Loxosoma discoides n. sp.

Figs. 2–15

urn:lsid:zoobank.org:act: 2470BF85-F6E0-41C4-813B-CC712D2BB822

Type material. Holotype: MNCN 26.01/10 Combarro Beach (Ria of Pontevedra) 42 o 26’N, 8 o 42’ W, intertidal, February 1976 . 24 Paratypes: MNCN 26.01 /11 Combarro Beach (Ria of Pontevedra) 42 o 26’N, 8 o 42’ W, intertidal, February 1976 . 3 Paratypes: MNCN 26.01/12 Meira Beach (Ria of Vigo) 42 o 17’ N, 8 o 43’W, intertidal, June 1976.

Etymology. The specific epithet refers to the disc shape of the calyx.

Description. Body length of 500–1300 µm and stalk length of 307–450 µm. Regarding the holotype (Fig. 2), its body length is 1264 µm long and the stalk length 441 µm. The calyx is large, with two wide wings conferring disc shape, thus giving the whole specimen a “table-tennis bat” appearance (Figs. 2–4). The wings arise as lateral expansions from the basal area of the stalk, totally surrounding the atrium. The calyx and the wings show an epidermis covered with a cuticle and an internal mesenchyme (Fig. 5). The atrium is enclosed by a crown with 16–21 tentacles (Figs. 5, 6). The long stalk slightly enlarges at the end forming a sucking disc (Figs. 2–4, 7). A foot gland was not observed but small lappets with gland cells were seen in radial array at the stalk end (Figs. 8, 9). The whole body has strong, mainly longitudinal musculature, but well-developed crossed diagonal musculature occurs in the transition between calyx and stalk (Fig. 10). Six rows of gland cells are found along the stalk, three of them frontal and the other three abfrontal (Fig. 11). The stomach is a large sac (Fig. 12), with two well-developed lateral pockets (Fig. 4).

Buds of different developmental stages are found in many specimens (Figs. 2, 4, 6, 13). The buds arise in the anterolateral areas, at the level of the upper part of the stomach. No seasonal pattern of bud occurrence was observed. One or two pedunculated, elongate, drop-shaped structures are found at the frontal side near the basal end of the stomach of some specimens (Figs. 2, 14, 15). They consist of a monolayer of epidermal cells covered with a cuticle, like that of the calyx. The epidermal layer is very thin in the distal part, but quite thick at the peduncle. Below the epidermal cells, the structures have a cavity divided in two chambers by a transverse wall; the cavity is filled with tightly packed, acidophilic granules. The mesenchyme of these organs is continuous with that of the calyx (Fig. 15).

Habitat. The specimens of this new species, which is interstitial, were collected in the intertidal zone of the beaches of Meira and Combarro (Galicia, NW Spain) (Fig. 1) at tidal level between +0.5 and + 1.6 m. The substrate consisted of fine or medium sand with moderate selection coefficient; it showed an average organic content of 0.5%, and its porosity oscillated between 44% and 47%; the recorded salinity of interstitial water was around 34%.