Leiochrides yokjidoensis, Jeong, Man-Ki, Wi, Jin Hee & Suh, Hae-Lip, 2017

Jeong, Man-Ki, Wi, Jin Hee & Suh, Hae-Lip, 2017, A new species of Leiochrides from the Korean subtidal waters with notes on the taxonomic status of the genus Pseudomastus (Annelida, Capitellidae), ZooKeys 685, pp. 91-103 : 94-97

Leiochrides yokjidoensis sp. n. Figs 2 A–F, 3 A–H

Material examined.

Holotype (complete specimen): MABIKNA00145754, sex uncertain, Yokjido, 34°31.1'N, 128°21.6'E (DDM), subtidal, sandy mud bottom, 53 m depth, April 2016, collector: Man-Ki Jeong. Paratypes (3 incomplete specimens): MABIKNA00145755-NA00145757, same information as holotype.

Diagnosis.

Thorax with achaetigerous peristomium and 12 chaetigers. First chaetiger without neuropodia. Chaetigers 1-11 with capillary chaetae only, chaetiger 12 with notopodial capillaries and neuropodial hooks. Abdominal chaetigers with hooded hooks only. Branchiae present on posterior abdominal segments as 2-4 digitate filaments near notopodia. Approximately ten preanal chaetigers without branchiae. Pygidium with four anal cirri.

Description.

One complete specimen and eight incomplete specimens. Largest specimen 27 mm long, 0.34 mm wide for 159 chaetigers. Smallest specimens 7 mm long, 0.25 mm wide for 34 chaetigers. Body thread-like, cylindrical, widest in anterior thoracic chaetigers, tapering from abdomen to pygidium. Color in alcohol yellowish or reddish brown.

Prostomium short, conical, wider than long, with blunt anterior end; presence of nuchal organs indistinct, eyespots not observed in preserved specimen (Figs 2 A–C, 3A). Everted proboscis with numerous short, rounded, papillae, without cilia on tip of papillae (Figs 2C, 3A). Peristomium achaetigerous, wider than long, weakly biannulated and tessellated, subequal or slightly longer than first chaetiger (Figs 2 A–C, 3A).

Thorax with 13 segments including single peristomium and 12 chaetigers (Fig. 2 A–B). Thoracic segments biannulate, wider than long, with shallow intra- and inter-segmental grooves (Figs 2 A–B, 3A). Anterior thoracic segments 1-5 slightly expanded and tessellated. First chaetiger uniramous with only notochaetae, both parapodia of chaetigers 1-11 and notopodia of chaetiger 12 each with 8-12 capillaries per fascicle; neuropodia of chaetiger 12 with 8 hooded hooks per fascicle (Fig. 2A). All capillary chaetae unilimbate, with narrow wing, whip-like, broad basally, and narrow apically; dorsal notochaetae without spinules on distal region of chaeta (Fig. 3B). Notopodia dorso-lateral and neuropodia ventro-lateral (Fig. 2 A–B). Lateral organs distinct, oval shape, not protruding; present between notopodia and neuropodia, nearer to notopodia (Figs 1A, 2B, D). Genital pores not observed.

Transition between thoracic and abdominal region distinguished by change in position and type of chaetae and length of segments; abdominal segments longer and slightly narrower than thoracic segments, gradually smaller posteriorly; notopodial hooded hooks first present on chaetiger 13 (first abdominal chaetiger) (Fig. 2 A–B). Abdominal chaetigers with hooded hooks on posterior end of segment; thoracic chaetigers with capillary chaetae or neuropodial hooks in center of segment (Fig. 2 A–B).

Abdominal parapodial lobes slightly developed, located in posterior half of segment, well separated from each other; parapodial lobe gradually reduced posteriorly (Fig. 2 A–B, D). Abdominal notopodia with 5-6 hooded hooks per fascicle; neuropodia with 8-10 hooded hooks per fascicle, 2-3 hooks on terminal segments (Fig. 2 A–B).

Hooded hooks short, with main fang extending slightly beyond hoods; hood flared; shaft slightly enlarged like manubrium (Figs 2F, 3E). Hooks with three rows of small teeth above main fang; two in basal row, three in middle row, and 3-5 in superior rows (Figs 2E, 3F).

Branchiae digitiform, cylindrical, retractile; abdominal chaetiger 120-150 each with 3-5 branchiae per fascicle emerging from notopodia which lack hooks in this region; eight preanal 8 segments without branchiae (Figs 2D, 3H). Pygidium an oval ring, with four digitate caudal cirri (Figs 2D, 3H).

Methyl green staining pattern.

Prostomium not stained. Peristomium and thoracic chaetigers 1-5 slightly stained in blue but rapidly fades. Chaetigers 6-9 stained blue, with narrow transverse blue speckled band near intra-segmental furrow (Fig. 3G). Post-chaetal region of chaetiger 10 and pre-chaetal region of chaetiger 11 with intense blue speckles on epidermis (Fig. 3G). Abdominal segments without distinct staining pattern.

Etymology.

The new species is named for its occurrence in Yokjido, Korea.

Distribution.

Leiochrides yokjidoensis sp. n. is distributed in the subtidal habitat (53 m) of the southern part of Korea.

Ecology. The surface sediment is mainly composed of sandy mud with fragmented shells. Mediomastus Hartman, 1944 and Notomastus M. Sars, 1851, also belonging to the Capitellidae , also occurred at the same location.

Remarks.

Leiochrides yokjidoensis sp. n. is distinct in the morphological combination of 12 thoracic chaetigers, chaetigers 1-11 with only capillary chaetae, and the last thoracic chaetiger with the notopodial capillaries and neuropodial hooks. Among the genera of Capitellidae the presence of 12 thoracic chaetigers and neurohooks in last thoracic chaetiger are shared with Leiochrides , Pseudomastus , and Scyphoproctus Gravier, 1904. However, Scyphoproctus is clearly separated from the new species by the presence of the unique anal plaque, acicular spines in the posterior abdomen, and two achaetous segments in the anterior part of the thorax. In this study, the new species was placed under the genus Leiochrides , because the generic diagnosis of Pseudomastus mostly agreed with that of Leiochrides (see details in discussion section). Leiochrides yokjidoensis sp. n. closely resembles L. hemipodus and P. deltaicus in the presence of the neurohooks in the thorax, the uniramous first chaetiger, the two distinct basal teeth above the main fang, and the presence of the branchiae in the posterior abdomen (Table 1). In particular, L. yokjidoensis sp. n. and P. deltaicus correspond in the presence of multiple cirri on the pygidium (Table 1). However, the new species is discriminated from P. deltaicus by the following morphological characteristics: the absence of eyespots in the preserved materials, dorsal notochaetae without distal spinules, a proboscis without cilia on the tip of the papillae, the number of capillary chaetae (8-12 vs. 13-20) and neurohooks (8-10 vs. 11-12) per fascicle, the number of teeth above the main fang (8-10 vs. 7), the absence of neuropodial hooks in chaetiger 11, and the number of anal cirri (4 vs. 3). On the other hand, the holotype of L. hemipodus has identical chaetal arrangement to L. yokjidoensis sp. n., but it differs in the number of teeth above the main fang (3 vs. 8-10), the maximum number of branchiae per fascicle (12 vs. 5), and the species-specific MGSP (chaetigers 1-12 vs. 6-11, Table 1). In addition, L. hemipodus has been reported only in deep basin near California, but L. yokjidoensis sp. n. was found in shallow waters of southern Korea (Table 1). The paratype of L. hemipodus has a different chaetal arrangement (chaetigers 11-12 with neuropodial hooks) to the holotype of L. hemipodus , however these type specimens were almost identical in the remaining characteristics ( Blake 2000, Green 2002, Table 1). Generally, capitellids have developmental variation in the chaetal arrangement on the thorax, and the hooded hooks are replaced by capillaries with development ( Fredette 1982, Blake 2009). Thus, the differences in chaetal arrangement between the type specimens of L. hemipodus may be associated with the developmental variation within a species. Blake (2000) had reported L. hemipodus from Santa Maria basin (603 m) and compared his specimens with the characteristics of the paratype of L. hemipodus Hartman, 1960. According to his description, L. hemipodus also differs from L. yokjidoensis sp. n. in the presence of a band of glands on chaetiger 6 and the shape of the branchiae (Table 1).