Description of Mastobranchus uru sp. nov. (Annelida: Capitellidae) from Iriomote Island, Japan Author Tomioka, Shinri Faculty of Science, Hokkaido University, N 10 W 8, Sapporo, Hokkaido 060 - 0810, Japan E-mail: shinri. tomioka @ gmail. com & Corresponding author shinri.tomioka@gmail.com Author Yoshida, Ryuta Tateyama Marine Laboratory, Marine and Coastal Research Center, Ochanomizu University, Kou-yatsu 11, Tateyama, Chiba 294 - 0301, Japan Author Kajihara, Hiroshi Faculty of Science, Hokkaido University, N 10 W 8, Sapporo, Hokkaido 060 - 0810, Japan E-mail: shinri. tomioka @ gmail. com shinri.tomioka@gmail.com text Species Diversity 2017 2017-11-25 22 127 132 journal article 10.12782/sd.22_127 2189-7301 10093035 D677E7B8-909E-4C11-B96A-1188EEED31D5 Mastobranchus uru sp. nov. [New Japanese name: uru-itogokai] ( Figs 1–4 ) Etymology. The new specific name is taken from the Ryukyu dialect uru (sand made up of dead-coral debris) referring to the species’ habitat. The specific name is thus treated as indeclinable. The new Japanese name for this species, uru-itogokai , is the combination of uru and the Japanese name for capitellids ( itogokai ). Material examined. We examined 11 specimens , including the holotype ( ICHUM 5347 ) and 10 paratypes ( ICHUM 5302–5309 , RUMF-ZO-0018, 0019) . Table 1 indicates for these specimens the preservation state, presence or absence of the anterior end and pygidium, number of chaetigers, number of chaetigers with mixed fascicles, and pattern of methyl-green staining. The sex was uncertain for all specimens examined. Diagnosis. Thorax with 11 chaetigers. All thoracic chaetigers with capillary chaetae. Chaetiger 1 without neuropodial capillary chaetae. Fang of hooded hooks with 12–14 teeth in four rows, 3–4 teeth in first row closest to fang, 3–4 teeth in second row, 3–4 teeth in third row, 2 teeth in fourth row. Description. Holotype (ICHUM 5347; Fig. 1 ) with 272 chaetigers including 11 thoracic chaetigers and 261 abdominal chaetigers; with pygidium; length 141.61 mm ; maximum width 2.16 mm at chaetiger 4. Body color red in life; whitish pink in ethanol. Nephridiopores not visible. Epithelium tessellated on peristomium and anterior few chaetigers, smooth in subsequent chaetigers. Prostomium ( Figs 1 , 2A ) conical, with short palpode. Pair of ellipsoid patches consisting of numerous eyespots present. Peristomium 0.44 times as wider than long; slightly longer than chaetiger 1; almost same width as chaetiger 1; achaetous ( Figs 1 , 2A ). Thoracic chaetigers cylindrical, biannulate. Chaetiger 1 uniramous with fascicles of capillary chaetae in notopodia. Chaetiger 2 biramous with both noto- and neuropodia ( Figs 1 , 2A ). Capillary chaetae thin, without wing; 4–27 chaetae per fascicle ( Fig. 3A ); increasing in number from anterior to posterior chaetigers. Thoracic chaetal fascicles situated on antero-posteriorly middle portion of chaetigers. Fig. 2. Mastobranchus uru sp. nov. , holotype, ICHUM 5347. A, Anterior end of body, right dorsolateral view; B, four abdominal chaetigers (chaetigers 19–22), right lateral view; C, four abdominal chaetigers (chaetigers 255–258), right lateral view; D, pygidium, left lateral view; E, notopodial capillary chaeta from chaetiger 12; F, notopodial hooded hook from chaetiger 99, frontal view; G, notopodial hooded hook from chaetiger 99, left lateral view. Abbreviations: Abd, abdomen; Br, branchia; CaC, caudal cirrus; CC, capillary chaeta; Fa, fang; HH, hooded hook; Ho, hood; MF, mixed fascicle; Per, peristomium; PR, parapodial ridge; Pro, prostomium; Tho, thorax; To, tooth. Transition from thorax to abdomen marked by alteration in shape of chaetigers, methyl-green staining pattern (see the next section), chaetal component of fascicles, and also by the location occurring the fascicles of chaetae ( Figs 2A , 3E ). Abdomen with parapodial ridges ( Figs 1 , 2A–C , 3E, F ); consisting of chaetigers 12–272. Parapodial ridges on the posterior half of segment; becoming larger from anterior to middle abdominal chaetigers, smaller from middle to posterior chaetigers ( Fig. 3E–G ). Neuropodial ridges larger than notopodial ones. Chaetigers 12–28 with mixed fascicles of capillary chaetae and hooded hooks on notopodial ridges (1–15 capillary chaetae and 10–22 hooks per fascicle; Fig. 3B ), and with fascicles of hooded hooks on neuropodial ridges (15–64 hooks per fascicle). Chaetigers 29–272 with fascicles of hooded hooks on both noto- and neuropodial ridges. Abdominal capillary chaetae same as thoracic ones ( Figs 2E , 3B ). Hooded hooks with obvious fang ( Figs 2F, G , 3C, D ); hoods with opening; fang with 11–14 teeth in four rows ( 3–4 in first row closest to fang, 3–4 in second row, 3–4 in third row, 2 in fourth row; Fig. 1F ); without distinct node or constriction on shaft. Paired tufts of digitate branchiae situated dorsolaterally between noto- and neurochaetal fascicles on chaetigers 109– 159; 3–8 branchiae per tuft ( Figs 2C , 3G ). Pygidium with four, short, rounded, cylindrical caudal cirri ( Figs 2D , 3G ). Variation. Number of chaetigers with mixed fascicles of capillary chaetae and hooded hooks on notopodia varies from 9 to 49 among 11 type specimens ( 17 in the holotype ). Fig. 3. Mastobranchus uru sp. nov. , SEM images (A–D) and photographs showing methyl-green staining pattern (E–G); A–B, paratype, ICHUM 5303; C–D, paratype, ICHUM 5306; E–G, holotype, ICHUM 5347. A, Neuropodial capillary chaetae from chaetiger 2; B, notopodial capillary chaetae and hooded hooks from chaetiger 11; C, neuropodial hooded hooks from chaetiger 16; D, notopodial hooded hooks from chaetiger 12; E, anterior end of body, right lateral view, showing the boundaries of the first 12 chaetigers and of the staining-pattern zones; F, staining pattern in chaetigers 28–33 (labeled), left lateral view; G, posterior end of body, left lateral view. Abbreviations: Abd, abdomen; Ba, band zone; Br, branchia; CaC, caudal cirrus; CC, capillary chaeta; Da, dark zone; Fa, fang; HH, hooded hook; Ho, hood; Li, light zone; PR, parapodial ridge; Tho, thorax. Table 2. List of morphological characters of Mastobranchus uru sp. nov. and three known species, indicating the presence or absence of noto- and neuropodial chaetae on chaetiger 1, number of teeth of hooded hooks, and presence or absence of node on shaft of hooded hooks.

Chaetae on chaetiger 1 present (+) or absent (−)		Hooded hooks
Species	References
Notopodia	Neuropodia	Number of teeth	Node on shaft present (+) or absent (−)
Mastobranchus loii	−	−	no data	no data	Gallardo (1968)
Mastobranchus trinchesii	+	+	no data	no data	Eisig (1887)
Mastobranchus uru sp.nov.	+	−	12–14	−	this study
Masstobranchus variabilis	+	−	7–8	+	Ewing (1984)

Fig. 4. Diagram showing the methyl-green staining patterns observed in the thorax of 10 specimens of Mastobranchus uru sp. nov. , with the chaetigers numbered at the top and different patterns (A–E) labeled on the left vertical axis. A, ICHUM 5302, 5305, RUMF-ZO-0018, 0019; B, ICHUM 5306; C, ICHUM 5347 (holotype); D, ICHUM 5303, 5307, 5309; E, ICHUM 5308. Abbreviations: Ba, band zone; Da, dark zone; Li, light zone. Methyl-green staining. The methyl-green staining pattern was observed in 10 specimens for which the prostomium and peristomium, thorax, and at least the anterior part of the abdomen were present. Three zones were evident in the thorax; from anterior to posterior, these comprised a zone of 1–3 lightly stained chaetigers, a zone of 3–4 deeply stained chaetigers, and a zone of 4.5 to 6 banded chaetigers ( Figs 3E , 4 ). The prostomium and peristomium were stained uniformly and lightly, as were the anterior 1–3 thoracic chaetigers (Li, or light zone; Figs 3E , 4 ). The first 2.5 chaetigers were stained in the holotype ( Figs 3E , 4C ); in other specimens, this zone comprised chaetigers 1–3 ( ICHUM 5302 , 5305 , 5306 , RUMF-ZO-0018 and 0019; Fig. 4A, B ), chaetigers 1–2 ( ICHUM 5303 , 5307 , and 5309; Fig. 4D ), or only chaetiger 1 ( ICHUM 5308 ; Fig. 4E ) . The succeeding 3–4 chaetigers in the thorax were uniformly darkly stained (Da, or dark zone; Figs 3E , 4 ). In the holotype , this zone included the posterior half of chaetiger 3, chaetigers 4–5, and the anterior half of chaetiger 6 ( Figs 3E , 4C ); in other specimens, it comprised either 3 chaetigers ( ICHUM 5306 ; Fig. 4B ), 3.5 chaetigers ( ICHUM 5302 , 5305 , RUMF-ZO-0018, 0019; Fig. 4A ), or 4 chaetigers ( ICHUM 5303 , 5307–5309 ; Fig. 4D, E ) . The thoracic chaetigers posterior to the dark zone comprised a zone (Ba, or band zone; Figs 3E , 4 ) in which staining occurred in narrow bands of intense blue encircling the body at the boundaries between the chaetigers; a region of irregular, intermittent, annularly arranged blue staining in the middle of each chaetiger; and tiny stained dots scattered over the surface of each chaetiger. The band zone stretched for 4.5 chaetigers ( ICHUM 5302 , 5305 , RUMF-ZO-0018 and 0019; Fig. 4A ), 5 chaetigers ( ICHUM 5303 , 5306 , 5307 , 5309 ; Fig. 4B, D ), 5.5 chaetigers ( holotype ; Figs 3E , 4C ), or 6 chaetigers ( ICHUM 5308 ; Fig. 4E ) . In the abdominal chaetigers, the noto- and neuropodial ridges were densely stained, appearing as interrupted bands ( Fig. 3F ). In the anterior abdomen, the surfaces of the chaetigers except for the noto- and neuropodial ridges were stained uniformly; these surficial spots gradually became sparser in the posterior abdomen ( Fig. 3F ). The branchiae and the pygidium did not stain ( Fig. 3G ). Sequences. The 16S rRNA gene sequence (303 bp) was determined for the holotype and each of six paratypes ( ICHUM 5302–5305 , RUMF-ZO-0018, 0019; Table 1 ); the aligned 16S rRNA gene sequences were all identical, i .e. , were the same haplotype. Remarks. Mastobranchus uru sp. nov. is similar to M. variabilis because the chaetal arrangement in the first chaetiger is completely the same between the two; however, the chaetal arrangement in M. uru differs from that in M. loii and M. trinchesii ( Eisig 1887 ; Gallardo 1968 ; Ewing 1984 ; Table 2 ). Mastobranchus uru differs from M. variabilis in the number and arrangement of the teeth on the hooks (in M. uru , each hook bears 12–14 teeth distributed in four rows vs. in M. variabilis , each hook bears 7–8 teeth distributed in three rows), and in lacking a node on the shaft of the hood- ed hooks ( Ewing 1984 ). Methyl-green staining patterns were not reported in the original descriptions of any of the three congeners ( Eisig 1887 ; Gallardo 1968 ; Ewing 1984 ). Green (2002) reported methyl-green staining patterns for “ Mastobranchus near loii Gallardo, 1968 ” and “ Mastobranchus near variabilis Ewing, 1984 ”. These two forms differed from M. uru in the staining pattern in the thorax: in M. uru , the last 4–6 chaetigers comprise a banded zone, whereas in the two forms reported by Green (2002) , the last three or four chaetigers were darkly stained but not banded.