Mastobranchus uru, Tomioka, Yoshida & Kajihara, 2017

Tomioka, Shinri, Yoshida, Ryuta & Kajihara, Hiroshi, 2017, Description of Mastobranchus uru sp. nov. (Annelida: Capitellidae) from Iriomote Island, Japan, Species Diversity 22, pp. 127-132 : 128-131

publication ID	https://doi.org/ 10.12782/sd.22_127
publication LSID	lsid:zoobank.org:pub:D677E7B8-909E-4C11-B96A-1188EEED31D5
persistent identifier	https://treatment.plazi.org/id/82CA9713-3910-41CB-8A55-C1C415520015
taxon LSID	lsid:zoobank.org:act:82CA9713-3910-41CB-8A55-C1C415520015
treatment provided by	Felipe
scientific name	Mastobranchus uru
status	sp. nov.

Treatment

Mastobranchus uru sp. nov.

[New Japanese name: uru-itogokai] ( Figs 1–4 View Fig View Fig View Fig View Fig )

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 View Materials ) and 10 paratypes ( ICHUM 5302–5309 View Materials , 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 View Fig ) 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 View Fig , 2A View Fig ) 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 View Fig , 2A View Fig ).

Thoracic chaetigers cylindrical, biannulate. Chaetiger 1 uniramous with fascicles of capillary chaetae in notopodia. Chaetiger 2 biramous with both noto- and neuropodia ( Figs 1 View Fig , 2A View Fig ). Capillary chaetae thin, without wing; 4–27 chaetae per fascicle ( Fig. 3A View Fig ); increasing in number from anterior to posterior chaetigers. Thoracic chaetal fascicles situated on antero-posteriorly middle portion of chaetigers.

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 View Fig , 3E View Fig ).

Abdomen with parapodial ridges ( Figs 1 View Fig , 2A–C View Fig , 3E, F View Fig ); 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 View Fig ). 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 View Fig ), 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 View Fig , 3B View Fig ). Hooded hooks with obvious fang ( Figs 2F, G View Fig , 3C, D View Fig ); 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 View Fig ); 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 View Fig , 3G View Fig ).

Pygidium with four, short, rounded, cylindrical caudal cirri ( Figs 2D View Fig , 3G View Fig ).

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).

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 View Fig , 4 View Fig ).

The prostomium and peristomium were stained uniformly and lightly, as were the anterior 1–3 thoracic chaetigers (Li, or light zone; Figs 3E View Fig , 4 View Fig ). The first 2.5 chaetigers were stained in the holotype ( Figs 3E View Fig , 4C View Fig ); in other specimens, this zone comprised chaetigers 1–3 ( ICHUM 5302 View Materials , 5305 View Materials , 5306 View Materials , RUMF-ZO-0018 and 0019; Fig. 4A, B View Fig ), chaetigers 1–2 ( ICHUM 5303 View Materials , 5307 View Materials , and 5309; Fig. 4D View Fig ), or only chaetiger 1 ( ICHUM 5308 View Materials ; Fig. 4E View Fig ) .

The succeeding 3–4 chaetigers in the thorax were uniformly darkly stained (Da, or dark zone; Figs 3E View Fig , 4 View Fig ). In the holotype, this zone included the posterior half of chaetiger 3, chaetigers 4–5, and the anterior half of chaetiger 6 ( Figs 3E View Fig , 4C View Fig ); in other specimens, it comprised either 3 chaetigers ( ICHUM 5306 View Materials ; Fig. 4B View Fig ), 3.5 chaetigers ( ICHUM 5302 View Materials , 5305 View Materials , RUMF-ZO-0018, 0019; Fig. 4A View Fig ), or 4 chaetigers ( ICHUM 5303 View Materials , 5307–5309 View Materials ; Fig. 4D, E View Fig ) .

The thoracic chaetigers posterior to the dark zone comprised a zone (Ba, or band zone; Figs 3E View Fig , 4 View Fig ) 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 View Materials , 5305 View Materials , RUMF-ZO-0018 and 0019; Fig. 4A View Fig ), 5 chaetigers ( ICHUM 5303 View Materials , 5306 View Materials , 5307 View Materials , 5309 View Materials ; Fig. 4B, D View Fig ), 5.5 chaetigers (holotype; Figs 3E View Fig , 4C View Fig ), or 6 chaetigers ( ICHUM 5308 View Materials ; Fig. 4E View Fig ) .

In the abdominal chaetigers, the noto- and neuropodial ridges were densely stained, appearing as interrupted bands ( Fig. 3F View Fig ). 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 View Fig ).

The branchiae and the pygidium did not stain ( Fig. 3G View Fig ).

Sequences. The 16S rRNA gene sequence (303 bp) was determined for the holotype and each of six paratypes ( ICHUM 5302–5305 View Materials , 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.