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Acanthodasys paurocactus Atherton & Hochberg 2012

Description

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The description is based on specimens measured in vivo; most specimens were dorsoventrally curled (see Fig. 1B). Body strap-shaped and 300–450 µm long (subadults ~ 300 µm long, most specimens 350–400 µm long) (Fig. 1). Terminal mouth 30–35 µm wide; body width increasing slightly to 43 µm at PIJ and to 67 µm in adults with developing ova. The trunk gradually tapers and leads to a pair of distinct caudal pedicles (Fig 1. inset). The entire body is covered with scales and spined scales except for the hood-like region around the mouth (Fig 1, 4). Epidermal glands to 13 µm diameter, up to 15–20 per side (Figs. 1A, 2). Cuticlular armature.Scales and spined scales present (Figs. 1A, 2–4). Scales often appear as interwoven fibers in brightfield optics, but DIC reveals numerous scales in between the spined scales (uniancres); several scales with various raised structures at their center (es, Fig. 3A). At high magnification with DIC (1000X) and SEM (> 1000X), at least two types of scales are observed: elongate, lanceolate-shaped scales (ls) and shorter, eye-shaped scales (es, Figs. 3, 4B); scales of intermediate size and shape are also present (Fig. 4B). All scales have a slightly thickened rim and central depression that extends along the longitudinal axis of the scale (Figs. 3B, 4B). Scales are arranged in several different orientations (longitudinal, transverse, oblique) across the dorsal and lateral body walls (Fig. 4C). SEM reveals that several scales, both lanceolate and eye shaped, have either a raised, oval bump at the center of the depression (white arrow, Fig. 3B) or a raised, bar-shaped ridge that is parallel (es, Fig. 3A) or perpendicular (white arrow, Fig. 3B) to the long axis of the scale. Lanceolate scales measure to 7 µm long and eye-shaped scales to 4 µm long with a maximum width to 1.5 µm. Spined scales bearing uniancres are interspersed among spineless scales (Fig. 3A–C). Uniancres with a cross-shaped (cruciform) sectional profile (asterisk, Fig. 3B) arise from the center of thick-rimmed scales that also have a somewhat quadrangular shape (Figs. 3B, 4B). Dorsal and lateral uniancres close to the oral hood are 3–5 µm long and increase in length along the trunk and reach a maximum of 15 µm long. Several small uniancres (2–3 µm) extend onto the caudal pedicles. Uniancres are mostly straight and oriented perpendicular to the body surface or in a slightly posterior direction; some uniancres had a bent tip that might have been the result of dehydration during preparation for SEM. Openings to the epidermal glands were surrounded by a raised cuticular ridge. Ventrolaterally, the uniancres decrease in size to 4 µm long where they border the locomotory cilia (Fig. 3C). Several very small uniancres, 1–3 µm long, are scattered among the cilia on the ventral body wall (Fig. 3C). Several tiny (1–2 µm) and slightly larger (2–4 µm) uniancres are present in between the ciliary columns in the trunk region. Cilia.Sensory cilia to 10 µm long extend across the oral hood and form a thin corona around the head (Figs. 1A, 2A). A thicker patch of sensory cilia on either side of the head extends to 15 µm length. Smaller cilia 5–8 µm long line the mouth rim on the ventral body wall. At least ten stiff, hair-like cilia to 12 µm long extend down the length of the body on either side. Sensory cilia were observed to project out between the scales under SEM (Fig. 3B). Ventral locomotory cilia cover most of the pharyngeal region, extending from approximately U05 to the PIJ (Figs. 3C, 4A). At the PIJ, the cilia continues as a series of continuous rows to the posterior end but with a narrow column of naked cuticle (and uniancres) in between (Fig. 3C). Adhesive tubes.Five pairs of anterior adhesive tubes (TbA) up to 5 µm long are present at the mouth margin: one either side of the midline is a close-set pair of tubes that is present medially and three tubes that form a group that is oriented diagnonally and closer to the lateral margin of the body (Fig. 4). Four pairs of TbL are present in the trunk region. Each tube is 21–25 µm long and robust in appearance. One specimen showed tubes at U45, U54, U70 and U80; three specimens were curled and difficult to measure. One specimen only had two TbL at positions U68 and U79. Up to twenty ventrolateral adhesive tubes (TbVl) to 12 µm long are inserted posterior to the PIJ. Most TbVl appear evenly spaced down the trunk; five TbVl become slightly more lateral in position and are clustered anterior to the caudal pedicles. The pedicles reach a maximum of 16 µm long including the posterior adhesive tubes (TbP) and bear a total of four TbP each: one lateral (6 µm), two terminal (4–5 µm), and one medial (4 µm) (Fig. 1 inset). Digestive tract.Mouth terminal and circular to 35 um wide (Figs. 1B, 2B), surrounded by naked cuticle that forms a dorsal oral hood with a 12 µm rim (Fig. 2A, B); the naked cuticle around the ventral rim of the mouth is only 6 µm wide (hd, Figs. 2C). Pharynx to 136 µm long and 22 µm wide. Pharyngeal pores near base of pharynx (~ U34), not observable in all specimens. Intestine narrow and tapering at posterior; anus not observed. Reproductive system.Hermaphroditic, with paired, bilateral testes beginning at the PIJ around U36 (Fig. 4A). Vasa deferentia extend posteriorly but could not be followed beyond mid-trunk region. Caudal organ observed in one specimen (body length: 400 µm), and pear-shaped, but the animal was too damaged for measurements. Rosette organ to 28 µm in diameter at U43–U46 in largest specimen (Fig. 4A). Paired ova were observed on either side of the posterior intestine in one specimem, with one large egg dorsal to intestine at approximately U65.
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Sarah Atherton, Rick Hochberg
bibliographic citation
Atherton S, Hochberg R (2012) Acanthodasys paurocactus sp. n., a new species of Thaumastodermatidae (Gastrotricha, Macrodasyida) with multiple scale types from Capron Shoal, Florida ZooKeys 190: 81–94
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Sarah Atherton
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Rick Hochberg
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