Re-description of Parasabella fullo (Grube, 1878) (Polychaeta: Sabellidae) and diagnostic characteristics for detection in California

Abstract

The original description of the fan worm Parasabella fullo (Grube, 1878) is brief and mainly focused on the color. This paper provides a redescription based on syntype material from northern Japan kept at Museum für Naturkunde of Berlin and new records in California (USA). Diagnostic characters used in redescribing the species are the shapes of inferior thoracic notochaetae, ventral thoracic shields and dorsal collar margins. Although this Japanese species was collected on vessels’ hulls in California, it is not clear if and where the species is established here, due to past difficulties in identification without well-defined characters. Nevertheless, a resident population appears to exist in the region, given the species occurrence on local recreational vessels. The redescription provides information to distinguish it from the local Californian indigenous species Parasabella pallida Moore, 1923.

Keywords:

• Non-indigenous species
• biological invasions
• shipping
• fouling
• syntype

Introduction

In a recent taxonomic analysis of invertebrates collected from the hulls of vessels in California, USA, the western Pacific polychaete Parasabella fullo (Grube, 1878) was identified by L. H. Harris (Los Angeles County Museum of Natural History, Allan Hancock Foundation), representing a first record for the state, and reported by Ashton et al. (2012). Although distinct from the California native Parasabella pallida Moore, 1923, these congeners are challenging to distinguish from each other based on existing descriptions.

Parasabella fullo was originally described from northern Japan, but drawings or diagnostic features were not included by Grube (1878). Zachs (1933) also reported Sabella fullo from northern Japan, suggesting it belonged to the genus Demonax Kinberg, 1867. Zachs (1933) also suggested the species was possibly synonymous with D. leucaspinus (sic) (Kinberg 1867), a species originally described from Peru, based on illustrations of thoracic and abdominal chaetae provided by Johansson (1925: 24, fig. 8) for D. leucaspius (sic). Later, Annenkova (1938), Uschakov (1955) and Buzhinskaja (1967) also reported S. fullo in the northwestern Pacific under D. leucaspius (sic), probably following Zachs (1933). It is remarkable that S. fullo was not mentioned in any contributions by Johansson (1922, 1925, 1927) on sabellid polychaetes for this region.

Tovar-Hernández and Harris (2010) replaced the name Demonax with Parasabella and recognized 25 species in the genus Parasabella, but P. fullo was omitted. Subsequently, Buzhinskaja (2013) placed S. fullo within Parasabella, although a diagnosis or redescription of the species was not included. To date, P. fullo is only known to have established populations in northern Japan and eastern Russia (Zachs 1933; Annenkova 1938; Uschakov 1955; Buzhinskaja 1967). Capa and Murray (2015) considered P. fullo to be a valid taxon, and they highlighted the translocation of some species of Parasabella beyond their natural distribution. Notwithstanding the foregoing work, a full redescription and illustrations are still needed to properly identify and detect P. fullo, especially outside of its native range where other congeners occur.

This study examines and characterizes the syntypes of P. fullo, providing a formal redescription. We also examine records of P. fullo and P. pallida in California, stressing the main characters to discriminate indigenous from non-indigenous species of Parasabella along the northeastern Pacific.

Material and methods

Syntype material of Parasabella fullo (Grube, 1878) from Museum für Naturkunde Leibniz in Berlin (Germany) (ZMB-5731) and syntypes of P. japonica (Moore & Bush, 1904) from the Academy of Natural Sciences of Philadelphia, Pennsylvania, USA (ANSP 1082) were requested and examined. These were compared to specimens of P. fullo and P. pallida from California, deposited at the Smithsonian Environmental Research Center, Invasion Lab (SERC). Only entire, complete syntypes of P. fullo were photographed.

The specimens from California were collected from three locations in previous studies (Figure 1). In San Francisco Bay, fouling panels were deployed for 3 months during summer and retrieved in September 2016 for analysis of benthic invertebrates (see Bastida-Zavala et al. 2017 for description). In Santa Barbara Harbor and San Diego, the hulls of recreational vessels were surveyed and sampled by divers, to analyze associated benthic invertebrate species (Ashton et al. 2012). These two studies are referenced in this paper as the panel and vessel surveys, respectively.

Figure 1. Map of California with the three bays sampled: San Francisco, Santa Barbara and San Diego. Parasabella fullo was found in Santa Barbara and San Diego in 2011

Taxonomic accounts

Systematics

Order SABELLIDA Latreille, 1825Family SABELLIDAE Latreille, 1825Genus Parasabella Bush, 1905

Parasabella fullo (Grube, 1878), redescriptionFigures 2–6

Figure 2. Parasabella fullo syntype ZMB 5731: (a) thoracic ventral view (b) thoracic dorsal view

Figure 3. Parasabella fullo syntype ZMB 5731 stained with methyl green: (a) thoracic ventral view (b) thoracic dorsal view

Figure 4. Parasabella fullo syntype ZMB 5731: tip of radioles

Figure 5. Parasabella fullo syntype ZMB 5731: (a) notopodial thoracic chaetae (b) neuropodial thoracic companion (c) thoracic uncini

Figure 6. Parasabella fullo syntype ZMB 5731: (a) notopodial inferior thoracic chaetae type B

Sabella fullo Grube, 1878: 105.

?Demonax fullo. — Zachs 1933: 134. — Buzhinskaja 1985: 188, Figure 22.

Demonax leucaspius (sic). — Annenkova 1938: 213–214 (non D. leucaspis (Kinberg)).

Demonax (sic) leucaspius. — Uschakov 1955: 412, Figure 156 J–I. — Buzhinskaja 1967: 115–116 (non D. leucaspius Kinberg).

Parasabella fullo. — Buzhinskaja 2013: 12. — Capa & Murray 2015: 768, figures 4–C, 5–O.

Examined material

Parasabella fullo (Grube, 1878), ZMB 5731, five complete syntypes (three entire, two broken in two parts under histolysis) and one detached crown plus one specimen of Bispira spirobranchia (Zachs, 1933). Parasabella fullo (Grube, 1878), recreational boats’ project: California, USA. SERC: 2 specimens from the 2011 vessel survey previously identified by Leslie Harris and deposited in Invasion Lab at SERC collection (Maryland). Vial # 147893 (1 specimen): collected on 13 July 2011 from a recreational boat hull berthed (visiting) in Santa Barbara Harbor (34°24ʹ21.38”N, 119°41ʹ33”W). Vial # 162979 (1 specimen) collected on 25 October 2011 from recreational boat hull berthed (visiting) in San Diego Police Dock (32° 42ʹ 35” N, 117° 14ʹ 03” W).

Additional material examined

Parasabella japonica (Moore & Bush, 1904), syntype, ANSP 1082.

Diagnosis

Radiolar eyes absent. Broad radiolar flanges along radioles. Radiolar tips medium-length (the length of two thoracic segments), digitiform. Dorsal lips broad basally, with radiolar appendages (mid-rib) and a long filament, which is longer than dorsal lips lateral lamellae length. Dorsal collar margins long, flap-like. Thoracic ventral shields in contact with neuropodial tori. Inferior thoracic notochaetae broadly hooded with progressively tapered tips (type Aaccording to Capa & Murray 2015).

Redescription of syntypes and Californian specimens (SERC)

Min-Max body length 18–58 mm (syntypes), 16–37 mm (SERC). Min-Max body width 2–4.5 (syntypes), 2.3–3 mm (SERC). Min-Max radiolar crown length 4.5–14 mm (syntypes), 5.5–8 mm (SERC). Pairs of radioles: 12–26 (syntypes), 13–19 pairs (SERC). Thorax with eight segments (syntypes, SERC). Abdomen with 67–108 segments (syntypes), 52–84 (SERC). Radiolar crown with basal lobes as long as 1.5–2 thoracic segments, arranged in two semicircles, involute ventrally in largest syntype and specimens from recreational boat in California (Figures 2, 3 and 7). Radioles spotted in Californian specimens (Figure 7(a-b)); although not seen in preserved syntypes but present at least at the base of the radioles and mentioned in original description, this feature may have been diminished due to preservation (Figure 2(a-b)). Radiolar tips bare, digitiform, as long as the length of two thoracic segments, with broad flanges (Figure 4). Broad radiolar flanges present along the entire radiolar length. Number of skeletal cells were not counted but more than 30 were reported by Capa and Murray (2015). Dorsal lips as long as 5–6 thoracic segments, broad basally, with radiolar appendages (mid-rib) tapered distally. The tip projection of the radiolar appendages is longer than the lateral lamellae length of the dorsal lip. One or two pairs of short pinnular appendages attached on the first two dorsal radioles. Ventral lips rounded, slightly folded and short. Parallel lamellae prominent, arising from the anterior margin of collar ventral shield, and covering the entire margin of ventral peristomium. Brown spots, unequal in size along radiolar rachis (fade off in some syntypes). Collar as long as three thoracic segments in dorsal view (from the anterior margin of collar to the first intersegmental division), covering the base of radioles. Low ventral lappets with rounded anterior margins, separated completely by a long incision (Figures 2(a) and 3(a)). Dorsal collar margins not fused to faecal groove (Figures 2(b) and 3(b)), flap-like. Ventral shield of collar incised median-anteriorly by a small notch (Figure 7(a)), from where lamellae arise. Collar chaetae elongate, narrowly hooded. Thoracic ventral shields similar in size, two times wider than long, in contact and indented by adjacent neuropodial tori (Figures 3(a) and 7(a)). Brown spots located between thoracic neurochaetal tori and notochaeta. Superior thoracic notochaetae elongate, narrowly hooded (Figure 5(a)); inferior group with two rows of shorter, broadly hooded chaetae of type B (Figure 5(a)), with hoods 1.5–2 times width of the shaft (A/B), and 3–4 times as long as maximum width (C/B) (Figure 6). Thoracic neuropodial uncini with about seven to nine rows of similar-sized teeth above main fang, covering half the length of main fang, neck shorter than breast or as long as breast (E/F), well-developed breast and long handles (2.5–3 times the distance from main fang to breast) (H/G) (Figure 5(c)). Thoracic neuropodial companion chaetae with subdistal end enlarged, and thin distal mucro compressed laterally (Figure 5(b)). Abdominal chaetae narrowly hooded in both anterior and posterior rows, uncini with 7 to 10 rows of similar-sized teeth above main fang covering about half the length of main fang, breast well-developed and medium-size handle (1–1.5 times the length of the distance between breast and main fang). Pygidium forming a rounded lobe with approximately 25 black eyespots, all unequal in size in California records (eyespots not seen in syntypes, perhaps they faded off).

Figure 7. Parasabella fullo from California (SERC, Vial 147893): (a) thoracic ventral view (b) thoracic dorsal view

Distribution

Northern Japan, Eastern Sea of Russia, California (Ashton et al. 2012). Although detected in California, this species is not known to be established here (see Discussion), as it was found only on two vessels to date.

Remarks

Parasabella fullo was originally described as Sabella by Grube (1878) from northern Japan. Unfortunately, drawings or diagnostic features were not included in his original description in German: “Weisslich mit roth-brauner Unterseite oder ganz blassbraun, jederseits 18 blass rothbraune Kiemenfäden, ihr Schaft mit 2 Längsreihen abwechselnd kreideweisser schmalen unregelmässigen bräunlichen Binden. Eine Basalmembran an den Kiemen nicht wahrnehmbar; letztere 7, der Leib 24 mm lang” that can be translated as: Whitish with a brownish-brown background, or entirely pale brown, 18 pale red-brown radioles on each side, with two longitudinal chalky-white narrow bands alternated by irregular brownish bandages. A basal membrane not visible on the crown; the latter 7 mm long, while the body is 24 mm.

In the contribution by Capa and Murray (2015), a description of P. fullo is not provided, but they include some characters in their table 2: P. fullo do not present radiolar eyes; the thoracic ventral shields are in contact with the neuropodial tori; and type B inferior thoracic notochaetae (broadly hooded with progressively tapered tips). Also, they reported a drawing of numerous rows of axial cells supporting the radioles at their base (>30 cells, Fig. 4C in Capa and Murray (2015)) and long-handled thoracic uncini (2.5 times the distance between the fang and the breast, Fig. 5O in Capa and Murray (2015)).

The redescription, provided in the present study, in addition to the features proportioned by Capa and Murray (2015), includes the presence of broad radiolar flanges along radioles; radiolar tips digitiform, of medium-length; dorsal lips broad basally, with radiolar appendages (mid-rib) and a long filament that it is longer than the lateral lamellae of dorsal lips; and dorsal collar margins flap-like.

In Japan, in addition to P. fullo, other three species of the genus have been described: P. aulaconota (von Marenzeller, 1884) from Nagasaki; P. albicans (Johansson, 1922) from Misaki among holfasts of the alga Laminaria; and P. japonica (Moore and Bush, 1904) from Suruga Bay. At the present, the co-occurrence of multiple Japanese species create challenges in individual species identification, because original descriptions are brief, illustrating only chaetae and uncini (except for P. albicans, where a collar in dorsal view was illustrated by Johansson 1922, pl. I, fig. 7). These and subsequent records do not include a comparison of morphological features useful for identification (e. g. Okuda 1938; Imajima & Hartman 1964; Uchida 1968). Capa and Murray (2015) examined types of P. aulaconota and P. albicans and some features for both species were included in their table 2, and these are used below for comparative purposes with P. fullo, as well as the examination of the type of P. japonica (ANSP 1082 reviewed in the present study).

Parasabella aulaconota have 8–10 vacuolate cells of the cross-section radiole near the base, while more than 30 cells are present in P. fullo (Capa & Murray 2015). Parasabella albicans shows radioles with short tips, and the tips are medium-length in P. fullo. In P. japonica, ventral shields are not in contact with neuropodial tori, and those in P. fullo are in contact with neuropodial tori.

For the USA west coast, three different species of Parasabella have been described: P. pallida Moore, 1923 from Santa Cruz, California; P. media (Bush, 1905) from Alaska to Monterrey Bay; and P. rugosa (Moore, 1904) from San Diego, California. Types of P. rugosa were examined by Banse (1979), and Perkins (1984) provided redescriptions of all three species. These species were found from the intertidal to 140 m depth, in a variety of habitats: rocky crevices, shell and mud, in seagrass, associated with pilings, and on vessel hulls (Table I).

Table I. Species of Parasabella described from California (USA)

Species	Type locality	Type material	Reference, habitat and depth
Parasabella pallida (Moore, 1923)	California	USNM 17360, ANSP	Moore 1923; fine grey sand and rock; 18 m.
Parasabella media (Bush, 1905)	Alaska to Monterrey Bay	Yale (YPM 2691, 2692, 2693)	Bush 1905; shell and mud or between seagrass; 18 m. Hartman 1944: rocky crevices. Blake & Ruff 2007: rocky habitats, in crevices.
Parasabella rugosa (Moore, 1904)	Baja California to San Diego	ANSP 2596	Moore 1904; on pier piling, shell and cobble; 22–140 m. Blake & Ruff 2007: associated with pilings and hard substrata.
Parasabella fullo (Grube, 1878)	Northern Japan	ZMB	This study; as hull fouling of recreational boats.

For P. fullo and P. pallida, radiolar eyes are absent, the thoracic ventral shields are in contact with neuropodial tori, and both have thoracic chaetae type B (Table II). However, these species also have some dissimilarities: the dorsal collar margins are longer in P. fullo than P. pallida (as long as three thoracic segments in the former, as long as two thoracic segments in the second); P. fullo have medium-size, digitiform radiolar tips with broad flanges, whereas P. pallida shows long-size, filiform tips with narrow flanges; in P. fullo radiolar appendage projection of dorsal lips is longer than dorsal lip lateral lamellae length compared to the projection of P. pallida that is shorter than the length of the dorsal lip lateral lamellae. Moreover, P. fullo has larger basal radiolar lobes than P. pallida (length of 1.5–2 thoracic segments in P. fullo versus one segment in P. pallida), and P. fullo has a higher number of radiolar cells than P. pallida (>30 versus 8–10 in P. pallida) (Table II).

Table II. Comparison between Parasabella fullo (Grube, 1878) and P. pallida Moore, 1923

	P. fullo	P. pallida
Type locality	Northern Japan	Santa Cruz, California
Radiolar eyes	Absent	Absent
Number of vacuolated cells supporting radioles, at base, in cross section	+30^1	8–10
Radiolar crown basal lobes length	≥1.5–2 thoracic segments	≥ 1 thoracic segment
Radiolar tips	Wide, length ≥ 2 thoracic segments	Filiform, length ≥ 3 thoracic segments
Radiolar flanges	Broad	Narrow
Dorsal lips length	≥ 5–6 thoracic segments	≥ 5 thoracic segments
Tip projection of radiolar appendage (mid-rib)	Longer than dorsal lip lateral lamellae length	Shorter than dorsal lip lateral lamellae length
Dorsal collar	Flap-like, length ≥ 3 thoracic segments	Flap-like, length ≥ 2 thoracic segments
Gap between ventral shields and neuropodial tori	Absent, thoracic ventral shields and neuropodial tori in contact	Absent, thoracic ventral shields and neuropodial tori in contact
Inferior thoracic chaetae	Type B	Type B^2
A/B, width hoods/shaft	1.5–2	1.5–2
C/B, hood length/width	3–4	4–5
H/G, length of handle/distance from breast to main fang	Long, 2.5–3.5	Medium, 1–1.5
E/F, length neck/breast	0.5–1	0.2–0.5
Pygidial eyes	Present	Present

¹Not dissected in this study, feature based on Capa and Murray (2015). ²Contrary to Capa and Murray (2015), chaetae are considered type B.

Parasabella pallida Moore, 1923Figure 8

Figure 8. Parasabella pallida (SERC, Vial 239815) from San Francisco Bay: (a) thoracic ventral view; (b) thoracic dorsal view; (c) (d) tips of radioles

Parasabella pallida Moore 1923: 241, 242. — Loi 1980: 144. — Tovar-Hernández & Harris 2010: 15. — Bastida-Zavala et al. 2016: 407–408, figs 2 (map), 10D.

Sabella media. — Hartman, 1944: 285 [in part, not pl. 23, fig. 42] fide Perkins 1984.

Demonax medius. — Hartman, 1969: 675, 676 [in part, not figs 1–5] fide Perkins 1984.

Demonax pallidus. — Perkins 1984: 313–315, figs 15–16. — Tovar-Hernández et al. 2009: 325–326, figs 2b, f, 3c–d, 4c–e.

Examined material

Parasabella pallida Moore, 1923. San Francisco Bay, Ballina Island Marina collected on 13 September 2016: plate 18320: vial # 222933; plate 18229: vial # 222943; plate 17859b: vial # 239815; Lake Merritt Boat House collected on 16 September 2016: plate 18343: vial # 239817; plate 18192: vial # 239944. Deposited in Invasion Lab at SERC collection (Maryland).

Diagnosis

Radiolar eyes absent. Narrow radiolar flanges along radioles. Radiolar tips long-length (the length of three thoracic segments), mostly filiform. Dorsal lips broad basally, with radiolar appendage (mid-rib) and a filament that is shorter than dorsal lips lateral lamellae length. Dorsal collar margins short, flap-like. Thoracic ventral shields in contact with neuropodial tori. Inferior thoracic notochaetae broadly hooded with progressively tapered tips (type A according to Capa & Murray 2015).

Description of Californian specimens

Min-Max body length 28–33 mm. Body width 3.5 mm. Min-Max radiolar crown length 14–17 mm. Pairs of radioles: 22–24. Thorax with eight segments. Abdomen with 52–68 segments. Radiolar crown arranged in two semicircles, involute ventrally with basal lobes as long as one thoracic segment (longitudinal length). Radiolar tips bare, slender, and filiform as long as approximately three thoracic segments. Narrow radiolar flanges present along the entire radiolar length. Dorsal lips as long as five thoracic segments, broad basally with a radiolar appendage (mid-rib) that projects anteriorly as a filament. This filament is shorter than dorsal lip lateral lamellae length. Two-three pairs of short pinnular appendages attached on the first two dorsal radioles. Ventral lips rounded, and short. Parallel lamellae arising from the anterior margin of ventral shield of collar, and covering the entire margin of ventral peristomium. Crown with brown bands, each band extending over three pinnules; radiolar rachis with numerous brown-coloured spots, unequal in size, distributed irregularly along radiolar length. Collar as long as two thoracic segments in dorsal view (from the anterior margin of collar to the first intersegmental division), covering slightly the base of radioles. Low ventral lappets with rounded anterior margins; dorsal collar margins not fused to faecal groove, flap-like. Ventral shield of collar M-shaped, incised median-anteriorly by a small notch, from where a large parallel lamellae arises. Collar chaetae elongate, narrowly hooded. Thoracic ventral shields similar in size, two times wider than long, in contact and indented by adjacent neuropodial tori. Brown spots between thoracic neurochaetal tori and notochaeta absent. Superior thoracic notochaetae elongate, narrowly hooded; inferior group with two rows of shorter, broadly hooded chaetae of type B with hoods 1.5–2 times width compared to the shaft (A/B) or 4–5 times as long as maximum width shaft (C/B). Thoracic uncini avicular with 6–7 equal-size teeth above main fang and covering half of the main fang length, neck shorter than breast (E/F), breast well-developed, medium-size handle, 1–1.5 times the distance from main fang to breast (H/G); companion chaetae with very long, tapered mucros. Abdominal uncini with 6–7 equal-size teeth above main fang, similar to those in thorax but shorter. Pygidium rounded with irregularly arranged eyespots.

Distribution

Southern California, southern Gulf of California (Tovar-Hernández et al. 2009) and southern Mexican Pacific (Bastida-Zavala et al. 2016).

Remarks

Capa and Murray (2015), based on papers by Perkins (1984) and Tovar-Hernández et al. (2009), reported that Parasabella pallida has inferior thoracic chaeta of type A (with broad hoods and distal ends narrowing abruptly, nearly paleate shape) (see Capa and Murray (2015)’s Figure 2A and table 2). However, specimens from San Francisco, California, herein examined, present chaetae type B, which are observed also in P. pallida from Southern Gulf of California, Mexico, as reported in Tovar-Hernández et al. (2009, figure 4d).

In addition, dorsal lips of P. pallida were reported as short in Capa and Murray (2015), although measurements were not provided. In specimens from San Francisco, dorsal lips are as long as five thoracic segments, and therefore described as long in our description (Figure 8(c–d)).

Perkins (1984) already commented about the difficulty to distinguish juveniles of P. media, P. pallida and P. rugosa, since these are very similar. He also noted that the degree of spiralling is size-related (Perkins1984: 295); consequently, it is not a reliable character to distinguish among these three species. Perkins also reported 20–60 vacuolated cells supporting radioles in P. media, 33–41 in P. rugosa and 8–10 in P. pallida. A more useful character observed in all adult stages of the specimens examined in the present study could be the shape of the dorsal lips. In fact, the dorsal lips of P. media and P. rugosa are triangular and tapered (lateral lamellae are narrow, covering the radiolar appendage or mid-rib, that ends as a long filament); in P. pallida, dorsal lips have a broad, rounded base formed by lateral lamellae and a medium-size distal filament.

In Table II, Capa and Murray (2015) suggested some characters to distinguish the different species of Parasabella. One of the characters considered useful to distinguish P. fullo from P. pallida was reported to be the type B inferior thoracic notochaetae in the first and type A in the latter, respectively. However, this appears to be in error. Our analysis found that specimens of P. pallida from San Francisco Bay have the same type of chaetae of P. fullo.

Key to the species of Parasabella in California

• Ventral shield of collar about twice broader than long 2

  - Ventral shield of collar about three times broader than long 3

• Radiolar tips digitiform with broad flanges; dorsal collar margins as long as 3 thoracic segments in dorsal viewP. fullo (Grube, 1878)

  - Radiolar tips filiform with narrow flanges; dorsal collar margins as long as 2 thoracic segments in dorsal view P. pallida Moore, 1923

• Radioles in partial-spiraled arrangement at least in large specimens P. rugosa (Moore, 1904)

  - Radioles in semicircular arrangement on all sizes P. media (Bush, 1905)

Conclusive remarks

The analysis and re-description of Parasabella fullo is important to clarify the characters and provide elements for identification, especially considering biogeography and detecting new invasions by non-indigenous species. The recent confirmed records of P. fullo suggest the species may have invaded the coast of California, being detected in two different bays several hundred kilometers apart in 2011 (Figure 1), but it is not yet clear whether there are established populations here. It is noteworthy that (a) the specimens examined in our analysis were collected only on small boats, which are transient, rather than resident substrate in these bays, and (b) this species was not detected in 2017 and 2018 during our more recent panel surveys (n > 50 panels analyzed in each year; Ruiz et al., unpublished data) in Long Beach, California, which occurs between San Diego and Santa Barbara. Thus, while record of the species occurrences in California are reported by Ashton et al. (2012), and it is listed in the recent regional checklist by SCAMIT (2018), careful analysis of past records of Parasabella spp. and additional surveys are needed to confirm whether and where the P. fullo has established populations in the region. We hope the diagnostic characters outlined in this paper will facilitate such analysis and future detection.

Despite the limited records on transient vessels, we nonetheless hypothesize that P. fullo is established in California waters, because the type of small vessels involved in California are primarily involved in regional routes (Zabin et al. 2014); moreover, visits to ports in Japan and Russia are extremely rare for any single one of these vessels, let alone two. Small recreational and fishing boats likely play an important role in the secondary, coastwise spread of NIS (Zabin et al. 2014). Therefore, we surmise that one or more populations of P. fullo is likely to exist along the northeastern Pacific, allowing colonization of vessels operating within (and restricted to) this region.

The potential impact of an invasion by P. fullo in California and the northeastern Pacific is poorly understood. If established in one or more bays, the species has the opportunity to spread coastwise across latitudes, as most introduced species to this coastline have undergone secondary spread to additional bays (Ruiz et al. 2011). However, the effects of most introduced marine species are not known (Ruiz et al. 1999; Ojaveer et al. 2015), as these are quantified for relatively few species. Even when documented, such effects vary in space and time, causing high uncertainty in predictions of new invasions. More specifically, for Parasabella species, relatively little is known about its ecological effects. In Southern Gulf of California, P. pallida reaches densities of 400 ind/m² on buoys during summer (Tovar-Hernández & Yáñez-Rivera 2010, technical report). Tovar-Hernández et al. (2017) reported transverse fission and regeneration in P. columbi (Kinberg, 1867) as a common phenomenon, suggesting the potential for both sexual and asexual propagation and spread. This characteristic is similar to that present in Branchiomma bairdi (McIntosh, 1885), which may contribute to its high abundance and geographic spread. Another sabellid worm, Sabella spallanzanii (Gmelin, 1791), has invaded Australia and New Zealand and had significant impacts on infaunal community composition (Ahyong et al. 2017). Since species of the genus Parasabella have some ecological, reproductive and physiological traits similar to S. spallanzanii and B. bairdi, this suggests they also may have the potential disperse, colonize, invade and impact new habitats (Read et al. 2011; Tovar-Hernández et al. 2011; Ahyong et al. 2017), but studies are critically needed to understand the role of P. fullo and other NIS Parasabella species in new habitats.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Acknowledgements

We are grateful to the Curator Birger Neuhaus of the Museum für Naturkunde Leibniz in Berlin (Germany) and Academy of Natural Sciences of Philadelphia (Pennsylvania) for the syntype material, to Ian Davidson and Gail Ashton to provide the material from Recreational Boat project.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Marine Invasive Species Program of the California Department of Fish and Wildlife, and Smithsonian Institution.