Desmodorella tenuspiculum Allgen, 1928

Fadeeva, Natalia, Mordukhovich, Vladimir & Zograf, Julia, 2016, Free-living marine nematodes of Desmodorella and Zalonema (Nematoda: Desmodoridae) with description of two new species from the deep sea of the North Western Pacific, Zootaxa 4175 (6), pp. 501-520 : 503-507

Desmodorella tenuspiculum Allgen, 1928

( Figs 2–4 )

Material examined. 6 males, 5 females and 15 juveniles (Table 2).

Locality. Table 1 .

Measurements. See Table 2.

Description. Moderately long spindle-shaped, body, swollen in mid-body region of reproductive system. Body yellowish to brownish, with epidermal inclusions. Body cuticle marked by fine transverse annuli and longitudinal ridges. Cuticle annulated in anterior region except for smooth cephalic capsule (annuli 0.8–1.0 µm wide), finely annulated at mid-body (0.2–0.3 µm annuli width) and smooth at the terminal cone. Posterior to cephalic capsule eight longitudinal rows of ridges ( Fig. 5 C, D), covered by fine "spines" (3.0–4.0 µm) seen only with SEM. 16–18 longitudinal rows of ridges present in the middle of the body. Distance between ridges increases in swollen areas of body, particularly in area of gonads, and then the number of ridges decreases to the terminal cone ( Fig. 5 G). Tail region with only 6–10 longitudinal rows of ridges, with fine spine like ornamentation, ending 20 µm anterior to tip of tail.

Anterior sensilla arranged in three circlets: six inner labial papillae (1µm), six short outer labial (2µm) setiform papillae, and four slender cephalic setae at level of the anterior margin of the amphideal fovea. An irregular circle of about eight cervical setae at or close to posterior end of the cephalic capsule.

Cheilostom reinforced by twelve cuticularised rugae. Cephalic capsule elongated (height to width 22–25 µm to 25–31 µm), cylindrical with bluntly rounded lip region ( Fig. 2 B, 3B). Cephalic capsule composed of a thin-walled short anterior part separated by a suture from a thick-walled main part, ornamented with minute pores. A few minute pores with thin canals running through thickened capsule wall, only seen by light microscopy. Anterior border of thick-walled capsule portion anteriorly protruding, i.e. following the rounded outline of the amphideal fovea at 5–7 µm distance ( Fig. 2 B, 3B, 4B, E). An irregular circle of about eight cervical setae at or close to posterior end of the cephalic capsule.

Amphidial fovea dissimilar in size between sexes: spiral with 2.0–2.1 turns; in female diameter of fovea is 13– 14 µm, relatively large, in male it is 16–18 µm (60% of corresponding width of cephalic capsule), as seen by SEM ( Fig. 4 ).

Buccal cavity small, with one dorsal tooth, ventro-sublateral denticles not visible. Pharynx cylindrical, muscular, with small posterior bulb and plasmatic interruptions. Nerve ring not seen. Cardia and excretorysecretory system not observable. Tail conical with unstriated tip 6–10 µm long, with short setae.

Male . Reproductive system monorchic, anterior testis lying to the right of the intestine. Spicule long (2.3–2.9 c.b.d), slender and slightly arcuate, proximally expanded. Gubernaculum (18–20 µm), parallel to distal parts of the spicules, poorly developed. No precloacal supplements but a few pre- and postcloacal subventral setae present, 5–6 µm long.

Female. Reproductive system didelphic, amphidelphic with equally developed genital branches; ovaries reflexed, and both genital branches to right of the intestine. Vulva an oblique slit, posterior to mid-body, situated 623–805 µm from anterior end. Intra-uterine egg not seen. Postanal subventral setae present, 6–10 µm long.

Juveniles. Only 15 specimens of fourth juvenile stage stages were found. Body shape, body annuli, pattern of somatic setae similar to adults.

Relationships. Desmodorella tenuispiculum from the Sea of Japan is characterized by having a large spiral amphidial fovea with 2.0–2.1 turns, occupying main part of cephalic capsule; a relatively large number (16–18) of longitudinal rows of ridges covered by fine "spines" in the middle of the body and eight rows at the anterior and posterior body ends, and numerous small precloacal setae in males, sexual dimorphism in number of turns of amphid and size. Given the disparate mixture of minor differences between our specimens and those of other authors, we assume that they are all conspecific and correctly identified as D. tenuispiculum .

Recently examined specimens agree well with the original description of the specimen of Desmodorella tenuispiculum (Allgen, 1928) Verschelde, Gourbault & Vincx, 1998 from Campbell Island in general morphology, measurements, shape of body, ornamentation of cuticular annules with longitudinal rows of ridges, large rounded head capsule, large and multispiral amphideal fovea, pharynx with rounded or slightly lengthened terminal bulb, and form of spicules and gubernaculum. Unfortunately, the original description of this species is insufficiently illustrated to allow any further comparisons and does not show sufficient deviation to be assigned to a different species (Allgen 1928). Females were recorded later from the coast of the Falkland Islands, South Georgia, Graham Land ( Allgen 1959). Gerlach (1963) synonymized Desmodora cephalata Cobb, 1920 with D. tenuispiculum (Allgen, 1928) . Later, the subgenus Desmodorella of Desmodora was raised to the rank of genus ( Verschelde et al. 1998). Subsequent findings were recorded from North Carolina ( Chitwood 1936) , from sublittoral areas of the Galapagos Island ( Gerlach 1963), sublittoral sand of de la Perre Noire (West Channel) ( Boucher 1975); the Fuegian Archipelago and Northumberland coast, North East England ( Platt & Warwick 1988); the south-east coast of India from the Pichavarum mangroves ( Chinnadurai et al. 2006; Annapuma et al. 2012); and from the Canary Islands ( Riera et al. 2012). The record of Desmodorella tenuispiculum listed in Leduc & Wharton (2010) is based on the original description by Allgen from Campbell Island, which lies within the New Zealand Exclusive Economic Zone.

Some records were not confirmed by descriptions, e.g., the African coast of the Indian Ocean ( Raes et al. 2007); and the Maldivian Archipelago ( Semprucci & Balsamo 2014). Our identification is mainly based on the subsequent re-descriptions of D. teniuspiculum published by Gerlach (1963), Boucher (1975) and Platt & Warwick (1988).

Figures

FIGURE 2. Desmodorella tenuispiculum Allgen, 1928. Male: A. Entire body; B. Head; C. Tail region. p — pores. Scale bars: A— 150 µm, B— 15 µm, C— 100 µm.

FIGURE 3. Desmodorella tenuispiculum Allgen, 1928. Female: A. Entire body; B. Head; C. Tail region. Scale bars: A— 100 µm, B— 15 µm.

FIGURE 4. Desmodorella tenuispiculum Allgen, 1928. SEM. Male: A. Entire body; E. Head. С, D. Detail of cuticle after cephalic capsulae and in mid-region of body; G. Terminal part of the tail; F. Tail. Female: B. Head. Scale bars: A— 100 µm, B, C, E— 2 µm; D, F, G— 10 µm.

FIGURE 5. Zalonema kamchatkaensis sp. nov. Male: A. Entire body; B. Head; C. Tail region. D. Entire body. Female: E. Head. F. Posterior body region of female. Scale bars: A— 100 µm; B, C, E— 50 µm; D— 500 µm; F— 200 µm.