Marcus E 1950 (citation) pg. 105-106: 'Microstomum ulum, n. sp. (Fig. 42-48) lives in coarse sand with single tufts of Padina and other algae, below the regular low-water line on the coast of the island of São Sebastião. Big specimens of Gyratrix hermaphroditus Ehrbg. and Dolichomacrostomum mortenseni are characteristic of the acompanying fauna. Eyes are absent; the ciliated pits (w) are very well developed. The nuclei of the epidermal epithelium are normal. The erythrophilous rhabdites (r), 50 of which are bundled in one cell (0,025 mm) , are similar to those of M. trichotum. Other volumous cells (y) with thick, faintly stained rods are perhaps adhesive, but they resemble those in M. gabriellae (Fig. 35, r) that are considered as rhabditogenous. The nematocysts (s) that occur scarcely are in the integument always lodged in these cells (y). The head-glands (h) open singly. The caudal plate has erythrophilous, depressed adhesive cells (k). The brain (c) has a distinct capsule. At the entrance of the ciliated pits (w), where the postero-lateral nerve (n) passes dorsally, a tuft of long cilia belongs to the sensory cells (t). The mouth (b) is round; the pharyngeal glands (g) are acidophil. Some club-shaped cells of Minot (m) surround the entrance of the intestine (i). The lumen of the latter disappears, when its cells during certain digestive phases form a syncytial mass. The pre-oral intestine (q) is short. As food Hydrozoa, and once an egg-sac (e) of a Copepod, were observed. The present chains are composed of up to 4 zooids; gonads are not developed. The 10 other marine species of Microstomum without eyes show combinations of characters that make specific separation of ulum necessary; also Stenostomumum sieboldii is different.'
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