Amphicorina mobilis (Rouse, 1990)

Yoshihara, Taiki, Hiruta, Shimpei F., Katoh, Toru & Kajihara, Hiroshi, 2012, Three species of Amphicorina (Annelida, Sabellida, Sabellidae) from Japan, with descriptions of two new species, ZooKeys 187, pp. 45-62 : 50-54

Amphicorina mobilis (Rouse, 1990) Figs 56

Oriopsis mobilis Rouse, 1990: 230-231, fig. 5 a–i.

Amphicorina mobilis : Giangrande et al. 1999: 197, Table 1; Nogueira and Amaral 2000: 622; Rousset et al. 2004: Table 3; 2007: 47, Table 1; Kupriyanova and Rouse 2008: 1177, Table 1; Capa et al. 2010: 2, Table 1; Huang et al. 2011: 3, Table 1.

Amphicorina ? sp. Giangrande et al. 1999: 199-200, fig. 4 a–g.

Fabricia ventrilinguata ?: Fitzhugh 1990: 14. Not Johansson (1922).

Fabricia sabella ?: Imajima and Hartman 1964: 366. Not Ehrenberg (1836).

Material examined.

Morphology.Twenty-five specimens. ZIHU 3938, among botryllid ascidian colonies, 42°16'N, 142°27'E, Higashi-shizunai, Hokkaido, Japan, 10 June 2010; ZIHU3939, among algae, 42°16'N, 142°27'E, Higashi-shizunai, Hokkaido, Japan, 10 June 2010; ZIHU 3940, 3941, among algae, 42°06'N, 139°25'E, Okushiri-Island, Hokkaido, Japan, 9 May 2010; ZIHU 3942, among algae, 42°16'N, 142°27'E, Higashi-shizunai, Hokkaido, Japan, 10 June 2010; ZIHU 3943, among botryllid ascidian colonies, 43°12'N, 140°51'E, Oshoro, Hokkaido, Japan, 16 October 2009; ZIHU 3944, among algae, 42°16'N, 142°27'E, Higashi-shizunai, Hokkaido, Japan, 10 June 2010; ZIHU 3945, among Mytilus , 43°12'N, 140°51'E, Oshoro, Hokkaido, Japan, 23 May 2010; ZIHU 3946, among algae, 43°12'N, 140°51'E, Oshoro, Hokkaido, Japan, 24 May 2010; ZIHU 3947, among algae, 42°06'N, 139°25'E, Okushiri-Island, Hokkaido, Japan, 9 May 2010; ZIHU 3948, among algae, 43°12'N, 140°51'E, Oshoro, Hokkaido, Japan, 23 March 2010; ZIHU 4273, two specimens, among sessile organisms on culture panel for the vase tunicate Ciona intestinalis (Linnaeus, 1767) hung from a raft, 35°09'N, 139°36'E, Misaki, Kanagawa, Japan, 22 February 2012, K. Kakui leg; ZIHU 4274, three specimens, same locality data as ZIHU 4273 [ZIHU 3938, 3043-3948, 4273, intact specimens, fixed in 10% seawater formalin, preserved in 70% ethanol; ZIHU3939, dissected, with half of the branchial crown removed; ZIHU 3940, 3941, whole mount on slide; ZIHU 3942, mounted on SEM stub; ZIHU 4273, fixed in Bouin's fluid, preserved in 70% EtOH; ZIHU 4274, fixed and preserved in 99% EtOH].

DNA analysis.

Two specimens: one collected among algae, 42°06'N, 139°25'E, Okushiri-Island, Hokkaido, Japan, 9 May 2010; the other collected among laminarian holdfasts, 42°18'N, 140°59'E, Muroran, Hokkaido, Japan, 19 April 2011.

Description.

Complete specimens have eight thoracic and five abdominal chaetigers (Fig. 5A). Total length 1.2-3.2 mm (mean, 2.3 mm; n = 9), crown length 0.2-0.6 mm (mean, 0.4 mm; n = 9), maximum width 0.3 mm. Three pairs of radioles with lateral flanges; proximal 1/7 of radioles connected by palmate membrane; each radiole with six pairs of pinnules ending with terminal pinnule; all pinnules ending at same height as terminal pinnule. Each radiole with two longitudinal internal cellular supporting axes; each pinnule with one internal cellular supporting axis. One pair of ventral radiolar a ppendages present, nearly as long as radioles, with one internal cellular supporting axis (Fig. 5B). One pair of elongate dorsal lips present, with neither pinnular nor radiolar appendages; one pair of triangular ventral lips present (Fig. 5B). Distal end of ventral lobe on anterior peristomial ring bifurcate, extending slightly beyond collar margin (Figs 5B, 6A). Posterior peristomial ring collar margin smooth, with small ventral notch (Fig. 6A). Collar with dorsal gap (Fig. 6B). Small ciliated patch located on posterior peristomial ring (Figs 5B, 6A). One pair of red eyes present on peristomium (not visible in preserved specimens). Glandular ridge on second chaetiger (not visible in preserved specimens).

Superior thoracic notochaetae elongate, narrowly hooded, 3-7 per fascicle (n = 10; usually 4-5 within single specimen) (Fig. 6C). Inferior thoracic notochaetae bayonet type, 3-7 per fascicle (n = 10) (Fig. 6C). Thoracic acicular uncini 3-8 per torus (n = 10); each uncinus with three rows of teeth above main fang; teeth on first row distinctly larger than those on upper rows (Figs 5C, 6D). Abdominal uncini quadrangular, with nine rows of teeth above small basal tooth (Figs 5D, 6E), 4-17 uncini per fascicle (n = 10). Abdominal neurochaetae three in number (two in the smallest specimen, ZIHU 3947) (n = 10), needle-like capillaries in form (Fig. 6F).

Pygidium rounded, with one pair of red eyes; color of eyes faded in preserved specimens.

In living specimens, paired statocysts are evident in first thoracic chaetiger; oocytes found in sixth to eighth thoracic chaetigers.

DNA analysis.

We obtained sequences for each of the three target gene fragments for this species (GenBank accession numbers AB646767, 18S, 1777 bp; AB646763, 28 S-D1, 380 bp; AB646766, 28S-D3-7, 1998 bp). Both strands were sequenced for 18S and 28S-D1; part of the 28S-D3-7 sequence is based on only one strand. In a reliably aligned 320 bp stretch of the 28S-D1 sequence, we observed one indel difference (gap) from the aligned homologous sequence from an Australian specimen (EF116217, Kupriyanova and Rouse 2008). In an aligned 1779-bp region of 18S, we observed two indel differences between our sequence and that from an Australian specimen (EF116206, Kupriyanova and Rouse 2008).

Remarks.

Amphicorina mobilis was previously known only from Australia ( Rouse 1990). A similar form was reported by Giangrande et al. (1999) as Amphicorina sp. from the Mediterranean, but it was not identified to species due to the poor condition of the specimens available.

Our specimens are quite similar to those in the original description of Amphicorina mobilis by Rouse (1990), with differences in body size, in ranges of number of chaetae and pinnules, and in the arrangement of teeth in the thoracic uncini. The Australian specimens were reported to be 1.1 mm in body length, while specimens from this study are up to 3.2 mm. Numbers of chaetae and pinnules reported by Rouse (1990), followed by those in our Japanese material in parentheses, are: thoracic superior notochaetae 3-4 (3-7), thoracic inferior notochaetae 3-4 (3-7), thoracic uncini 3-5 (3-8), abdominal uncini 3-9 (4-17), and abdominal neurochaetae 1-2 (2-3); and pairs of pinnules 5 (6). Rouse (1990) reported that Amphicorina mobilis has thoracic unicini with two rows of teeth above the main fang; the first row above the main fang has a large central tooth flanked by smaller teeth. By comparison, our specimens possessed no smaller teeth juxtaposing the large central tooth above main fang.

The DNA sequences shed little light on species identity, as the 18S and 28S genes evolve too slowly to reliably detect significant variation between closely related species, and the few mutations detected could as well be attributed to PCR or sequencing errors. Nonetheless, the Australian and (putative) Japanese populations of Amphicorina mobilis showed much less sequence divergence from one another than did either from a clearly morphologically distinct species, Amphicorina ascidicola sp. n. which lends weight to the interpretation that the Japanese and Australian populations are conspecific.

We consider that the specimen now labeled as the holotype of Fabricia ventrilinguata Johansson, 1922 deposited in the Zoologiska Museet, Uppsala (ZUM 206), might represent Amphicorina mobilis . We concur with Fitzhugh (1990) in that the original specimen (i.e., true Fabricia ventrilinguata ), or its label, was likely to be replaced later by accident. Fabricia ventrilinguata was originally described from Misaki, Japan, based on a polychaete collection made by Sixten Bock in 1914. Imajima and Hartman (1964) and Fitzhugh (1990) observed the “holotype” of Fabricia ventrilinguata and pointed out discrepancies between Johansson’s (1922) original description and the actual specimen; these include (character states in the parentheses refer to those given in Johansson (1922) vs. those in the actual specimen): the length of the body (6.5 mm vs. 2.1 mm), the number of thoracic chaetigers (4 vs. 8), and the posterior peristomial ring collar (absent vs. present). Because Johansson’s (1922) original description lacks important morphological characters used in identifying genera and species within Fabriciidae , the name Fabricia ventrilinguata should be treated as a nomen dubium. On the other hand, specimen ZUM 206 redescribed by Fitzhugh (1990) is applicable to Amphicorina , and possibly to Amphicorina mobilis . Taking into account that ZUM 206 might represent an undescribed species, however, further examination for a positive identification is necessary with respect to the shape of the thoracic notochaetae and the size of the tooth on the abdominal uncini. The fact that our specimens from Misaki, the same locality as ZUM 206, were identified as Amphicorina mobilis with certainty does not contradict our speculation that ZUM 206 would actually represent Amphicorina mobilis . If this is the case, Amphicorina mobilis was present in Misaki before 1914.

Distribution.

Southeastern Australia and eastern Japan; questionably the Mediterranean. At present we have no definitive evidence whether this distribution pattern represents a natural one or has been artificially expanded. If the latter is the case, much more thorough population genetic studies may reveal the native locality and invasion pathways. Incidentally, among sabellids, Sabella spallanzanii (Gmelin, 1791) has been reported to be introduced from European waters to Australia, possibly either via ballast water or hull fouling ( Patti and Gambi 2001). The same species has been also reported from New Zealand, introduced either via Australia or directly from Europe ( Read et al. 2011). Another sabellid, Branchiomma bairdi (McIntosh, 1885), originally distributed in the Caribbean Sea, was recorded in the southern Gulf of California; hull fouling was considered the most probable vector for the translocation ( Tovar-Hernández et al. 2009).