Magnetia, Hochberg & Cannon, 2003

Hochberg, Rick & Cannon, Lester R. G., 2003, Magnetia Queenslandica, A New Genus And New Species Of Typhloplanid Flatworm (Platyhelminthes: Rhabdocoela) From Magentic Island In North Queensland, Australia, Raffles Bulletin of Zoology 51 (1), pp. 1-6 : 2-3

Magnetia , new genus

Type species. – Magnetia queenslandica , new species, by present designation.

Diagnosis. – A marine typhloplanid worm with anatomy characteristic of the family Typhloplanidae . Body is bottleshaped. Anterior fan of adenal rhabdites bifurcates posteriorly into two sets of finger-like processes. Vertical

= 4 km.

pharynx rosulatus in posterior one-third of body. Male reproductive system consists of paired elongate testes at anterior tip of head and ventral to adenal rhabdites and vitellaria. Paired pea-shaped seminal vesicles in posterior third of body lead to sclerotic stylet. Female reproductive system consists of paired vitellaria with a solitary posterior ovary, seminal receptacle and copulatory bursa.

Etymology. – Generic name refers to Magnetic Island. Gender feminine.

Remarks. – Magnetia , new genus, bears strong resemblance in body shape and general anatomy to most members of the Typhloplanidae Graff, 1905 . The body is highly deformable and the head and neck regions often cycle through numerous extensions and retractions while the animal remains stationary. The extensive array of adenal rhabdites is similar to many species of the families Trigonostomidae and Typhloplanidae , with a fan-like anterior zone, thin middle zone, and branching posterior zone ( Figs. 2 , 3 ). The presence of eye-like rhabdite patches at the anterior end is however unknown from any other species. Histologically, each patch consisted of several eosinophilic spindle-shaped rhabdites. A membrane around the rhabdite patches was not observed. The caudal haptic region in Magnetia appears morphologically similar to the haptic girdles of kalyptorhynchs. However, the adhesive region of Magnetia is in the form of a patch rather than a belt-like girdle and the papillae are much smaller.

Concerning the reproductive system, the location of the testes and the structure of the copulatory stylet are unique. Only species of Anthopharyx Karling, 1940, Tensopharynx Ehlers, 1972 , and Trisaccopharynx Karling, 1940 (Solenopharyngidae) possess a similar anterior placement of the testes; however, the testes in Magnetia are much more anteriorly directed and elongate than in any other genus ( Figs. 2 , 3 ). The unusual boot-like shape of the stylet is also unique, especially with its thickened proximal walls and the teardrop shaped distal opening ( Figs. 6 , 7 ). The two groove-like lines present around the neck of the stylet are similar to the “knickstellen” on the stylets of species of Haloplanella Luther, 1946 (e.g., Ehlers & Sopott-Ehlers, 1989).

The new genus can be diagnosed by the structure of the reproductive system and the location of excretory pores. Cannon (1986) and Kolasa (1991) indicate that genera can be separated taxonomically (not necessarily with phylogenetic relevance) based on a dorsal or ventral position of the testes relative to the vitellaria. In Magnetia , the testes are located ventral to the adenal rhabdites and the vitellaria. The relative position of the testes is difficult to establish in wholemounts because the animals are often stretched out and the testes are anterior of the vitellaria. However, sections of contracted specimens showed a consistent overlap of the vitellaria on the distal end of the testes. In relaxed specimens, it seems likely that only the spermatic ducts will be ventral to the vitellaria. The location and branching pattern of protonephridial ducts was difficult to observe. In only a single specimen were protonephridial ducts found to open in the region of the mouth/pharynx. According to Cannon (1986), these characters indicate the new genus belongs to the subfamily Typhloplaninae Luther, 1963 .

Relationships within the Typhloplaninae remain unknown, but in-group relations may be tentatively classified according to the topology of general anatomical and reproductive characters. Accordingly, Magnetia might be closely related to Haloplanella Luther, 1946 . Shared features include prominent rhabdite tracts, pharynx in mid to posterior body region, testes anterior to pharynx, posterior pea-shaped seminal vesicles, short copulatory organ (relative to Pratoplana Ax, 1960 ) and strongly sclerotic stylet.

Figures

Fig. 2. Magnetia queenslandica, new genus, new species. A, light micrograph. B, frontal section. C, stained wholemount. fr, finger-like rhabdite branches; ph, pharynx; rh, rhabdites; rf, rhabdite fan; rt, rhabdite tract; te, testis. Scale bar = 125 m.

Fig. 3. Magnetia queenslandica, new genus, new species. Schematic illustration of general anatomy. ca, caudal adhesive region; bc, bursa copulatrix; ep, eye-like rhabdite patch; fr, fingerlike rhabdite branches; ov, ovary; ph, pharynx; rf, rhabdite fan; rt, rhabdite tract; sr, seminal receptacle; st, stylet; te, testis; vi, vitellaria; vs, vesicula seminalis. Scale bar = 125 m.

Fig. 6. Magnetia queenslandica, new genus, new species. Sclerotic stylet. A, lateral view. Arrows point to paired grooves on neck. B, ventral view. Scale bar = 20 m.

Fig. 7. Magnetia queenslandica, new genus, new species. Camera lucida drawings of sclerotic stylet. A, Holotype: QM G218757, dorsal view of stylet. B, Paratype: QMG218758, proximal end view of stylet. C, Paratype: QMG218759 “back” view of stylet. D, Paratype: QMG218760, distal end view of stylet. Scale bar = 20 m.