Heteromastus filiformis ( Claparède, 1864 )

Choi, Hyun Ki & Yoon, Seong Myeong, 2016, First record of Heteromastus filiformis (Polychaeta: Capitellidae) from Korean waters, with a taxonomic note on the genus, Journal of Species Research 5 (3), pp. 264-271 : 265-4

Heteromastus filiformis ( Claparède, 1864)

ŀqoiẖ갯mǵÑ (ṳAE)

Capitella filiformis Claparède, 1864: 509 , pl. 4, fig. 10.

Heteromastus filiformis Fauvel, 1927: 150 , fig. 53a­l; Hartman, 1947: 427, pl. 52, figs. 1-4; Uschakov, 1965: 304; Day, 1967: 601, fig. 28.3a-d; Hutchings and Rainer, 1981: 374; Blake, 2000: 69, fig. 4.8; Dean, 2001: 75, figs. 10­12; GarcÍa­Garza and León­González, 2011: 27 .

Material examined. Korea, 25 specimens, Jeollabuk­do, Buan­gun, Byeonsan­myeon, Daehang­ri (126°35′02″E, 35°41′44″N), 13 Aug 2014 ; 14 specimens, Jeollanam­do, Suncheon­si, Byeollyang­myeon, Haksan­ri (127°29′03″ E, 34°50′50″N), 24 May 2013 .

Description. Body filiform and cylindrical, about 30 to 35 mm long with approximately 130­150 segments, width 0.8­1.0 mm in thoracic segments and about 1.0 mm in abdominal segments.

Prostomium small, conical. Proboscis globular with numerous minute papillae on surface. Peristomium slightly longer than chaetiger 1; single pair of subepidermal eyespots on dorsal surface appeared in immature materials ( Fig. 1A, B ).

Thorax distinct and biannulate, with weak wrinkles on surface, and composed of achaetigerous peristomium and 11 chaetigers; thoracic chaetigers 1­5 with narrowly bilimbate capillary chaetae composed of 4 or 5 per fascicle in noto­ and neuropodia; chaetigers 6­11 with long handled hooded hooks composed of 3­6 per fascicle. Thoracic hooded hooks with indistinct node on shaft and 5 or 6 teeth in 2 transverse rows above main fang. Nephridial and genital pores invisible ( Fig. 1A, F, G ).

Transition between thorax and abdomen distinct. Abdomen biannulate, smooth on anterior segments but with many wrinkle on posterior segments, composed of about 120­140 segments; parapodia located at slightly posterior of segment; length between noto­ and neuropodia longer than thoracic segments; anterior abdominal segments slightly longer and wider than posterior, gradually tapered toward end; posterior abdominal segments with parapodial lobes projecting posteriorly; abdominal chaetigers with short handled hooded hooks composed of 4­7 per fascicle. Abdominal hooded hooks with distinct node on shaft and 3 or 4 teeth above main fang( Fig. 1A, C, D, H ).

Pygidium with single digitate caudal cirrus ( Fig. 1E ).

Branchiae short, broadly­based and rounded lamellae projecting posteriorly over adjacent segment, and well developed in about 100­120 segments ( Fig. 1D ).

Methyl green staining pattern. Korean materials of H. filiformis usually have the following patterns: the thoracic segments are weakly stained with faintly speckled bands, one of them is on the chaetiger 1 and others are on the chaetigers 3­11( Fig. 2A ); the abdominal segments are intensely stained with two longitudinal bands on the mid­ventral side ( Fig. 2B ).

Remarks. Korean materials of the present study show the several characteristics that are generally agreed well with several previous works including the original description of H. filiformis as follows: the thoracic hood­ ed hooks have indistinct nodes on the shaft and several teeth above the main fang; the abdominal hooded hooks possess distinct nodes on the shaft and a few teeth above the main fang; the branchiae appearing in posterior abdominal segments are broadly­based and rounded lamellae projecting posteriorly ( Claparède, 1864; Fauvel, 1927; Hartman, 1947; Day, 1967; Hutchings and Rainer, 1982; Blake, 2000; Dean, 2001).

Korean materials of H. filiformis have a minor difference in the morphology of teeth on the abdominal hood­ ed hooks from the neotype materials of Hutchings and Rainer (1982): the abdominal hooded hooks have 11­15 teeth above the main fang in the description of Hutchings and Rainer (1982), but those of our materials have only 3­4 teeth above the main fang. However, it is known that the number of teeth on the hooded hooks is a doubtful feature because it can vary depending on the orientation of the hooks under a light microscope ( Yabe and Mawatari, 1998), and the real structure of them is unclear in the original description ( Claparède, 1864). Therefore, the taxonomic validity of this difference is still in need of further study.

In the methyl green staining patterns, our materials are slightly different from the materials of Blake (2000) collected from California, North America in having weakly staining thorax with faintly speckled bands on the chaetiger 1 and chaetigers 3­11. Blake (2000) described that his materials have the thoracic segments staining solidly green with distinct bands on the chaetigers 5­9. In this respect, the materials of Blake (2000) could be a distinct species from Korean materials. However, the methyl green staining patterns have been poorly described in the most previous reports of H. filiformis except for Blake (2000), so the further study is required to verify the taxonomic value of these patterns.

In East Asia, H. filiformis is readily differentiated from H. tohbaiensis Yabe and Mawatari, 1998 , which was recorded from Hokkaido in northern Japan, by following characteristics: the thoracic hooded hooks of H. filiformis have indistinct nodes on the shaft, while those of H. tohbaiensis have distinct nodes on the shaft; the branchiae on posterior abdominal segments are composed of broadly­based and rounded lamellae projecting posteriorly in H. filiformis , but those are absent in H. tohbaiensis ( Yabe and Mawatari, 1998) ( Table 1).

Habitat. The materials of present study were collected from mud or muddy sand of intertidal zone. Dean (2001) suggested that this species is widely distributed in all type sediments, and mainly found in the muds of intertidal zone.

Distribution. Italy ( Eisig, 1887), France ( Fauvel, 1927), the Mediterranean Sea ( Claparède, 1864), Southern Africa ( Day, 1967), Australia ( Hutchings and Rainer, 1982), Costa Rica ( Dean, 2001), Mexico ( GarcÍa­Garza and León­González, 2011), North America (California) ( Hartman, 1947; Blake, 2000), Thailand ( Green, 2002), Japan ( Uschakov, 1965), Korea (present study).

Discussion. It is known that the thoracic and abdominal hooded hooks have indistinct or distinct nodes on shaft, while having been regarded as a minor character of the genus by many previous works of Heteromastus species ( Hartman, 1947; Day, 1967; Fauchald, 1977; Hutchings and Rainer, 1982; Green, 2002). However, Yabe and Mawatari (1998) described H. tohbaiensis as a new species, and pointed out that indistinct or distinct nodes on thoracic and abdominal hooded hooks are the significant characteristic features in the genus.

Heteromastus species have been confused with the genus Mediomastus Hartman, 1944 because they have similar diagnostic characteristics such as the presence of achaetigerous peristomium and hooded hooks in the thoracic segments ( Fauchald, 1977; Warren et al., 1994). However, this two genera are clearly distinguished from each other by the following characteristics: the thorax of Heteromastus has 11 chaetigers, while that of Mediomastus has usually 10 chaetigers; Heteromastus possesses the capillary chaetae on chaetigers 1­5 and the thoracic hood­ ed hooks on chaetigers 6­11, but Mediomastus possesses the capillary chaetae on chaetigers 1­4 and the thoracic hooded hooks on chaetigers 5­10; the branchiae are usually present in Heteromastus , while those are absent in Mediomastus ( Hartman, 1947; Day, 1967; Fauchald, 1977; Hutchings and Rainer, 1982; Warren et al., 1994; Green, 2002).

Because having high similarities between Heteromastus and Mediomastus , some species belonging to these genera have been newly combined ( Warren et al., 1994). The species previously known as Heteromastus deductus Pillai, 1961 is now treated as a species belonging to Mediomastus because its original description shows a significant characteristic of Mediomastus species such as chaetiger 5 with hooded hooks instead of capillary chaetae ( Pillai, 1961; Warren et al., 1994). On the contrary, Mediomastus caudatus Hartman, 1976 was emended as a Heteromastus species, H. caudatus ( Hartman, 1976) , because it has the capillary chaetae on thoracic chaetigers 1­5, which is one of the key characteristics of Heteromastus species ( Hartman, 1976; Warren et al., 1994). H. caudatus is discriminated from its congeners by having the uncinial spines conspicuously projected on the posterior segments ( Warren et al., 1994) ( Table 1).

The morphology of branchiae is considered as a very important character in the taxonomy of Heteromastus ( Southern, 1921; Berkeley and Berkeley, 1932; Hartman, 1947; Hartman, 1976; Yabe and Mawatari, 1998; Blake, 2000; Green, 2002). H. similis Southern, 1921 from Chika lake in India and H. hutchingsae Green, 2002 from Andaman Sea in Thailand, both have the posterior abdominal segments with triangular­shaped branchiae carrying abdominal hooded hooks, are distinguishable from H. filiformis by this characteristic branchiae ( Southern, 1921; Green, 2002). H. filobranchus Berkeley and Berkeley, 1932 from Northeast Pacific also can be readily discriminated from its congeners by having the palmately arranged filamentous branchiae ( Berkeley and Berkeley, 1932; Hartman, 1947; Blake, 2000). On the other hands, the original description of H. tohbaiensis and H. caudatus show that the species has the abdominal segments without branchiae ( Hartman, 1976; Yabe and Mawatari, 1998) ( Table 1).

Heteromastus species also show several taxonomic features in the development of abdominal segments and chaetal structures ( Southern, 1921; Yabe and Mawatari, 1998; Green, 2002). H. similis differs from H. filiformis in that the length of anterior abdominal segment is similar to that of thoracic segment, and has a unique feature such that the node is located posterior to the middle of the shaft in the abdominal hooded hooks ( Southern, 1921; Green, 2002). On the other hands, H. hutchingsae is distinguished from H. similis by having the node situated anterior to the middle of the shaft and the hood covering half of the length from crest to node in the abdominal hooded hooks ( Green, 2002). H. tohbaiensis is differentiated from its congeners by a unique feature of thoracic hooded hooks bearing distinct nodes ( Yabe and Mawatari, 1998) ( Table 1).

Among the species described as Heteromastus ones, it is known that Heteromastus giganteus Zachs, 1933 from North Japanese Sea has also the thorax composed of the first achaetigerous peristomium and following 11 thoracic chaetigers ( Zachs, 1933; Uschakov, 1965). However, this species differs from Heteromastus species by having six anterior thoracic segments bearing capillary chaetae ( Zachs, 1933; Uschakov, 1965). This characteristic feature of H. giganteus is regarded as one of the diagnostic features of other genus, Barantolla Southern, 1921 ( Fauchald, 1977). Therefore, H. giganteus is need­ ed to further study with the type materials for its definite affiliation as a member of Heteromastus species.

Conclusively, we suggested six valid species of Heteromastus according to the morphologies of branchiae, abdominal segment, and chaetae including capillary chaetae and hooded hooks. In the present study, a comparison of the characteristic features among worldwide Heteromastus species is provided with a key.

Figures

Fig. 1. Heteromastus filiformis(Claparède, 1864).A, anterior lateral view including thoracic segments; B, anterior dorsal view of specimens with subepidermal eyespots in immature state; C, lateral view of posterior abdominal segments; D, lateral view of posterior abdominal segments with branchiae; E, pygidium; F, notopodial capillary chaeta; G, thoracic notopodial hooded hook; H, abdominal notopodial hooded hook. Scale bars:A­E=0.5 mm, F­H=0.025mm.

Fig. 2. Photograph of Heteromastus filiformis (Claparède, 1864) showing methyl green staining patterns.A, anterior lateral view of thoracic segments; B, mid­ventral view of abdominal segments. Scale bars:A=1.0 mm, B=0.5 mm.