Cyathoshiva, Datta, Tridip Kumar, Miljutin, Dmitry M., Chakraborty, Susanta Kumar & Mohapatra, Anil, 2016

Datta, Tridip Kumar, Miljutin, Dmitry M., Chakraborty, Susanta Kumar & Mohapatra, Anil, 2016, Cyathoshiva amaleshi gen. n. sp. n. (Nematoda: Cyatholaimidae) from the coast of India, Zootaxa 4126 (4), pp. 577-586 : 579-580

Cyathoshiva gen. n.

Genus description. Cyatholaiminae . Body cylindrical with truncated anterior end and conical tail. Cuticle transversely punctated. Lateral differentiation in form of slightly enlarged dots. Large cuticular pores arranged in longitudinal rows. Outer labial sensilla and cephalic sensilla arranged in one circle. Amphideal fovea multispiral. Cheilostoma cup-shaped, surrounded by twelve rugae. Pharyngostoma with one large pointed cuticularised dorsal tooth and smaller subventral teeth. Pharynx muscular, without developed posterior bulb. Male reproductive system diorchic; anterior testis outstretched, posterior testis reflexed. Anterior and posterior testes lying right and left of intestine, respectively. Spicules arcuate. Gubernaculum proximally fused, distally paired, with serrations at dilated distal end. Precloacal supplements present. Ovaries paired, opposed and reflexed. Anterior ovary lying right to intestine; posterior ovary laying left to intestine.

Differential diagnosis. The new genus differs from other known Cyatholaiminae genera in the combination of three characters: proximally unpaired gubernaculum; well-developed dorsal and subventral teeth; presence of noncup-shaped supplements (supplements are absent or cup-shaped in other genera of the subfamily). Such a combination is unknown in other Cyatholaiminae genera.

Well-developed dorsal and subventral teeths are characteristic for the genera Longicyatholaimus , Marylynnia , Paramarylynnia , Phyllolaimus , and Xyzzors as well. However, species of the genus Longicyatholaimus possess cup-shaped supplements (versus non-cup shaped in the new genus). Marylynnia is characterized by the gubernaculum with paired proximal end and cup-shaped supplements. Paramarylynnia has no supplements. Phyllolaimus has one very prominent dorsal tooth (versus not so prominent in the new genus) and has no supplements. Characteristic features of the genus Xyzzors are one very large dorsal tooth (versus not so large in the new genus) and cup-shaped supplements (versus non-cup shaped in the new genus).

Non-cup-shaped (tubular) supplements are known in the genus Praeacanthonchus , however this genus is characterized by the reduced dorsal tooth and lacking subventral ones (versus well developed dorsal and subventral teeth in the new genus).

Finally, a fused proximal end of the gubernaculum is known in the genera Cyatholaimus , Longicyatholaimus , Metacyatholaimus , Paralongicyatholaimus , Paramarylynnia , Phyllolaimus and Praeacanthonchus . However, of them, Cyatholaimus , Metacyatholaimus , Paralongicyatholaimus , Paramarylynnia and Phyllolaimus are lacking in supplements. Cup-shaped supplements are the characteristic features of the genus Longicyatholaimus . The rest genus, Praeacanthonchus has a resemblance to the new genus in a construction of supplements (tubular, i.e. noncup-shaped) but differs from the latter in an armament of the pharyngostoma (reduced dorsal tooth and lacking subventral teeth versus well-developed dorsal and subventral teeth, respectively.

Type species. Cyathoshiva amaleshi gen. n. sp. n.

Etymology. The new genus has a cup-shaped (Greek. Cyatho) cheilostoma similar to that of other members of Cyatholaimidae . Lord Shiva is one of the major deities of Hindu mythology. During the “Samudra Manthan” (“Churning of the Ocean”) event, Lord Shiva consumed poison to protect creation. In recognition of the essential role of free-living nematodes in marine ecosystems, the name of the Hindu God is used.

Discussion. The new genus has characters which place it in the family Cyatholaimidae : multispiral amphid; outer labial and cephalic sensilla joined in one ring; stoma with twelve rugae and teeth; punctated cuticle; characteristic large cuticular pores associated with hypodermal glands; two testes (outstretched anterior and reflexed posterior) and two antidromous ovaries located on different sides on the intestine.

The new genus differs from genera of the subfamily Pomponematinae by the structural morphology of the precloacal supplements (tubular with a setoid part versus knob-like and flattened, respectively) and morphology of the proximal part of the gubernaculum (unpaired (in most cases) versus paired, respectively). The monotypic subfamily Xenocyatholaiminae has distinct longitudinal ridges, cuticular punctations only anterior to the amphid and on the tail, and a short gubernaculum. These morphological features do not occur in Cyathoshiva gen. n. The other monotypic subfamily Nyctonematinae ( Bussau, 1993) has outer labial and cephalic sensillae arranged in two separate circles (versus arranged in one circle in Cyathoshiva gen. n.) and the amphid located distant from the head end (versus not distant in the new genus).

Cyathoshiva gen. n. has non-cup-shaped supplements which are known from several genera of Cyatholaiminae and Paracanthonchinae subfamilies only. These two subfamilies are difficult to distinguish, having similar and overlapping features. Nevertheless, the Cyathoshiva gen. n. should be placed in the subfamily Cyatholaiminae because of its proximally unpaired gubernaculum; this feature is unknown in the subfamily Paracanthonchinae (with the exceptions of some doubtful species, see Miljutina & Miljutin 2015).

As Cyathoshiva gen. n. is monotypic, it is difficult to predict which morphological characters will have diagnostic value for species differentiation. Structure of spicules and gubernacula and the arrangement of head sensillae are usually stable for species within any one genus in Cyatholaimidae . However, the number and size of teeth, length of head and somatic sensilla, number of turns in the amphideal spiral, shape of gubernaculum, number and construction of supplements, and appearance of the lateral field of the cuticle may vary in different species of the same genus. These characters could be useful for species differentiation in Cyathoshiva gen. n.

The supplements of the type species of Cyathoshiva gen. n. consist of two parts: basal tubular and distal setoid (or papilloid) ones. This form of supplements is known in Cyatholaimidae (see, e.g. descriptions of Paracyatholaimus vancouverensis Sharma & Vincx 1982 ; P. huanghaensis Huang & Xu 2013 ; Paracanthonchus olgae Tchesunov 2015 ). Shape of supplements of similar construction may vary within the same species ( Tchesunov 2015): from tubular to setoid, with an intermediate two-component form (having a basal tubular and a distal setoid part). Thus, other species of the new genus may have tubular or setoid supplements. However, it is unlikely that other species of the new genus will have cup-shaped supplements.