Philactinoposthia brevis, Nilsson, Karin Sara, Wallberg, Andreas & Jondelius, Ulf, 2011

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 : 3

Philactinoposthia brevis sp.nov.

( Figs. 1 , 2 , 3 )

Type Material: Holotype: SMNH Type-8041. Paratype 1: SMNH Type-8042, Paratype 2: SMNH Type-8043.

Type Locality. Red Sea, Eilat (29° 30' 2" N, 34° 55' 36" E), at 15 m water depth in fine sand.

Other Material examined. Living specimens in squeeze preparations; 4 sets of 4-5 μm serial sagittal sections of paraffin-embedded specimens.

Etymology. Brevis = short, small in latin, and refers to the short body size, small bursal nozzle and small copulatory organ.

Description. Active swimmer. Living specimens up to 500 μm long and ~85 μm wide. Body shape cylindric, both ends rounded. Epidermis completely ciliated with cilia that are 4 μm long. Brown colored rhabdoid glands present, 10 μm long, sparsely scattered across body, absent in anterior end and almost completely lacking on ventral side ( Fig. 1 AE). Rhabdoid glands compact with oval shape in sections, separate rods not detectable. Epidermis uncolored in transmitted light. Statocyst, 8 μm in diameter, located 50 μm from anterior end, U10.

Frontal organ present, cell bodies of frontal organ extend from U0 to U20. Mouth ventral, located in middle of body. Digestive central syncytium with brownish coloration, extends from U20 to U80.

Ovary unpaired, one large oocyte, extends from level of mouth to bursal nozzle, U65 to U82 ( Fig. 1 BDE). Female gonopore ventral, positioned posteriorly at U84, opens to small globular seminal bursa with bursal nozzle that connects anteriorly, difficult to detect in live specimens ( Fig. 1 BD). Bursal nozzle ~30 μm long with a zigzaglike appearance.

Male gonopore ventral, positioned posteriorly at U90, opens immediately to small arrow-shaped male copulatory organ with sclerotized stylet needles surrounded by sperm. At least four needles detectable, short in relationship to body size, 30 μm long ( Fig. 1 B). Glands surrounds copulatory organ ( Fig. 1 D). False seminal vesicle located at proximal end of stylet-like structure. Sperm with granules ( Fig. 1 BC).

Figures

FIGURE 1. Philactinoposthia brevis sp. nov. Photomicrographs of living specimens A – C. A. Dorsal view of whole specimen. Scale bar: 60 µm B. Dorsal view of posterior part of body. Scale bar: 40 µm. C. Showing sperm. Scale bar: 15 µm. Photomicrographs of sagittal histological sections stained with hematoxylin-eosin D – E. D. Section through posterior part of body. Scale bar: 30 µm. E. Section through length of body. Scale bar: 100 µm.

FIGURE 2. Philactinoposthia brevis sp. nov. Reconstructions show arrangement of organs. A. Dorsal reconstruction of whole living animal. B. Sagittal reconstruction of the whole animal. Scale bar: 80 μm.

FIGURE 3. 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. P. b re v i s sp. nov., P. ischiae sp. nov. and P. novaecaledoniae sp. nov. are placed in a clade composed of Philactinoposthia species with maximum support.