taxonID	type	description	language	source
B178CF60FFDF6A4EFF14FB34FC0FFD66.taxon	materials_examined	Type Material. Holotype: AMNH _ IZC 00386160, one set of 1.5 - µ m-thick serial sagittal sections of epoxy-embedded specimens stained with toluidine blue, collected on June 14, 1998. Paratypes: AMNH _ IZC 00386161, one set of 1.5 - µ m-thick serial sagittal sections of epoxy-embedded specimens stained with toluidine blue; and AMNH _ IZC 00386162, epoxy-embedded whole mount, both collected in September 2004. Type Locality. Crow Neck, Cobscook Bay, Maine, U. S. A. (44 ◦ 52 ’ 35 ” N, 67 ◦ 07 ’ 36 ” W). Medium to coarsegrained sand, often with detritus, from the upper subtidal (almost intertidal). Other Material Examined. Numerous living specimens in squeeze preparations; 5 sets of 2 - or 1.5 - µ m-thick serial sections of epoxy-embedded specimens; 6 whole mounts for fluorescence imaging of musculature. Etymology. The species name is the Latin transliteration of the Greek (Kallaion) for a rooster’s comb, and refers to the red color and crenulated body margins of the species. Synonyms. Myopea “ callaeum ”: Hooge (2001), Hooge et al. (2002), Todt (2009); Myopea sp.: Todt & Tyler (2006), Jondelius et al. (2011), Atherton & Jondelius (2021), Atherton & Jondelius (2022), Nilsson (2011), Kånneby & Jondelius (2013). Description. Mature specimens up to 1500 µ m long and ~ 260 µ m wide (Fig. 1 A.) Anterior and posterior ends rounded and lateral body margins of posterior half crenulated. Body color mostly red in both transmitted and reflected light (from pigment dissolved in tissue fluids). With lateral chordoid tissue (Fig. 1 A), which is especially prominent in starved animals. Epidermis completely ciliated, composed of insunk mucoid epithelial cells that stain metachromatically with toluidine blue. Without prominent rhabdoid or mucoid glands. Frontal organ opens as small pit at frontal pore, its glands moderately developed, reaching posteriorly approximately one-quarter the length of the body, to shortly behind pharynx (to U 26; Figs. 1 A, 2 A, 3 A). Body-wall musculature a simple grid of outer circular and inner longitudinal muscle fibers (Fig. 2 B) as described by Hooge (2001). Mouth opening oval and positioned subterminally at U 10 – U 20, thus close to anterior tip of the body (Fig. 2, 3 A). Frontal mouth area (a shallow groove in the epidermis) extends anteriad from the mouth to anterior tip of the body. Pharynx extending ~ 300 µ m posteriorly from mouth, with ciliated epithelium and musculature like that of body wall — i. e., with longitudinal muscles immediately under the epimyum (that part of epidermis superficial to musculature; Crezée 1975) and circular muscle fibers deep (abluminal) to them as described by Todt & Tyler (2006) and Todt (2009). Strong sphincter fibers around the mouth, but no prominent posterior sphincter at the juncture between pharynx and digestive syncytium (Fig. 2 B). Clusters of long-necked unicellular pharyngeal glands bearing acidophilous secretory granules lie lateral to the pharynx, their cell bodies situated along the posterior end of the pharynx and their gland necks opening into its distal quarter to half. At its juncture with the digestive syncytium, the pharynx is wrapped in a conspicuous thick layer of cells containing numerous lipid droplets. Testis unpaired, dorsal, compact; positioned posterior to pharynx and anterior to male copulatory organ (U 20 – U 30; Fig. 1 A, 3 A). Tracts of sperm reach to the anterior end of the seminal vesicle without forming a false seminal vesicle. Ovary unpaired, dorsal; germinal area behind copulatory organ and reaching posteriorly to U 75 – U 80 (Figs. 1 A, C; 3 A). Common gonopore on ventral surface in anterior half of body (U 44). It opens to a short ciliated common antrum which connects it to an elongate (100 µ m by 58 µ m), thick-walled (8 µ m), muscular seminal vesicle (Fig. 1 C, 3). The penis, at the distal, ventroposteriorly directed end of the seminal vesicle is muscular and fully invaginated into the seminal vesicle. Its center is lined by globose secretory cells with finely granular contents that stain orthochromatically with toluidine blue and that appear prominently in squeeze preparations of live specimens (Fig. 1 B). At the posterior edge of the gonopore and antrum is an indistinct seminal bursa composed of diffuse, fibrous tissue (Fig. 1 C, 3). No sperm were seen within seminal bursa. Remarks. In having a muscular penis invaginated into the seminal vesicle and a relatively short and cupshaped pharynx with a wreath of glands emptying into its distal portion, Myopea callaeum sp. nov. fits clearly into the genus Myopea. It stands distinct from the other two described species of Myopea — M. crassula Crezée, 1975, and M. latafaucium Crezée, 1975, both from North Carolina, U. S. A. — in its red coloration, its prominently glandular (and less muscular) penis, and its elongate, thick-walled seminal vesicle. It is more similar to M. crassula in possessing a diffuse seminal bursa; a bursa is not present in M. latafaucium. The quite short ciliated antrum in M. callaeum sp. nov. stands in contrast to the much longer ciliated antrum of M. crassula and more resembles the short ciliated portion of the otherwise longer antrum of M. latafaucium. M. callaeum sp. nov. is more like M. crassula in having its mature oocytes extending no farther posteriorly than the first two-thirds to three-quarters of the body length, while they reach to the posterior tip of the body in M. latafaucium.	en	Hooge, Matthew D., Todt, Christiane, Tyler, Seth (2025): New solenofilomorphids (Solenofilomorphidae: Acoela) from the northwest Atlantic. Zootaxa 5686 (1): 121-131, DOI: 10.11646/zootaxa.5686.1.5, URL: https://doi.org/10.11646/zootaxa.5686.1.5
B178CF60FFDA6A4DFF14F926FAECF818.taxon	materials_examined	Type Material. Holotype: AMNH _ IZC 00386163, one set of 1.5 - µ m-thick serial sagittal sections of epoxy-embedded specimens stained with toluidine blue, collected on February 28, 1999. Paratypes: AMNH _ IZC 00386164, one set of 2 - µ m-thick serial sagittal sections of epoxy-embedded specimens stained with toluidine blue; and AMNH _ IZC 00386165, epoxy-embedded whole mount, both collected in February 2005 from Bakeman Beach, Cape Rosier, Maine, U. S. A. (44 ◦ 18 ’ 39 ” N, 68 ◦ 48 ’ 11 ” W). Type Locality. Wadsworth Cove, Castine, Maine, U. S. A. (44 ◦ 24 ’ 13 ” N, 68 ◦ 48 ’ 33 ” W). Fine-grained shallow subtidal sediment. Other Material Examined. Numerous living specimens in squeeze preparations; 9 sets of 2 - µ m-thick serial sections of epoxy-embedded specimens; 8 whole mounts for fluorescence imaging of musculature. Etymology. Species named for Michael Crezée, in gratitude for his friendship during the writing of his seminal monograph on the Solenofilomorphidae and in celebration of the 50 th aniversary of that monograph. Synonyms. Solenofilomorpha “ crezeei ”: Hooge (2001), Todt (2009); Solenofilomorpha sp. 2: Todt & Tyler (2006), Jondelius et al. (2011), Atherton & Jondelius (2021), Atherton & Jondelius (2022), Nilsson (2011), Kånneby & Jondelius (2013). Description. Mature specimens ~ 1.4 mm long and 75 − 220 µ m wide (Figs. 4 A, 5 A – D) but up to 2.2 mm in length when fully stretched. Body cylindrical, with anterior and posterior ends rounded. Anterior quarter of body slightly narrower than rest; posterior quarter of body with crenulated margins and usually held slightly curled as the animal glides over substrate (Fig. 5 B). Epidermis completely ciliated; without prominent mucoid or rhabdoid glands. Body translucent; almost colorless in reflected light and light brown in transmitted light. Eggs and gut contents dark brown to olive, often with large transparent vacuoles in digestive tissue. Body-wall musculature a simple grid of outer circular and inner longitudinal muscle fibers as described by Hooge (2001). Frontal glands well developed, reaching beyond the posterior end of the pharynx (to U 32). Strand-like mucoid parenchymal glands throughout the body stain a more intensive, darker shade of pink than frontal glands. Mouth opening slit-like on the ventral surface in anterior half of body (U 24, Figs. 4 A, 5 E). Mouth without strong sphincter muscles, opens to long (U 24 – U 32), tubular, muscular pharynx composed of a ciliated, insunk, glandular epithelium subtended by longitudinal and deeper (abluminal) circular muscle fibers as described by Todt & Tyler (2006) and Todt (2009). A well-developed, prominent, funnel-like sphincter delimits the proximal end of the pharynx. Testis unpaired, compact; extending from a level posterior to the pharynx to the male copulatory organ (U 32 – U 58; Figs. 4 A, B). Ovary unpaired, dorsal; extending from frontal glands posteriorly to bursa (U 37 – U 63; Fig. 4). Common gonopore on ventral surface shortly behind middle of body (U 63); opens to a long ciliated, tubular antrum (Fig. 4 A, B, 5 A, 6 A, B). Anteriorly, the antrum opens directly to the male copulatory organ (at U 60) conspicuous in squeeze preparations of live animals where the seminal vesicle forms a dark cap on the proximal end of the penis (Fig. 5 A). Copulatory organ comprises a muscular penis capped by a squat sclerotized cone (Figs. 5 F, 6 B) and a seminal vesicle filled with sperm (Figs. 4 A, 5 F, 6). The proximal end of the antrum is richly glandular, its long-necked glands filling much of the volume around the copulatory organ. Seminal vesicle, penis, and the proximal glandular part of the antrum are surrounded by a thick common muscular sheath, mostly of thin, somewhat disorganized circular fibers (Fig. 6). The seminal vesicle itself is spherical, 50 µ m in diameter, with a thick muscular wall composed of strong longitudinal fibers extending from the antrum and with thinner, less-well-organized circular fibers (Figs. 4 B, 5 F, 6 A, B). The penis is slightly longer than broad (~ 25 µ m × ~ 20 µ m) and consists of stacked crescent-shaped muscle-bound chambers; the sclerotized cone capping its distal end stems from actin-reinforced cell processes originating from globular cells surrounding it just outside the muscular sheath where that meets the antrum (Figs. 4 B, 6). The penis cone is only weakly refractile, not as prominent in brightfield or even phase-contrast microscopy as sclerotized bursal nozzles of other acoels, for example, and it appears simpler, less well-organized, than those nozzles. The seminal bursa (at U 63 – U 69), which connects to the antrum on its posterior side, appears syncytial, without a clear lumen, and contains loosely packed allosperm (Figs. 4 B, 5 F). Remarks. In its habitus — that is, elongate, cylindrical body with rounded ends and narrow rostrum, crenulated posterior, and elongate pharynx — Solenofilomorpha crezeei sp. nov. looks like other species of Solenofilomorpha. More specifically, its elongate mouth, tubular pharynx with glandular epithelium but lacking pharyngeal glands and having a narrow opening to the digestive syncytium, and its seminal vesicle without invaginations, all fall in line with the diagnosis of the genus. The genus Solenofilomorpha presently contains five species: S. funilis Crezée, 1975, from North Carolina, U. S. A.; S. guaymensis, Crezée, 1975, from Sonora, Mexico; S. longissima Dörjes, 1968, from Helgoland Island, Germany; S. justinei Nilsson, Wallberg, & Jondelius, 2011, from New Caledonia; and S. pellucida Kånneby & Jondelius, 2013, from Las Cruces, Chile.	en	Hooge, Matthew D., Todt, Christiane, Tyler, Seth (2025): New solenofilomorphids (Solenofilomorphidae: Acoela) from the northwest Atlantic. Zootaxa 5686 (1): 121-131, DOI: 10.11646/zootaxa.5686.1.5, URL: https://doi.org/10.11646/zootaxa.5686.1.5
B178CF60FFDA6A4DFF14F926FAECF818.taxon	description	A bursa comparable to that of S. crezeei sp. nov. is present in S. funilis and S. guayensis but absent from the other three species. In the three species with a bursa, it connects to the antrum rather proximally, just distal to what could be called a penis. That of S. funilis is more like that of S. crezeei sp. nov. in having a well-defined wall.	en	Hooge, Matthew D., Todt, Christiane, Tyler, Seth (2025): New solenofilomorphids (Solenofilomorphidae: Acoela) from the northwest Atlantic. Zootaxa 5686 (1): 121-131, DOI: 10.11646/zootaxa.5686.1.5, URL: https://doi.org/10.11646/zootaxa.5686.1.5
