Nematode eggshells: A new anatomical and terminological framework, with a critical review of relevant literature and suggested guidelines for the interpretation and reporting of eggshell imagery

Abstract

A literature review for a recent ultrastructural study of a trichinelloid eggshell revealed consistently occurring errors in the literature on nematode eggshell anatomy. Examples included nematodes of medical, veterinary, and agricultural importance in several orders. Previous researchers had warned of some of these errors decades ago, but a comprehensive solution was not offered until 2012 when a clarifying new anatomical and developmental interpretation of nematode eggshells was proposed by members of the Caenorhabditis elegans Research Community. However, their findings were explained using arcane acronyms and technical jargon intended for an audience of experimental molecular geneticists, and so their papers have rarely been cited outside the C. elegans community. Herein we (1) provide a critical review of nematode eggshell literature in which we correct errors and relabel imagery in important historical reports; (2) describe common reporting errors and their causes using language familiar to researchers having a basic understanding of microscopy and nematode eggs; (3) recommend a new hexalaminar anatomical and terminological framework for nematode eggshells based on the 2012 C. elegans framework; and (4) recommend new unambiguous terms appropriate for the embryonated/larvated eggs regularly encountered by practicing nematodologists to replace ambiguous or ontogenetically restricted terms in the 2012 C. elegans framework. We also (5) propose a resolution to conflicting claims made by the C. elegans team versus classical literature regarding Layer #3, (6) extend the C. elegans hexalaminar framework to include the polar plugs of trichinelloids, and (7) report new findings regarding trichinelloid eggshell structure.

Description, molecular identification and pathological lesions of Huffmanela persica sp. nov. (Nematoda: Trichosomoididae: Huffmanelinae) from the daggertooth pike conger Muraenesox cinereus

“…To describe the architecture of the eggs of H. persica sp. nov., the novel anatomical and terminological framework proposed by Bond and Huffman, 2023, was adopted [ 25 ]. Measurements are given in micrometers as range (minimum–maximum) followed by mean ± standard deviation (SD) in parentheses.…”

“…3 E, e; F, f), two easily distinguishable apparent shell layers and mild to moderate degrees of embryonic bending within the eggshell. Eggs in stage III elliptical or oblong in shape, brown in color, containing two protruding polar plugs, with bilayer shell inclusive of a thin and light (hyaline) inner layer alongside with a thick and dark outer layer (this layering is an optical illusion under light microscopy caused by the birefringent properties of chitin; see Bond and Huffman, 2023) [ 25 ]. Morphometric measurements of eggs ( n = 27) in stage III are summarized as follows: total length (with protruding polar plugs and UL) 59.39–70.98 (62.44 ± 2.60); total length (without protruding part of polar plugs and UL) 54.75–61.67 (57.39 ± 1.94); total width (with UL) 32.46–44.75 (34.95 ± 3.03); total width (without UL) 30.62–43.30 (32.88 ± 3.05); shell thickness (with UL) 3.81–5.73 (4.90 ± 0.52); shell thickness (without UL) 2.92–5.02 (3.77 ± 0.46); polar plug width 8.18–11.09 (9.39 ± 0.68).…”

“…30 of Bond, 2020 and Fig. 24 of Bond and Huffman, 2023) [ 25 ], resulting in manifestation of a fine superficial sculpture on the surface of eggs examined with light microscope (Fig. 3 K, O, S).…”