Trochamus timmi, Datta & Al-Helal, 2023

Datta, Tridip Kumar & Al-Helal, Md. Abdullah, 2023, Review of Euchromadorinae (Nematoda: Chromadorida) with description of a new species of Trochamus Boucher & De Bovée, 1971 from the Sundarban, India, Zootaxa 5278 (3), pp. 493-510 : 499-504

Description of Trochamus timmi sp. n.

( Figures 1–3 , Table 1 )

Material examined. Two adult males and four adult females on glycerine slides. Holotype male: Reg. No. WN3873/1 . Male paratype: Reg. No. WN3873/2 . Female paratypes: Reg. No. WN3873/3 , WN3873/4 , WN3873/5 and WN3873/6 .

Type habitat. Samples were collected from the muddy intertidal mangroves of the Sundarban, West Bengal, India; Collector: Tridip Kumar Datta, Date: 28 th April, 2018.

Etymology: The species name is given after Dr. Richard William Timm, popularly known as Father Timm (2 nd March, 1923–11 th September, 2020) for being the pioneer researcher on marine nematology of the Bay of Bengal and his remarkable contribution to the society.

Description.

Adults <1mm long with heavily annulated body. Anterior end flat to round and posterior end tapered. Cheilostome surrounded by twelve folded rugae. Pharyngostome with two subventral teeth and comparatively one large claw-like dorsal tooth. Anterior part of pharyngostome with six OLS (1–2 µm long) and four CS (2–3 µm long) setiform, arranged in a single crown. At the level of CS, cephalic diameter measures 16–18 µm. Amphideal fovea indiscernible, probably located at the cheilo-pharyngo junction as a slit, ca. 43–47% of cephalic diameter. Somatic setae present throughout body but sparse.

Pharynx muscular and cylindrical, measures 106–153 µm long, ca. 14–19% of total body length. Pharynx ends with one dilated bulb and two thin muscular interruptions anterior of it. Nerve ring located ca. 51–56% of pharynx in respect to anterior end. Cardia indiscernible. Excretory pore located ventral to pharyngeal bulb and ventral gland (28–32 µm long) as elongated bulb ventral to anterior part of intestine. Tail conical, 87–111 µm long, measures 4–5 abd long. Tail end non-annulated (10–12 µm) and spinneret bears two setae (4–5 µm).

Cuticle heterogeneous. Annulation starts just posterior to head capsule. Annulations appear as punctations varied from dotted at anterior end to oval shaped for most of the body. Annulation height less at both ends than rest of the body. Annulation pattern not fully understood because of complex arrangement of cuticular layers. Cuticle appears as corrugated roof-tile in overlapping pattern which in turn gives dotted and oval-shaped optical appearance under light microscopy. Lateral differentiation as elevated ridge (alae) starts at the level of nerve ring anterior to pharyngeal bulb ca. 73–79 µm posterior to head end and ends posterior to anus ca. 63–73 µm anterior to tail end. The width of ridges vary throughout the body being widest at the mid body level where cuticle appears more complex. Due to upper layer of cuticle the internal structures not properly visible, probably corrugated structures attached with a median rib and one side just beneath the preceding annule while other side above the next annule. The appearance changes with the direction of the cuticular annulations; first change in the annular direction appears ca. 31% of the anterior body part. Male and female both appears similar except reproductive structures and its associated forms.

Male (846–887 µm): Reproductive system monorchic with outstretched testis located right to intestine. Spicules long (48–51 µm in arc, 38µm in chord), arcuate. 1.9–2.0 of corresponding anal body. Manubrium (capitulum) without any prominence. Gubernaculum small, plate-like (10 µm) running parallel to dorsal of spicules. Germinative zone of testis with broadened anterior end. Vas deferens forms tubular part at distal end and joins with rectum to form cloacal opening. Pre-cloacal modification as cuticular thickening of 11–13 annules, located 72–80 µm (ca. 24 annules) anterior to cloacal opening. No further post-cloacal modification.

Female (720–811 µm): Reproductive system amphidelphic with reflexed ovaries; anterior ovary right to intestine and posterior left to it. Both ovaries almost similar in size; anterior being little larger (48–74µm) than posterior (45–72 µm). Body diameter at vulva being widest (36–39 µm) and located around the mid portion of the body (47–52%). Vulva visible with dilated cuticle. Vagina slit-like with refractive thick muscle and posterior wall folded back resulting in formation of short lumen.

Diagnosis. Adult <1 mm long. Lateral differentiation as elevated ridge starts at the level of nerve ring just anterior to pharyngeal bulb. Amphideal fovea indiscernible, probably slit-like at the level of cephalic sensilla. Spicules simple around 50 µm long in arc. Gubernaculum simple plate-like. Pre-cloacal thickening in male.

Figures

FIGURE 1. Illustration of Trochamus timmi sp. n. A) habitus of holotype male (WN3873/1); B) habitus of paratype female (WN3873/4); C) anterior part of holotype; D) anterior part of paratype female (WN3873/5); E) tail of holotype (WN3873/1); F) tail of paratype (WN3873/5); G) lateral view of reproductive part of holotype; H) cuticle at the anterior region of the body before the beginning of ridge; I) forwardly directed midbody cuticle; J) cuticle at anterior part tail region. Scale bar: A & B = 100 µm, C–J = 10 µm.

FIGURE 2. Photomicrographs of Trochamus timmi sp. n. Holotype male (WN3873/1) A) habitus, B) cephalic region and buccal cavity, C) reproductive region along with precloacal cuticular outgrowth (arrows), D) oesophageal bulb and the opening of excretory pore (e). Paratype female (WN3873/4) E) habitus, F) anterior body part showing nerve ring (n) and ventral gland (v). Scale bar: A & E = 100 µm, B–D & F = 10 µm.

FIGURE 3. Photomicrographs of Trochamus timmi sp. n. Holotype male (WN3873/1) A) anterior region showing the origin of alae or ridge (arrow), B) tail region showing the end of alae, C) cuticle at anterior region; D) paratype female (WN3873/5) cuticle at anterior region; E) Holotype male (WN3873/1) cuticle at posterior to pharyngeal bulb; F) paratype female (WN3873/3) tail; G) paratype female (WN3873/5) tail; H) paratype female (WN3873/5) vulva; I) paratype female (WN3873/4) reproductive region showing anterior and posterior ovaries. Scale bar: A & H = 10 µm, I = 100 µm.