Tetranchyroderma oligopentacrum, Hummon, William D. & Todaro, Antonio, 2009

Hummon, William D. & Todaro, Antonio, 2009, Italian marine Gastrotricha: VI. Seven new species of Macrodasyida, Zootaxa 2278, pp. 47-68 : 64-66

Tetranchyroderma oligopentacrum new species [Tet olpn]

Figure 7 A–E

Tetranchyroderma sp. II (Evans, Todaro & Hummon 1993: Tab. I)

Tetranchyroderma sp. W ( Todaro, Hummon, Balsamo, Fregni & Tongiorgi 2001: p. 128); ( Hummon 2001 – 2009: W Med Database)

Diagnosis: Adult Lt 550 Μm; PhJIn at U23. Head end rounded, without tentacles or sensorial knobs; trunk broadest in the midgut region, narrowing to the caudal base; caudal pedicles short, with a concave medial border indenting to U97. Epidermis partially covered with small pentancres that occur as epaulets or lateral stripes, sometimes with rump patches. Glands small, 50–60 per side, with a cluster of a dozen in the rump region. TbA 5 per side, form a shallow transverse arc, tubes inserting directly on the body, the most medial separated from the 4 more lateral by a small gap; TbL 25 per side, 1 in the fore pharyngeal region, the others regularly spaced and of similar size occur along the intestine at U25 to the anus, with 2 inserting behind the anus; TbD/TbV absent; TbP 3 per side on the caudal pedicles, forming the fused ‘two fingers and a thumb’ typical of the family, with 3 more tubes in the interpeduncular space (total 5), but lacking any element inserting between the ‘fingers’ Locomotor ciliature: a single field covers the ventral body surface. Mouth subterminal, as broad as the fore end of the body, oral hood reaches to U05; buccal cavity non-cuticularized; pharynx has basal pharyngeal pores; intestine narrows front to rear; anus at U93. Testis is on left as seen from below; vas deferens opens into the rear of the small caudal organ that lies in front of the anus; developing eggs (3, plus 2 germinal vesicles) occur in the reargut region; small frontal organ is spherical, hyaline, and contains mobile sperm.

Description: Adult Lt 550 Μm; LPh 129 Μm to PhJIn at U23 ( Fig. 7 A, B). Body long and thin as an adult, ventrally flattened, dorsally vaulted; head end rounded, without tentacles or sensorial knobs; trunk narrows in the PhJIn region, broadens gradually to the midgut region, then narrows to the caudal base; caudal pedicles short (L 19 Μm) naked, with a concave margin separating the two groups, indenting medially to U97. Widths at mouth/PhJIn/midgut/caudal base and locations along the length of the body are as follows: 45/36/54/40 Μm at U08/U23/U63/U97, respectively. Glands 50–60 per side (4–8 Μm diam.) are scattered along the sides in lateral and dorsal columns, with a cluster of 10–12 lying just before the caudal base.

Cuticular Armature: Small pentancres, show variable coverage, including most, some or none of the dorsal and lateral epidermis; ancres ( Fig. 7 E; width and height 2–3 Μm) are rather constant in size from one location to another. They may occur as epaulets ( Fig. 7 A) of 0, 2, 7, or 25 ancres, or they may occur as stripes down the sides of the body ( Fig. 7 C), with perhaps small to larger patches in the neck and/or rump region, or they may occur as interrupted patches ( Fig. 7 D) down the sides and across the rump.

Adhesive tubes: TbA 5 per side (L 6–10 Μm), forming a shallow transverse arc, the tubes inserting directly on the postoral body surface at U05-U06, the most medial pointing forward, and after a small separation the 4 more lateral pointing obliquely forward; TbL 25 per side (L 8–12 Μm), with 1 in the fore pharyngeal region at U10, none in the hind pharyngeal region, 22 regularly spaced in the intestinal region between U25 and the anus at U93, and 2 inserting behind the anus; TbD/TbV are absent; TbP 3 per side on the caudal pedicles, forming the fused ‘two fingers and a thumb’ typical of the family, (L terminal tubes 8 Μm, L tube on the inner margin also 8 Μm), with 3 additional tubes in the interpedicular space for a total of 5, but lacking any element inserting between the ‘fingers’.

Ciliation: Short sensory cilia (L 4–7 Μm) surround the entire oral opening, with longer vibratile cilia (L 16–19 Μm) on each side of the oral hood; other hairs (L 18–20 Μm) occur regularly along the lateral, dorsolateral and dorsal body surfaces, numbering 16–18 per side. Ventral locomotor ciliature forms a single field of transverse rows beneath the body, extending from U07 to the anus at U94; individual cilia are 10–12 Μm in length.

Digestive tract: Mouth subterminal, as broad as the fore end of the body, width 42 Μm, the oral hood extending from its tip 26 µm to U05; non-cuticularized buccal cavity narrows quickly; pharynx has basal pharyngeal pores at U22; intestine is broadest in the mid-body, narrowing gradually to the rear; anus is at U93.

Reproductive tract: Testis is on the left side as seen from below; vas deferens opens into the rear of the ovoid caudal organ (14 x 23 Μm) that lies in front of the anus; developing eggs (3, plus 2 germinal vesicles) are in the mid-gut on the opposite side (largest 21 x 50 Μm); frontal organ is a hyaline sphere (11 Μm diam.), containing mobile sperm.

Ecology: Occasional in frequency of occurrence (10–30% of samples), rare in abundance (less than 1% of a sample); littoral in very fine, well to medium sorted, sand at 0-10 cm depth MLW-MLWS; sublittoral in very fine to fine, well to medium-well sorted sand at 1.0–2.0 m water depth.

Geographical distribution: MED: EUROPE: ITALY: Campania {Lido di Fusaro [video]}; Friuli Venezia Giulia {Grado [video], Foce dell’Isonzo [video]}; Liguria {Diano Marina ^ 43°,54'N/08°,05'E [2-videos], San Remo [video]; Puglia {Siponto}; Toscana {Tombolo di Feniglia, Mortelliccio}; Ve ne t o {Bibione [video]}.

Remarks: The study is based on 10 specimens, 7 of which were captured on video. The description follows (WDH video #1543, Fig. 7 A, B, a holotype, ICZN Article 73.1.1). Two other videos, designated as paratypes (ICZN Article 72.4.5), include WDH #1544, a subadult from Lido Fusaro: Lt c. 300 Μm; LPh c. 130 Μm, with TbA 3 per side, TbL 7 per side, and TbP 3 per side; and WDH #1541, a juvenile from Diano Marina: Lt 167 Μm; LPh 70 Μm, with TbA 2 per side, TbL 5 per side, and TbP 3 per side. Tetranchyroderma oligopentacrum n. sp. represents one of six scantily clad members of the genus, its pentancrous covering being incomplete and even more variable than usual for such species. It is the eidostic pattern of morphology and the presence of pentancrous specimens collected from the same location that allowed us to assign the specimen with no ancres to this species. Juvenile: (#1541 Fig. 7 D) Lt=167 Μm; L to PhJIn =83 Μm at U49; TbA 2 per side, TbL 5 per side, TbP 3 per side.

Etymology: The species is named for the few (Greek: oligos) pentancres (Greek: pente, Greek: ankyra), present on the body.

Taxonomic affinities: Tetranchyroderma oligopentacrum n. sp. is among six species that are scantily clad with ancres. Of these, 3 species are tetrancrous, 2 of which have been described, and with T. oligopentacrum there are now 3 species that are pentancrous. T. oligopentacrum is longer and thinner than the others, and alone has 0 TbL in the rear pharyngeal region, and when ancres occur in stripes has lateral but no medial elements. T. hypopsilancrum Hummon, Todaro & Tongiorgi, 1993 (p. 122, Fig. 13) is closest in overall body shape and morphology, despite having tetrancres. In fact, the first T. oligopentacrum that we saw, one with epaulets from Mortelliccio, we thought was T. hypopsilancrum , except that it had pentancres rather than tetrancres. Note that only these two species thus far have been found to have epaulets, with T. oligopentacrum often having fewer ancres per epaulet than T. hypopsilancrum . Subsequently, we have had to assess the type of ancres that are present in an individual as part of the identification process. This of course raises the question of the relationship and importance of tine numbers in ancres as taxonomic characters.

Figures

FIGURE 7. Tetranchyroderma oligopentacrum n. sp. A—dorsal, B—ventral views of an adult (Lt = 550 µm, LPh = 148 µm), from Diano Marina, Italy, dorsal with glands and the cuticular armature shown as epaulets of 0, 2, 7 and 25 pentancres in the pharyngeal region, ventral with digestive and reproductive tracts, adhesive tubes and the ventral locomotor ciliary band. C—dorsal view showing a more complete covering of pentancres on both sides, D—dorsal and ventral views of a juvenile (Lt = 167 µm, LPh = 70 µm), from Diano Marina, Italy, and E—a pentancre with a separate scalebar.