Phoronis emigi, Hirose, Masato, Fukiage, Ryuma, Katoh, Toru & Kajihara, Hiroshi, 2014

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 : 11-16

Phoronis emigi sp. n. [New Japanese name: Amakusa-houkimushi]Figures 8-11

Material examined.

Eleven series of transverse sections and two series of longitudinal sections, and nine whole specimens. Holotype: NSMT-Te 714, 5-μm transverse sections stained with HE. Paratypes: NSMT-Te 703-708, seven intact specimens, fixed and preserved in 10% formalin seawater; NSMT-Te 711-713, 715-721, 5-μm transverse sections stained with HE; and NSMT-Te 722, 723, 5-μm longitudinal sections stained with HE. Other material examined: NSMT-Te 709, 710, two intact specimens.

Etymology.

The specific name, a masculine noun in the genitive case, is in honor of the French researcher Dr. Christian C. Emig for his remarkable contributions to lophophorate systematics.

Description.

Body except lophophore 4.42-20.06 mm in length (holotype 9.67 mm; avg. 10.87 ± 4.70 mm, n = 10); 0.34-0.66 mm in diameter at ampula (holotype 0.39 mm; avg. 0.47 ± 0.10 mm, n = 9); reddish in living state, yellowish white after fixation (Fig. 8). Lophophore horseshoe-shaped, without significant coiling (Fig. 9); 2.00-3.51 mm in length (holotype 3.18 mm; avg. 2.77 ± 0.52 mm, n = 10), 0.54-0.76 mm in diameter at base (holotype 0.68 mm; avg. 0.67 ± 0.07 mm, n = 10); tentacles 136-170 in number (holotype 137; avg. 147 ± 13.17, n = 6).

Nephridium 205.00-324.00 μm in length (holotype 310 μm; avg. 276.78 ± 38.69 μm, n = 5), with straight ascending branch (ab) and short descending branch (db) (Fig. 10A), ab/db length ratio 3.5 (n = 5). Ascending branch with single chamber (Fig. 10C). Nephridiopore situated on anal papilla. Tip of ascending branch (i.e., nephridiopore) lying against intestine. Nephridia slightly offset along body axis (Fig. 10B); left nephridiopore lower (in living orientation) than anus, right nephridiopore same level as anus. Single nephridial funnel present, with aperture at tip of descending branch (Fig. 10D).

Body-wall longitudinal muscles of feathery type (Fig. 11A, 11B); 56-72 (holotype 67) in number, arranged in following formula ( Selys-Longchamps 1907):

Composite formula

Mean formula

(n = 74 sections from 7 individuals)

Left and right lateral mesenteries present (Fig. 11A). Single giant nerve fiber, 15.98-36.03 μm in diameter (holotype avg. 27.40 ± 6.29 μm, based on 5 sections from different parts of the body; avg. 25.93 ± 6.05, based on 11 sections from different parts of the body, from five individuals [5 sections from holotype and 6 sections from 4 paratypes]), situated at base of left lateral mesentery (Fig. 11A, 11B). Esophageal valve absent.

Gonads not observed in any of our specimens; sex could thus not be determined.

Distribution and habitat.

Phoronis emigi is known only from a sandy bottom in northern Tomioka Bay, Amakusa, Japan, where we detected densities of up to about 90 individuals per 100 cm2. We observed no chitinous tubes after agitation and decantation during sampling, but the tubes would be fragile and might have been lost.

Remarks.

Phoronis emigi sp. n. is morphologically most similar to Phoronis psammophila Cori, 1889, with which it has in common 1) a long ascending branch of nephridium that is more than three times the length of the descending branch, 2) a single nephridial funnel, with the aperture situated at the tip of the descending branch, 3) a single giant nerve fiber situated on the left side, and 4) two lateral mesenteries. Phoronis emigi differs from Phoronis psammophila in the number of longitudinal muscle bundles in the body wall (56-72 vs. 25-50 in Phoronis psammophila ) and the position of the right nephridiopores (at the same level as the anus vs. lower than the anus in Phoronis psammophila ) (cf. Andrews 1890, Selys-Longchamps 1907, Marsden 1959, Long 1960, Emig 1968, 1971b, 1979).

Naturally, Phoronis emigi is morphologically similar to, but distinct from, the nominal Phoronis architecta Andrews, 1890, which is regarded as a junior synonym of Phoronis psammophila ( Emig 1971b, 1974). Based on the descriptions by Andrews (1890) and Brooks and Cowles (1905), Emig (1971b, 1974) noticed that Phoronis psammophila and Phoronis architecta are morphogically identical, with the exception of the differences in larval brooding type and the presence of nidamental gland. Subsequently, Emig (1977) found that Phoronis psammophila shows a sympatric occurrence with Phoronis muelleri in the type locality of Phoronis architecta ; therefore, he concluded that the larval brooding type and the absence of nidamental gland of Phoronis architecta described in Brooks and Cowles (1905) came from a specimen of Phoronis muelleri . On the other hand, some researchers have suggested the need of reexamination of the synonymy ( Stancyk et al. 1976, Santagata and Zimmer 2002). Although we could not observe the larval brooding type of Phoronis emigi , the present species is clearly different from any of these species, Phoronis psammophila , Phoronis muelleri , and nominal Phoronis architecta , in the adult morphologies such as number of longitudinal muscle bundles.

The lack of gonads in our specimens was probably due to breeding seasonality. The breeding period of phoronid species previously studied is generally from spring to autumn ( Rattenbury 1953, Emig 2003), whereas our material was collected at the end of November. Our specimens were likely in the post-breeding condition, following spawning and the relaease of embryos.