Maldane adunca, Wang, Yueyun & Li, Xinzheng, 2016

Wang, Yueyun & Li, Xinzheng, 2016, A new Maldane species and a new Maldaninae genus and species (Maldanidae, Annelida) from coastal waters of China, ZooKeys 603, pp. 1-16 : 4-8

Taxon classification Animalia Capitellida Maldanidae

Maldane adunca sp. n. Figs 3, 4, 5

Type material examined.

Holotype: MBM 008111, complete. Original label: South China Sea, Station 6076, mud sediment, 39 m, 21 April 1959. Paratypes, same collecting data as holotype, MBM 240860-240861, nine specimens.

Other material examined: MBM 008125, 1 complete specimen, south of Macao, 21°30'N, 113°30'E, Station 6062, silt sediment, 35 m, 24 April 1959; MBM 006330, 10 complete specimens, northeast of Hainan Island, 20°00'N, 111°30'E, Station 6119, mud sediment, 70 m, 12 April 1959; MBM 201498, 1 anterior part, Beibu Gulf, Station 6209, mud sediment, 56.8 m, 6 July 1960; MBM 201496, 1 complete worm, Beibu Gulf, Station 7905, silt sediment, 29 m, 1 January 1962; MBM 201494,1 complete worm, Beibu Gulf, Station 6200, mud sediment, 32.5 m, 13 July 1960.

Type locolity.

China, southwest of Macao, 21°00'N, 113°00'E, 21 April 1959.

Comparative material examined.

Maldane sarsi . MBM 241068, 2 complete specimen, west of Point Barrow, 71°29.170'N, 161°58.899'W, Station C17, mud sediment, 45 m, 8 August 2008; MBM 008150, 2 complete specimen, north of Yantai, Shandong Province, 38°06'N, 121°31.98'E, Station 2009, mud sediment, 57.5 m, 18 October 1958; MBM 008062, 1 complete specimen, the Yellow Sea, 36°30'N, 124°00'E, Station 3022, mud sediment, 70 m, 21 January 1959; MBM 008228, 1 complete specimen, east of Zhoushan Islands, 29°45'N, 122°30'E, Station 4128, mud sediment, 54 m, 12 July 1959; MBM 008009, 1 complete specimen, the East China Sea, 28°30'N, 123°30'E, Station 4074, mud sediment, 77 m, 9 December 1959; MBM 201497, 1 complete specimen, west of Hainan Island, 18°35.36'N, 106°50.58'E, Station 7702, mud sediment, 55 m, 20 January 1962;

Diagnosis.

Cephalic plate obliquely truncated, elliptical. Cephalic rim low and divided into lateral and dorsal lobes by lateral incisions. Lateral cephalic rim confluent with prostomial palpode. Prostomial palpode bluntly rounded. Nuchal grooves deep and strongly curved outward anteriorly, J-shaped. Anal plate almost truncate and rounded. Rim of anal plate low, with deep lateral incisions.

Description.

Holotype about 65 mm in length, 1.5 mm in width. Largest specimen more than 70 mm in length, and 3.0 mm in width. Segments short on anterior and posterior body, longer on middle body (Figs 3A, 4D).

Body with 19 chaetigers, two preanal achaetigerous segments followed by a pygidium. Cephalic plate obliquely truncated, elliptical (Figs 3B, E, H, 4A). Prostomial palpode bluntly rounded, perfectly fused with cephalic rim. Cephalic rim lower and smooth, with two lateral notches. Cephalic keel remarkable, high and long, with posterior part widens (Figs 3B, E, 4A, B). Nuchal grooves short, anteriorly strongly curved outward, J-shaped (Figs 3B, E, H, 4A). Nuchal grooves isolated from cephalic rim. Mouth trilobed, and divided into upper and lower lips by a transverse fissure. Upper lip incised medially (Fig. 3G).

First five chaetigers biannulate (Figs 3A, D, 4D). First chaetiger without neurochaetae. Neurochaetae typical rostrate uncini similar on all chaetigers (Fig. 5A, B). Neurochaeta with several transversal rows of small teeth on main fang. Anterior chaetigers with capillary notochaetae. Middle and posterior chaetigers with spirally fringed notochaetae (Fig. 5D, H); spinose spiral bands closely imbricated over main shaft (Fig. 5C). Short companion chaetae geniculate (Fig. 5F, J, I), narrowly limbate (Fig. 5E) and bilimbate (Fig. 5G, J).

Two short and rudimentary preanal achaetigerous segments (Figs 3I, 4C), which deeply stained with methyl green. Anal pore with a less-developed anal valve (Fig. 3I). Anal mound well developed. Anal plate truncated, nearly rounded; median part of plate with a shallow furrow dorso-ventrally extended (Fig. 3C). Rim of anal plate low and incised laterally (Fig. 3C, I). Dorsal part of rim smooth. Ventral part of the rim smooth to weakly serrated.

Variation.

Body wall of small individuals thin but thick in large ones. Body of small individuals smooth, semitransparent and lacking epidermal glands. Large individuals with glandular pads on parapodial tori and ventral side of chaetigers 3-5.

Etymology.

The specific epithet is the Latin adjective adunca (feminine, meaning hooked) and refers to the strongly curved nuchal grooves.

Remarks.

Maldane adunca sp. n. is distinctive in the genus Maldane with its low cephalic rim and hook-like nuchal grooves. Maldane adunca sp. n. is close to Maldane sarsi Malmgren, 1865, a potential species-complex, which is thought to be a cosmopolitan species ( Day 1967, Hartman 1961). However, the new species differs from the latter by possessing a low cephalic rim, strongly curved nuchal grooves which are isolated from the cephalic rim, and lacking crescentic glandular bands on the dorsal surface of the fifth chaetiger. In Maldane sarsi , the cephalic rim is well developed, its posterior part forms a deep pocket-like structure (Arwidsson 1906) and overlaps the posterior part of cephalic keel, cephalic keel is strongly arched, the nuchal grooves are narrow and slightly curved and connected with margin of cephalic rim, and the dorsal surface of the fifth chaetiger sometimes bears a crescentic glandular band ( Green 1991, Fauvel 1953). Maldane adunca sp. n. is also closely related to Maldane glebifex Grube, 1860. The new species differs from the latter in the form of the anal rim and nuchal grooves. Maldane glebifex has a crenulated border to the anal plate while Maldane adunca sp. n. has a smooth to slightly crenulated anal rim. The nuchal grooves of Maldane adunca sp. n. are much more curved than that of Maldane glebifex . In terms of geographical distribution, Maldane glebifex is a Mediterranean/North Atlantic species ( Fauvel 1927), and it is unlikely to occur in the South China Sea.

Light (1991) revised the subfamily Maldaninae and recognized 16 species of Maldane , of which Maldane pellucida Sars, 1869 was recognized later as nomina nuda ( Oug et al. 2014). At present, Maldane includes 18 species: Maldane adunca sp. n., Maldane arctica , Maldane californiensis , Maldane capensis , Maldane cristata , Maldane cuculligera , Maldane decorate , Maldane glabra , Maldane glebifex , Maldane gorgonensis , Maldane malmgreni , Maldane marsupialis , Maldane meridionalis , Maldane monilata , Maldane philippinensis , Maldane pigmentata , Maldane sarsi , Maldane theodori . Maldane sarsi includes two subspecies: Maldane sarsi antarctica Arwidsson, 1911 and Maldane sarsi borealis Imajima, 1963 but their validity is doubtful. Maldane sarsi antarctica resembles the stem species. Color and gland pattern is main difference between the subspecies and its stem species according to Arwidsson (1911), but they are not robust taxonomic characters. Imajima (1963) collected only one specimen to erect Maldane sarsi borealis. This subspecies has 18 chaetigers, and anal plate of it incised ventrally. The chaetiger number is unusual in Maldane (usually, 19 chaetigers in Maldane species). Table 1 compares morphological characters for all known species of genus Maldane .