Nematoplana ezoplanoides, 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 : 1039-1041

Nematoplana ezoplanoides sp. nov.

(gures 7, 8E, L; table 2)

Material examined

HOLOTYPE: Australia, Queensland, Mackay, Shoal Point , lower intertidal in coarse sand (July 1996), whole mount: (lactophenol): G211829 . PARATYPES: same data as holotype, three specimens sagittally sectioned (G211830 –2) .

Other material. Four specimens from the type locality studied karyologically (July 1996).

Etymology The species is named after the super cially similar genus Ezoplana Tajika, 1982 .

Description

A medium-sized Nematoplana : the holotype is an adult worm, about 4.3 mm long in xed condition, without pigment or pigmented eye-spots. Anterior end elongate, provided laterally and terminally with sensory bristles. Epithelium with non-depressed (intra-epithelial) nuclei, and entirely ciliated. Cilia about 4 Mm long. Brain ovoidal, surrounded by a thin membrane.

Mature specimens had two collar-shaped pharynges, lying close together. The posterior pharynx was larger, weaker and degenerating in most specimens. The anterior pharynx was smaller, and in most specimens clearly still in stages of formation. Juveniles had only one pharynx. Pharynges are located in the posterior seventh of the body.

Male genital organs. Few testes irregularly arranged among vitellaria in front of the pharynx. The copulatory organ consists of two partly fused seminal vesicles, and a bulb provided distally with a stylet. The two seminal vesicles enter the bulb at its proximal base. Anteriorly, they are lined with a thin epithelium, surrounded by a thick layer of circular muscles. The muscular coating ends abruptly after about 60 Mm in the holotype. Posteriorly, the vesicles become much narrower, and they fuse caudally into one common vesicle, lined with a thin epithelium. Spermiducts enter the seminal vesicles anteriorly. The nuclei of spermatozoa are elongate, and spirally coiled. The bulb is ovoid (about 45 Mm high in the holotype). It is lined with a thick coating of circular musculature, and provided with numerous prostatic glands. The stylet is a funnel-shaped, intracellular, sclerotized structure, with a broad, oblique, ventral proximal opening and a narrow distal opening. The stylet is 37 Mm high in the holotype (measuring 40 and 41 Mm in the two semi-squashed karyological mounts). The base is about 21 Mm high in the holotype, with a maximum width of about 11 Mm. A at apophysis (about 15 Mm long) is present. It is almost of constant width along all of its length. A thick bundle of longitudinal muscles is connected proximally to the circular muscle sheath surrounding the bulb, and distally to the apophysis. The distal part of the stylet above the apophysis narrows abruptly into a nearly straight tube, about 12 Mm long. It is provided distally with a straight distal tip, orthogonal to the main axis of the stylet, and ending in a spike about 8 Mm long. The dorsal side of the stylet is thickened, particularly above the apophysis. The distal part of the stylet protrudes into a narrow male antrum, apparently unciliated. The antrum opens to the outside through a male pore, which is located close to the mouth.

Female genital organs. With two, large, isolated oocytes medially in front of the pharynx. Vitellaria stretch from behind the brain to in front of the ovaries. The oviducts fuse at the level of the copulatory bulb into a common female duct, which opens to the outside through a female pore, surrounded by female glands.

Karyotype. With n 53. Chromosomes diOEer only slightly in size. Chroms 1 and 2 are metacentric; Chrom. 3 is submetacentric, at the lower border of the class (gures 7C, 8L, table 2).

Discussion

Among the Unguiphora , the presence of two pharynges over at least part of the life cycle is among the de ning features of the genus Ezoplana (Tajika, 1982) . However, the position of the new pharynx diOEers: in front of the ovaries and much more anterior than the old one in Ezoplana ; posterior to the ovaries and close to the old one in N. ezoplanoides . Furthermore, the new species has none of the other diagnostic features of the genus Ezoplana (i.e. presence of one pair of seminal receptacles in front of the (posterior) pharynx; stylet characteristically base-less, consisting only of an apophysis and a tubular, elongate, angled distal part) (Tajika, 1982, 1988). On the contrary, it presents the diagnostic feature of the genus Nematoplana , i.e. the partial, posterior fusion of the seminal vesicles, and is hence considered as such. There are reports of pharynx degeneration during or after sexual maturity in other species of the genus Nematoplana and in Tabaota curiosa Marcus, 1950 ( Marcus, 1950; Sopott, 1973; Ax and Ax, 1974; Ehlers and Ehlers, 1980; personal observation), but simultaneous formation of a new pharynx has never been observed. A life cycle which includes degeneration and reconstitution of the pharynx, may however be more widespread in the Unguiphora than hitherto hypothesized, and possibly linked to the long life span (in some cases partly biennial) of (at least some of) its representatives ( Sopott, 1973; Ax, 1977). In any case, the presence of both pharynges (in various stages of development/degeneration) in adult stages of the new species, is unique in the genus, and allows immediate recognition. Furthermore, its chromosome number (n 53) is peculiar to the new species, and the lowest known among the Unguiphora . The stylets of N. ezoplanoides and N. cannoni are somewhat similar in size and general shape. However, in N. cannoni the base is slimmer, and the peculiarly angled apophysis is inserted at 45ss with the main axis, while it is ap-like, and orthogonal to the main axis in the new species. Furthermore, the two species are immediately recognizable by the lack of pigmented eye-spots in the new species. The stylet of N. ezoplanoides is similar in size and shape to that of N. nigrocapitula , which however is pigmented, and is provided with eye-spots, cnidosacs, cephalic gut and chorda intestinalis.

Nematoplana ezoplanoides , N. cannoni and N. rubra share a unique feature for the genus Nematoplana , i.e. the presence of only two oocytes, arranged medially in a single row. However, at least in N. rubra , this seems to be a transitory stage, with the plesiomorphic condition occurring in part of the life cycle. The poor knowledge of life cycles of extra-boreal unguiphorids and the limitation of sampled specimens per species do not allow inferences on the signi cance of this feature. Therefore, on a cautionary basis, it has not been used for taxonomic purposes. It should also be mentioned that no obvious synapomorphy appears shared by any of the three species above.