Pharyngia furva

Nilsson, Karin Sara, Wallberg, Andreas & Jondelius, Ulf, 2011, New species of Acoela from the Mediterranean, the Red Sea, and the South Pacific, Zootaxa 2867, pp. 1-31 : 22

Pharyngia furva gen. et sp.nov.

( Figs. 19 , 20 , 21 , 22 )

Type Material: Holotype: SMNH Type-8044. Paratype 1: SMNH Type-8045.

Type Locality. Eilat, (29° 30' 27" N, 34° 56' 16" E), animals occurred at 20–25 m water depth in fine sand.

Other Material examined. Living specimens in squeeze preparations.

Etymology. Species name refers to the dark brown appearance of body, furva = dark-colored in latin.

Description. Living specimens up to 2000 μm long and 500 μm wide (1/5). Body extremely fragile, therefore no anesthetization was used before fixation in Bouin. Specimens fixed for histological sectioning contracted. Body shape cylindrical, anterior end rounded, posterior part tapering ( Fig. 19 A). Epidermis uncolored and completely ciliated with 5 μm long cilia. The margins of body are clear, the rest of body with dark brown coloration. Statocyst located 280 μm from anterior end, at U12. Frontal organ present, cell bodies located at level of statocyst, extending from U10 to U20. Mouth opening on ventral surface in anterior end, slightly anterior to statocyst, at U10. Mouth opens to ciliated tube-shaped pharynx, extending from U10 to U22 ( Fig. 20 AB). In live specimens pharynx is difficult to see due to dark coloration of body. Digestive central syncytium diffuse.

Ovary unpaired, ventral, with up to 4 oocytes, extending from the posterior end of pharynx to middle of body, U58 to U30. In live specimens oocytes are dark brown and highly visible ( Fig. 19 AB). Seminal bursa or any other female accessory organs absent in all collected specimens.

Testes paired, lateral to ovary, compact, extend from posterior of pharynx to male copulatory organ, U28 to U60. Male gonopore positioned posterior to mid-ventral oocyte, at U65, and opens to 60 μm long well-developed ciliated antrum followed by the male copulatory organ consisting of 15 μm long penis-papilla weakly stained by eosin ( Figs. 19 B, 20AC).

Penis invaginated into muscular seminal vesicle, about 40 μm in diameter, with well developed wall. Copulatory organ 55 μm long and 48 μm wide in total.

Remarks In the Bayesian analysis Pharyngia furva gen. et n.sp. is the first branch in a clade composed of all included Isodiametridae and some species currently classified in Actinoposthiidae and Haploposthiidae Westblad, 1948 ( Fig 22 ). Hence, classifying it in one of the currently recognized genera would render that genus non-monophyletic. This species is therefore classified in the new genus Pharyngia within Isodiametridae on the basis of the male copulatory organ which has a penis invaginated into a muscular seminal vesicle.

Diagnosis. Pharyngia gen. nov. Isodiametridae with a pharynx but without copulatory bursa or any other secondary female organs.

There are only two previously known species in the family Isodiametridae that have a pharynx, Isodiametra helgolandica ( Dörjes, 1968) and Praeaphanostoma longum Dörjes, 1968 . However, in Isodiametra Hooge & Tyler, 2005 there is a seminal bursa with a bursal nozzle and in Praeaphanostoma Dörjes 1968 there is a tubular copulatory organ and a seminal bursa. Faerlea glomerata Westblad, 1945 has a similar copulatory organ to the one in P. f u r v a, but the penis is tubular instead of a small penis-papilla, the male antrum is much shorter, the animal is unpigmented and translucent and there is no pharynx.

P. f u r v a can appear similar to Hallangia proporoides Westblad, 1946 , however P. f u r v a has a copulatory organ with penis-papilla, a long ciliated male antrum and the coloration of body is dark brown, while H. proporoides has a tube formed penis, a short male antrum and white to yellow coloration. Moreover, H. proporoides has a seminal bursa and the anterior end is somewhat pointed. Sequences of H. proporoides are included in the phylogenetic analysis and are more closely related to Hofstenia ( Fig. 26 ).

Figures

FIGURE 19. Pharyngia furva sp. nov. Photomicrographs of living specimens. A. Dorsal view of whole specimen. Scale bar: 320 μm. B. View of mid-body showing male copulatory organ. Scale bar: 100 μm.

FIGURE 20. Pharyngia furva sp. nov. Photomicrographs of sagittal histological sections stained with hematoxylin-eosin. A. Section through length of body. Scale bar: 50 μm. C. Section through posterior. Scale bar: 20 μm.

FIGURE 21. Pharyngia furva sp. nov. Reconstructions show arrangement of organs. A. Dorsal reconstruction of whole living animal. B. Sagittal reconstruction of the whole animal. Scale bar: 300 μm.

FIGURE 22. Detail from the majority rule consensus tree summarizing the result of the Bayesian analysis of the combined 18 S rDNA, 28 S rDNA and COI dataset with the GTR + G substitution model after 10 million generations sampled every 1000 generations after a burnin of 5 million generations. Pharyngia furva gen. et n. sp. is the first branch in a clade composed of all included Isodiametridae and some species currently classified in Actinoposthiidae and Haploposthiidae.

FIGURE 26. Detail from the majority rule consensus tree summarizing the result of the Bayesian analysis of the combined 18 S rDNA, 28 S rDNA and COI dataset with the GTR + G substitution model after 10 million generations sampled every 1000 generations after a burnin of 5 million generations. Solenofilomorpha justinei n. sp groups with other Solenofilomorphidae species with maximum support, although there is low support for relationships within the clade.