Gammanema magnum Shi & Xu, 2018, sp. nov.
Creators: name: Shi, Benze
name: Xu, Kuidong
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Nematoda
Chromadorea
Chromadorida
Selachinematidae
Gammanema
Gammanema magnum

description: Gammanema magnum sp. nov.
urn:lsid:zoobank.org:act:C86AD66F-ECB9-48A8-8D6A-15D777EB9749
Figs 1–4; Table 1
Diagnosis
Body cylindrical, length 2540–4085 μm. Six short leaf-like inner labial setae with broad base, six long leaf-shaped outer labial setae with broad base and four slender cephalic setae arranged in three circlets. Anterior buccal cavity broad and cup-shaped, reinforced by 12 sclerotized rhabdia, each rhabdion with about six denticles at posterior end; posterior buccal cavity narrow and cylindrical with six broad rhabdia, surrounded by pharyngeal tissue. Amphideal fovea exhibiting extreme sexual dimorphism: large loop in about 1.3 turns occupying 79–82% of corresponding body diameter in males and very small spiral in about two turns occupying 12–14% of corresponding body diameter in females. Pharynx with anterior end slightly swelling, but not bulb-like enlarged. Two opposed testes. Sperm globular to oval. Two spicules unequally long and slightly curved, with left spicule (51–56 μm long) slightly shorter than right one (62–69 μm long). Two reflexed ovaries. Spermatheca large, filled up with sperm. Three caudal glands with spinneret. Tail short and conical.
Etymology
The specific epithet is from the Latin adjective ‘ magnus ’ (large) and refers to two distinct features of the species, i.e., the large body size and the large amphideal fovea in male.
Material examined
Holotype EAST CHINA SEA: ♂, Nanji Islands, Dasha’ao Beach, 27°27.76′ N, 121°3.48′ E, May 2014, intertidal sandy sediment, temperature 22°C, salinity 28 psu during sampling, median particle diameter of sediment about 612 μm (coarse sand), sediment organic matter content about 2.5%, Benze Shi and Kuidong Xu leg. (MBMCAS NJ-20140513-73).
Paratypes EAST CHINA SEA: 2 ♂♂, 7 ♀♀, same collecting data as for holotype (MBMCAS NJ-20140513-22, MBMCAS NJ-20140513-71, MBMCAS NJ-20140513-73, MBMCAS NJ-20140513-83, MBMCAS NJ-20140513-84).
Description
MEASUREMENTS. See Table 1.
BODY. Cylindrical. Cuticle thick and distinct annulated, rows of punctuations on the annules, without lateral differentiation (Figs 1A, 2D, 3A). Head blunt with six pairs of thin, membrane-like cuticle extensions. Anterior sensilla in three circles: six inner labial setae leaf-shaped with a broad base, six outer labial setae leaf-shaped with a broad base and four slender cephalic setae (Figs 1A–B, 2B–C, 3A–B). Buccal cavity spacious, divided into two portions. Anterior buccal cavity broad, cup-shaped, with 12 cuticularized rhabdia, each rhabdion with about six pointed denticles at its posterior end. Posterior buccal cavity narrow and cylindrical, surrounded by six broad rhabdia (Figs 1B, 2C, 3B, 4A). Pharynx cylindrical, with slight anterior end swelling, not bubliform, surrounding the posterior buccal cavity, without posterior bulb. Numerous cells surrounding the pharynx. Intestine cells large, filled of orangebrown inclusions. Intestine lumen with irregular and variable appearance. Prey nematode species often observed in the intestine are probably members of Epacanthion Wieser, 1953, as observed in the intestine of a paratype specimen (Fig. 4F). Three caudal glands with spinneret. Tail short and conical (Figs 1D, 2A, 3E).
Male
Amphideal fovea large loop-shaped, in about 1.3 turns, covering 79–82% of corresponding body diameter (Figs 1A, 3A). Two opposed testes, situated ventrally left to the intestine. Sperm cells globular to oval (Figs 1D, 3D, F). Two spicules unequally long and slightly curved, with left spicule slightly shorter than right one (Fig. 1E). Gubernaculum absent. Precloacal supplement absent.
Female
Similar to male in body shape. Outer labial setae slightly shorter than in male but cephalic setae slightly longer than in male.Amphideal fovea small spiral, in about two turns, covering 12–14% of corresponding body diameter (Figs 2B, 4B). Two reflexed ovaries. Vulva a transverse slit, located at 62–67% of body. Vagina surrounded by well-developed constrictor muscles. Uterus broad. Spermatheca large, filled up with sperm (Fig. 4D).
Remarks
The new species is assigned to the genus Gammanema Cobb, 1920 based on its broad and cup-shaped anterior buccal cavity reinforced by 12 cuticularized rhabdia each with about six pointed denticles at posterior end and a narrow and cylindrical posterior buccal cavity surrounded by six broad rhabdia. The genus Gammanema now contains 13 valid species (Leduc 2013). Among these, sexual dimorphism in the amphideal fovea occurs in species where both males and females are known. However, the males of two species, G. mediterraneum Vitiello, 1970 and G. cancellatum Gerlach, 1955, remain hitherto unknown. Compared to the females, Gammanema magnum sp. nov. differs from G. mediterraneum in the greater body size, which is four times larger, the leaf-like labial setae (vs papillate) and the absence (vs presence) of long somatic setae. It differs from G. cancellatum in the leaf-like outer labial setae distinctly shorter than the cephalic setae (vs slender outer labial setae longer than the cephalic setae).
Gammanema magnum sp. nov. is a striking species exhibiting extreme sexual dimorphism in the amphideal fovea: large loop-shaped in males and small spiral in females. Only G. fennicum Gerlach, 1953, G. conicauda Gerlach, 1953 and G. agglutinans Leduc, 2013 show such dimorphism. However, Gammanema magnum sp. nov. differs distinctly from the three aforementioned species by the two unequally long spicules without gubernaculum (vs equal sized spicules with gubernaculum) and the lack of precloacal supplement (vs with supplements). The new species differs also distinctly from G. conicauda and G. agglutinans by its larger amphideal fovea in males (in 1.75 turns covering 79– 82% of cbd vs a single loop covering 34–41% of cbd and a small open loop covering 28–29% of cbd, respectively) and the leaf-like labial setae (vs slender and conical setae, respectively).
description: Published as part of Shi, Benze & Xu, Kuidong, 2018, Two new rapacious nematodes from intertidal sediments, Gammanema magnum sp. nov. and Synonchium caudatubatum sp. nov. (Nematoda, Selachinematidae), pp. 1-17 in European Journal of Taxonomy 405 on pages 3-9, DOI: 10.5852/ejt.2018.405, http://zenodo.org/record/1181135