Dorymenia sarsii ( Koren and Danielssen, 1877 )

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 : 3000-3004

Dorymenia sarsii ( Koren and Danielssen, 1877)

( Figures 6 , 7 )

Dorymenia tortilis Scheltema and Schander (2000, p. 126)

Material examined

Forty-eight specimens. Two specimens cut in serial sections, three specimens dissected to study the radula and copulatory stylets and two more specimens dissected to study copulatory stylets. Gulf of Cádiz (INDEMARES/Chica 0211), 469–667 m depth ( Table 1) .

Distribution

Type locality. Norwegian west coast (Bergen). Further records: Scandinavia; Cape Breton; Bay of Biscay and Gorringe Bank. 190–681 m depth ( García-Álvarez and Salvini-Plawen 2007; Salvini-Plawen 2008), Gulf of Cádiz (this report).

Description

Specimens with long and narrow body (17.8–62 mm long; 1.1–1.5 mm wide) with a digitiform projection on the posterior body; without keels or lumps ( Figure 6A ). Cuticle 80–140 μm thick, with epidermal papillae.

Hollow acicular sclerites with different degrees of curvature and trowel-shaped and knife-shaped scales ( Figure 6C ). The hollow acicular sclerites are divided into three size classes: large (245–350 μm long; 12.5–25 μm wide), medium-sized (140–215 μm long; 10–15 μm wide) and small (50–140 μm long; 5–10 μm wide). The trowelshaped scales (80–185 μm long; 5.25–15 μm wide) are inserted among the acicular sclerites along the whole animal ( Figure 6B ) and there are two types: distally pointed and distally rounded scales. Knife-shaped scales (60–145 μm long; 10–15 μm wide) on both sides of the pedal groove of two types: knife scales with a straight margin and curved knife scales.

Common atriobuccal cavity with numerous papillae. The muscular foregut has a pair of pouches enclosing the frontal area of the radula complex. The radular complex consists of a polyserial radula with a paired sheath at its posterior end and a radular sac surrounded by thick circular musculature. Two big buccal ganglia are located at the muscular junction between the radular sac and the radular sheath. Polyserial radula with 16 teeth per row, number of rows between 22 and 28 with median furrow. The length of the internal teeth (near the furrow) is 25–30 µm, medial teeth 40–50 µm length, lateral teeth 60–90 µm length, tooth bases 7.5–20 µm wide.

Pericardioducts with small pouches internally (one to three) that serve as seminal vesicules. The spawning ducts are paired; in its posterior half they enlarge ventrally to form a spacious pouch just before uniting and opening into the pallial cavity. Hook-shaped abdominal spicules in the pallial cavity, near the opening (60–105 μm long; 5–7.5 μm wide) ( Figure 6E ). A pair of long and narrow copulatory stylets are present (3.01–3.2 μm long; 0.11–0.6 μm wide) ( Figure 7A, B ). They have a bulbous proximal end with variable appearance in the specimens studied ( Figure 7A, B, E ) where the accompanying muscular fibres are inserted; twisted body ( Figure 7C, D ), clearer in the distal area, tapering to a sharp and slightly curved end ( Figure 7F ), with a hyaline core.

Throughout the whole body of the examined animals numerous internal sclerites were found. These sclerites were found within the connective tissue, and they have a well-characterized appearance: short and wide (85–155 µm long; 15–25 µm wide), with truncated ends, grooved longitudinal lines and tetraradial star-shaped cross section ( Figure 6D ).

Taxonomic remarks

Earlier, Dorymenia tortilis Scheltema and Schander, 2000 , was described from northwest of Gibraltar, at a site about 200 km to the west of where the specimens studied herein came from. The distinction between D. tortilis and D. sarsii was based on the radula morphology – especially the number of tooth rows and shape of the bases of teeth – the type and shape of mantle sclerites, the shape of abdominal spicules, the absence or presence of accessory copulatory spicules and the morphology of the copulatory stylet ( Scheltema and Schander 2000). No details of internal morphology have been published for D. tortilis .

In our specimens, the number of rows and teeth per row of the examined radulae corresponds to those assigned to D. sarsii by Scheltema and Schander (2000), as does the morphology of most of the teeth (length to width ratio of the tooth bases). Some teeth, however, have a length width ratio corresponding to D. tortilis ( Scheltema and Schander 2000) .

We did not find epidermal sclerite morphology to be useful in assigning our specimens to D. sarsii and D. tortilis , either, because in all the specimens we found a mixture of sclerites as described for the two species by Scheltema and Schander (2000). The abdominal spicules of our specimens correspond to the morphotype of D. tortilis but some of the abdominal spicules were broken and their appearance was then similar to the morphology described for D. sarsii ( Scheltema and Schander 2000) . The morphology of the isolated copulatory stylets corresponds to that described for D. tortilis ( Scheltema and Schander 2000) , but the stylets depicted for D. sarsii might have been eroded (see also Salvini-Plawen 2008).

The sclerites described as accessory copulatory spicules by Scheltema and Schander (2000) for D. sarsii were present in our specimens, but they were situated not only in areas near the copulatory stylets but distributed over the whole body (internal sclerites in this report). Thus, a close relationship with the copulatory system has to be discarded. The internal sclerites’ shape and fine structure are similar to what is seen in the bulbous end of the copulatory stylet, which suggests a structural role.

Research done by Handl and Salvini-Plawen (2002) assumed that it can not be certainly stated that D. tortilis and D. sarsii are different species. Subsequently, Salvini-Plawen (2008) concluded with the synonymy of both species. The results obtained in the present study reveal that our specimens, which come from the same geographic area and depth regime as D. tortilis , combine characteristics of both species. Our data thus support the synonymy of the two species, even though a more detailed study including a direct comparison of the internal anatomy and analyses based on molecular data would be desirable. Here, we conclude that the differences in hard part morphology seen between specimens of D. sarsii and D. tortilis are due to intraspecific variation.

Habitat and associated fauna

The 48 specimens studied were collected from the Gulf of Cádiz at 469–667 m depth. Seven specimens were collected at the volcano Tarsis and its adjacent area, on substrata of sandy mud and a habitat defined by communities of Pennatulacea ( Kophobelemnon stelliferum (Müller) , Funiculina quadragularis (Pallas) and Pennatula aculeata Danielssen ) and species of the order Alcyonacea , mainly of the species Isidella elongata (Esper) . Four specimens were from the volcano Chica with bottoms of thick sand and gravel inhabited by communities of pennatulaceans ( K. stelliferum , F. quadrangularis ) and gorgonians ( Acanthogorgia hirsuta , Callogorgia verticillata ). Nineteen specimens were collected at the volcano Anastasya and its adjacent area on sandy bottoms dominated by communities of pennatulaceans ( K. stelliferum , F. quadrangularis , P. aculeata ). Eighteen specimens were from areas adjacent to the volcano Pipoca from muddy sand, also dominated by pennatulaceans ( K. stelliferum , F. quadrangularis ) and gorgonians ( I. elongata ). No cnidocysts were found in the midguts of any of the sectioned specimens.

Figures

Figure 6. Dorymenia sarsii. (A) Habitus; (B) ESEM micrograph of the body wall with sclerites; (C) drawing of the sclerites: 1. large hollow acicular sclerites curve shallow and pronounced; 2. medium size hollow acicular sclerites curve shallow and pronounced; 3. small hollow acicular sclerites curve shallow and pronounced; 4. distally pointed trowel-shaped scales en face and from side; 5. distally rounded trowel-shaped scales en face and from side; 6. small trowelshaped scales en face and from side; 7. knife-shaped scales with one straight margin; 8. curved knife-shaped scales; (D) ESEM micrograph of an accessory copulatory spicule; (E) abdominal spicule.

Figure 7. Dorymenia sarsii copulatory stylet. (A) Photograph of a copulatory stylet under dissecting microscope; (B) ESEM micrograph of other copulatory stylet; (C) medial twisted region (optical microscope); (D) ESEM micrograph of the medial twisted region; (E) ESEM micrograph of a proximal end type; (F) ESEM micrograph of the distal end.