Aphelochaeta intinctoria, Choi & Jung & Yoon, 2018

Choi, Hyun Ki, Jung, Tae Won & Yoon, Seong Myeong, 2018, Two new species of Aphelochaeta (Annelida: Polychaeta: Cirratulidae) from Korean waters, Zootaxa 4504 (4), pp. 586-594 : 590-592

Aphelochaeta intinctoria new species

Figures 1 B–C, 3A–F

Material examined. Type locality: South Korea, Jeollanam-do Province: Jindo-gun County, Imhoe-myeon , Namdong-ri , 126°09′10″E, 34°21′35″N, 31 Jul. 2016, intertidal soft bottom. Holotype: incomplete specimen ( NIBRIV0000325699 ). Paratypes: one complete specimen (MABIKNA00155291); one incomplete specimen (MABIKNA00155292); one incomplete specimen (MABIKNA00155293); one incomplete specimen (MABIKNA00155294); one incomplete specimen (MABIKNA00155295) on stub for SEM observation. Non-type material: 11 specimens, collection details same as type material (MABIKNA00155296) .

Description. Holotype. Incomplete; body slender, 4.6 mm long and 0.6 mm maximum wide; thoracic region distinct, consisting of eight uncrowded segments, swollen dorsally, slightly flattened ventrally; ventral groove present; abdominal region as wide as thoracic region with distinct moniliform segments longer than thoracic segments, with a shallow ventral groove; pygidium with simple ventral lobe observed in paratype ( Figs. 1 C–D, 3A–C).

Prostomium slightly wider than long, distally rounded, eyespots absent, nuchal organs located near posterolateral prostomial border. Peristomium wider than prostomium, with distinct dorsal crest, and with three annulations, third one longest; dorsal crest extending posteriorly over two-thirds of chaetiger 1. Paired dorsal tentacles arising at posterior margin of peristomium, lateral to base of dorsal crest. Branchiae weakly annulated in alcohol; first pair arising from posterior of chaetiger 1 dorsal to notochaetae, and subsequent branchiae at posterior margin of chaetigers. Thoracic parapodia slightly projecting laterally; notopodial lobes very low. Abdominal parapodia rudimentary ( Figs. 1 C–D, 3D).

Chaetae emerging from lateral body wall, long, simple capillaries, with conspicuous fibrils of varying lengths along one edge; thoracic chaetigers with 7–11 noto- and 6–9 neurochaetae, abdominal chaetigers with 4–7 noto- and neurochaetae; notochaetae slightly longer than neurochaetae ( Fig. 3 E–F).

Methyl green staining pattern (MGSP). The body is unstained lacking distinct staining patterns ( Fig. 3A ).

Etymology. The composite epithet of the specific name, intinctoria , is a combination of the Latin prefix in- and the Latin tinctorius, meaning “undyed”. This name refers to the fact that the thoracic region does not stain using the methyl green.

Habitat/Distribution. This species was collected from sandy mud sediments in the intertidal zone located at Jindo-gun in the southern coast of Korea.

Remarks. Aphelochaeta intinctoria n. sp. has distinct moniliform segments in the abdominal region which has been described as a diagnostic feature of A. monilaris ( Blake 1996) . However, the new species shows several morphological differences from A. monilaris . The dorsal crest on the peristomium of A. intinctoria n. sp. is distinct while it is indistinct in A. monilaris . The first pair of branchiae is located on chaetiger 1 in the new species while in A. monilaris they are on the peristomium. The thoracic region is not expanded in the new species as it is in A. monilaris and the body of A. intinctoria n. sp. does not retain any methyl green stain while there are darkly stained ventral band in the thorax in A. monilaris ( Blake 1996; Dean & Blake 2016).

The lack of a distinctive staining pattern on the venter of the thorax using methyl green in A. intinctoria n. sp. is shared with A. bullata Doner & Blake, 2009, A. guttata Doner & Blake, 2009, A. malefica Elías & Rivero, 2009, A. multifilis (Moore, 1909), and A. zebra Dean & Blake, 2016 ( Blake 1996; Elías & Rivero 2009; Doner & Blake 2009; Dean & Blake 2016). However, A. intinctoria n. sp. is readily separated from these relatives based on the following characteristics: the dorsal tentacles and a pair of the first branchiae are present on the peristomium and chaetiger 1, respectively while in A. bullata, A. guttata, and A. multifilis they are both on the peristomium and in A. malefica and A. zebra both the dorsal tentacles and the first pair of branchiae are on chaetiger 1. The peristomial dorsal crest is distinct while it is indistinct in A. multifilis and A. zebra; the thoracic region is not expanded while it is expanded in A. bullata, A. guttata, A. multifilis, and A. zebra; the prostomium is rounded distally versus pointed in A. malefica ( Blake 1996; Elías & Rivero 2009; Doner & Blake 2009; Dean & Blake 2016).

Recently, Dean and Blake (2016) have suggested three types of chaetal structures in Aphelochaeta species related to the development of fibrils or denticles on the chaetal surface, fibrillated, microserrated, and smooth. The chaetal structure of A. intinctoria n. sp. has relatively long fibrils of varying lengths ( Fig. 2F ), belonging to the fibrillated type. While that of A. petila n. sp. has short fibrillar extensions and is assigned to the microserrated type ( Fig. 3F ).

Figures

FIGURE 1. Aphelochaeta petila n. sp., A, B, holotype (NIBRIV0000325701); Aphelochaeta intinctoria n. sp., C, D, holotype (NIBRIV0000325699). A, anterior end, dorsal view; B, anterior end, lateral view; C, anterior end, dorsal view; D, anterior end, lateral view. Scale bars: A–D=0.25 mm. Abbreviations: branchia (br), dorsal crest (dc), dorsal tentacle (dt), nuchal organ (nuO), peristomium (per), prostomium (pr).

FIGURE 2. Aphelochaeta petila n. sp., A, B, holotype (NIBRIV0000325701); C–F, SEM observation in paratype (MABIKNA00155289). A, MGSP of thoracic region, ventro-lateral view; B, posterior end, lateral view; C, thoracic region, lateral view; D, anterior end, lateral view; E, basal region of thoracic capillary chaeta; F, distal region of thoracic capillary chaeta. Scale bars: A–C=0.5 mm, D=0.25 mm, E=0.01 mm, F=0.005 mm. Abbreviations: branchia (br), dorsal tentacle (dt), nuchal organ (nuO), peristomium (per), prostomium (pr).

FIGURE 3. Aphelochaeta intinctoria n. sp., A, holotype (NIBRIV0000325701); B, paratype (MABIKNA00155291); C–F, SEM observation in paratype (MABIKNA00155295). A, MGSP of anterior end, lateral view (no reaction); B, posterior end, lateral view; C, anterior and mid-body segments, dorsal view; D, anterior end, dorsal view; D, E, basal region of thoracic capillary chaeta; F, distal region of thoracic capillary chaeta. Scale bars: A=0.5 mm, B=0.25 mm, C=0.5 mm, D=0.1 mm, E, F=0.005 mm. Abbreviations: branchia (br), dorsal crest (dc), dorsal tentacle (dt), nuchal organ (nuO), peristomium (per), prostomium (pr).