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

Abstract

Sedentarian annelids are a diverse and heterogeneous group of marine worms representing more than 8600 species gathered in ca. 43 families. The attention brought to these organisms is unevenly distributed among these families, and the knowledge about them sometimes scarce. We review here the current knowledge about the families Acrocirridae, Cirratulidae (including Ctenodrilidae), Cossuridae, Longosomatidae, Paraonidae, and Sternaspidae in terms of biodiversity as well as the evolution of the taxonomy and systematics of each group. We present the challenges faced when studying these organisms and compare methodologies across groups and perspectives in future research.

New species and records of Heterospio (Annelida, Longosomatidae) from continental shelf, slope and abyssal depths of the Atlantic Ocean, Pacific Ocean, Indian Ocean and adjacent seas

“…Ehlers (1874Ehlers ( , 1875 originally placed his new genus in the Spionidae and even after being referred to a new family (Hartman 1944(Hartman , 1965 it was considered a spioniform (Fauchald 1977, Rouse & Fauchald 1997, Blake & Arnofsky 1999Read & Fauchald 2022). However, recent interpretation of morphology and newly obtained molecular data supports a close affiliation of Longosomatidae with Cirratulidae (Blake & Maciolek 2019;Rouse et al 2022); this position was also taken by Wilson (2000) and Grosse et al (2021). Longosomatids are similar to cirratulids in having long filamentous branchiae that differ from the broad flattened branchiae of spionids, a pair of long dorsal tentacles and in most species, the arrangement of abdominal setae into cinctures that mostly surround the body.…”

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].…”