Neomenia carinata Tullberg, 1875

Pedrouzo, Lucía, Cobo, M. Carmen, García-Álvarez, Óscar, Rueda, José L., Gofas, Serge & Urgorri, Victoriano, 2014, Solenogastres (Mollusca) from expeditions off the South Iberian Peninsula, with the description of a new species, Journal of Natural History (J. Nat. Hist.) 48 (45 - 48), pp. 2985-3006 : 2989-2992

Neomenia carinata Tullberg, 1875

( Figure 1 )

Material examined

Seven specimens. Two specimens cut in serial sections and one specimen dissected to study copulatory stylets. Internal anatomy manually reconstructed ( Figure 1E ). Gulf of Cádiz (INDEMARES/Chica 0610 and 0211): two specimens, 456–478 m depth. Alborán Sea (DEEPER 0409 and INDEMARES/Alborán 0911): five specimens, 121–365 m depth ( Table 1) .

Distribution

Type locality. Swedish west coast. Further records from Kattegat-North Sea (Scandinavia to Scotland); Iceland; British Isles; Roscoff ( France); Gulf of Cádiz (this report); from the West Mediterranean Sea to the South Adriatic Sea. 10–565 m depth ( Salvini-Plawen 1997; García-Álvarez and Salvini-Plawen 2007, 2011; this report).

Description

Short and thick-bodied specimens (4.65–15.3 mm long; 1.96–5.4 mm wide) with truncated ends and a clear dorso-longitudinal crest. This crest or keel discriminates the species distinctly from other Iberian congeners but not from other Neomeniamorpha ( Salvini-Plawen 2006). White-yellowish colour in 70% ethanol ( Figure 1A ). The following description of internal anatomy is based on two immature specimens: measurements and reconstructions are based on one of them, which was about 8.5 mm long and 2.08 mm wide.

Cuticle 30–50 μm thick with numerous epidermal papillae. Solid sclerites of four types: acicular (60–120 μm long; 2.5–5 μm wide) arranged all over the cuticle; excavated scales with a soft keel on the distal end (55–100 μm long; 1.5–5 μm wide) which had not been previously described ( Nierstrasz and Stork 1940) ( Figure 1C ); excavated scales (90–105 μm long; 15 μm wide) ( Figure 1B ), both inserted among the acicular sclerites and arrow pointed sclerites with a rim in the basal area (65–105 μm long; 15–20 μm wide) inserted at the dorsal crest ( Figure 1D ). Pedal groove with up to 5 folds, of which the central one is the longest ( Figure 1F ). Large pallial cavity with 18 to 30 radial respiratory folds ( Figure 1H ). The lower number of pedal and respiratory folds observed and compared to Nierstrasz and Stork (1940) is due to the sexual immaturity of the specimens studied here. The pallial cavity has a wide anteroventral pouch, into which the spawning ducts, the copulatory stylets, and their associated glands open. Common atriobuccal cavity with mouth located in the end of a muscular pharynx tube, which was retracted in the specimens studied, leading to the formation of a dorsal fold in the pharynx. Medial part of the foregut surrounded by a thick muscle layer that diminishes in thickness posteriorly: the foregut tube becomes narrower until it opens centrally into the midgut.

Very slightly developed gonads. Voluminous pericardium (360 µm high, 540 µm wide and 440 µm long) with the anterior part of the heart connected to its anterior dorsal wall. The greater part of the heart extends in the shape of a tube along the interior of the pericardium and its posterior half divides into two lateral atria. Long and narrow pericardioducts, which originate from the lateroventral region of the pericardium. Long and narrow paired spawning ducts, with two pouches located anteriorly to the union with the pericardioducts, which can be interpreted as a pair of incipient seminal receptacles. The posteriorly fused spawning ducts open dorsally into the anteroventral pouch of the pallial cavity. There is a pair of sets of copulatory stylets located ventrolaterally in the posterior body. Each stylet group is made up of two stylets 210 µm long: one acicular and narrow (10–15 µm diameter) with a pointed distal part, within a second thicker grooved stylet (15–20 µm wide), which is more malleable than the acicular one. The grooved stylet is half-moon shaped when cut in cross-section, and encloses the acicular stylet partially ( Figure 1G ). Each pair of stylets is accompanied by a very voluminous gland, its proximal part extends anteriorly and its posterior part accompanies the stylets along their whole length. Glands and copulatory stylets open ventrally into the anteroventral pouch of the pallial cavity. In the studied specimen which has the pallial cavity opening closed, the dorsoterminal sense organ is located within the posterior part of the pallial cavity. The dorsoterminal sense organ is characterized by the presence of ciliated cells and is connected to the pallial cavity by a groove. The sense organ is exposed only when the animal opens the pallial cavity wide.

Taxonomic remarks

The present specimens were assigned to the species N. carinata based on the habitus with a crest and general characteristics of the copulatory stylets and sclerites. One type of sclerites was found, which has not been previously described (keeled excavated scales) and which cannot be found in specimens from Scandinavia (2014 letter from C. Todt to Lucía Pedrouzo; unreferenced). The juvenile specimen used for reconstruction of internal anatomy had well-developed copulatory stylets, but the gonads were small, the spawning duct epithelium relatively low, and a muscular genital papilla with cone-shaped sclerotized protusions, as typically found in Scandinavian N. carinata (‘mushroom-like organ’ in Tullberg’ s (1875) original description; 2014 letter from C. Todt to Lucía Pedrouzo; unreferenced), was lacking. Due to the overall similarity of our specimens with the original description of the species from Scandinavia ( Tullberg 1875) and the successive description of specimens from the Mediterranean by Nierstrasz and Stork (1940), we assign our Iberian specimens to N. carinata . Future investigations directly comparing fully mature specimens from Scandinavian and Mediterranean waters are desirable.

Habitat and associated fauna

Both specimens from the Gulf of Cádiz were collected on the seafloor adjacent to the mud volcano Gazul, on a bottom of bioclasts and muddy sand associated to aggregations of the crinoid Leptometra phalangium (Müller) and the actiniarian Actinauge richardi (Marion) , at depths of 456– 478 m. One of the five specimens collected in the Alborán Sea was found on the seafloor close to Alborán Island on muddy gravel at 121–169 m depth, where the holothuroidean Parastichopus regalis Clark was very abundant. Four specimens were collected on the seamount Avempace at 349–365 m depth on sediment of bioclastic gravel with large aggregations of L. phalangium .

It is not known what N. carinata feeds on and none of the specimens collected here was directly associated with a potential prey organism. No cnidocysts were found in the midgut on the sectioned specimens.

Figures

Figure 1. Neomenia carinata. (A) Habitus; (B) excavated scale; (C) excavated scale with distal keel; (D) sclerite with arrow point; (E) schematic organization of the anterior and posterior body; (F) detail of the pedal groove; (G) detail of the copulatory sclerites and gland; (H) section through the pallial cavity and respiratory folds. at, atrium; cg, cerebral ganglion; co, copulatory stylet; cog, copulatory stylet gland; cu, cuticle; dc, anterodorsal midgut caecum; dso, dorsoterminal sense organ; he, heart; mc, musculature; mg, midgut; mo, mouth; pa, pallial cavity; pc, pericardium; pd, pericardioduct; ph, pharynx; pp, pedal pit; re, rectum; rf, respiratory folds; sc, suprarectal commissure; sd, spawning duct; vg, ventral ganglion; vp, ventroanterior pouch of the pallial cavity.