Picola renei Achatz & Hooge 2006

Achatz, Johannes G., 2008, Convolutidae (Acoela) from the Andaman Sea, Zootaxa 1824, pp. 1-16 : 14-15

Picola renei Achatz & Hooge 2006 ( Fig. 10 )

Material. PMBC 24800 and PMBC 24801, two complete sets of serial sagittal sections of mature specimens, and living specimens in squeeze preparations.

Collection locality. In fine-grained sediment between corals at the entrance of Makham Bay (Port of Phuket; 7°48’42.5” N, 98°24’22.9” E) and in front of the PMBC (7°48’9.4” N, 98°24’27.9” E).

Description. Mature animals are egg-shaped, 300–400 µm long and up to 190 µm wide ( Fig. 11 A).

A statocyst measuring ~16 µm in diameter is present ~30 µm behind the anterior tip ( Figs. 11 A, E).

Numerous yellow-brown zooxanthellae are scattered throughout the parenchyma ( Figs. 11 A, B, C, D, E). A few rhabdoid gland cells containing refractive, needle-shaped rhabdoids are distributed on the dorsal side. The frontal organ fills the anterior third of the animal, and in front of the statocyst a large reservoir is formed.

The mouth is positioned in the anterior half of the body and opens to an indistinct digestive syncytium, which often contains diatoms.

The diffuse testes are paired, lying dorsolateral to the ovary, and originate in an unpaired germative zone behind the statocyst. Droplet-shaped spermatids enter the seminal vesicle on its dorsoventral side.

The unpaired ovary lies ventral to the testes. Female gonopore and vagina are both absent. The welldeveloped seminal bursa has a distinct wall and a bursal nozzle that is ~16 µm long and directed anteroventrally ( Figs. 11 B, C).

The male gonopore lies in a subterminal indentation of the body wall. The male copulatory organ consists of a seminal vesicle and a glandular bladder, which contains a ~15 µm long, sclerotized penial structure ( Fig. 11 D).

Remarks. The copulatory organs clearly place this species in the genus Picola , and the diffuse gonads, the droplet-shaped sperm filling the seminal vesicle, and the absence of large vacuoles within the parenchyma show the conspecificity with the type species of the genus, Picola renei Achatz & Hooge, 2006 . However, I could detect a small difference between the animals in Tanzania and Phuket Island. The bursal nozzle of all investigated specimens were straight in contrast to the animals in Tanzania, which have a bulge at the proximal end of the bursal nozzle (in Picola caribbea Achatz et al., 2007 the bulge is at the distal end of the bursal nozzle). I refrain from taking this difference as a species-specific character but interpret it as an indicator for a distinct population.

The occurrence of Picola renei in Tanzania and Thailand suggests a distribution at least throughout the whole northern Indian Ocean.

Figures

FIGURE 10. Convoluta schuelii sp. nov.; whole mounts stained with Alexa- 488 - labeled phalloidin and viewed with confocal microscopy. A. Projection of dorsal body-wall musculature. B. Projection of ventral body-wall musculature. C. Projection of male copulatory organ. Arrowheads point to the pair of thicker longitudinal muscles; asterisk marks the male gonopore.

FIGURE 11. Picola renei; photomicrographs of living specimen. A. Dorsal view of whole specimen. B. Dorsal view of posterior end. C. Dorsal view of female copulatory organ. Inset: bursal nozzle. D. Dorsal view of male copulatory organ. E. Dorsal view of statocyst and frontal organ. Inset: cluster of refractile granules. Arrow points to distal end of frontal gland cells, arrowheads to clusters of refractive granules double-arrowhead to penis-like structure.