Amphicorina ascidicola sp. n.

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 : 47-49

Amphicorina ascidicola sp. n. Figs 12

Material examined.

Morphology.Holotype: ZIHU 3926, intact specimen, fixed in 10% seawater formalin, preserved in 70% ethanol, among botryllid ascidian colonies, 42°16'N, 142°27'E, Higashi-shizunai, Hokkaido, Japan, 10 June 2010. Paratypes: ZIHU 3927, among botryllid ascidian colonies, 42°18'N, 140°59'E, Muroran, Hokkaido, Japan, 16 April 2010; ZIHU 3928, 3929, among laminarian holdfasts, 42°33'N, 141°55'E, Mukawa, Hokkaido, Japan, 9 June 2010; ZIHU 3930, 3931, among botryllid ascidian colonies, 43°01'N, 144°50'E, Akkeshi, Hokkaido, Japan, 23 June 2009; ZIHU 3932, 3933, same data as for holotype; ZIHU 3934-3937, among laminarian holdfasts, 42°33'N, 141°55'E, Mukawa, Hokkaido, Japan, 9 June 2010 [ZIHU 3927, 3933-3937, intact specimens, fixed in 10% seawater formalin, preserved in 70% ethanol; ZIHU 3928, dissected, with half of branchial crown removed; ZIHU 3929, 3930, whole mounts on slides; ZIHU 3931, serial sagittal sections on slide; ZIHU 3932, mounted on SEM stub].

DNA analysis.

One specimen, among algae, 42°18'N, 140°59'E, Muroran, Hokkaido, Japan, 19 April 2011.

Descri

ption. Body with eight thoracic and six abdominal chaetigers (Fig. 1A). Total length 2.8 mm, crown length 0.7 mm, maximum body 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 (Fig. 1A). Each radiole with two longitudinal internal cellular supporting axes; each pinnule with one internal cellular supporting axis. One pair of ventral radiolar appendages present, with one internal cellular supporting axis, nearly 1/2 radiole length (Fig. 1A). One pair of elongate dorsal lips present, with neither pinnular nor radiolar appendages; one pair of triangular ventral lips present (Fig. 1B). Distal end of ventral lobe on anterior peristomial ring bifurcate (Fig. 2B). Posterior peristomial ring collar absent; border between anterior and posterior peristomial ring obscure (Figs 1B, 2A, 2B). Small ciliated patch on posterior peristomial ring (Figs 1B, 2A, 2B). One pair of red eyes present on peristomium (not visible in preserved specimens). Glandular ridge absent.

Superior thoracic notochaetae elongate, narrowly hooded, 3-5 per fascicle (Fig. 2C). Inferior thoracic notochaetae bayonet type, five per fascicle in first thoracic chaetiger; second to eighth thoracic chaetigers with 3-4 narrowly hooded and 5 bayonet-type inferior thoracic notochaetae (Fig. 2C). Thoracic acicular uncini 5-7 per torus; each uncinus with three rows of irregular-sized teeth above main fang (Figs 1C, 2D). Abdominal uncini quadrangular, with eight rows of teeth above large basal tooth (Figs 1D, 2E), 5-15 uncini per torus. Abdominal neurochaetae needle-like capillaries in form, three per fascicle (Fig. 2F).

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

One pair of statocysts in first thoracic chaetiger evident in living state. Oocytes found in sixth to eighth thoracic chaetigers.

DNA analysis.

We obtained sequences for two of the three target gene fragments for this species (GenBank accession numbers AB646764, 18S, 1677 bp; AB646765, 28S-D1, 377 bp); we were unable to sequence 28S-D3-D7. Both strands were sequenced for 28S-D1; part of the 18S sequence is based on only one strand. Among species of Amphicorina , DNA sequence data were available only for Amphicorina mobilis ( Rousset et al. 2004; Kupriyanova and Rouse 2008). In a 1687 bp alignment of 18S sequences, Amphicorina ascidicola differed in sequence from the Australian (GenBank accession number EF 116206, Kupriyanova and Rouse 2008) and Japanese specimens (AB646764) of Amphicorina mobilis by 15 indels and 17 substitutions in each case. In a 321 bp alignment of the 28S-D1 region, Amphicorina ascidicola differed in sequence fromthe Australian (EF116217, Kupriyanova and Rouse 2008) and Japanese (AB646765) specimens of Amphicorina mobilis by five substitutions and one indel in each case.

Etymology.

The specific name, a noun, is a combination of ascidia (sea squirt) and -cola (dweller), referring to the fact that the species was frequently found among botryllid ascidian colonies.

Remarks.

Among the 38 congeners, the following eight species have been reported to exhibit a reduction in the collar [= absence of posterior peristomial ring collar] as in Amphicorina ascidicola : Amphicorina alata (Ehlers, 1897), Amphicorina brevicollaris (Rouse, 1990), Amphicorina gracilis (Hartman, 1969), Amphicorina grahamensis Giangrande, Montanaro & Castelli, 1999, Amphicorina minuta (Berkeley & Berkeley, 1932), Amphicorina neglecta (Banse, 1957), Amphicorina pectinata (Banse, 1957), and Amphicorina triangulata López & Tena, 1999. However, the present new species can be distinguished from those by the combination of characters and their states summarized in Table 2.