Caligocanna mirabilis Bussau et Vopel, 1999

Miljutin, Dmitry M. & Miljutina, Maria A., 2009, Deep-sea nematodes of the family Microlaimidae from the Clarion-Clipperton Fracture Zone (North-Eastern Tropic Pacific), with the descriptions of three new species *, Zootaxa 2096 (1), pp. 137-172 : 145-150

Caligocanna mirabilis Bussau et Vopel, 1999

( Figs 5–8 , Table 3)

Material examined: 5 males and 2 females ( Table 3).

Locality: Tables 1, 3.

Measurements: Table 3.

Description of male: Body cylindrical, with slightly narrowed anterior end and conical tail. Cuticle annulated along whole body except at anteriormost cephalic capsule. Cephalic capsule short, its length less than its width. Cuticular annuli strongly pronounced, each approximately 1.7 µm in width, with very close and fine longitudinal bars. There are distinctly bordered deep furrows between annuli. Cuticle thickness approximately 0.7 µm at level of cephalic capsule and approximately 1 µm at rest body. Cuticle thickness being equal both under annuli and under furrows between annuli. Somatic setae not found. Sensilla of cephalic end arranged in 3 rings spaced from each other: 6 very short papilloid inner labial sensilla approximately 0.3 µm long at level of cephalic tip, 6 outer labial setae approximately 1.3 µm at level of middle of cephalic capsula, and 4 submedian cephalic setae approximately 0.5 µm long near posterior border of cephalic capsule. Amphid monospiral, round, 58–70% c.b.d. in diameter. Anterior half of amphid situated on cephalic capsule, whereas posterior one lying at annulated zone of body under the cuticle. Small pore visible behind amphid. Vestibulum possessing 12 slight ribs. Cuticular walls of pharyngeal internal lumen of stegostoma looking thicker than in other, more posteror part of pharynx. Length of whole stoma approximately 4 µm. Two long dorsal teeth and two short ventral teeth visible in anterior part of stegostoma. Pharynx cylindrical but having a terminal oval bulb 68–85% of c.b.d. in width. Thin radial plasmatic interruptions visible in bulb. Anterior part of pharynx bearing stoma bordered from posterior part by plasmatic interruptions. Nerve ring at a middle of pharynx. Cardia cylindrical, approximately 1/3 of c.b.d. in width. Both testes lying ventrally from intestine. Two zones of spermatogenesis visible in anterior testes: small roundish spermatogonia with fine-graned content, large oval spermatogonia with fibrillar content. Largest spermatogonium 10 x 40 µm in size. A single large intracellular structure resembling long meandering coniferous branch with needles visible in each of mostly matured spermatogonia. Vas deferens thick, approximately 1/3 of total body length, filled with puck-shaped spermatids approximately 6 µm in diameter with large-grained content. Spicules strongly curved, thick, with complex proximal knob and velum. There is also longitudinal rib at distal half of spicule. Gubernaculum in shape of a curved, thin rod. Supplementary organs not found. Length of whole reproductive system occupying about a half of total body length. Tail conical. Tail of all examined specimens being S-shaped.

Female: Females very similar to males in most parameters, except their pharyngeal bulbus being smaller relative to c.b.d. (50–67%). Reproductive system short, didelphic, amphidelphic, with outstretched ovaries. Anterior ovary lying to the right of intestine, posterior one lying to the left of intestine. There are no morphologically distinct borders between ovaries, oviducts and uterus. Whole reproductive system occupying approximately 30% of total body length. Size of mature oocyte 16x38 µm. Spermatozoa not found. Vulvar glands present. Both females possessing shelters consisting of some mucus covered with small inorganic particles.

Abundance: The density of this species was 0.6–1.6 inds/ 10cm 2 and relative abundance within nematode community was 1–2% at the stations where it was found.

Remarks: C. mirabilis was initially described by Bussau and Vopel (1999) from the abyssal eastern tropical South Pacific ( Peru Basin), which is located about 5200 km from the area we report them from. The specimens from the new area resemble those described by Bussau and Vopel (1999) very well. There are several insignificant distinctions only. The maximum body length of new specimens is slightly more than in specimens of type series (483 µm vs. 450 µm respectively); body is thinner (a=17.5–24.3 vs. 12.6–18.0), tail is shorter (c=6.5–7.9 vs. 5.1–6.4). The ring of labial papillae was not described in the original description, whereas this ring, consisting of 6 papilloid sensilla, was found in new specimens. Several somatic setae were found in type specimens, whereas they were not visible in new individuals. However, such distinctions are insufficient for assigning new species and may be explained by intraspecific variation and by difference in methods of treatment (new specimens were preserved in alcohol, whereas type specimens were kept in formaldehyde).

The characteristic number of teeth in the stegostoma is three for the genus Microlaimus . However, four teeth were found in the buccal cavity of C. mirabilis both in the Bussau’s and Vopel’s (1999) original description and in the present work. So, the presence of four teeth cannot be considered an error. It may be due to a secondary division of the initially single dorsal tooth.

Intracellular structures resembling long winding non-ramifying coniferous branch with needles visible in each of mostly matured spermatids are probably major sperm proteins (MSP). This unique cytoskeleton was found only in nematodes and only in male germ cells ( Justine 2002).

Figures

FIGURE 5. Caligocanna mirabilis, males. A, specimen No. 1, head; B, specimen No. 1, anterior end; C, specimen No. 1, total view; D, specimen No. 3, copulatory apparatus. Scale bars: A, B = 20 µm; C = 100 µm; D = 10 µm.

FIGURE 6. Caligocanna mirabilis, female, specimen No. 7, a total view. Scale bar = 50 µm.

FIGURE 7. Caligocanna mirabilis, males, light micrographs. A, specimen No. 1, head; B, specimen No. 1, region pharyngeal bulb; C, specimen No. 1, spermatogonia; D, specimen No. 1, anal region, optical section at level of gubernaculum (marked by arrow); E, specimen No. 1, longitudinal striation of cuticular annuli; F, specimen No. 3, anal region, optical section at level of distal part of spicule. Scale bars: A, B, D, F = 10 µm; C = 20 µm; E = 5 µm.

FIGURE 8. Caligocanna mirabilis, light micrograph. Female (specimen No. 6) in the tube of fine-grained ground particles attached to the grain of sand (the latter is marked with arrow). Scale bar = 100 µm.