Morphology and ultrastructure of the gut inSpadella cephaloptera (chaetognatha)

A non-bilaterian perspective on the development and evolution of animal digestive systems

“…Colours as in (c). b is based on following, non-exhaustive list of references: Choanoflagellates (Dayel and King 2014), Ctenophora (Bumann and Puls 1997; Hernandez-Nicaise 1991), Porifera (Imsiecke 1993; Leys and Eerkes-Medrano 2006; Weissenfels 1982; Willenz and Van De Vyver 1982), Placozoa (Grell and Ruthmann 1991; Smith et al 2014), Cnidaria (Arai 1997; Bouillon et al 2006; Van-Praët 1985), Xenacoelomorpha (Israelsson 2008; Markosova 1986; Pedersen 1964), Cephalochordata (Biuw and Hulting 1971), Urochordata (Thomas 1970; Yonge 1937), Vertebrata (Karasov and Hume 1997), Hemichordata (Bridges and Woodwick 1994), Echinodermata (Tokin and Filimonova 1977), Chaetognatha (Arnaud et al 1996), Nematoda (Clokey and Jacobson 1986; Riley 1973; Wright 1991), Tardigrada (Biserova and Mustafina 2015; Dewel et al 1993; Yonge 1937), Onychophora (Heatley 1936; Manton 1937; Storch and Ruhberg 1993), Arthropoda (Ceccaldi 1989; Fahrenbach and Arango 2007; Filimonova 2008; Miguel-Aliaga et al 2018; Wägele et al 1981), Scalidophora (Kristensen 1991; Kristensen and Higgins 1991; Storch 1991; Storch et al 1989), Rotifera (Wurdak 1987; Yonge 1937), Micrognathozoa (Møbjerg Kristensen and Funch 2000; Yonge 1937), Gnathostomulida (Lammert 1991),Platyhelminthes (Antoniazzi and Silveira 1996; Bowen et al 1974; Jennings 1968; Ruppert et al 2004), Gastrotricha (Ruppert 1991; Ruppert et al 2004; Teuchert 1977), Entoprocta (Morton 1960; Ruppert et al 2004), Mollusca (Boucaud-Camou and Yim 1980; Lobo-da-Cunha 2000; Owen 1974; Yonge 1937), Annelida (Jennings and Van Der Lande 1967; Jeuniaux 1969; Michel et al 1984; Yonge 1937), Nemertea (Ruppert et al 2004), Brachiopoda...…”

Morphological study of the gut in Sagitta setosa, S. serratodentata and S. pacifica (Chaetognatha). Functional implications in digestive processes

“…The oesophagus begins in the oblique part, and comprises the horizontal part including the bulb. In the trunk region, the intestine of the species examined presents a homogeneous structure as in all the chaetognaths, but contrary to S. cephaloptera (Parry, 1944;Arnaud et al, 1996) and several species of Sagitta (Dallot, 1970), no pair of intestinal diverticula exist.…”

“…Thus, it seems that the short oblique part connecting the oral cavity to the rest of the gut has been assimilated into the oesophagus. In Spadella cephaloptera, this segment, associated with the oral cavity, was also observed but was interpreted as a pharynx connecting the mouth with the oesophagus (Arnaud et al, 1996). In Sagitta, we prefer to designate the pharynx and the oesophagus respectively by oblique and horizontal parts because the cellular composition of their epithelium is very similar.…”

“…composed of only three types of secretory cells. In Spadella cephaloptera, it is composed of only two types (Arnaud et al, 1996): the pharyngeal cells, occurring round the oral cavity and containing numerous light granules, correspond to the S1-cells found in Sagitta, while the oesophageal cells, which display smaller and darker granules, are homologous to the S3-cells. The S2-cell type seems to be absent from these species.…”

“…The major contributions to the histology of the digestive system still remain those of John (1933) on Spadella cephaloptera, a benthic species, Parry (1944) on both S. cephaloptera and Sagitta setosa, and Dallot (1970) who described the anatomy of the gut of some forty species. Ultrastructural contributions are minimal and the only complete study concerns S. cephaloptera (Arnaud et al, 1996). Using light and electron microscopy, more particular studies were devoted to di¡erent aspects of the intestine in several species: development of digestive processes and formation of faecal pellets in Sagitta hispida (Reeve et al, 1975), functional morphology in S. elegans (Welsch & Storch, 1983), buoyancy adaptation in S. setosa and S. elegans (Bone et al, 1987), cell junctions in S. setosa (Duvert et al, 1980), and visceral musculature in several chaetognaths (Duvert & Salat, 1995).…”