Odetenema gesarae, Bezerra & Pape & Hauquier & Vanreusel, 2021

Bezerra, Tania Nara, Pape, Ellen, Hauquier, Freija & Vanreusel, Ann, 2021, Description and distribution of Erebussau nom. nov. pro Erebus Bussau, 1993 nec Erebus Latreille, 1810 with description of a new specie, and of Odetenema gesarae gen. nov., sp. nov. (Nematoda: Desmoscolecida) from nodule-bearing abyssal sediments in the Pacific, Zootaxa 4903 (4), pp. 542-562 : 555-556

Odetenema gesarae gen. nov., sp. nov.

( Figs 8 , 9 and 10 ; Tables 1 and 3)

Material examined for description: One male and two females. The holotype male (Inventory No. UGMD 104404 ) and one paratype female (Inventory No. UGMD 104405 ) are deposited in the Zoology Museum of Ghent Univer-sity—Museum voor Dierkunde ( UGMD) .

Type habitat and locality: Deep-sea with sediment grain size dominated by silt, containing nodules. The male holotype was found in a sample from the GSR license area in the CCFZ at about 4500 m depth, during expedition GSRNOD15–A, MUC006 , 0-5 cm deep in the sediment .

Description: Male: Body slender, tapering anteriorly and posteriorly. Anterior width 50 % of the maximum body diameter. Cuticle with 184 dorsal and 247 ventral rings. The first 23 (dorsal) and 52 (ventral) rings, as well as the last 16 (dorsal) and 25 (ventral) have a well defined outline. The first 6 (dorsal) and 4 (ventral) rings, together with the last 5 ones, show the most explicit defined outline on the body. Desmen not present. Inversion ring not visible. Cuticle at mid-body almost smooth impairing the ring counting. Few somatic setae, relatively thick on short peduncles. Cephalic region longer than wide, with cuticularised walls on lateral view. Cuticle without concretions or ornaments. External labial sensilla indistinct. Cephalic setae located on small peduncles. Amphidial fovea large and vesicular, reaching posteriorly the first ring. Round fovea clearly visible. Buccal cavity small, unarmed. Pharynx anteriorly surrounded by elongated glands and slightly enlarged posteriorly. Nerve ring at 39 µm from the anterior end, 74 % of pharyngeal length. Pseudocoelomocytes not recognizable. Pigment spots of different sizes at the anterior part of the intestine on both sides of the body. Phasmata small, can be easily overlooked. Reproductive system diorchic, testes opposed. Posterior testis reflexed. Vas deferens not clearly distinguished. Spicules slightly curved. Gubernaculum without apophysis. Two small rounded gland cells with distinct nucleus posterior to the gubernaculum. A row of four thick setae on small peduncles are ventrally positioned from the spicules towards the anterior end. Three caudal glands can be observed but two separate tubular outlets, close to one another, are present. Tail conical, end ring with two tubular outlets.

Females: Longer, but otherwise similar to males in most aspects. Nerve ring not visible on females due to the amount of glands covering the pharynx. Pseudocoelomocytes visible ventrally of the intestine. No sexual dimorphism detected. Reproductive system didelphic, amphidelphic, with outstretched ovaries. Vulva positioned at 56 % of the body from the anterior end. No perivulvar glands observed. Vagina short, transverse and thick-walled. Uterus not well distinguished, appearing to be uniform. Oviduct indistinct. Ovaries outstretched, anterior one more developed than the posterior one with a single fully grown oocyte. Phasmata larger than in males. Terminal caudal glands opening with same morphology as in males, showing two separate tubular outlets. Tail conical.

Juvenile: Similar to adults in most morphological aspects.

Etymology: The species is named after the Global Sea Mineral Resources (GSR), the deep-sea exploratory division of the DEME Group.

Differential diagnosis: Odetenema gesarae gen. nov., sp. nov. differs from all other Tricominae genera described to date, by the special appearance of the cuticle, almost smooth at mid body. The long cephalic region, not offset, tapering to a narrow, and elongated anterior end, forming a kind of rostrum, combined with the short cephalic setae and the long amphid result in an exclusive anterior end. The two separate caudal gland outlets are unique to the order Desmoscolecida .

Although other specimens were observed, they were not well preserved and perhaps the measurements would not be accurate. For this reason we decided to measure the three specimens which were better preserved and could be measured with accuracy.

Figures

FIGURE 8: Distribution of Odetenema gesarae gen. nov., sp. nov. Imagery reproduced from the GEBCO Grid, version 1.3.0, ETOPO1 Global Relief Model (Amante & Eakins, 2009)

FIGURE 9: Odetenema gesarae gen. nov., sp. nov. (Drawings of holotype male and paratype female) A: male habitus, arrows pointing towards anterior and posterior testes; B: anterior end, arrow pointing towards pigment spot; C: posterior end, arrows pointing towards pre cloacal supplements; D: male posterior end, arrows pointing towards ejaculatory gland, phasmata and glands outlet; E: female reproductive system, arrow pointing towards vulva (Scale bars = 20 µm)

FIGURE 10: Odetenema gesarae gen. nov., sp. nov. (Photos of holotype male and paratype female) A: male habitus; B: female habitus, arrows pointing towards anterior and posterior ovaries; C: male anterior end; D: female anterior end, arrows pointing at pigment spots; E: male posterior end, arrow pointing towards pre cloacal supplement; G: female reproductive system, arrow pointing at vulva. (Scale bars A, B = 100 µm; C, D = 20 µm; E, F = 50 µm)