Defecation by the ctenophore Mnemiopsis leidyi occurs with an ultradian rhythm through a single transient anal pore

Abstract

Defecation in the ctenophore Mnemiopsis leidyi is a stereotyped sequence of effector responses that occur with a regular ultradian rhythm. Here I used video microscopy to describe new features and correct previous reports of the gastrovascular system during and between defecations. Contrary to the scientific literature, individuals defecated through only one of the two anal canals which possesses the only anal pore. The anal pore was not visible as a permanent structure as depicted in textbooks, but appeared at defecation and disappeared afterward. Time intervals between repeated defecations in individual animals depended on body size, ranging from ~10 min in small larvae to ~1 hr in large adults. Differential interference contrast microscopy revealed that both the opening and closing of the anal pore resembled a reversible ring of tissue fusion between apposed endodermal and ectodermal layers at the aboral end. Individuals of M. leidyi thus appear to have an intermittent anus and therefore an intermittent through‐gut that reoccur at regular intervals. The temporality of a visible anal pore in M. leidyi is novel, and may shed light on the evolution of a permanent anus and through‐gut in animals. In addition, mirror image dimorphism of the diagonal anal complex occurs in larval ctenophores but not in adults, indicating developmental flexibility in diagonal symmetry of the anal complex.

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

“…Absorption of both food and ferritin particles into ciliated, epithelial cells of the canal system suggest that both phagocytosis and pinocytosis are active in these cells (Bumann and Puls 1997; Franc 1972; Presnell et al 2016). It was recently re-confirmed that excretion of undigested particles in ctenophores occurs mainly through ‘anal pores’ opposite of the mouth (Agassiz 1850; Bumann and Puls 1997; Chun 1880; Main 1928; Presnell et al 2016; Tamm 2019). The functional similarities between the through-guts of ctenophores and bilaterians raised speculations about their common ancestry, but the lack of diagnostic genes for cnidarian or bilaterian pharynx, midgut or anus (e.g.…”

Early animal evolution: a morphologist's view

“…The cnidarian gut is a sac with only one opening, functioning as both mouth and anus, whereas the ctenophores have a gut with a mouth, a stomach and a pair of anal canals leading to temporal anal openings ( pores) [19,64,65].…”

Bodily Complexity: Integrated Multicellular Organizations for Contraction-Based Motility

“…The food is processed in three phases as it passes through the acidic environment of the pharynx and then it moves through one alkaline phase along the folds of the pharynx and through another one near the so-called stomach, where food particles are broken down by cilia. The small particles are distributed to the body by the endodermal system of meridional canals that run subjacent to the comb rows, while the remaining larger (mainly exoskeletal) particles will be egested back out of the pharynx (Bumann and Puls, 1997; Tamm, 2014, 2019).…”

“…Defecation is preceded by the combination of the constriction of the walls of esophagus together with the slowing down of cilia beating. Although these systems haven’t been thoroughly studied, there is experimental evidence that the adjustment of the ciliary beating in opposing directions and the various muscle contractions for food ingestion/digestion and fluid circulation, as well as the modulation of cilia beating prior to defecation is likely to be regulated by local electrical conduction realized through epithelial gap junctions or by neural nets (see Tamm, 2014, 2019 for details; Simmons and Martindale, 2015 for a relevant review).…”

“…21In a recent work Tamm (2019) reports that the widening and narrowing of the endodermal canals that play a major role in food distribution and waste elimination are more possibly due to fluctuations in hydrostatic pressure within the canal lumens caused by fluid flow driven by the cilia that are lining the canal walls.…”