Sphaerolaimus qeshmensis, Tchesunov & Eskandari & Hosseinvand & Hajializadeh, 2024

Tchesunov, Alexei V., Eskandari, Ali, Hosseinvand, Manouchehr & Hajializadeh, Parima, 2024, Free-living marine nematodes of the family Sphaerolaimidae (Chromadoria, Monhysterida) from the mangroves of the Qeshm Island, Persian Gulf, Zootaxa 5468 (3), pp. 523-540 : 525-529

Sphaerolaimus qeshmensis sp. n.

( Figures 1–2 , 7A–B and Table 1 )

Type material. Holotype male, one paratype male and two paratype females. Holotype male (slide 59/16) and paratype male (slide 50/17) specimens are deposited in the nematode collection of the Center of Parasitology , A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences , Moscow, Russia. Two paratype female specimens are kept in the nematode collection of Department of Invertebrate Zoology , Faculty of Biology , M. V. Lomonosov Moscow State University, Moscow, Russia. All the type specimens are mounted in permanent glycerin slides.

Type locality and habitat. Intertidal silty sediment close to Avicennia marina tree, salinity of interstitial water: 33.8 ppt, temperature on the sediment surface: 29.7 °C, north coast of Qeshm Island, Strait of Hormuz, Hormozgan Province, southern Iran, November 2021, (26°48’29.2”N, 55°45’05.5”E) .

Etymology. The species epithet is derived from the type locality, Qeshm Island.

Descriptions.

Males. Body short and stout, nearly cylindrical. Cuticle thick, with fine cross striations. No apparent lateral cuticular differentiation but borders of the lateral epidermal chords distinctly visible. Anterior end widely conical, and its cuticle not striated. Mouth opening surrounded with six small lips.

A circle of six minute inner labial papillae located at the base of the labial region. Outer labial and four cephalic sensilla arranged in a joined circle of ten small setae at the level of the anterior edge of the cheilostoma ribs. Subcephalic setae arranged in eight groups (two dorso- and two ventro-sublateral, two dorso- and two ventrosubmedian) at the level of the anterior edge of the shagreen band. Each subcephalic group consists of three to four setae of various lengths. Somatic setae arranged in eight longitudinal rows; the setae rather long and dense in the preneural region, short and sparse posterior to the nerve ring along the body. Amphideal fovea as an irregular longitudinal oval shape situated at the posterior edge of the shagreen band.

Mouth opening leads to the complicated buccal cavity. Major anterior part of the buccal cavity formed by modified somatic cuticle and thus qualified as cheilostoma. Anterior conical part of the cheilostoma further subdivided into two chambers, (1) anterior conical smooth-walled chamber surrounded by lips, and (2) posterior chamber shaped as a truncate cone with fine longitudinal striations (ribbing). There is a circle of tiny light-reflected granules at the anterior edge of the ribbing. The next voluminous barrel-shaped chamber with thick walls of light-refracted spongious material (shagreen band, see also family diagnosis above). Walls of the shagreen band with some light irregular longitudinal areas; posterior edge of the shagreen band projected outwardly into a circular crest. Amphideal area bulges by half into the shagreen band. Posterior wide conical part of the buccal cavity presents a pharyngostoma; it shaped by modified internal cuticle of the pharyngeal tissue. The anterior part of the pharyngostoma, the gymnostoma, is a narrow part just posterior to the shagreen band; gymnostoma walls look like a posteriorward continuation of the shagreen band. Stegostoma, the rearmost part of the buccal cavity, is surrounded with muscular pharyngeal tissue. Spongious rhabdions of the gymnostoma continue posteriorly and are soldered with the cuticle of the stegostoma. The cuticles of the gymnostoma and stegostoma are distinct from one another in the site of contact. Pharynx strongly muscular along its length, almost cylindrical, slightly broadened gradually to the cardia. Inner cuticular lining of the pharynx strong and wide and looks like several stripes because of the irregular width of the cuticle on a transverse section. Cardia hemispheric, with strong internal cuticular lining. Nerve ring at 46–47% of the pharynx length. Ventral gland ampulla and pore just posterior to the nerve ring. Ventral gland cell body not discernible.

Males reproductive organs poorly discernible. Anterior outstretched testis situated to the right of the intestine. Posterior testis not found. Fine-granular vas deferens situated to the right of the intestine. Spicules large, strong, thick-walled, arcuated, with both ends blunt. Gubernaculum consists of a basal trough and paired dorso-caudal apophyses. About eight tiny precloacal midventral supplementary papillae.

Tail conico-cylindrical. Tail end thickened and provided with three long terminal setae, one dorsal and two ventro-lateral. A ventro-lateral row of about six setae on conical part of the tail.

Females. Amphideal fovea of females notably smaller than that of males. Female reproductive system consists of a single prodelphic outstretched ovary situated to the right of the intestine.

Diagnosis. Sphaerolaimus with body length 1139–1610 μm; a = 12.9–14.4, b = 3.9–5.0, c = 7.0–7.3, V% = 74.3–77.7%; subcephalic setae length 3–17 μm, amphideal fovea diameter (width) 6–9 μm situated at the posterior edge of the shagreen band; stoma length 49–53 μm, midstoma width 18–35 μm, height of the shagreen band 18–20 μm; spicules arcuated, 116–140 μm long, gubernaculum with dorso-caudal apophyses 22–23 μm long.

Differential diagnosis. Basing on set of characters, the most similar species are: Sphaerolaimus kleini Jensen, 1992 ; S. limosus Fadeeva, 1983 ; S. makrolasius Schulz, 1932 ; and S. micropapillatus Tchesunov & Miljutin, 2006 . All those related species share position of the amphideal fovea at the level of the pharyngostoma, presence of a dorso-caudal apophysis of the gubernaculum and arcuated medium-sized spicules. S. qeshmensis sp. n. differs from S. kleini by significantly smaller amphideal fovea (males: width 8–9 μm versus 12 μm), longer spicules (116–140 μm versus 73–80 μm); from S. limosus by shorter subcephalic setae (males: 3–16 μm versus 7–22 μm), position of the amphideal fovea at the posterior edge of the shagreen band versus at the level of the gymnostoma or further posterior, and longer spicules (116–140 μm versus 85–100 μm); from S. makrolasius by smaller body length (males: 1139–1610 μm versus 2040 μm) and relatively longer spicules (ratio spicules length along the arc divided by cloacal body diameter 1.6–2.1 versus 1.1); from S. micropapillatus by larger amphideal fovea (males: 8–9 μm versus 6–7 μm), longer spicules (116–140 μm versus 63–64 μm) and less prominent, smaller, precloacal supplementary papillae.

Figures

FIGURE 1. Sphaerolaimus qeshmensis sp. n., entire view and heads. A: holotype male, entire; B: paratype female, entire; C: paratype female, head; D: holotype male, head. Scale bars: A, B—100 μm; C, D—10 μm.

FIGURE 2. Sphaerolaimus qeshmensis sp. n., holotype male, details. A: anterior body; B: posterior body. Scale bars: 100 μm.

FIGURE 7. Queshm Island species of Sphaerolaimidae, photographs. A: Sphaerolaimus qeshmensis, anterior end, holotype male; B: Sphaerolaimus qeshmensis, copulatory apparatus, holotype male. C: Parasphaerolaimus brevisetosus, anterior end, male; D: Parasphaerolaimus brevisetosus, male copulatory apparatus; E: Parasphaerolaimus brevisetosus, lateral alae, male; F: Parasphaerolaimus sp. 1, anterior end, female; G—Parasphaerolaimus 2, anterior end, female. Scale bars: 20 μm.