Radicipes Stearns 1883

Genus Radicipes Stearns, 1883

Radicipes StearnS, 1883: 97.— KinoShita, 1913: 5.— JungerSen, 1915: 1183.— Kükenthal, 1919: 540 (in part: not R. squamiferus).— Verrill, 1922: 41.— Kükenthal, 1924: 410.— Deichmann, 1936: 236. — MadSen, 1944: 44.— Bayer, 1956: F216, text-fig. 3.— Bayer & Muzik, 1976: 68 (key to genuS).— Bayer & Stefani, 1988: 258 (key to genuS).—WilliamS, 1992: 252. — Pante & France, 2010: 600 (key to genuS, molecular phylogeny).— Cordeiro et al., 2015: 94.

Lepidogorgia Verrill, 1884: 220 (type SpecieS: L. gracilis Verrill, 1884, by monotypy); 1885: 512.—VerSluyS. 1902: 5.— ThomSon & HenderSon, 1906: 26 –27 (tabular key to SpecieS).— Nutting, 1908: 587 –588 (in part: not L. gibbosa).— ThomSon, 1927: 20.

Strophogorgia Wright, 1885: 691 (nom. nud.).

Strophogorgia Studer, 1887: 41 (nom. nud.).

Strophogorgia Wright & Studer, 1889: 2 (type SpecieS: Strophogorgia challengeri Wright & Studer, 1889, SubSequent deSignation).

Type species. Radicipes pleurocristatus Stearns, 1883, by monotypy.

Diagnosis. Unbranched (flagelliform) chrysogorgiids, brittle, sometimes elongate (up to 1 m long), and often loosely coiled, arising from a root-like calcareous holdfast. Polyps arranged uniserially along one side of aXis, delimiting a polypar and an abpolypar face, the former usually facing inner part of colony spiral. Coenenchyme usually quite thin. AXis slightly quadrangular to round in cross-section. Sclerites composed of irregularly shaped scales and rods.

Discussion. Three genera were proposed almost simultaneously: Radicipes Stearns (1883), Lepidogorgia Verrill (1884) and Strophogorgia Wright (1885). Kinoshita (1913) was the first author to establish the synonymy among these three genera. The first publication in which the name Strophogorgia appears (Wright, 1885) has no descriptions or specimen designations. Along with the creation of the subfamily Strophogorginae, Studer (1887) provided the first description of Strophogorgia (by monotypy), but did not list any species. Descriptions associated with species were given only subsequently, by Wright & Studer (1889). Thus, Strophogorgia Wright, 1885 and Strophogorgia Studer, 1887 are considered herein as nomen nudum, and the neXt available publication date is Strophogorgia Wright & Studer, 1889. Its type-species is Strophogorgia challengeri Wright & Studer, 1889, in accordance with recommendation 69A of the International Code of Zoological Nomenclature (ICZN, 1999).

Among the 15 genera previously assigned to Chrysogorgiidae, only five have unbranched colonies: Radicipes, Helicogorgia Verrill, 1883, Chalcogorgia Bayer, 1949, Distichogorgia Bayer, 1979 and Flagelligorgia Cairns & Cordeiro, 2017. Radicipes can be distinguished as being the only unbranched chrysogorgiid genus to have uniserially arranged polyps, the other three unbranched genera having bi- or multiserially arranged polyps. The monophyly of Radicipes implied by this morphological distinction is reinforced by molecular sequencing of both mitochondrial and nuclear genes (Pante et al., 2012), its sister group suggested to be Chrysogorgia (Pante & France, 2010; Pante et al., 2012).

The low number of morphological characters, as well as the low number of samples for some species makes the systematics of this genus difficult. Intracolony variation is also a challenge. For instance, in a single colony, the basal coenenchymal sclerites may be quite different from those in the median region. Similarly, some species have the coenenchyme between polyps filled with the same sclerites as those seen in the body wall (Table 1). Sclerite densities in polyps may also vary according to age and position in a colony. Also, size, arrangement and shape of the sclerites from the polyp base can be drastically modified within a specimen, when it is fully developed or seXually mature (Figs. 1 E, 2H-I’). In the same way, mature polyps usually show an enlargement at the base and at the oral portion.

The unbranched and usually coiled nature of the Radicipes colony (Figs. 1 A,D) make it similar to other deepwater unbranched Cnidaria, such as some species of octocorals of the genera listed as follows: Ainigmaptilon, Bathygorgia, Callozostron, Calyptrophora, Ellisella, Helicoprimnoa, Lepidisis, Narella, Narelloides, Onogorgia, Ophidiogorgia, Perissogorgia, Viminella and the antipatharian genera Cirripathes and Stichopathes. Thus in situ observations based on photographs must be made with care.

Distribution. The genus Radicipes shows a broad distribution, latitudinal and bathymetric (Fig. 3 and Table 1: 241–3580 m), with most of the records (about 80%) for the genus belonging to two species, Radicipes gracilis (Verrill, 1884) and R. pleurocristatus. The least reported species is Radicipes spiralis (Nutting, 1908), recorded only at the occasion of its description. The records incorporated herein were given by Watling et al. (2011) and Pante et al. (2012). Another source of biogeographic information is the “Ocean Biogeographic Information System” (OBIS), which also provides environmental conditions to better understand the requirements for the occurrence of Radicipes populations (see: http://iobis.org/eXplore/#/taXon/502435).

As most of the records of the genus given by Watling et al. (2011) were based on eXpedition and collections data (see Watling et al., 2011: p.70, fig. 2.5), it is likely that their Antarctic record was based on one previously misidentified specimen (USNM 1019007—a clavulariid attached to a Primnoella sp. stem). Indo-Pacific specimens recorded by Pante et al. (2012) and Alderslade et al. (2014) and South African specimens noted by Williams (1992) were identified only to genus level. Buhl-Mortensen et al. (2010: 43, fig. 42) show Radicipes sp. at around 700 m in Norwegian waters. Other records include the mid-Atlantic Ridge (Mortensen et al., 2008), off Norway (Gonzalez-Mirelis & Buhl-Mortensen, 2015), the Gulf of Vizcaya (France) (Altuna, 2010), and the Gulf of Cádiz (Spain) (Rueda et al., 2012) (Fig. 3).