Convoluta lacrimosa

Achatz, Johannes G., Hooge, Matthew D. & Tyler, Seth, 2007, Convolutidae (Acoela) from Belize, Zootaxa 1479, pp. 35-66 : 49-52

Convoluta lacrimosa nov. sp.

( Figs. 11–13 )

Diagnosis. Convoluta with ~60 µm long unciliated, muscular vagina. Seminal bursa filled with spongy tissue, bursal nozzle tissue contains numerous small vacuolated spaces. Both are walled by a mesenchymal layer and thin muscles. Bursal nozzle is straight, ~37 µm long, and directed rostrad. Penis is ~120 µm long, with outer longitudinal muscles, which are continuous with muscles of the penis sac, and inner circular muscles. Penis sac is 90 µm high, 75 µm wide, and 120 µm long when filled with sperm and glandular secretions. At its distal end it is filled with cells containing cyanophilic vesicles. Where penis terminates, basophilic vesicles with a diameter of ~3 µm are densely packed, lying freely within the vesicle. Units: st 20, m 43, fgp 64, mgp 82.

Type material. Holotype: USNM 1096741, one set of 1.5-µm-thick serial sagittal sections of epoxyembedded specimen stained with toluidine blue. Paratype: USNM 1096742, one set of 1.5-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue.

Other material examined. Living specimens in squeeze preparations, four sets of serial histological sections stained with toluidine blue, two sets of serial histological sections stained with Heidenhain’s hematoxylin, six whole mounts for fluorescence microscopy.

Collection locality. On algae in Grouper Gardens at Twin Cays, Belize (16°49’46.3” N, 88°06’10” W).

Etymology. The species name is derived from the Latin lacrimosus, meaning tearful, and refers to the distinctive teardrop-shaped body of the species.

Description. Mature animals are ~850 µm long, ~500 µm wide, and have slightly enfolded sides. The body is mostly without color except for brightly colored rhabdoid gland cells and zoochlorellae. A pair of eye fields, ~66 µm in width and ~40 µm in length, devoid of rhabdoids and algae, occurs at the anterior margin of the body, lateral to the statocyst. Two pairs of dorsal longitudinal nerve cords can be seen as translucent stripes ( Fig. 11 A).

The epidermis is ciliated entirely, with cilia ~6 µm long. The epidermal nuclei are sunken beneath the body-wall musculature.

A statocyst, 25 µm in diameter, lies ~100 µm behind the anterior tip.

Numerous green zoochlorellae are scattered throughout the parenchyma. Mucous gland cells and rhabdoid gland cells, which contain 20–80 red rhabdoids each, are scattered over the entire surface ( Fig. 11 A). Frontal gland cells, which occur in the anterior 200 µm of the body, protrude through a frontal pore at the anterior tip.

The nervous system consists of a pair of ganglia lateral to the statocyst, two dorsal pairs and one ventrolateral pair of nerve cords. Two brown eyespots lie medial to the eye fields and lateral and slightly anterior to the statocyst.

The mouth lies 500 µm behind the anterior tip ( Fig. 12 A). The digestive syncytium extends from behind the statocyst to the seminal vesicle and sometimes contains crustaceans.

The paired testes originate behind the statocyst and mature toward the seminal vesicle. Sperm form false seminal vesicles in front of the seminal vesicle and pass the penis sac through ventro-lateral openings ( Figs. 11 B, 13A).

The paired ovaries are positioned ventrally, medial to the testes.

The female gonopore is positioned 120 µm in front of the male gonopore. The vagina is ~60 µm long and surrounded by circular muscles ( Figs. 12 B, 13B). Mesenchymal tissue and thin muscles wall the seminal bursa and the bursal nozzle tissue ( Figs. 13 A, B). The cavity of the seminal bursa is filled with spongy tissue, and the bursal nozzle tissue contains numerous small vacuolated spaces, both also visible in live observation ( Figs. 11 B, 12A, B, C). The bursal nozzle is straight, ~37 µm long, and directed rostrad ( Figs. 11 B, 12A).

The male gonopore is positioned ~100 µm in front the posterior end. The penis is ~120 µm long, inserted into a penis sac, and its lumen is lined with an epithelium that contains very small vesicles ( Fig. 12 B). The penis musculature consists of outer longitudinal muscles, which are continuous with muscles of the penis sac, and inner circular muscles ( Fig. 13 C). The penis sac is 90 µm high, 75 µm wide, and 120 µm long when filled with sperm and glandular secretions ( Figs. 11 B, 12A, B, 13A). At its distal end it is filled with cells containing cyanophilic vesicles, which dissolved during processing for embedment. The nuclei of these cells lie outside the seminal vesicle or at its wall. In the center of the distal part, where the penis terminates, basophilic vesicles with a diameter of ~3 µm are densely packed, lying freely within the vesicle. The nuclei of the gland cells producing these basophilic vesicles lie within the parenchyma outside the penis sac ( Figs. 11 B, C, 12B).

Remarks. Most species within the genus Convoluta possess a weakly lined vagina and seminal bursa. Exceptions to this are found in Convoluta boyeri Bush, 1984 , which has a sphincter between vagina and seminal bursa, and in C. lacrimosa and C. pygopora Antonius, 1968 , in which the vagina, the seminal bursa, and the bursal nozzle tissue are surrounded by musculature — circular muscles in the case of C. lacrimosa , and a fine meshwork of muscle fibers in C. pygopora . Convoluta lacrimosa also differs from other known Convoluta species in having spongy tissue that fills the cavity of the seminal bursa and the numerous, small, vacuolated spaces in the bursal nozzle tissue. The bubbly mucus-like material Bush (1984) describes as lining the vagina and seminal bursa of Convoluta boyeri seems to be distinctly different from this spongy tissue in C. lacrimosa .

In all of the known species of Convoluta , the male copulatory organ is associated with gland cells, and their arrangement and type of secretion may be useful as systematic characters. Convoluta lacrimosa , C. thela ( Antonius, 1968) , and C. krana ( Antonius, 1968) have male copulatory organs that are associated with similar gland cells that fill the distal part of the penis sac, and other gland cells that release vesicles into the lumen of the penis sac ( Achatz & Hooge 2006). Unfortunately, our knowledge of these gland cells and their glandular secretions are poorly known in the other described species of Convoluta , in part because the histological methods used often failed to reveal these characters.

Figures

FIGURE 11. Convoluta lacrimosa sp. nov.; photomicrographs of living specimen. A. Dorsal view of whole specimen. Arrowhead points to eye fields, arrows point to nerve cords. B. View of male and female copulatory organs. C. Detail of B. Arrow points gland cell, arrowhead to large vesicle.

FIGURE 12. Convoluta lacrimosa sp. nov.; photomicrographs of sagittal histological sections stained with toluidine blue. A. Section through length of body. B. Section through male copulatory organ. Black arrows point to distal parts of gland cells inside penis sac, black arrowheads to proximal parts outside penis sac, white arrow points to vesicles in the penis epithelium. C. Section through bursal nozzle tissue.

FIGURE 13. Convoluta lacrimosa sp. nov.; whole mounts stained with Alexa- 488 - labeled phalloidin and viewed with confocal microscopy. A. Projection of male and female copulatory organs. Arrow points to vagina, arrowheads point to openings for sperm in penis sac. B. Projection of female copulatory organ. C. Projection of the distal ends of penis and penis sac where they meet body-wall muscles. Arrow points to circular penis muscle, arrowhead to longitudinal penis muscle.