The Early Branching Group of Orbiniida Sensu Struck et al., 2015: Parergodrilidae and Orbiniidae

Abstract

This review addresses the state of the art of the systematics and the improvements in the biology, ecology and species diversity of the two annelid taxa Parergodrilidae and Orbiniidae, the early branching group of Orbiniida sensu Struck et al., 2015 according to molecular studies. An effort to identify gaps of knowledge is given to understand the distribution, dispersal and the diversity Parergodrilidae and Orbiniidae hold, as well as to give several directions for future research. Parergodrilidae is a taxon of interstitial annelids constituted by the terrestrial Parergodrilus heideri (monotypic genus up to date), reported throughout Europe but also in Korea and North America, and the genus Stygocapitella, which includes eleven species from the upper shore of sandy beaches distributed along Europe and other regions of the world. Orbiniidae contains more than 200 described species spread over 20 valid genera, varying in size from a few millimeters up to 30 cm, distributed globally and living in a wide variety of soft bottoms. Improving the knowledge on these two sister-taxa is crucial for the understanding of the evolution to interstitial forms by progenesis in Annelida.

Annelids in Extreme Aquatic Environments: Diversity, Adaptations and Evolution

“…The Parergodrilidae are represented by two genera, the monotypic Parergodrilus (P. heideri), and Stygocapitella which is represented by 11 cryptic species. Parergodrilus heideri is found terrestrially in the humus-rich upper layers of soil in the Palearctic Region and Stygocapitella species are found worldwide, excluding the tropics, in the supralittoral zone of sandy beaches (i.e., semi-terrestrial) [44][45][46][47][48][49]. Both families have reduced (or an absence of) nuchal organs, the epidermis shows less (or no) ciliation, there are fewer types of receptor cells, and in Parergodrilidae embryos develop directly inside cocoons (Table 1) [45,49,50].…”

Annelid Diversity: Historical Overview and Future Perspectives

“…The current ranges of valid nominal species in the literature go from 14,000 to 20,000 [7,[86][87][88], and databases such as WoRMS currently considers 23,774 accepted species of extant annelids [89]. Recounting the number of species after the latest revisions, such as the Handbook of Zoology chapters [29][30][31] and the present special issue ( [90][91][92][93][94][95][96][97][98][99][100][101]), there seems to be around 20,000 currently accepted nominal species (Figure 3). There is a continuous documentation of new species and diversity patterns as new taxonomic surveys are carried out in poorly explored geographic areas and localities, in new environments, such as the deep-sea and, surprisingly, also in apparently well-known zones when using different collecting gear, sorting methods or identification techniques, such as SEM and molecular taxonomy.…”

“…com. [94]; Terebelliformia [93]; Arenicolidae [89]; Opheliidae [90], Salibregmatidae and Travisia [89,90]; Capitellida [89]; Spionida [103][104][105][106]; Sabellariidae [89,107]; Sabellida [99]; Siboglinidae [108]; Cirratuliformia [89,100]; Orbiniida [95]; Phyllodocida [101]; Eunicida [91]; Sipuncula [97]; Amphinomida [89].…”

“…For the present special issue, we aimed at gathering updated information and discuss the recent advances in different diversity aspects and in recent systematic revisions of some of the major Annelida clades, including Palaeoannelida, Sipuncula, Phyllodocida, Eunicida, Orbiniida, Cirratuliformia, Sabellida, Opheliida and Scalibregmatidae, Terebelliformia, and Clitellata [90,91,[93][94][95][96][97][99][100][101]. Other chapters take a more ecological approach, for example the papers on extreme or interstitial annelids [92,98].…”

Still Digging: Advances and Perspectives in the Study of the Diversity of Several Sedentarian Annelid Families

“…Within this incomplete picture, there are several lineages whose relationships with the remaining Sedentaria remain particularly obscure, including Cossuridae Day, 1963 [5], Paraonidae Cerruti, 1909 [6], Siboglinidae Caullery, 1914 [7], Hrabeiella Pizl, 1984 [8], Aeolosoma Ehrenberg, 1828 [9], Potamodrilus Lastochkin, 1935 [10], Scalibregmatidae Malmgren, 1867 [11], and Travisiidae Hartmann-Schröder, 1971 [12], among many others. Many recent studies have reviewed the current knowledge of several of these sedentarian lineages [13][14][15][16], including several articles within this issue [17][18][19][20][21], while others have received less attention (See [4]). In this article we focus on the cirratuliform families Acrocirridae Banse, 1969 [22], Cirratulidae Ryckholt, 1851 [23], and Sternaspidae Carus, 1863 [24], as well as the families Longosomatidae [25], Paraonidae, and Cossuridae, with the goal of providing an updated overview of our current knowledge on their diversity and systematics.…”