Laxus undetermined

Armenteros, Maickel, Ruiz-Abierno, Alexei & Decraemer, Wilfrida, 2014, Taxonomy of Stilbonematinae (Nematoda: Desmodoridae): description of two new and three known species and phylogenetic relationships within the family, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 171 (1), pp. 1-21 : 7-9

LAXUS PARVUM SP. NOV.

Measurements: Table 2; Figures 3 , 4 .

Type material: Holotype male, deposited at the Center for Marine Collections, National Aquarium (Habana, Cuba) with collection number ANC_04.063 . Paratypes: Two male paratypes, collection numbers CN_1533.10 and CN _1541.7, one female paratype CN _1552.9 and two paratype juveniles CN_1541.3 and CN _1541.9 deposited in the Nematode Collection at Centro de Investigaciones Marinas, Universidad de La Habana (Habana, Cuba). Four deposited at the Royal Belgian Institute of Natural Science (Brussels, Belgium): collection numbers RIT 816 (two females) and RIT 817 (one juvenile and one male) .

Habitat type: Coralline sand in the reef lagoon, ∼ 2 m depth, Punta Francés coral reef (21°36′29.68′′N, 83°10′34.40′′W).

Etymology: The specific epithet (i.e. parvum ) is the neuter Latin word for ‘small’ and refers to the small body size of the species compared with most of the other stilbonematins.

Description: Body habitus filiform and coiled, largest body diameter at neck region. Cuticle largely covered by a thin film of mucus, with faint fine striation (annuli ∼0.2 μm width), surrounding the anterior part of the amphidial fovea; under SEM, lip region appears smooth. Head capsule with thickened cuticle with a marked median layer. Six inner labial sensilla and six outer labial sensilla setiform papillae. Four cephalic sensilla setiform (8–12 μm long) at level of anterior border of fovea and very close to outer labial papillae. Four short subcephalic setae (<3 μm long) located very close to the cephalic setae. Another four short sublateral setae (<3 μm long), each pair located just Holotype measurements are included in the male averages and ranges.

c′, tail length relative to the anal body diameter; c.b.d., corresponding body diameter; J, juveniles; N, number of specimens; V %, distance (relative to body length) of vulva to anterior apex.

All measurements are in μm.

at the posterior border of the amphidial fovea. Eight longitudinal rows of short somatic setae (1–2 μm long), connected to conspicuous epidermal glands, and extending from the head to tail; setae slightly longer in tail region. Amphidial fovea spirally coiled in 1.5 turns, located laterally, subterminally on the head, approximately 0.4 c.b.d. of relative size. Buccal cavity minute, no sclerotized structures. Pharynx muscular, relatively short, corpus hardly swollen, posterior bulb almost round, lumen not sclerotized, cardia shape rounded and inconspicuous; nerve ring approximately around mid-pharynx. Ventral gland not observed. Tail conical and relatively short, tip smooth, with swollen spinneret having two apertures for the caudal glands. Coccoid bacteria attached to the cuticle and also in the intestine lumen; the arrangement patterns on the cuticle could not be ascertained.

Male monorchic, anterior testis to the left of the intestine. Spicules paired and curved, with marked capitulum; gubernaculum broad and curved with apophysis directly dorsally, no precloacal supplements.

Female didelphic, ovaries antidromously reflexed, both genital branches to the left of intestine. Vulva approximately in the mid-body.

Diagnosis: The new species is characterized by a body length less than 4 mm, pharynx corpus rather slender, spicule relatively long [> 1.8 anal body diameter (a.b.d.)] and strongly cephalated, gubernaculum broad and curved, tail length of female equal or larger than 2 a.b.d., ectosymbiotic bacteria coccoid-shape.

Differential diagnosis and relationships: Laxus parvum sp. nov. belongs to the genus Laxus based on the particular structure of the head capsule constituted by a block-layer located on the basal layer of the cuticle, the amphidial fovea spirally coiled in 1.5 turns and located laterally close to the apex, the relatively short conical tail, the spicule capitulum cephalated, and the characteristic somatic setae protruding from the body surface giving a thorny aspect.

Within Laxus , currently two species group can be differentiated based on body length: (1) a group with a body length of less than 4 mm consisting of two species ( Laxus gerlachi and La. sigma ) and the new species, and (2), a group of four species with a body that is at least twice as long as those in group (1) ( La. cobbi , La. cosmopolitus , La. longus , and La. oneistus ). As far as we know, the shorter species possess coccoid bacteria, whereas for two of the longer species rod-shaped bacteria have been described. Within the short-bodied species, La. parvum can be differentiated from the other two species by having long spicules strongly cephalated and the presence of a thick gubernaculum with dorsally slightly curved apophyses.

Figures

Figure 3. Laxus parvum sp. nov. holotype ♂. A, habitus; B, anterior region; C, testis and epidermal glands; D, tail region and copulatory apparatus.

Figure 4. Laxus parvum sp. nov. A, habitus (posterior region), specimen 1♂; B, head (lateral-frontal view), specimen 2 (indeterminate sex); C, head (lateral-frontal view), specimen 3♂; D, mid-body, specimen 3♂; E, tail region, specimen 3♂; F, tail region, specimen 4 (indeterminate sex).