Type locality. -- West European Basin 50¡19.3'N, 12¡55.8'W, 2,498 m (INCAL [CENTOB] WS-02, 30.vii.76).

Holotype. -- MNHN (alcohol specimen, spicule slide). Length 3.2 mm, height and width at midbody 0.8 and 1.0 mm, respectively.

Etymology. -- macello = a pick; aciculata = like a small needle

Very spiny with thickset spicules, contracted body usually tightly curved, length to a little over 3 mm, of nearly equal height and width throughout, to 1.0 mm in diameter; rounded anteriorly and posteriorly; area around mouth and mantle cavity opening flattened, contracted mouth and mantle cavity openings longitudinal slits (Fig. 12B); pedal groove covered by long spicules. Epidermis 25 µm thick to 30 µm beside pedal groove, with many unstalked papillae, cuticle one-half as thick as epidermis, 12 µm; body wall musculature thin; vestibular papillae long, 18 or 20 in number, with long cilia at opening to vestibule, mouth opening at back of vestibule; pedal glands voluminous, pedal pit large, filling one-third of space in cross-section, with long cilia; foot single ridge 62 µm in height; single duct of ventral salivary glands above and of greater diameter than radular sac; midgut sacculate, no nematocysts observed; with 3 pairs of deep respiratory folds.

Pedestal of epidermal spicules rectangular (spicules 1, 6, 7) to trapezoidal (spicules 3, 8), curved against body, varying from 20 to 47 µm in greatest dimension by 13 to 20 µm, sometimes incompletely formed (spicule 9); solid needles straight or nearly so, greatest length to more than 300 µm, greatest width to 11 µm; pedestal dimensions not correlated to needle length (cf. spicules 1, 10); spicules from beside pedal groove of two types: (1) flat, thin, curved, in single longitudinal row, distally sharply pointed, proximally rimmed with rim sometimes abruptly terminated at an angle to rest of spicule (spicules 11-13); (2) numerous short, curved needles lateral to flattened spicules, <100 µm long by 5 µm wide with rimmed pedestals 11 µm long (spicule 5).

One isolated radula examined: tiny, 58 µm total length, with 16 rows of 15-µm long bars bearing 5 denticles; radular sac and odontophore 49 µm in length in histologic sections.

Reproductive system. -- No specialized spicules were observed at mantle cavity opening. The reproductive system posterior to the gonads is dominated by two large tubular seminal receptacles 140 to 180 µm long by 130 µm at their broadest (Figure above). These seem to be the elongated horns of the shell gland "longer than itself" described by Pruvot (1891) for Macellomenia palifera. The seminal receptacles are connected to the gametoducts through a narrow, muscular duct which seems to join the upper gametoduct on its ventral side posterior to its union with the lower gametoduct, although the connection was not clearly seen. The lower gametoducts are united for most of their length, which about equals that of the seminal receptacles. The exits from the pericardial cavity into the upper gametoducts are not from the usual terminal end of the pericardium, but from a distance only one-third of the way from the anterior end of the pericardium, as described by Pruvot for M. palifera.

Remarks. -- The genus Macellomenia is unique in the form of the spicules, with the adpressed pedestals perhaps functioning as skeletal spicules, and in the form of the radula. M. aciculata apparently is not a cnidarivore. It differs from a species of Macellomenia referred to M. palifera (Pruvot) reported from the Irish Sea (Caudwell et al., 1995) in smaller size, stubbier body shape, longer spines, and rectangular rather than ovate pedestals. M. aciculata differs from M. palifera s.s. in number of tooth denticles, smaller body size, shape of spicule pedestal, and spicule length.

From Ophelia 51 (1): 1-28 (1999).