Macrodasys acrosorus, Hummon, William D. & Todaro, Antonio, 2009

Hummon, William D. & Todaro, Antonio, 2009, Italian marine Gastrotricha: VI. Seven new species of Macrodasyida, Zootaxa 2278, pp. 47-68 : 50-51

Macrodasys acrosorus new species [Mcd acsr]

Figure 1 A, B

Macrodasys sp. E ( Todaro, Hummon, Balsamo, Fregni & Tongiorgi 2001: p. 89); ( Hummon 2001 – 2009: W Med Database)

Diagnosis: Adult Lt 706 Μm; PhJIn at U35. Head ovoid, without swelling, pestle organs at U02; trunk broad throughout, narrowing near the caudum. Glands inconspicuous. TbA 5 per side, in transverse rows that insert directly on the body; TbL 17 per side, symmetrical, from U30 to the rear, with 3 between the pharyngeal pores and the PhJIn, and 14 in the intestinal region; TbD and TbV absent; TbP 5 per side surrounding the caudum. Locomotor ciliature: paired tracts run from just behind the pestle organs, paralleling the body sides, and joining beneath the caudum rearward of the anus. Mouth sub-terminal, rim bears a corona of fine projections; buccal cavity cup-shaped, lightly cuticularized; pharyngeal pores are sub-basal; intestine broadest in front, narrowing quickly, circling around the reproductive structures to the rear; anus at U90. Hermaphroditic; testes extend rearward from just before the PhJIn; only one small egg was seen; caudal organ is elongate pyriform, homogeneous but hollow toward the front, with a more normal rear, having fine spiral striations throughout, but no coarse spiral or longitudinal musculature being seen; frontal organ has a sharp beak-like apex, a longitudinally bilobed interior chamber that contained active sperm, and a basal cell to the rear; caudal organ overlaps the rearmost part of the frontal organ itself.

Description: Adult Lt 706 Μm; LPh 250 Μm to PhJIn at U35 ( Fig. 1 A, B). Body medium in length as an adult, ventrally flattened, dorsally vaulted; head ovoid, without swelling, but bearing pestle organs at U02; trunk broad throughout, narrowing gradually to the caudum. Widths at pestle organs/pharyngeal pores/PhJIn/tip of CO/anus/caudum (min.) and locations along the length of the body are as follows: 59/85/79/91/39/11 Μm at U02/U29/U35/U65/U90/U99, respectively. Epidermis unarmored, glands not conspicuous.

Adhesive tubes: TbA 5 per side (L 12 Μm), in transverse rows, which insert directly on the postoral body surface at U03 and project forward; TbL 17 per side (L 12–15 Μm), symmetrically placed, from U30 rearward, with 0 before the pharyngeal pores, 3 between the pores and the PhJIn, and 14 in the intestinal region; TbD and TbV are absent; TbP 5 per side surrounding the caudum posterior to the anus, all as long as or larger than the rearmost TbL.

Ciliation: Sensory cilia (L 14–28 Μm) occur on either side of the mouth, with a circlet of cilia surrounding the head above the pestle organs; longer sensory hairs (L similar) arise in two columns on either side of the body, lateral and dorsal, with 16–18 per column. Ventral locomotor ciliature: paired tracts of short cilia (L 10–12 Μm) run from just behind the pestle organs, paralleling the body sides, and joining beneath the caudum rearward of the anus.

Digestive tract: Mouth slightly subterminal, 24 Μm in diameter; mouth rim bears a corona of a dozen fine projections (L 8 Μm); buccal cavity expands with depth and is lightly cuticularized; pharynx has sub-basal pharyngeal pores at U29; intestine is broadest in front, narrowing quickly at about U50 and then circling around the reproductive structures to the rear; anus is at U90.

Reproductive tract: Testes extend rearward from just before the PhJIn, vasa deferentia not seen; eggs appear to develop from rear to front, only a small one being seen in this specimen, with no additional germinal vesicles; caudal organ is elongate pyriform, homogeneous with a hollow opening in the front but with a more normal rear end, having fine spiral striations throughout, but no coarse spiral musculature or longitudinal musculature being seen; frontal organ has a sharp beak-like apex, a longitudinally bilobed interior chamber that contained active sperm, a ventral opening in the rear of the anterior chamber, and a basal cell to the rear; caudal organ overlaps the basal cell and the rearmost part of the frontal organ itself.

Ecology: Sparse in frequency of occurrence (fewer than 10% of samples), rare in abundance (less than 1% of a sample); sublittoral in fine, medium to medium-well sorted clean sand at 1.5–3.0 m water depth.

Geographical distribution: MED: EUROPE: ITALY: Campania Archipelago { Isola d’Ischia: Bagnetielli, Spiaggia d'Ischia Porto^ 40°,45’N/13°,56’E [video]}.

Remarks: The description of Macrodasys acrosorus n. sp. is taken from a single specimen, the only one found (WDH video #262, a holotype, ICZN Articles 73.1.2). Unusual is the ventral ciliation of paired lateral tracks, the homogeneous caudal organ, having fine spiral striations, and the longitudinally bilobed frontal organ with a beak-like apex.

Etymology: The species is named for the sharply pointed beak-like tip (Greek: akros) of the hollow (Greek: soros) frontal organ.

Taxonomic affinities: To the 28 species currently in the genus Macrodasys are being added two new species M. acrosorus n. sp. and one to be described below, bringing the number to 30. No other species of medium length in this genus has the following combination of characters: ventral ciliation with paired lateral tracks, a homogeneous caudal organ, having only fine spiral striations, and a longitudinally bilobed frontal organ with a beak-like apex, PhJIn at U35, TbA 5 per side, TbL/TbP 17/5 per side, occurring regularly from the pharyngeal pores rearward.

Figures

FIGURE 1. Macrodasys acrosorus n. sp. A—dorsal and B—ventral views of an adult (Lt = 706 µm, LPh = 250 µm), from Spiaggia d'Ischia Porto, Isola d’Ischia, Italy, dorsal with digestive and reproductive tracts; ventral with adhesive tubes and ventral locomotor ciliary bands.