Halichaetonotus sanctaeluciae, Todaro, M. Antonio, Zotto, Matteo Dal, Bownes, Sarah J. & Perissinotto, Renzo, 2011

Todaro, M. Antonio, Zotto, Matteo Dal, Bownes, Sarah J. & Perissinotto, Renzo, 2011, First records of Gastrotricha from South Africa, with description of a new species of Halichaetonotus (Chaetonotida, Chaetonotidae), ZooKeys 142, pp. 1-13 : 3-7

Halichaetonotus sanctaeluciae sp. n. Figs 23

Type locality.

South Africa, KwaZulu-Natal, St. Lucia beach (28°23'S; 32°25'E); among medium, moderately siliceous grains on a high-energy sandy beach at mid-tide level.

Type specimens.

Holotype, the 146.5 μm long adult specimen shown in Figure 3.

Material examined.

Four specimens, two adults (including the holotype) plus one subadult collected on 22 February 2010 (NAF Miranda legit) and 1 adult collected on 7 October 2010 (SJ Bownes legit)

Diagnosis.

Medium-sized Halichaetonotus (LT to 146.6 μm), head, neck and trunk well defined; head rounded, lacking hypostomion but with a small cephalion; medium-long furca projecting from the posterior of the trunk. Body enveloped by 15 columns (7 dorsal, 2 lateral + 2 ventrolateral hydrofoil scales, 2+2 ventral small scales) of alternating keeled scales each with 17-19 scales. Scales, round on head and neck becoming oval to semi-elliptical on the trunk; in general, keel extending beyond the edge of the scales as short spiny processes; on three posterior scales, one median and two lateral, keels forming long and robust spines extending beyond end of trunk. Two small spiny scales on dorsal and several keeled scales on ventral base of furca. Laterally and ventrolaterally, 2+2 columns of hydrofoil scales of varying length; ventrally, 2+2 additional columns of smaller scales; locomotory cilia arranged in two longitudinal bands, interciliary ventral field naked except for two pairs of perianal ovoid keeled/spiny scales. Almost circular mouth opening into cylindrical pharynx with 2 teeth, then sack-like intestine and terminal ventral anus. All specimens parthenogenetic, sometimes with single large egg in position dorsal to mid intestine.

Etymology.

The specific name alludes to the geographic locality where the new species has been found.

Description.

The description is mainly based on an adult specimen, 146.5 μm in total length. Head rounded, slightly elongated along anterior/posterior axis, bearing a shallow cephalion but no pleural lobes or visible hypostomion; neck narrower than head, trunk sac-like, terminating in a furcate caudum. Body widths at the head/neck/trunk/caudum are 31/22.5/34.5/22 μm, at U11/27/58/81, respectively. Caudum of medium length (26.6 μm), paired laterally divergent adhesive tubes (20 μm in length) with a slightly swollen base (6.5 μm), covered by scales.

Cuticular armature. Head, neck, and trunk covered dorsally and lateroventrally by alternating columns (7 dorsal, 1+1 lateral and 1+1 ventrolateral hydrofoil, 2+2 ventral) of 17-19 keeled scales, barely overlapping. On dorsal side, head and neck scales are round (3-5 μm in diameter), while trunk scales are oval to semi-elliptical (9.5 × 5.5 - 12.7 × 6.6 μm). In general, keel on dorsal scales extends beyond the edge of scales as short spiny process; however, on two lateral and one median trunk scales, at U63 and U71, respectively, keels form robust, very long spines projecting 26 μm beyond scales. On posterior trunk region are two oval, double keeled scales (5 × 4 μm) each anchoring a sensorial bristle at U79.5 and a couple of oval spiny scales (4 × 3.5 μm) bearing spines (4-5 μm long) protruding into the furcal indentation. Lateral and ventrolateral spines of hydrofoil scales bearing flattened lamellae, most of which taper into a long hairy process; lamellae bearing spines of the lateral scales are longer than related ventrolateral ones (up to 25 vs up to 19), while lamellae of a column are longest at mid trunk. On ventral side, up to five keeled scales, 3-4 μm long, cover the fleshy portion of each furcal branch; the interciliary field appears naked except for two pairs of oval keeled scales in the perianal region; scales of anterior pair are larger (9.5 × 4.5 μm) than posterior ones (6.0 × 3.5 μm).

Ventral ciliation. paired longitudinal bands extending from U03 to approximately U77; each broadly club-shaped anteriorly, but narrowing considerably from the posterior pharyngeal region; bands approach each other immediately behind the mouth, but remain separate throughout their entire length; individual cilia are about 11 μm in length.

Digestive tract:Mouth of medium size (ca.6 μm in diameter), projecting very slightly ventrally and leading progressively into a 32 μm long pharynx; pharynx muscular, roughly cylindrical (8 μm in diameter), showing a bulb anteriorly (12 μm in diameter); two cuticular teeth are visible within the bulb; pharynx connected to sack-like intestine at pharyngeo-intestinal junction at U25; intestine straight, narrowing posteriorly, anus ventral at U77.

Reproductive tract. Three specimens were in parthenogenic phase, two of which with a large egg filling much of the trunk.

Taxonomic affinities.

Highly variable cuticular armature distinguishes the 30 species of Halichaetonotus described so far ( Hummon and Todaro 2010, Hummon 2010). The new species most closely resembles Halichaetonotus marivagus , Balsamo, Todaro & Tongiorgi, 1992, and Halichaetonotus australis Nichols & Todaro, 2005, in that all three species are characterised by three dorsal spines close to the posterior end of the trunk. Spines are longest in Halichaetonotus australis (up to 46 µm), intermediate in Halichaetonotus sanctaeluciae sp. n. (up to 26 µm) and shortest in Halichaetonotus marivagus (up to 15 µm).

Halichaetonotus marivagus known from the Mediterranean, can easily be distinguished from the new species also on the basis of its wide hypostomion, which is absent in Halichaetonotus sanctaeluciae sp. n., and for exhibiting a large cephalion that covers much of the dorsal side of its head ( Balsamo et al. 1992).

Halichaetonotus australis described from the east coast of Australia, is unique in that the large median dorsal spine precedes the lateral ones (the opposite is true for Halichaetonotus sanctaeluciae sp. n.). Moreover, the keel of the dorsal scales does not extend beyond the edge of the scales ( Nicholas and Todaro 2005), whereas in Halichaetonotus santaeluciae sp. n. keels form a spiny process.

The new species also resembles Halichaetonotus aculifer (Gerlach, 1953) in terms of size and, most importantly, the shape of the hydrofoil scales. However, the presence of three long spines on the posterior trunk and the absence of ventral interciliary field scales in Halichaetonotus sanctaeluciae sp. n. are features that can easily differentiate this species from Halichaetonotus aculifer (see Gerlach 1953).