Euchone pseudolimnicola, Giangrande & Licciano, 2006

Giangrande, Adriana & Licciano, Margherita, 2006, The genus Euchone (Polychaeta, Sabellidae) in the Mediterranean Sea, addition of two new species and discussion on some closely related taxa, Journal of Natural History 40 (21 - 22), pp. 1301-1330 : 1307-1309

Euchone pseudolimnicola n. sp.

( Figure 3 )

Holotype: South Coast of Ustica Island , 50 m depth, 38 ° 4195000N, 13 ° 0997800E, on softbottom mainly composed of medium sand, biogenic and volcanic particles together with a significant amount of red calcareous algae, MNCN 16.01 /10327 . Paratypes: six specimens from the same locality of holotype ; one specimen from Gulf of Policastro , 1987, Tyrrhenian Sea, 40 m depth, PCZL ; two specimens from Brindisi , 1989, Adriatic Sea, 40 m depth, PCZL .

Description

Holotype complete with eight thoracic and 28 abdominal chaetigers ( Figure 3A, B ), of which nine form the anal depression. Branchial crown length 2.3 mm; total thorax– abdomen length 4 mm; maximum width 0.3 mm. Branchial lobes each with six fully developed radioles with palmate membrane for about half of their length; radiolar flanges present distal to palmate membrane; radioles terminating as extra long filaments ( Figure 3F ). Dorsal lips pointed with internal blood vessel, dorsal radiolar appendage as long as enlarged basal dorsal lip length ( Figure 3G ). Ventral lips not detected, four pairs of ventral radiolar appendages about three-quarters length of the radioles ( Figure 3A ). Collar high, slightly higher ventrally, irregularly crenulated except dorsally, with two very long ventral lappets and a mid-dorsal narrow gap ( Figure 3A, C ); ventral lobe of anterior peristomial ring covered by collar margin. Ventral shield visible only after staining. Very uniform staining pattern degrading towards the end of the thorax ( Figure 3A ) and reduced to only small spots in the abdomen ( Figure 3D ). Glandular ridge present on chaetiger 2. Notopodia in chaetiger 1 with six narrowly hooded chaetae. Notopodial fascicle from chaetigers 2–8 with superior group of four elongated narrowly hooded chaetae ( Figure 3N ) and inferior group with two paleate chaetae posteriorly and two bayonet-type anteriorly. Paleate chaetae with long tip ( Figure 3O ). Neuropodial uncini eight per torus, with teeth of different sizes over the main fang, one of which very developed ( Figure 3M ). Abdominal neuropodial fascicles with modified, elongate narrowly hooded chaetae. Notopodia with 9– 10 avicular uncini, with main fang surmounted by three or four rows of teeth of different size as in the thorax uncini ( Figure 3H, L ). Intratorus variation absent. Uncini of the anal depression not highly modified, but with more teeth of similar size over the main fang ( Figure 3I ). Anal depression formed by nine chaetigers, with a distinct ridge present only in the uppermost part. Pygidium rounded showing in most of the specimens a filiform appendix ( Figure 3E ). Tube incrusted with detritus and sand.

Etymology

The species is named after the similarity to the very peculiar anal depression of E. limnicola .

Remarks

Euchone pseudolimnicola is similar to E. limnicola Reish, 1960 in having the anal depression without wings, but showing a distinct ridge marking the anterior edge. However, a lot of characters make the first species different from the latter: the crenulated margin of the collar; the less development of palmate membrane; the higher number of abdominal chaetigers; the shape of thoracic uncini with teeth of unequal size above the main fang; the lower number of abdominal uncini; the absence of ventral shields.

The holotype, which has been chosen for the best preservation of the branchial crown, lacks pygidial appendage, which, however, has been detected in most of the paratypes, underlining that this structure can be easily lost. Lastly, the dentition pattern of both thoracic and abdominal uncini appears very peculiar, with a second highly developed and asymmetric tooth over the main fang.

Habitat

Deep detritic bottom.

Figures

Figure 3. Euchone pseudolimnicola n. sp. (A) Staining pattern of the anterior end, ventral view; (B) entire worm; (C) collar, dorsal view; (D) staining pattern of abdominal chaetigers, ventral view; (E) ventral and lateral views of the anal depression; (F) tip of eadioles; (G) internal structure of branchial crown after dissection; (H) abdominal uncini in profile; (I) abdominal uncinus, the first abdominal chaetiger, frontal view; (L) abdominal uncinus from the anal depression region; (M) thoracic uncini; (N) thoracic superior notochaeta; (O) thoracic inferior paleate chaeta. dra, dorsal radiolar appendage; dl, dorsal lip.