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. 2019 Feb 4;(822):1–15. doi: 10.3897/zookeys.822.29922

An illustrated key to the species of the genus Narella (Cnidaria, Octocorallia, Primnoidae)

Stephen D Cairns 1,✉, Michelle L Taylor 2
PMCID: PMC6370750  PMID: 30766419

Abstract Abstract

A history of the description of the 50 valid species of Narella is given, beginning with the first species described in 1860. To help differentiate the various species, a tabular and a polychotomous key are provided. The species in the keys are arranged using nine characters or character sets that are believed to be of value at the species level. New characters or new significance given to previously described characters used in our keys include: 1) the nature of the dorsolateral edge of the basal scale, being ridged or not, 2) the thickness of the body wall scales, and 3) the arrangement of the coenenchymal scales (imbricate or mosaic), their thickness (thin or massive), and their outer surface ornamentation (ridged or not). All characters used in the keys are illustrated.

Keywords: Alcyonacea , Calcaxonia , dichotomous key, Primnoidae , tabular key

Introduction

The first species of Narella was described as Primnoaregularis by Duchassaing and Michelotti (1860) collected off Guadeloupe, Lesser Antilles at an unknown depth. This is somewhat remarkable in that 366 m is the shallowest depth from which this species is known, and it was thus collected at a time when deep-water animals were not thought to occur below approximately 200 m. Primnoaregularis was made the type (by monotypy) of the newly described genus Narella by Gray (1870), calling it that name perhaps because the polyps resembled a series of small noses (Latin naris = nostril). The holotype is deposited at the Turin Museum (Volpi and Benvenuti 2003) but because of its poor condition was set aside to be replaced by a neotype (Cairns and Bayer 2004; ICZN 2005).

The next species to be described in the genus, Stachyodesregularis Wright & Studer, 1889, from the Kermadec Islands, was unfortunately also called regularis, but placed in the newly described genus Stachyodes Wright & Studer, 1887 in Studer (1887), a junior synonym of Narella. Because Versluys (1906) considered it and P.regularis of Duchassaing and Michelotti (1860) to be in the same genus, the Wright & Studer species was thought to be a junior homonym and thus it required a new name, which he gave as S.studeri Versluys, 1906. It also became the type species of Stachyodes. Yet another genus name that was subsequently synonymized with Narella was proposed by Wright and Studer (1889) as Calypterinus, the type species being C.allmani Wright & Studer, 1889 (Fiji).

In the first of several species to be described based on specimens collected by the US Fish and Wildlife Service vessel Albatross, Studer (1894) described Stachyodes (= Narella) ambigua from off the Galapagos Islands.

Next followed Versluys’ (1906) beautifully illustrated and finely described revision of the deep-water octocorals of the Siboga Expedition from Indonesia, which included the description of seven new species, all of which he also placed in Stachyodes. This work set the standard for future morphological descriptions within the genus.

In the next ten years a flurry of new species were described from around the world: four from off Japan (Kinoshita 1907), one from off Sumatra (Kükenthal 1907), one from the Hawaiian Islands (Nutting 1908), three from the North Atlantic (Hickson 1909; Kükenthal 1912, 1915), and one from the southwest Indian Ocean (Thomson 1911). Narellaelegans Tixier-Durivault & Lafargue, 1968 is believed to be a junior synonym of N.versluysi (Hickson, 1909), originally described in Stephens and Hickson (1909). Thomson also described a species from the southwest Indian Ocean, S.capensis Thomson, 1917, which was later synonymized with N.gilchristi (Thomson, 1911). But most notable from this time period was Kükenthal’s (1919) report on the deep-water octocorals of the Siboga expedition, in which he re-described all the species of Narella (as Stachyodes) and provided a morphological key to the 18 valid species. One hundred years later these are still the characters used to discriminate species and form the basis for the keys presented herein.

Aurivillius (1931) described one new species from off Japan, and Deichmann (1936) two new species from the northwest Atlantic Ocean. Finally, the “modern” era of Narella taxonomy was introduced by Bayer (1951), who finally synonymized Stachyodes and Calypterinus with Narella, and also described a new species from Indonesia. He later described two new species from off the Hawaiian Islands (Bayer 1995, 1997), one of them, N.nuttingi Bayer, 1997, later being synonymized with N.dichotoma (Cairns & Bayer, 2007). In collaboration with Cairns, Bayer also revised the Narella species from the northwest Atlantic (Cairns and Bayer 2003), describing two new species, and from the Hawaiian Islands (Cairns and Bayer 2007), describing six new species. They subsequently also placed the genus in phylogenetic perspective in a morphology-based cladogram, and listed the 38 known species at that time (Cairns and Bayer 2009). Also in 2007, Cairns and Baco (2007) described five new species from deep seamounts in the Gulf of Alaska.

Cairns described five more new species from the New Zealand region (Cairns 2012) and six from the northern and central Pacific (Cairns 2018), which prompted the need for this synthetic key to the species. Cairns (2018) also made one previously described species of Narella, N.mesolepis Cairns, 2012, the basis for a new genus, Pseudonarella. Taylor and Rogers (2015) placed Narella in a phylogenetic perspective using molecular data, and listed the 44 species known at that time, although S.regularis should be considered as junior synonym of N.studeri, and Cairns (2018) considered N.irregularis to be a junior synonym of N.horrida. Finally, Taylor and Rogers (2017) described three new species from the southwest Indian Ocean, and listed all species known at that time.

The genus Narella represents a highly successful adaptive radiation within the primnoids and more species are expected to be discovered. This is the reason why we here present two keys (a tabular and polychotomous key), the first since Kükenthal’s (1919) work, i.e., to facilitate comparison of species for identification purposes, and to examine this genus before new species are described.

Materials and methods

Many of the descriptions and diagnoses are based on original literature, which is duly cited. Descriptive terms used are found in the trilingual glossary of Bayer et al. (1983). Reviewing holotypes involved preparing sclerites for viewing under a light microscope following procedures well-documented elsewhere (Alderslade 1998; Fabricius and Alderslade 2001; Cairns 2016).

Taxonomy

Subclass Octocorallia

Order Alcyonacea

Suborder Calcaxonia
Family Primnoidae Milne Edwards, 1857
Genus. Narella

Gray, 1870

Diagnosis.

Colonies branched dichotomously (laterally or equal), pinnately, in a lyrate fashion, or unbranched. Polyps arranged in whorls, all polyps facing downward in contracted condition. Each polyp covered with three (rarely four) pairs of abaxial body wall scales (i.e., one pair of basals, one or rarely two pairs of medials, and one pair of buccals) and a variable number of pairs of smaller adaxial scales, nonetheless leaving the adaxial face largely naked. Articular ridge not present on basal scales. Paired infrabasal scales often present. Opercular scales keeled on inner surface. Coenenchymal scales thin and imbricate or thick and mosaic in placement, and sometimes prominently ridged.

Type species.

Primnoaregularis Duchassaing & Michelotti, 1860, by monotypy.

Discussion.

Currently there are 50 valid species in the genus Narella, the most speciose in the family Primnoidae (Taylor and Rogers 2015). The species in both keys (tabular (Table 1) and polychotomous, below) are roughly presented in an order that follows the major characters as outlined below, these characters we purport to be valuable in the distinction of species of Narella.

Table 1.

Tabular Key to the species of the genus Narella.

Species Dorsolateral edge of basal scale Pairs of body wall scales Polychaete commensalism Branching mode Body wall scale thickness Coenenchymal scales: imbricate, thickness; ridged Polyps/whorl; whorl diameter (mm) Polyp length (mm) Distal edge of basal scales Other characters Geographic and depth range
N.macrocalyx Cairns & Bayer, 2007 Small ridge 3 Present Sparse, Thin Thin, imbricate; rarely ridged 4–6; 7–11 4.5–5.5 Lobate, smooth Hawaiian Islands, 1206–1807 m
N.gilchristi (Thomson, 1911) Small ridge 3 Present lyrate, secondarily dichotomous Thin Thick, mosaic; unridged 4–8; 4–9 2––3 Lobate, smooth Southwest Indian Ocean, 90–1365 m
N.ferula Cairns, 2018 Multi-ridged 3 Absent Unbranched Thin Thin, imbricate; ridged 2–3; 3.6 2.3–2.5 Serrate cowl, spurs Medial scales also with serrate margin Palmyra Atoll, 1023 m
N.hawaiinensis Cairns & Bayer, 2007 Inconspicuous basal ridge 3 Absent Unbranched Thin Thin, imbricate; ridged 3–5; 5–6 3.4–4.1 Lobate, smooth HI, Johnston Atoll, 1492–1944 m
N.muzikae Cairns & Bayer, 2007 Multi-ridged 3 Absent Common coenosteum (bolus) Thin Thin, imbricate; ridged 3–6; 3–4 1.7–2.2 Lobate, serrate Base strongly calcified Hawaiian Islands, 326–381 m
N.merga Cairns, 2018 Two ridges basally 3 Absent Y-shaped Thin Thin, imbricate; ridged 3; 4.4 4 Lobate (short cowl) Wake Island, 2575 m
N.fordi Cairns, 2018 Multi-ridged 3 Absent Sparse, equal dichotomous Thin Thin, imbricate; ridged 3;3.4–3.5 2.1–2.6 Lobate, smooth Medial scales ridged Phoenix Islands, 1899 m
N.cristata Cairns & Baco, 2007 Single ridge 3 Absent Sparse, equal dichotomous Thin Thin, imbricate; ridged (sail scales) 2–4; 3.4 2.1–3.0 Lobate, smooth Medial and buccals ridged; occasionally four pairs of bw scales Gulf of Alaska seamounts, 3385 m
N.alvinae Cairns & Bayer, 2003 Single ridge 3 Absent Sparse, equal dichotomous Thin Thin, imbricate; ridged 4; 3.8 2.7–3.1 Lobate. smooth Medial scales elongate Bermuda, 3419 m
N.bayeri Cairns & Baco, 2007 Single ridge 3 Absent Sparse, equal dichotomous Thin Thin, imbricate; ridged (sail scales) 5–7; 3.5 2.2–3.4 Lobate, smooth Medial scales ridged Gulf of Alaska seamounts, 3277–4091 m
N.alaskensis Cairns & Baco, 2007 Low ridge 3 Absent Sparse, equal dichotomous Thin Thin, imbricate; ridged (sail scales) 5–9; 7.5 2.7–3.2 Lobate (narrow), smooth Medial scales ridged Gulf of Alaska seamounts, 2377–3075 m
N.arbuscula Cairns & Baco, 2007 Tall, short ridge 3 Absent Sparse, equal dichotomous Thin Thin, imbricate; ridged (sail scales) 6–7; 6.8 3.4–4.7 Lobate, smooth Whorls crowded Gulf of Alaska seamounts, 2775–3465 m
N.pauciflora Deichmann, 1936 Multi-ridged 3 Absent Equal dichotomous Thin Thin, imbricate; complex ridging 2–5; 4 2.6–2.8 Lobate, smooth Adaxial buccals as ridged ascus scales Northwest Atlantic, 738–1473 m
N.bowersi (Nutting, 1908) One ridge basally 3 Absent Equal dichotomous Thin Thin, imbricate; ridged 3–4; 4.5 2.5–3.2 Tall, serrate Buccal scales serrate Hawaiian islands, 1218–1758 m
N.gaussi (Kükenthal, 1912) Multi-ridged 3 Absent Equal dichotomous Thin Thin, imbricate; ridged 4–5; 3 2.1–3.0 Lobate (low), smooth Radial ridges on all body wall scales Antarctica, 2450 m
N.parva (Versluys, 1906) Multi-ridged 3 Absent Equal dichotomous Thin Thin, imbricate; ridged 4–6; 2.5–3.2 2.0–2.4 Tall, narrow, smooth Adaxial buccal scales ridged Southwest Pacific, 920–2400 m
N.regularis (Duchassaing & Michelotti., 1860) Multi-ridged 3 Absent Equal dichotomous Thin Thin, imbricate; ridged 4–5; 3.2 2.0–2.3 Lobate, smooth Medial and buccals ridged Northwest Atlantic, 366 – 792 m
N.valentine Taylor & Rogers, 2017 One tall ridge 3 Absent Lyrate, secondarily dichotomous Thin Thin, imbricate; flat 4–5; 2.4–2.8 1.5–1.8 Tooth-like apex Medials ridged Southwest Indian Ocean, 383–444 m
N.virgosa Cairns, 2018 Multi-ridged 3 Absent Lyrate, secondarily dichotomous and bushy Thin Thin, imbricate; ridged (sail scales) 3–4; 3.3–4.2 2.6–2.8 Lobate, smooth Medials and buccals ridged Hawaiian Islands and Johnston Atoll; 1901–1985 m
N.bellissima (Kükenthal, 1915) Low ridge basally 3 Absent Lyrate, secondarily dichotomous Thin Thin, imbricate; ridged (sail scales) 3–8; 3.15 2.0–2.2 Lobate, smooth Amphi-Atlantic, 161–1968 m
N.ornata Bayer, 1995 Multi-ridged 3 Absent Unknown Thin Thin, imbricate; ridged 3–4; 3.5 3 Serrate distal margin All scales, including adaxial buccals, radially ridged Hawaiian Islands, 748–1007 m
N.spectablis Cairns & Bayer, 2003 One tall ridge 4 Absent Unbranched Thin Thin, imbricate; ridged (sail scales) 3; 2.8 3.5 Lobate, smooth (low) All body wall scales ridged Bahamas, 1485 m
N.abyssalis Cairns & Baco, 2007 Multi-ridged 4 Absent Sparse, dichotomous Thin Thin, imbricate; ridged (sail scales) 2–4; 2.8 1.9–2.4 Lobate, smooth (low) All body wall scales ridged Gulf of Alaska seamounts, 4594 m
N.laxa Deichmann, 1936 Absent 4 Absent Equal dichotomous Thin Thin, imbricate; multiple ridges 3–5; 3.6 3 Lobate, smooth 3 pairs of adaxial buccal scales Amphi-North Atlantic, 2980–3186 m
N.horrida (Versluys, 1906) Absent 3 Present From common bolus Massive Thick, mosaic; unridged 5–6; 6–9 2.0–3.4 Spinose (massive) Medial scales also spinose Indonesia, 204 m
N.hypsocalyx Cairns, 2012 Absent 3 Present From common bolus Thin Thin, imbricate; unridged 9; 13 2.7 Tall and serrate Adaxial buccals elongate New Zealand, 510–1118 m
N.clavata (Versluys, 1906) Absent 3 Present Sparse, dichotomous Massive Thick, mosaic; unridged 4–14; 7–8 2––3 Tall, narrow, smooth Adaxial buccals numerous Indonesia, Philippines, 128–335 m
N.ambigua (Studer, 1894) Absent 3 Present Sparse, dichotomous Thin Thick, mosaic; unridged 5–7; 6–7 2.5–3.0 Lobate, tall, smooth 3 pairs adaxial buccals Galapagos, Gulf of Panama, 702– 1463 m
N.aurantiaca Cairns, 2018 Absent 3 Present Sparse, dichotomous Thin Thin, interlocking; ridged 4–6; 6.5–7.0 2.8–3.2 Lobate, smooth Wake Island, 745 m
N.leilae Bayer, 1951 Absent 3 Present Sparse, dichotomous Thin Thin, imbricate; ridged (sail scales) 4–6; 5.2–5.6 2.0–2.5 Serrate cowl Edges of buccals undulate Indonesia, 740 m
N.alata Cairns & Bayer, 2007 Absent 3 Present Equal dichotomous Thin Thin, imbricate; medial scale 4–5; 4–5 2.5–3.1 Lobate, tall (cowl), smooth Whorls closely spaced Hawaiian Islands, 477–750 m
N.vermifera Cairns & Bayer, 2007 Absent 3 Present Equal dichotomous Thin Thick, mosaic; very low ridges 3–5; 4 1.8–2.0 Lobate, tall, smooth Buccals in closed position Hawaiian Islands, 275–527 m
N.allmani (Wright & Studer, 1889) Absent 3 Present Equal dichotomous Thin Thick, mosaic; unridged 4–7;5 3 Tall, serrate Fiji, depth unknown
N.obscura (Versluys, 1906) Absent 3 Present Equal dichotomous Thin Thick, mosaic; unridged 4–6; 6–7 2.7–2.8 Lobate (undulate), smooth (cowl) Indonesia, 984 m
N.dampieri Cairns, 2012 Absent 3 Present Equal dichotomous Thin Thick, mosaic; unridged 5–8; 7 1.4–1.9 Lobate, tall, narrow Numerous adaxial buccal scales Lord Howe Islands, 342 m
N.mosaica Cairns, 2012 Absent 3 Present Equal dichotomous Massive Thick, mosaic; unridged 3–5; 5–6 2.7–3.1 Lobate, slender, smooth New Zealand, 228–294 m
N.vulgaris Cairns, 2012 Absent 3 Present Equal dichotomous Massive Thick, mosaic; unridged 4–6; 4–5 2.0–2.4 Lobate, smooth 2 pairs adaxial buccals are ridged New Zealand, 335–1165 m
N.orientalis (Versluys, 1906) Absent 3 Present Unknown Thin Thin, imbricate; unridged (concave) 6; 5.8 2.2–3.0 Lobate, smooth Indonesia, 520 m
N.calamus Cairns, 2018 Absent 3 Absent Unbranched Thin Thin, imbricate; ridged (sail sacles) 4; 5 4.5–5.0 Serrate, blunt Wake Island, 2073 m
N.versluysi (Hickson, 1909) Absent 3 Absent Unbranched or very sparsely Thin Thin, imbricate; medial ridge 4–7; 5–7 3.2–3.7 Lobate, smooth Basal scale ridged internally Amphi-North Atlantic, 550–3100 m
N.speighti Taylor & Rogers, 2017 Absent 3 Absent Sparse, dichotomous Thin Thin, imbricate; unridged 3–4; 2.5–3.6 2.0–2.2 Lobate (slender), smooth Southwest Indian Ocean, 870 m
N.grandiflora (Kükenthal, 1907) Absent 3 Absent Sparse, dichotomous Thin Thick, mosaic; unridged 4–5; 4.5 3 Lobate, smooth Numerous adaxial buccal scales Indonesia, 805 m
N.studeri (Versluys, 1906) Absent 3 Absent Equal dichotomous Massive Thick, mosaic; unridged 4–8; 4–5 3.0–3.3 Lobate, smooth Smooth body wall scales New Zealand, Indonesia, 732–1392 m
N.biannulata (Kinoshita, 1907) Absent 3 Absent Equal dichotomous Massive Thick, mosaic; unridged 6–7; 4.8 1.8–2.0 Lobate, smooth Adaxial buccals absent; medial scales closed Japan, depth unknown
N.candidae Taylor & Rogers, 2017 Absent 3 Absent Equal dichotomous Thin Thick, mosaic; unridged (smooth) 4–6; 4–5 2.0–2.4 Lobate, smooth Southwest Indian Ocean, 763 m
N.japonensis (Aurivillius, 1931) Absent 3 Absent Equal dichotomous Thin Thin, imbricate; unridged 3–6; 3.5–4.0 2––3 Lobate, smooth Stem stiff Japan, 732 m
N.gigas Cairns & Bayer, 2007 Absent 3 Absent Equal dichotomous Thin Thin, imbricate; ridged 10–14; 9–12 2.5–3.0 Lobate, tall, narrow, smooth Hawaiian Islands, 362–399 m
N.dichotoma (Versluys, 1906) Absent 3 Absent Equal dichotomous Thin Thin, imbricate; low ridges 3–5; 4–5 2.8–3.1 Lobate, smooth Hawaiian Islands, Malaysia, 204–1448 m
N.megalepis (Kinoshita, 1908) Absent 3 Absent Equal dichotomous Thin Thin, imbricate; ridged 5–8; 6–7 2.5–3.0 Lobate, smooth Numerous small adaxial buccal scales Japan, depth unknown
N.compressa (Kinoshita, 1908) Absent 3 Absent Lyrate Massive Thick, mosaic; unridged 7–8; 3 2 Lobate, smooth Japan, Phoenix Islands, 501 m
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Dorsolateral edge of basal scale ridged or not ridged: The dorsolateral edge (the point of inflexion of the scale from the dorsal region to the lateral region) of the basal scale is consistently ridged or not ridged (Fig. 1E) in each species, with the only exception of N.macrocalyx, which is inconspicuously ridged, and sometimes (rarely) lacks the ridge. This external ridging may help give strength to basal sclerites. The ridge may be single and extend from the base to the tip of the scale (Fig. 1A, B), or partial, occurring only at the base of the scale (Fig. 1C). Or, there may be multiple short ridges occurring in this region of the scale (Fig. 1D). The ridges may be tall or low. This character is relatively easy to observe, but usually requires the removal of a polyp from a whorl, drying the specimen, and then applying a dye to help see the characteristic ridging structure.

Figure 1.

Figure 1.

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A, B lateral view of a polyp showing dorsolateral ridge for entire height of basal scale (AN.parva from Versluys (1906)BN.bayeri) C basal scale of N.hawaiinensis showing dorsolateral ridge only on lower half of scale D whorl of polyps of N.pauciflora showing multiple dorsolateral ridges on the basal scales E basal scale of N.vulgaris showing the lack of a dorsolateral ridge, and a lobate distal edge F polyp whorl of N.bellissima showing the three pairs of body wall scales G polyp of N.laxa having four pairs of body wall scales H polyp whorl of N.hypsocalyx showing highly modified basal scales forming a cross section view of a cylindrical worm tube I polyp whorl of N.vulgaris showing highly modified basal scales forming a lateral view of a cylindrical worm tube J unbranched colony of N.versluysiK, L branching from a basal bolus of N.hypsocalyxM sparse, dichotomous branching of N.macrocalyxN equal, dichotomous branching of N.vulgarisO lyrate branching of N.bellissimaP massive basal scales of N.clavata.

Number of pairs of body wall scales: Most species of Narella have three pairs of abaxial body wall scales (basal, medial, and buccal, Fig. 1F), but in three species there is consistently an extra pair of medial scales (Fig. 1G). Also, specimens of some species that have otherwise three pairs of body wall scales will have occasional polyps with four pairs of body wall scales. This is a fairly easily observed character when using a dissecting microscope.

Worm commensalism: The commensal association with a polychaete worm, usually a polynoid (Cairns and Bayer 2008, Cairns 2012, Britayev et al. 2014, Serpetti et al. 2017), is considered to be characteristic of the species, and is easily observed even without a microscope. The facing basal scales of two adjacent polyps are greatly enlarged and modified (reflexed) in order to make an elongate cylindrical tube for the worm (Fig. 1H, I).

Branching mode: The mode of branching, and thus colony shape, is considered to be characteristic of the species. Modes include: unbranched (Fig. 1J), branching from a common basal coenenchyme or bolus (Fig. 1K, L), sparse equal dichotomous branching (Fig. 1M), equal dichotomous branching (Fig. 1N), and lyrate (Fig. 1O), which is often followed by dichotomous branching. Lyrate branching might be considered as a special case of dichotomous branching in which the outer component of each bifurcation maintains a straight line while the inner branches remain roughly parallel to one another.

Body wall scale thickness: In some species the body wall scales are quite thick, or massive (Figs 1P, 2A). This trait is often correlated with having thick coenenchymals as well (see next character). This character is best seen using scanning electron microscopy of individual sclerites.

Figure 2.

Figure 2.

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A massive basal scales of N.clavataB thin, imbricate coenenchymal scales of N.fordiC thick, mosaic arranged coenenchymal scales of N.mosaicaD individual thick coenenchymal scale of N.mosaica with a finely granular outer surface E complexly ridged coenenchymal scale of N.muzikaeF single medial coenenchymal ridge of N.paucifloraG sail scale of N.spectabilisH serrate distal margin of body wall scales of N.bowersiI spinose body wall scales of N.horridaJ adaxial body wall scales of N.dampieriK polyp pair of N.leilae showing extensive cowl and serrate distal edges of body wall scales (from Bayer, 1951).

Coenenchymal scales arrangement and ornamentation: The coenenchymal scales of most species are relatively thin, having the same thickness as a body wall scale, and have edges that slightly overlap those of other adjacent coenenchymal scales (Fig. 2B). But some species have quite thick scales (Fig. 2C–D) that are so massive that they cannot overlap adjacent scales and thus produce a mosaic, polygonal, or tessellate pattern, also called “cobblestone” (Williams 1992). The term mosaic is used herein. Coenenchymal scales usually have a finely granular outer surface (Fig. 2D), but many species have scales that bear a single longitudinal (Fig. 2F) or multiple complexly arranged ridges (Fig. 2E). If these ridges are quite tall they have been termed sail scales (Cairns 2016)(Fig. 2G). Mosaic coenenchymals are not usually ridged (Fig. 2D). This character is best seen using SEM.

Polyps/whorl; whorl diameter: Although every specimen and species has a range of polyps/whorl and whorl diameter, sometimes these numbers help to differentiate species. This character is easily determined using a dissecting microscope.

Polyp length: As above, this character has a range for every specimen and species, but can sometimes differentiate among species. The polyp length is essentially the horizontal length of the polyp, which consist of the length of the buccal scale and whatever part of the operculars protrude from the buccal scale. This character is easily determined using a dissecting microscope.

Shape of the distal edge of basal scales: The distal edge of the basal scales are usually slightly lobate and smooth (Fig. 1E), but in some species are serrate (Fig. 2H, K) or even spinose (e.g., N.horrida, Fig. 2I). It may extend far beyond its junction with the proximal edge of the medial scales as a cowl (Fig. 2K) or be quite short (Fig. 1D). This character is also easily determined using a dissecting microscope.

Other characters: Other characters that are used to describe and differentiate species but are not consistently addressed in the keys include: shape and number of adaxial body wall scales (Fig. 2J), external ridging of the medial and buccal scales, closure of the body wall rings, aspects of the opercular scales, body wall formula (i.e., ratio of length of basal: medial: buccal scales), and number of polyps per cm.

Geographic and depth range.

All ocean basins, 128–4594 m (Cairns 2012).

Polychotomous key to the species of the genus Narella
1a Dorsolateral edge of basal scale bears a longitudinal ridge or ridges (Fig. 1A, D) 2
1b Dorsolateral edge of basal scale unridged (smooth) (Fig. 1F) 9
2a Three pairs of body wall scales per polyp (Fig. 1A, B, F) 3
2b Four pairs of body wall scales per polyp (Fig. 1G) 18
3a Polychaete commensalism present, causing extreme modification of basal scales to form a tube (Fig. 1H, I) 4
3b Polychaete commensalism absent (no tubes) 5
4a Colony branching sparse (Fig. 1M); coenenchymal scales thin and imbricate in arrangement (Fig. 2B); Hawaiian Islands N. macrocalyx
4b Colony branching lyrate (Fig. 1O); coenenchymal scales thick and mosaic in arrangement (Fig. 2C, D); South West Indian Ocean N. gilchristi
5a Colonies unbranched (Fig. 1J) 6
5b Branches of colony originate from a common base or from a basal bolus (Fig. 1K, L) N. muzikae
5c Branching in a Y-shape N. merga
5d Branching sparse, dichotomous (Fig. 1M) 7
5e Branching equal, dichotomous (Fig. 1N) 12
5f Branching lyrate, sometimes with subsequent dichotomous branching (Fig. 1O) 16
5g Branching pattern unknown; all scales radially ridged N. ornata
6a Multiple ridges on dorsolateral edge of basal scales (Fig. 1D); polyps less than 2.5 mm in length N. ferula
6b Single inconspicuous ridge on dorsolateral edge of basal scales (Fig. 1A, B); polyps greater than 3.5 mm in length N. hawaiinensis
7a Polyps less than 4 mm in length 8
7b Polyps more than 5 mm in length 10
8a Multiple ridges on dorsolateral edge of basal scales N. fordi
8b Single ridge on dorsolateral edge of basal scales 9
9a Buccal scales ridged (Fig. 1D); medial scales short; Gulf of Alaska N. cristata
9b Buccal scales unridged; medial scales elongate; Bermuda N. alvinae
10a Whorl diameter less than 4 mm N. bayeri
10b Whorl diameter greater than 6 mm 11
11a Polyp length 3.4–4.7 mm N. arbuscula
11b Polyp length 2.7–3.2 mm N. alaskensis
12a Extremely few polyps per whorl (occasionally only two) N. pauciflora
12b More numerous polyps per whorl (up to six)(Fig. 1F) 13
13a Whorl diameter greater than 3.5 mm 14
13b Whorl diameter less than 3.5 mm 15
14a Multiple ridges on dorsolateral edge of basal scales; Antarctica N. gaussi
14b Single ridge on dorsolateral edge of basal scales; Hawaiian Islands N. bowersi
15a Medial and buccal scales ridged; northwest Atlantic Ocean N. regularis
15b Medials and buccals not ridged; Indonesian region N. parva
16a Coenenchymal scales unridged (granular)(Fig. 2C, D) N. valentine
16b Coenenchymal scales ridged (Fig. 2E–G) 17
17a Polyps 2.6–2.8 mm in length; South Pacific N. virgosa
17b Polyps 2.0–2.2 mm in length; Northwest Atlantic N. bellissima
18a Colony unbranched; single ridge on dorsolateral edge of basal scales N. spectabilis
18b Colony sparsely dichotomous; multiple ridges on dorsolateral edge of basal scales N. abyssalis
19a Four pairs of body wall scales per polyp (Fig. 1G) N. laxa
19b Three pairs of body wall scales per polyp 20
20a Polychaete commensalism present, causing extreme modification of basal scales to form a tube 21
20b Polychaete commensalism absent (no tubes) 32
21a Branches of colony originate from a common base or from a basal bolus (Fig. 1K, L) 22
21b Branching sparse, dichotomous (Fig. 1M) 23
21c Branching equal, dichotomous (Fig. 1N) 26
21d Branching pattern unknown; margin of basolateral scales tall and serrate N. orientalis
22a Body wall scales massive (Figs 1P, 2A); coenenchymal scales mosaic in arrangement; margin of basal scale spinose N. horrida
22b Body wall scales thin (normal); coenenchymal scales imbricate; margin of basal scale serrate N. hypsocalyx
23a Coenenchymal scales thick (mosaic) and unridged (Fig. 2C, D) 24
23b Coenenchymal scales thin and ridged 25
24a Body wall scales massive; numerous small adaxial buccal scales; western Pacific (Figs 1P, 2A) N. clavata
24b Body wall scales thin; 3 pairs of large adaxial buccals (Fig. 2J); eastern Pacific N. ambigua
25a Polyps 2.8–3.2 mm in length; distal margin of basal scales lobate and smooth (Fig. 1C) N. aurantiacus
25b Polyps 2.0–2.5 mm in length; distal margin of basal scales a serrate cowl (Fig. 2K) N. leilae
26a Coenenchymal scales ridged (Fig. 2E–G) 27
26b Coenenchymal scales not ridged (Fig. 2C, D) 29
27a Coenenchymal scales thin and imbricate in arrangement; polyps 2.5–3.1 mm in length N. alata
27b Coenenchymal scales thick (Fig. 2D) and mosaic in arrangement; polyps 1.8–2.0 mm in length N. vermifera
28a Whorl diameter more than 6 mm 29
28b Whorl diameter less than 6 mm 30
29a Polyp length 2.7–2.8 mm; few adaxial scales N. obscura
29b Polyp length 1.4–1.9 mm; numerous small adaxial scales (Fig. 2J) N. dampieri
30a Polyp length 2.7–3.1 mm; adaxial scales not ridged N. mosaica
30b Polyp length 2.0–2.4 mm; adaxial scales ridged N. vulgaris
31a Colonies unbranched 32
31b Branching sparse, dichotomous 33
31c Branching equal, dichotomous 34
31d Branching lyrate, sometimes with subsequent dichotomous branching N. compressa
32a Polyp length 4.5–5.0 mm; distal margin of basal scales serrate N. calamus
32b Polyp length 3.2–3.7 mm; distal margin of basal scales lobate and smooth N. versluysi
33a Coenenchymal scales thick and mosaic in arrangement; polyp length approximately 3 mm N. grandiflora
33b Coenenchymal scales thin and imbricate in arrangement; polyp length 2.0–2.2 mm N. speighti
34a Body wall scales massive (Fig. 1P) 35
34b Body wall scales thin (normal) 36
35a Medial scales in open position; polyp length 3.0–3.3 mm N. studeri
35b Medial scales in closed position (fused); polyp length 1.8–2.0 mm N. biannulata
36a Coenenchymal scales unridged (granular) 37
36b Coenenchymal scales ridged 38
37a Coenenchymal scales thick and mosaic in arrangement; South West Indian Ocean N. candidae
37b Coenenchymal scales thin and imbricate in arrangement; Japan N. japonensis
38a Polyps per whorl fewer than 5 N. dichotoma
38b Polyps per whorl 5–8 N. megalepis
38c Polyps per whorl more than 9 N. gigas
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Supplementary Material

XML Treatment for Narella
zookeys.822.29922-treatment1.xml (70.5KB, xml)

Acknowledgements

We thank Robert Ford for composing the figures and our warm thanks go out to one very kind reviewer and our wonderful and thorough editor whose comments and edits improved this manuscript.

Citation

Cairns SD, Taylor ML (2019) An illustrated key to the species of the genus Narella (Cnidaria, Octocorallia, Primnoidae). ZooKeys 822: 1–15. https://doi.org/10.3897/zookeys.822.29922

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Associated Data

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Supplementary Materials

XML Treatment for Narella
zookeys.822.29922-treatment1.xml (70.5KB, xml)

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