Interstitial Annelida

Abstract

Members of the following marine annelid families are found almost exclusively in the interstitial environment and are highly adapted to move between sand grains, relying mostly on ciliary locomotion: Apharyngtidae n. fam., Dinophilidae, Diurodrilidae, Nerillidae, Lobatocerebridae, Parergodrilidae, Polygordiidae, Protodrilidae, Protodriloididae, Psammodrilidae and Saccocirridae. This article provides a review of the evolution, systematics, and diversity of these families, with the exception of Parergodrilidae, which was detailed in the review of Orbiniida by Meca, Zhadan, and Struck within this Special Issue. While several of the discussed families have previously only been known by a few described species, recent surveys inclusive of molecular approaches have increased the number of species, showing that all of the aforementioned families exhibit a high degree of cryptic diversity shadowed by a limited number of recognizable morphological traits. This is a challenge for studies of the evolution, taxonomy, and diversity of interstitial families as well as for their identification and incorporation into ecological surveys. By compiling a comprehensive and updated review on these interstitial families, we hope to promote new studies on their intriguing evolutionary histories, adapted life forms and high and hidden diversity.

Dinophiliformia early neurogenesis suggests the evolution of conservative neural structures across the Annelida phylogenetic tree

“…Dinophiliformia includes three clades: Lobatocerebrum , Dinophilus , and Dimorphilus ( Martín-Durán et al, 2021 ; Worsaae et al, 2021 ). We chose Dinophilus vorticoides and Dimorphilus gyrociliatus to analyze the cells, which express positive immunoreaction against a pan-neural marker–acetylated α-tubulin, in combination with immunoreaction to specific neuronal markers–5-HT and FMRFamide, during these worms’ development inside the egg capsule.…”

A new cave-dwelling genus and species of Nerillidae (Annelida) from the Ryukyu Islands, Japan

“…nov. is defined by a unique combination of morphological traits present in other genera (see Table 3). Nipponerilla gen. nov. possesses nine segments similar to all species of Leptonerilla, Meganerilla, Mesonerilla, Nerilla, and Speleonerilla isa Worsaae et al, 2018in Worsaae et al 2019a, whereas the remaining genera have either eight or seven segments (Jouin 1971;Tzetlin and Larionov 1988;Worsaae 2020a;Worsaae et al 2021). Except for Speleonerilla, the number of segments does not vary within genera (Jouin 1971;Tzetlin and Larionov 1988;Worsaae et al 2019aWorsaae et al , 2021Worsaae 2020a).…”

“…Plankton tows and slurp gun samples were sorted using an Olympus SZ51 microscope and photographed alive through the ocular lens using a handheld smartphone. The sediment samples were first anesthetized using isotonic MgCl 2 and decantated through a 63-µm mesh prior to sorting (Worsaae et al 2021). Specimens were fixed for morphological analyses or stored in 99% ethanol for molecular analyses (see below).…”

“…Nerillidae currently represents the most species-rich interstitial annelid family with 15 genera and 59 described species (e.g., Worsaae 2020a, b;Worsaae et al 2021). Nerillids range from 0.3 to 2.1 mm in length and consist of seven to nine distinct segments with conspicuous parapodia carrying chaetae and interramal cirri.…”

“…Nerillids range from 0.3 to 2.1 mm in length and consist of seven to nine distinct segments with conspicuous parapodia carrying chaetae and interramal cirri. Species of Nerillidae are found worldwide, from the intertidal zone to the deep sea and from marine oceanic to freshwater inland habitats (Jouin 1971;Westheide 2008;Worsaae 2020a;Worsaae et al 2021). The highest taxonomic diversity is found in shallow interstitial environments of sand and gravel.…”