Haplogonaria phyllospadicis, Hooge, Matthew D. & Tyler, Seth, 2003

Hooge, Matthew D. & Tyler, Seth, 2003, Two new acoels (Acoela, Platyhelminthes) from the central coast of California, Zootaxa 131, pp. 1-14 : 2-6

Haplogonaria phyllospadicis sp. nov. ( Figs. 1­4)

Type Material. Holotype ( AMNH PLATY 1636): set of 1.5­µm­thick serial sagittal sections of epoxy­embedded specimen stained with toluidine blue, collected May 2002. Paratype ( AMNH PLATY 1638): set of 2­µm­thick serial sections of epoxy­embedded specimen stained with toluidine blue.

Type Repository. American Museum of Natural History, New York, New York, USA.

Type Locality. East side of Bodega Head, Bodega Bay, California, USA (38° 18' 12'' N, 123° 03' 10'' W). Fine­grained sediment underlying either surf grass, Phyllospadix sp., or filamentous algae in the low intertidal.

Material. Living specimens in squeeze preparations; five sets of serial sections of epoxy­embedded specimens stained with toluidine blue; whole mounts for fluorescence imaging of musculature (eight specimens).

Etymology. Species name refers to the habitat from which we collected the type material, that is, from sediment underlying the surf grass, Phyllospadix .

Description. Mature specimens approximately 450 µm long and 100 µm wide ( Figs. 1, 2 A, 3). Body cylindrical. Anterior and posterior ends rounded.

Epidermis completely ciliated. Rhabdoids appear in distinct rows in live animals; in sectioned material rhabdoids are uncommon and scattered. Gland cells with spherical secretions scattered; mostly concentrated on ventral side ( Fig. 1 B).

Musculature with circular muscles that encircle the body along entire length of animal, but are inclined at caudal tip (as previously described for Convoluta pulchra , see Ladurner and Rieger 2000); straight longitudinal muscles present between frontal organ and anterior edge of mouth; longitudinal muscles with a longitudinal orientation anteriorly that bend medially to cross diagonally over the body (longitudinal­cross­over fibers) present in both dorsal and ventral body wall ( Fig. 3 ).

Frontal organ well developed; cell bodies of frontal glands positioned ~130 µm behind frontal pore ( Fig. 1 B).

Mouth opening on ventral surface, middle of body. Digestive central syncytium extends from frontal glands posteriorly to level of male copulatory apparatus.

Ovary unpaired, ventral; extend from anterior half of body posteriorly to seminal bursa ( Fig. 1 B).

Testes paired, dorsal, compact; separate from ovary. Testes extend anteriorly to frontal glands and extend posteriorly to level of male copulatory organ.

Female gonopore opens to unciliated vagina with a thick wall ringed by spaced sphincter muscles ( Figs. 1, 2 , 4 ). Distal end of vagina with small granules. Bursa wall appears present in living specimens, but indistinct in sectioned material.

Male gonopore situated close to female gonopore, leads to sperm­filled seminal vesicle ( Figs. 1, 2 , 4 ). Wall of seminal vesicle composed of widely spaced muscle fibers and large nuclei ( Figs. 1 C, 2B). Invaginated penis absent.

Remarks. Haplogonaria phyllospadicis is similar to other members of the genus in having an unpaired ovary, paired testes, and a seminal bursa that lacks a bursal nozzle; however, unlike other known species of Haplogonaria , H. phyllospadicis has separate male and female gonopores. Despite being a seemingly overly plastic character for diagnostics, gonopore number is often used in distinguishing acoel genera (e.g., Convoluta versus Conaperta ). In this case, we feel the difference in gonopore number is not significant enough to separate our species from species of Haplogonaria , so we now emend the diagnosis of the genus to include both gonopore conditions.

Figures

FIGURE 2. Haplogonaria phyllospadicis sp. nov. Photomicrographs of sectioned specimens. A. Sagittal section through middle of body. B. Sagittal section of posterior region of body. cop, male copulatory apparatus; e, egg; fg, frontal gland; fgp, female gonopore; m, mouth; mgp, male gonopore; sb, seminal bursa; sv, seminal vesicle.

FIGURE 3. Whole­mount of Haplogonaria phyllospadicis sp. nov. stained with Alexa­ 488 ­ labeled phalloidin and viewed with confocal microscopy. Left side, projection of dorsal body­wall musculature; right side, projection of ventral body­wall musculature. For explanation of muscle patterns see Hooge (2001).

FIGURE 4. Whole­mount of Haplogonaria phyllospadicis sp. nov. stained with Alexa­ 488 ­ labeled phalloidin and viewed with confocal microscopy. A. Musculature of posterior of body, viewed from ventral side. B. Musculature of posterior of body, viewed from lateral side. cop, male copulatory apparatus; fgp, female gonopore; mgp, male gonopore; sph, sphincter.