculans were <italic>Golfingia</italic>‐like and had epidermal organs, which might resemble the architecture of the <italic>Golfingia</italic>‐type epidermal organs in extant taxa. Thus, it can be hypothesized that bimodal secretory cells (e.g. basophilic secretory cells) were part of the sipunculan ground pattern. Moreover, bimodal secretory cells of <italic>Phascolion</italic> look strikingly similar to those found in various annelid glands and thus might even be part of the ground pattern of stem species of Sipuncula + Pleistoannelida.</p> </abstract>