Phoronis ijimai Oka, 1897

Hirose, Masato, Fukiage, Ryuma, Katoh, Toru & Kajihara, Hiroshi, 2014, Description and molecular phylogeny of a new species of Phoronis (Phoronida) from Japan, with a redescription of topotypes of P. ijimai Oka, 1897, ZooKeys 398, pp. 1-31 : 6-11

Phoronis ijimai Oka, 1897 [Japanese name: Hime-houkimushi]Figures 2-7

Phoronis ijimai Oka, 1897, 147-148.

Phoronis vancouverensis Pixell, 1912, 257-271, figs 1-5.

Phoronis svetlanae Temereva & Malakov, 1999, 627-630, figs 1, 3, 4.

Phoronis hippocrepia ?: Uchida and Iwata 1955, 1-3, text-figs 1, 2, pl. 1, figs A–D.

Material examined.

Five series of transverse sections and 34 whole specimens. NSMT-Te 878, several specimens, fixed and preserved in 10% formalin, collected at Etajima Island; NSMT-Te 879, several individuals, fixed and preserved in 10% formalin, collected in Moroiso Bay, attached to the pier in front of MMBS; NSMT-Te 880, several individuals on a living shell of Barbatia sp. ( Mollusca : Bivalvia ), collected in Sagami Bay; NSMT-Te 881, same data as NSMT-Te 879; NSMT-Te 882, same data as NSMT-Te 880; NSMT-Te 883, 6-μm transverse section stained with HE, collected at Etajima Island; NSMT-Te 884, same data as NSMT-Te 883; NSMT-Te 885, 6-μm transverse sections stained with HE, collected in Moroiso Bay; NSMT-Te 886, same data as NSMT-Te 885; NSMT-Te 887, 6-μm transverse sections stained with HE, collected in Sagami Bay.

Description.

Body except lophophore 2.40-16.83 mm in length (avg. 5.87 ± 4.04 mm, n = 34; average of topotypes 9.55 ± 4.78 mm, n = 12); 0.49-0.90 mm in diameter at ampula (avg. 0.64 ± 0.11 mm, n = 34; average of topotypes 0.59 ± 0.12 mm, n = 12); white and translucent in living state (Figs 2A, 2B, 3), yellowish white after fixation (Fig. 2C). Lophophore horseshoe-shaped, without significant coiling (Fig. 4); 0.87 -3.11 mm in length (avg. 2.17 ± 0.55 mm, n = 34; average of topotypes 1.66 ± 0.49 mm, n = 12), 0.27-0.99 mm in diameter at its base (avg. 0.61 ± 0.17 mm, n = 34; avg. of topotypes 0.43 ± 0.09 mm, n = 12); tentacles 106-151 in number (avg. 129 ± 18, n = 7; avg. of topotypes 110 ± 5, n = 3). Inhabits a transparent cylindrical tube either encrusting or burrowing in hard substrates (Fig. 2C).

Nephridium 162.00-204.00 μm in height (avg. 183.00 ± 29.70 μm, n = 2), with straight nephridial papilla and curved ascending branch (Fig. 5A, 5B). Descending branch absent. Ascending branch with single chamber. Nephridial papilla situated beside anus, 294.24-324.91 μm in length (avg. 309.57 ± 21.69 μm, n = 2); nephridiopore situated on nephridial papilla opening above (in living orientation) anus level (Fig. 5A, 5C). Ascending branch offset along body axis near intestine, with its lower end extending toward esophagus (Fig. 5B, 5D); 277.55-323.49 μm in length (avg. 300.52 ± 32.49 μm, n = 2). Two nephridial funnels present; anal funnel larger than oral funnel. Anal funnel large (avg. 69.00 ± 4.24 μm in height, 45.77 ± 3.15 μm in width at base, 111.94 ± 16.48 μm in maximum width at tip; n = 2), its aperture located at lower end of ascending branch. Oral funnel small (avg. 20.01 ± 1.40 μm in diameter, n = 2), its aperture opening on lateral surface of ascending branch, situated slightly lower than anal funnel.

Body-wall longitudinal muscles of generally bushy type (Fig. 6A, 6B) but sometimes feathery in lower part of body; 45-50 in number, arranged in following formula ( Selys-Longchamps 1907):

Composite formula

Mean formula

(n = 7 sections from 3 individuals)

Left and right lateral mesenteries present (Fig. 6A). Two giant nerve fibers present; left giant nerve fiber 3.16-10.61 μm in diameter (avg. 6.72 ± 3.27 μm, based on eight sections from different parts of the body, from two individuals), situated at base of left lateral mesentery (Fig. 6C); right giant nerve fiber 2.47-7.81 μm in diameter (avg. 4.55 ± 2.15 μm, based on nine sections of different parts of the body from two individuals), situated at base of right lateral mesentery. Esophageal valve absent.

Hermaphroditic; early-stage ova and spermatocytes found beside lateral blood vessel. Brooded eggs observed in specimens from Hiroshima (Fig. 7A, 7B, 7C); embryos of various developmental stages brooded on basal nidamental glands on lophophore (Fig. 7C).

Distribution and habitat.

Phoronis ijimai is widely distributed in the North Pacific, along the coasts of North America, Canada, Japan, and Russia, including the Sea of Japan ( Emig 1971a, 1974, Emig and Golikov 1990, Temereva and Malakhov 1999). Phoronis ijimai has been reported from hard substrates such as rocks, bivalve shells, and wood, and also from a sandy bottom; it often forms dense populations, up to about 15,000 individuals per m2 ( Emig 1974).

Remarks.

Our topotype material of Phoronis ijimai collected from Misaki perfectly agrees with previous morphological accounts of this species ( Oka 1897, Emig 1971a, 1974) in the following characters: 1) the long nephridial papilla and the large anal funnel of the nephridium, 2) the small diameter of the two giant nerve fibers, 3) the number of longitudinal muscles in the right oral and both anal coeloms, and 4) the brooding of embryos on lophophoral organs. These characters also agree with the description of Phoronis hippocrepia , but differ in 1) the large number of longitudinal muscles in the right oral coelom, and 2) the single chamber in the ascending branch of the nephridium. Our topotypes of Phoronis ijimai also match the description of Phoronis vancouverensis ( Pixell 1912, Emig 1971a, 1974). While our specimens have slightly fewer longitudinal muscles in the right anal and left oral coeloms compared to the original description of Phoronis vancouverensis by Pixell (1912) and the revised description of Phoronis ijimai by Emig (1974), respectively, the numbers are within the range of variation in Phoronis ijimai ( Emig 1974). The topotypes had fewer tentacles, probably due to the smaller size of the body and lophophore.