Cobbia bengalensis

Datta, Tridip Kumar, Bhowmik, Moumita & Choudhury, Amalesh, 2018, Cobbia bengalensis sp. nov. (Xyalidae: Monhysterida) from an eroding island of Sundarban, India, Zootaxa 4444 (2), pp. 179-188: 181-182

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Cobbia bengalensis

sp. nov.

Cobbia bengalensis  sp. nov.

( Figs 2 View Figure & 3 View Figure , Table 1)

Material examined. Four adult males, three adult females and one juvenile female on glycerine slides. Holotype male: Reg. No. ZSI/WN 1971/1 (Co-ordinates of the sampling site: 21.591463°N, 88.171176°E). Male paratypes: Reg. No. ZSI/WN 1971/2; Reg. No. ZSI/WN 1971/3; Reg. No. ZSI/WN 1972/1. Female paratypes: Reg. No. ZSI/ WN 1971/4; Reg. No. ZSI/WN 1973/1; Reg. No. ZSI/WN 1973/2; Reg. No. ZSI/WN 1972/2 (juvenile).

Type habitat. All the samples were collected on 14th November, 2016 from sandy beach and mudflat of Jambu Dwip.

Etymology: The specific epithet refers to its type locality in the largest bay of the world, the Bay of Bengal.

Main measurements (males and females together): L= 1049–1320 µm; a=41.9–61.4; b=5.4–6.5; c=8.7– 11.5; c’=5.5–7.3; V=76–77.

Description. Elongated body with rounded anterior and tapered posterior end. Annulation starts posterior to cephalic sensilla, lateral differentiation absent. Somatic setae sparse, subterminal setae at tail tip never present. Lip region high and rounded. Anterior sensilla arranged into two distinct circles forming sclerotized rings. Inner labial sensilla setiform, six in number, forming anterior circle. Six outer labial sensilla and four cephalic sensilla forming posterior circle. Outer labial sensilla longer than cephalic sensilla and very adjacent to each other, giving an appearance of common origin. Amphid circular in shape. Oval appearance can be caused by bending of anterior end. Distance from anterior end to amphid 20–26 µm, i.e. 10–12% of the pharynx length. Four small subcephalic setae (5–6 µm) present around the body at the level of amphid. Buccal cavity with one pointed dorsal tooth and two smaller equal subventral teeth. Pharynx muscular, cylindrical in shape without terminal bulb. Nerve ring located at 38–56% of pharynx length. Secretory-excretory system not observed. Cardia elongated, triangular in shape, fully inserted into the intestine. Body diameter widest at mid body level. Tail shape sexually dimorphic. Three caudal glands extend from the level of anus to the posterior end. Cuticle of tail tip folded with small pore to slit like opening as spinneret.

Male. Reproductive system diorchic. Anterior testis long (690–795 µm), located to the left from intestine; posterior testis smaller in length (123–150 µm), located to the right from intestine. Vas deferens  long, ventral to intestine. Spicules equal in size, strongly arcuate, ‘L’ shaped, cephalated proximally. Spicule length along arc and chord 18–28 µm and 15–21 µm respectively; capitulum bulbous; lamina with pointed end. Gubernaculum simple, shaft-like without apophysis. Distal end of gubernaculum without any teeth-like projection. Tail conical, gradually narrowing down posterior to anus.

Female (mature). Vulva slit-like, opens at 76–77 % of the body length. Vagina surrounded by glandular cells. Reproductive system monodelphic, outstretched, with one large anterior ovary located to the left from intestine. Spermatheca 51–59 µm long. Anterior branch of spermatheca elongated and posterior branch behind the vulva, condensed with dark brown cells. Growth zone of anterior ovary with large developing oocytes with maximum length of 50 µm and width 15 µm found in mature females. Tail conoid-attenuated; more than half of the tail length gradually narrowed down towards distal part that abruptly narrows into curved cylindrical section.

Female (immature). Little longer than 1mm. Reproductive system was not developed and the associated structures were inconspicuous. Except these, all the morphological characters were very close to mature females. Immature female can certainly be distinguished from the male by having female specific tail of the species. From this observation, it can be assumed that the developmental pathway of sexually dimorphic tail occurs before attaining sexual maturity.

Diagnosis. Cobbia bengalensis  sp. nov. is characterized by sexually dimorphic tail (conoid in male vs. conoidattenuated in female). Anterior sensilla are arranged into two head rings (six + ten); six outer labial sensilla with four shorter cephalic sensilla at posterior ring. Subcephalic sensilla at the level of amphid present. One sharp dorsal tooth and two smaller subventral teeth. Amphid circular. Muscular pharynx without terminal bulb. Cardia elongated and completely inserted into intestine. Strongly arched spicules, cephalated proximally with simple shaft-like gubernaculum. Single ovary.

Relationships. C. bengalensis  sp. nov. is characteristically distinct from C. macrodentata  , C. trefusiaeformis  and C. urinator  by the absence of dentated distal part of gubernaculum. C. bengalensis  sp. nov. differs from C. dentata  , C. truncata  and C. sinica  by the absence of setae (two in number) adjacent to tail terminus. C. urinator  and C. trefusiaeformis  also differ from C. bengalensis  sp. nov. by having very elongated tail with flagelliform terminus (de Man’s c=4.4 and 3.87–5.5 in C. urinator  and C. trefusiaeformis  respectively vs. 8.7–11.5 in C. bengalensis  ). C. truncata  also differs from C. bengalensis  sp. nov. by the presence of pronounced blunt to sharp dorsal apophysis of gubernaculum. C. macrodentata  can be distinguished from C. bengalensis  sp. nov. by the number and arrangement of cephalic sensilla. It was also reported that C. sinica  had small dorsal apophysis which is completely absent in C. bengalensis  sp. nov. C. triodonta  differs from C. bengalensis  sp. nov. by the size of teeth in buccal cavity (subequal vs. unequal dorsal and subventral teeth), position of amphid from anterior end (46 µm vs. 20–26 µm), size of amphid relative to head diameter (1/5th vs. 1/3) and distinct elongated flagelliform tail. The close similarity of C. bengalensis  sp. nov. is found with C. caledonia  . In case of C. bengalensis  sp. nov., amphids are smaller than in C. caledonia  and amphids are situated much more anterior than in C. caledonia  (20–26 µm vs. 34 µm); The difference in the length of inner labial, outer labial and cephalic sensilla can also be recognized between C. bengalensis  sp. nov. (5–7 µm, 19–25 µm & 16–18 µm) and. C. caledonia  (2.5 µm, 15 µm & 11 µm). C. bengalensis  also differs from C. dentata  by the absence of sheath like appearance of gubernaculum. A key to the valid species of Cobbia  has been constructed on the basis of tail shape, buccal armature, arrangement of anterior sensilla, size of amphid and its distance with anterior end, gubernaculum etc.