Halichoanolaimus pumilus, Leduc, 2020

Leduc, Daniel, 2020, New and known Halichoanolaimus de Man, 1886 species (Nematoda: Selachinematidae) from New Zealand’s continental margin, European Journal of Taxonomy 726, pp. 59-82 : 75-78

Halichoanolaimus pumilus sp. nov.

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Table 1 , Figs 10–11

Diagnosis

Halichoanolaimus pumilus sp. nov. is characterized by short body length, 756 µm long, two dorsosublateral rows of pore complexes with five pore complexes in anterior part of intestine and 10 pore complexes anterior to cloacal region, amphideal fovea with 6.5 turns, pharyngeal lumen distinctly cuticularized, spicule length 1.8 body diameters at level of cloacal opening, gubernaculum 24 µm long and tail 4.7 cbd long with cylindrical portion comprising ca 60% of total tail length.

Differential diagnosis

The new species is most similar to H. brandtae Zograf, Trebukhova & Pavlyuk, 2015 in tail shape (cylindrical portion <75% of total tail length) and high number of amphideal fovea turns (6.5). The new species differs from the latter by the markedly shorter body length (756 vs 1600–1700 µm in H. brandtae ), larger amphideal fovea (58 vs <40% cbd in H. brandtae ), shorter spicules (49 vs 82 µm in H. brandtae ), shape and number of precloacal supplements (three supplements in shape of cylindrical cuticularized structures vs five papillose precloacal supplements in H. brandtae ), and number and arrangement of cuticular pore structures (row of five dorsosublateral pore complexes in anterior part of intestine and 10 pore complexes anterior to cloacal opening vs row of 13–15 lateral 'cuticular pores' in posterior part of intestine in H. brandtae ). Halichoanolaimus pumilus sp. nov. is also similar to H. minutissimus Timm, 1961 in the short body length (<800 µm) but can easily be distinguished from the latter by the much shorter tail (4.7 vs 11.0 cbd in H. minutissimus ) and number of amphideal fovea turns (6.5 vs 3.5 in H. minutissimus ).

Etymology

The species name is derived from the Latin pumilus ('dwarfish', 'little') and refers to the small size of this species relative to most other species of Halichoanolaimus .

Material examined

Holotype

NEW ZEALAND • ♂; Challenger Plateau , 803 m water depth (40.1313° S, 170.2132° E, voyage TAN0707, station 98), sandy mud (82% silt/clay, 18% sand); 6 Apr. 2007; NIWA 139250 .

Type habitat and locality

Challenger Plateau , 803 m water depth (40.1313° S, 170.2132° E, voyage TAN0707, station 98), sandy mud (82% silt/clay, 18% sand).

Description

Male

BODY. Cylindrical, tapering slightly towards both extremities.Cuticle with transverse rows of punctations; lateral differentiation consisting of larger, more widely spaced punctations. Two dorsosublateral rows of pore complexes with five pore complexes in anterior part of intestine and 10 pore complexes anterior to cloacal region; each pore complex ca 2 µm in diameter. Somatic setae short, 3 µm long, sparsely distributed. Cephalic region slightly rounded, lip region slightly offset. Six inner labial papillae; six short outer labial setae, 3–4 µm long, at same level as four cephalic papillae of same length. Amphideal fovea relatively large, multispiral with 6.5 turns, situated ca 0.5 cbd from anterior end. Buccal cavity (pharyngostome) large, ca 20 µm deep, divided into anterior (gymnostome) and posterior portions (stegostome). Anterior portion of buccal cavity cup-shaped, with three sets of three cuticularized rhabdions, 8 µm long, terminating in three sets of paired teeth (denticles; exact number could not be determined); posterior portion of buccal cavity narrower, cylindrical, surrounded by three Y-shaped pairs of cuticularized rhabdions with swollen bases, 10 µm long. Pharynx cylindrical, muscular, without anterior or posterior bulb; pharyngeal lumen cuticularized. Nerve ring at ca 55% of pharynx length from anterior. Secretory-excretory system present. Renette cell small, 9 µm long, 7 µm wide, situated at level of cardia; single nucleated pseudocoelomocyte situated dorsally and opposite renette cell, pore situated slightly posterior to nerve ring. Cardia small, partially surrounded by intestine. Posterior extremity of intestine blind, rectum absent.

REPRODUCTIVE SYSTEM. Diorchic with outstretched testes. Anterior testis to the left of intestine, posterior testis to the right of intestine. Sperm cells globular, 6–10 × 8–14 µm. Spicules paired, curved, tapering distally, length 1.7 body diameters at level of cloacal opening. Gubernaculum consisting of two detached lateral pieces (crurae) tapering distally, median portion of gubernaculum (corpus and cuneus) not visible. Three precloacal supplements in shape of cylindrical cuticularized structures located 8–9 µm apart. Tail conicocylindrical, cylindrical portion ca 60% of total tail length; a few short and sparse somatic setae present. Three caudal glands and spinneret present.

Figures

Fig. 10. Halichoanolaimus pumilus sp. nov. Holotype ♂, NIWA 139250. A. Anterior body region. B. Posterior body region. C. Entire ♂. Scale bar: A = 25 µm; B = 42 µm; C = 60 µm.

Fig. 11. Halichoanolaimus pumilussp. nov. Lightmicrographs of holotype ♂ (NIWA 139250). A. Junction of pharynx and intestine, showing position of secretory-excretory gland (seg) and pseudocoelomocyte (pc). B. Mid-body cuticle, showing position of pore complexes (arrows). C. Cuticle near tail region, showing position of pore complexes (arrows). D. Spicular apparatus and precloacal supplements (numbered 1 to 3). Scale bar = 20 µm.