Nematoplana cyclops, Curini-Galletti & Oggiano & Casu, 2002

Curini-Galletti, M., Oggiano, G. & Casu, M., 2002, The genus Nematoplana Meixner, 1938 (Platyhelminthes: Unguiphora) in eastern Australia, Journal of Natural History 36 (9), pp. 1023-1046 : 1037-1039

Nematoplana cyclops n. sp.

(gures 6, 8G, I; table 2)

Material examined

HOLOTYPE: Australia, Queensland, Yeppoon , town beach, mid intertidal in very ne sand (July 1996), whole mount (lactophenol): G211827 . PARATYPE: same data as holotype, whole mount (lactophenol) (G211828).

Other material. Four specimens from the type locality studied karyologically, one of which was mature (July, 1996). Numerous juveniles observed alive.

Etymology Named after a mythological, similarly monocular, population.

Description

Animals minute, colourless. The holotype, the largest mature specimen found, is about 1.1 mm long. Anterior end elongate, provided with sensory bristles. With a single pigmented eye-spot, shaped as an inverted Y, located within the brain capsule. Distribution of pigment granules in the eye-spot is fairly variable (gure 6C).

The small, collar-shaped pharynx is located in the posterior third of the body.

Male genital organs. About 20 testes in one median line among vitellaria, in front of the pharynx. The copulatory organ consists of a single seminal vesicle, and a bulb provided distally with a stylet. The seminal vesicle enters the bulb at its proximal base. Sperm nuclei uncoiled. The bulb is spherical, about 35 Mm high in the holotype. The stylet is thin and diaphanous, irregularly brous in texture. It is shaped as a truncated cone. It is about 25 Mm high in the holotype (ranging from 18 to 27 Mm in the sample), with a proximal opening 16 Mm wide, and a distal opening 7 Mm wide. The proximal opening is markedly oblique. The distal opening is provided with a more strongly sclerotized rim, and with a distal spike. This spike is di cult to see in the whole mounts; it is about 4 Mm long in the karyological mount.

Female genital organs. With two ovaries, consisting of one mature oocyte each, laterally in front of the pharynx. Vitellaria stretch from behind the brain to the level of the female pore, which opens to the outside posterior to the male pore.

Karyotype. With n 55. Chromosomes diOEer slightly in length, the smallest is about three- fth of the largest. Chromosomes are meta- or submetacentric (gures 6B, 8I, table 2).

Discussion

Nematoplana cyclops is the smallest species in the genus. It is the only species with a single pigmented eye-spot—which appears clearly as the result of the fusion of the two eye-spots found in other Nematoplana species. Its diaphanous, truncated cone-shaped stylet, with a distal spike, is somewhat comparable only to that of N. martensi . It is however much smaller, comparatively shorter and broader, with a thickened, not denticulate, distal opening, and a largely oblique proximal opening.

The more or less straight, cylindrical to conical stylet, without apophysis, found in N. martensi , N. hamata , N. cyclops and N. pullolineata is a very rare feature for the genus Nematoplana , and for the Unguiphora as a whole (cf. Curini-Galletti and Martens, 1992). It may be assumed to be a synapomorphic feature for the above species. They share a further very rare character for the Unguiphora , i.e. the presence of a single seminal vesicle, known, among Nematoplana species , only for one additional species, N. naia Marcus, 1949 . The single-vesicle condition has been considered as a secondarily derived character status for the genus Nematoplana , resulting from the total fusion of the two partially fused vesicles found in the other species (Curini- Galletti and Martens, 1992). The presence in N. martensi , N. hamata , N. cyclops and N. pullolineata of two derived features strongly suggests that they constitute a monophyletic group within the genus Nematoplana . The position of N. naia , a Brazilian species with a tiny stylet, variously interpreted by diOEerent authors ( Marcus, 1949; Ax and Ax, 1974; Curini-Galletti and Martens, 1992), cannot be determined at present.

It should be noted that the derivation of the ‘single vesicle’ status, through a ‘two, partially fused, vesicles’ status stage (the autapomorphic feature for the genus Nematoplana ), might be debatable. In fact, there is no contrary evidence that the former might not have been attained directly from the plesiomorphic condition for the Unguiphora (i.e. two wholly unfused seminal vesicles). Therefore, the above species might not share the last ancestor common to the (rest of) Nematoplana species. A generic reassessment of the Nematoplanida e should however be postpone d until a more signi cant fraction of the world species is described and character distributions more extensively mapped.

Remarks

Albeit only three mature specimens were found, immatures— easily recognizable due to the single eye-spot—were abundant at Yeppoon, the single locality where the species has so far been found. The very ne sediment of the town beach, lacking any obvious silt-clay fraction, yielded a distinctive, similarly minuscule (and still undescribed) proseriate fauna—whose diminutive size seems clearly related to sediment texture.