Pareurythoe japonica Gustafson, 1930

Salazar-Vallejo, Sergio I. & Jimi, Naoto, 2025, Revision of Pareurythoe Gustafson (Annelida: Amphinomidae, Journal of Natural History 60 (1 - 4), pp. 21-62 : 40-43

Pareurythoe japonica Gustafson

( Figures 8 and 9 )

Eurythoe borealis : Fauvel 1936: 53–54 ( non Sars, 1862).

Pareurythoe borealis : Okuda 1938: 78–80, textfigs 1–2 ( non Sars, 1862).

Pareurythoe japonica Gustafson, 1930: 308 , 349, 391–393, pl. 1, fig. 5, pl. 2, figs 6–7, pl. 6, pl. 26, figs 3–

figs 4–7, pl. 29, figs 1–3; Imajima and Hartman 1964: 52–53.

Type material. Japan. Neotype (NSMT-Pol N-1001), in front of Sugashima Marine Biological ( 34.4845°N, 136.8756°E), Sugashima Island , Mie, intertidal, 11 April 2024, S. Shimooka and N. Jimi,

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36, left parapodium, posterior view. (G) Same, notochaetae. (H) Same, neurochaetae. Scale bars: A–B = 10 mm; C–E

F = 0.2 mm; G = 80 µm; H = 60 µm (authors’ work).

(complete; body 24–55 mm long, 2–4 mm wide, 59–75 chaetigers). Hong Kong. One specimen ( UF Tung Ping Chau ( 25,54°N, 114.44°E), 1 m, patchy coral, rocks, sand, 25 October 2017, G. Paulay and J. coll. (without posterior end; right parapodia of chaetigers 12 and 47 removed for observation (container); 30 mm long, 1.5 mm wide, 52 chaetigers; some features included in variation).

Diagnosis

Pareurythoe with caruncle extended along chaetigers 1–2, reaching posterior area of chaetiger 2;

furrow deep. Anterior eyes reniform, 2–5 times as large as posterior round ones. Median antenna ¼ long as caruncle. Branchiae from chaetiger 3 with a few filaments. Median segments with neurochaetae.

rectilinear; left parapodia of chaetigers 27, and right parapodia of chaetigers 32–36 removed for

(some in container), 41 mm long, 4 mm wide, 70 chaetigers.

Anterior region tapered ( Figure 5 (B)); prostomium round, anterior lobe bent ventrally, with antennae and palps directed laterally; palps and lateral antennae of similar size. Posterior lobe with red ( Figure 8 (C)), anterior eyes not visible dorsally, directed frontally, about 2–5 times as large as eyes ( Figure 5 (D)). Median antenna bulbous, slightly shorter than anterior lobe, 1/5 as long as caruncle

Caruncle sinuous, tapered, blunt, as long as chaetigers 1–2, reaching posterior portion of barely included in middorsal furrow running along chaetigers 1–6, indistinct in following chaetigers. partially exposed. Mouth between chaetigers 1 and 3.

Branchiae from chaetiger 3, with three filaments; anterior chaetigers with branchiae with up filaments; median and posterior chaetigers with up to 5 filaments; prepygidial chaetigers with filaments.

Parapodia biramous ( Figure 8 (E)). Notopodia with short conical lobes; dorsal and ventral cirri biarticulate, cirrostyles constricted, dorsal cirri longer than ventral ones throughout body.

Chaetae observed in a median segment; notochaetae include abundant thin capillaries, often denticulate, and transparent harpoon chaetae with some denticles; neurochaetae mostly capillaries finely denticulate, and a few spurred chaetae. Acicular chaetae with tips oval, slightly widened.

Posterior region tapered ( Figure 8 (F)); pygidium conical, anus terminal, anal plate minute. Oocytes 100 µm in diameter.

Variation

An additional specimen from Hong Kong ( Figure 9 (A)), posteriorly incomplete, has a terete prostomium is bent dorsally ( Figure 9 (B)), the lateral antennae are slightly shorter and thinner than median antenna minute, about ¼ as long as caruncle. The caruncle is sinuous, bent dorsally,

a depression reaching the anterior margin of chaetiger 3. Anterior eyes Black, posterior ones brown;

eyes about 8 times as large as posterior ones. Branchiae from chaetiger 3 with 4 filaments, up to 14

by chaetiger 15 ( Figure 9 (C)), decreasing in number and size posteriorly ( Figure 9 (G)), 3–4 in last Notochaetae include long thin capillaries, and furcate ones, some finely denticulate, medium-sized and harpoon chaetae, and aciculae with tapered tips ( Figure 9 (D,E)); neurochaetae include furcate of two different sizes, some denticulate, and furcate chaetae ( Figure 9 (F)), with shortest tine shorter notochaetae; neuraciculae are subdistally wider.

Remarks Pareurythoe japonica Gustafson, 1930 is the type species of Pareurythoe Gustafson, 1930 . The indicated that the specimen was collected in Japan, but no further details were given (Gustafson 308). A neotype is needed to clarify the status and propose a type locality (ICZN 1999, Art. 75.3.1), Sugashima Island, Mie, Japan. The differences from other species in the genus were incorporated in (ICZN 1999, Art. 75.3.2), and a complete description and illustrations are included to ensure the of the specimen designated as neotype (ICZN 1999, Art. 75.3.3). There is no type material in Stockholm Uppsala (L. Gustavson and P. Cardenas, email, November 2023); we think that the specimen Gustafson was used for histology, and must be regarded as destroyed (ICZN 1999, Art. 75.3.4). We think neotype matches what is known of the original specimen (ICZN 1999, Art. 5.3.5), although because specific locality was given in the original description, we cannot be sure the locality for the neotype to the original locality (ICZN 1999, Art. 75.3.6). The neotype has been deposited in the collections National Museum of Nature and Science, Tsukuba, Japan (ICZN 1999, Art. 75.3.7).

Pareurythoe japonica belongs in the group with branchiae from chaetiger 3, and it can be from other species in the group by having a short median antenna, being 1/5–1/3 as long as whereas the other species have median antenna at least half as long as caruncle.

The species was well characterised and illustrated by Okuda (1938, 78–80) although he used the P. borealis ; P. japonica is a species commonly found in the intertidal zone and shallow subtidal areas

JOURNAL OF NATURAL HISTORY tae. (E) Same, neuracicular chaetae and acicular one. (F) Same, furcate neurochaetae. (G) Chaetiger 47, right posterior view. Scale bars: A = 1.4 mm; B, C = 0.2 mm, D, E = 30 µm; F = 15 µm; G = 0.3 mm (authors’ work).

Pareurythoe japonica Gustafson, 1930 belongs in the group of species having branchiae from but it differs from all other species in the group because it has a short median antenna, 1/5–1/3 as caruncle, whereas the other species have them at least half as long as caruncle.

Distribution

South China Sea to Central Japan, in shallow-water mixed bottoms (intertidal to shallow subtidal).

Figures

Figure 5. Pareurythoe dubia (Horst) comb. n., holotype (ZMA V.Pol 293). (A) Complete, dorso-lateral view. (B) region, dorsal view, after Shirlastain A. (C) Anterior end, dorsal view. (D) Anterior end, frontal view. (E). Median

Figure 8. Pareurythoe japonica Gustafson, 1930, neotype (NSMT-Pol N-100). (A–D) Live specimen, (E–H) fixed specimen Dorsal view. (B) Ventral view. (C) Anterior end, dorsal view. (D) Same, ventral view. (E) Same, dorsolateral view. (F)

Figure 9. Pareurythoe japonica Gustafson, non-type specimen (UF 5688). (A) Dorsolateral view. (B) Anterior end, dorsal after methyl green staining. (C) Chaetiger 12, right parapodium, posterior view. (D) Same, harpoon and acicular