Comparative morphology of the foot structure of four genera of Loxosomatidae (Entoprocta): Implications for foot functions and taxonomy

Abstract

Entoprocta is a group of mostly cryptic, benthic invertebrates with a sedentary lifestyle. Here, we investigate the morphology of the entoproct foot, which is an important structure in attachment and locomotion. We describe the foot structure of four solitary entoprocts, Loxosoma monilis, Loxosomella stomatophora, Loxocorone allax, and Loxomitra mizugamaensis, by means of light and transmission electron microscopy. Gland cells containing secretory granules were found in the foot of all the four species. In L. monilis, the gland cells densely paved the underside of the disc-shaped foot, but no duct or groove was found. In L. stomatophora and L. allax, a foot gland was present at the frontal end of a foot groove. The foot gland was a solid cell mass in the former species but a sac-like structure in the latter. Two types of groove accessory cells were recognized in both species; groove bulge cells (GBCs) showed large cytoplasmic bulges extending into the groove lumen, while groove microvillus cells have microvillus mats in the lateral wall of the groove. The bulges of GBCs in L. stomatophora are slender and attached to one another with desmosomes, forming appendages that extend down to the substratum, hinting at their contribution to attachment and locomotion. The bulges in L. allax form large swellings that fill the groove lumen and are connected to the surrounding cells with hemidesmosomes. In the liberated buds of L. mizugamaensis, tripartite gland cell masses were found at the basal end of the stalk, but no groove was found. A small invagination, which may be the opening of the gland, was found at the center of the foot tip, where the liberated buds attach themselves to the substratum and then metamorphose into adults. No openings were found at the lateral terminal wings, which support locomotion in Loxomitra species.

Fine Structure of the Integumentary Cuticles and Alimentary Tissues of Pycnophyid Kinorhynchs Pycnophyes oshoroensis and Kinorhynchus yushini (Kinorhyncha, Homalorhagida)

“…An array of cuticular protrusions similar in size is known as the corneal nipple array in moth eyes and provides an anti-glare function (e.g., Bernhard, 1967). Similar structures have also been described in various marine invertebrates, such as annelids (Hausen, 2005), entoprocts (Nielsen and Jespersen, 1997;Iseto and Hirose, 2010), echinoderms (Holland, 1984), copepods (Østergaard and Bresciani, 2000;Hirose and Uyeno, 2014) and ascidians (Hirose et al, 1997). Several functions have been proposed for the nipple array in aquatic and endoparasitic environments, such as antireflection (Hirose et al, 2015), lubrication and antiabrasion (Holland, 1984), and suppression of the host hemocyte activity (Ballarin et al, 2015).…”

Does a nano-scale nipple array (moth-eye structure) suppress the settlement of ascidian larvae?

“…This structure was originally described as nipples on the compound eyes of a night moth (Bernhard, 1967) and known to form a gradient of refractivity, resulting in a reduction of light reflectance (moth-eye effect) (Bernhard, 1967; Wilson & Hutley, 1982). The presence of the nipple array has been reported in marine invertebrates across various taxa, such as tunicates (Hirose et al ., 1990, 1992, 1997, 1999), echinoderms (Holland, 1984), annelids (Hausen, 2005), parasitic copepods (Hirose & Uyeno, 2014, 2016; Uyeno & Hirose, 2018) and entoprocts (Iseto & Hirose, 2010). Because of the histological differences in integumentary tissues among the taxa, the nipple arrays of phylogenetically distant taxa would have convergently evolved in each lineage.…”

A new species of solitary Entoprocta, Loxosomella angusta sp.n., from the White Sea

“…Loxosomella species have a foot with a foot gland and a longitudinal foot groove, at least in the buds. Loxosoma never have a foot gland and attach to a substratum by a circular sucking disc (Nielsen, 1964(Nielsen, , 1989(Nielsen, , 1996Iseto, Hirose, 2010). Loxomitra Nielsen, 1964 could be accepted as a subgenus or a genus of Loxosomatidae with buds attaching to mother zooid by back of calyx or stalk and with the foot bearing a pair of terminal wings (Iseto, 2002;Iseto, Hirose, 2010).…”

“…Loxosoma never have a foot gland and attach to a substratum by a circular sucking disc (Nielsen, 1964(Nielsen, , 1989(Nielsen, , 1996Iseto, Hirose, 2010). Loxomitra Nielsen, 1964 could be accepted as a subgenus or a genus of Loxosomatidae with buds attaching to mother zooid by back of calyx or stalk and with the foot bearing a pair of terminal wings (Iseto, 2002;Iseto, Hirose, 2010). Iseto (2002) added the genus Loxocorone Iseto, 2002, which has the Loxosomella-type foot and buds attaching like in Loxomitra.…”