The chiton gill: Ultrastructure in Chiton olivaceus (Mollusca, Polyplacophora)

Abstract

Gills of Chiton olivaceus, a primitive mollusc, are relatively simple in their structure and ultrastructure but are well adapted to a life in the intertidal zone. In contrast to some other molluscs, there is no differentiation of the gill epithelium into functional regions other than respiratory ones. Ciliation of the epithelium in certain areas may optimize water flow from the outer to the inner part of the mantle cavity. The hemolymph sinuses are oriented so that hemolymph flows in the opposite direction. Interstitial cells link epithelial cells with nerve endings. Muscle cells as well as the collagenous matrix in the connective tissue differ within the main gill axis and the lateral lamellae. The life cycle of immunoactive cells within the connective tissue and the hemolymph is described.

Functional and evolutionary perspectives on gill structures of an obligate air-breathing, aquatic snail

“…Thus, the features found in the gill epithelium of Pomacea canaliculata contrast with those of the gill respiratory epithelia found in some other molluscan (Fischer et al, 1990; Gregory, George & McClurg, 1996; Le Pennec, Beninger & Herry, 1988; Manganaro et al, 2012; Nuwayhid, Davies & Elder, 1978) and non-molluscan taxa (Evans, Piermarini & Choe, 2005; Luquet et al, 2002) that are more dependent on water breathing, and which show cubic or squamous cells, with low nuclear/cytoplasmic ratios and a low content of mitochondria and other organelles. In turn, the gill structures found in Pomacea canaliculata are more similar to those of transporting epithelia (Berridge & Oschman, 2012), such as those of the vertebrate small intestine (Flik & Verbost, 1993), gallbladder (Housset et al, 2016), and renal tubules (Yu & Chir, 2017), and of the ionic/osmotic regulatory epithelia in the gills of crustaceans (Luquet et al, 2002; McNamara & Faria, 2012) and fishes (McDonald, Cavdek & Ellis, 1991).…”

Peer Review #1 of "Functional and evolutionary perspectives on gill structures of an obligate air-breathing, aquatic snail (v0.1)"

“…Thus, the features found in the gill epithelium of P. canaliculata contrast with those of the gill respiratory epithelia found in some other molluscan (e.g., Fischer et al 1990;Gregory et al 1996;Le Pennec et al 1988;Manganaro et al 2012;Nuwayhid et al 1978) and non-molluscan taxa (e.g., Evans et al 2005;Luquet et al 2002) that are more dependent on water breathing, and which show cubic or squamous cells, with low nuclear/cytoplasmic ratios and a low content of mitochondria and other organelles. In turn, the gill structures found in P. canaliculata are more similar to those of transporting epithelia (Berridge & Oschman 2012), such as those of the vertebrate small intestine (e.g., Flik & Verbost 1993), gallbladder (e.g., Housset et al 2016), and renal tubules (e.g., Yu 2017), and of the ionic/osmotic regulatory epithelia in the gills of crustaceans (e.g., Luquet et al 2002;McNamara & Faria 2012) and fishes (e.g., McDonald et al 1991).…”

Hooking some stem‐group “worms”: fossil lophotrochozoans in the Burgess Shale

“…(13) Thus, the flattened two-dimensional films that define most Burgess Shale fossils are readily identified as the remains of relatively recalcitrant, extracellular secretions, such as jaws, chaetae and cuticle, and do not include purely or primarily cellular tissues, such as muscles or gonads (problematic shelly fossils thought to be stem-group molluscs). (13) Insofar as the integument of modern molluscan ctenidia is entirely cellular, (31) there is little likelihood that the substantial, twodimensionally preserved gills of Odontogriphus are correctly…”