Ophryotrocha alborana, Paxton, Hannelore & Åkesson, Bertil, 2011

Paxton, Hannelore & Åkesson, Bertil, 2011, The Ophryotrocha diadema group (Annelida: Dorvilleidae), with the description of two new species, Zootaxa 3092, pp. 43-59 : 47-49

Ophryotrocha alborana sp. nov.

Figure 1 B; 3D–F; 4; 7; 8; 9; 10; 11; Table 1 ; 2

Ophryotrocha alborana nom. nud. Pleijel & Eide, 1996; Dahlgren et al. 2001; Heggøy et al. 2007; Macnaughton et al. 2010.

Material examined. Type material: holotype ( SMNH T- 8164), complete specimen, 3.0 mm long (21 chaetigers), 0.4 mm wide without parapodia; 10 paratypes ( SMNH T- 8165) 1.7–2.5 mm long (15–22 chaetigers); 10 paratypes (AM W.37217), 1.5–3.1 mm long (15–22 chaetigers); cultured from specimens collected in the harbour of Algeciras, Spain, by Nils Börjesson, February 1978. Other material: 40 specimens ( SMNH 117235), 0.5–2.6 mm long (4–20 chaetigers); 40 specimens (AM W.37218), 0.4–2.5 mm long (4–19 chaetigers); all specimens complete, measurements from preserved specimens, cultures from same collection; additional live material.

Description. Length of most live adults 3–4 mm (17–20 chaetigers), maximum length generally 5 mm (25 chaetigers) ( Table 1 ), although two exceptional individuals with 34 chaetigers observed. Live animals ( Fig. 1 B) translucent, preserved opaque white, lacking any pigmentation.

Prostomium anteriorly rounded, wider than long, dorsoventrally flattened, bearing pair of dorsal cylindrical antennae, palps absent, replaced by ciliated pads ( Fig. 4 A–D). Anterior part of prostomium and tips of antennae with small bundles of adjoined tactile cilia, appearing spike-like in living animals. Ciliary bands separated by gaps; two bands of cilia encircling prostomium, one complete circle in front of antennae, and one incomplete circle at level of antennae. Latter interrupted by antennae; cilia between antennae slanting posteriorly, separated by small mid-dorsal space, giving appearance of eyebrows. Additional ventral semicircle of cilia anterior to complete circle. Posterior border of prostomium indicated laterally by restrictions, dorsally by four nuchal organs, ventrally by mouth.

Peristomium represented by two apodous, achaetous segment-like rings, each surrounded by complete circle of cilia. Two eyes, slightly below border between prostomium and peristomium, between inner and outer nuchal organs. Eyes internal, visible only in living animals. Eyes with refractive crystalline platelets as typical for Ophryotrocha , appearing silvery white under incident light, but possessing also reddish pigment cups ( Fig. 1 B). Following chaetigers with dorsal and ventral ciliary bands, laterally interrupted by parapodia.

Parapodia uniramous, with acicular lobe and ventral retractile lobe supported by short simple chaeta; dorsal and ventral cirri absent. Supra-acicular fascicle consisting of 2–3 simple chaetae, subacicular fascicle with 2–4 heterogomph falcigers and inferiormost simple chaeta. Appendages of falcigers and upper part of simple chaetae serrated with simple distal tip. Mammillate rosette glands, two per segment, present dorsolaterally on up to 9 posterior segments ( Fig. 4 E, F). Pygidium bearing dorsal anus and pair of dorsal pygidial cirri; dorsal stylus absent.

Jaws consisting of mandibles and maxillae; former permanent, latter undergoing at least two moults. Mandibles consisting of two elongate shafts, widening distally into bifid serrated cutting plates with 22–28 tiny teeth and large blunt sublateral tooth-like projection at anterior cutting edge of each plate ( Fig. 3 D; 4G, H). Shafts of adult animals slender, 100–145 µm long ( Fig. 3 E). Maxillary apparatus of P-type only, consisting of forceps fused with carrier-like structure and seven pairs of anterior denticles (D) ( Fig. 4 I, J). Forceps of adult worms 60–85 µm long, median edge of anterior part of forceps with distal fang and 3–5 large teeth irregularly alternating with small teeth, distal fang only slightly larger than other large teeth ( Fig. 3 F); D1–D3 with distal fang and coarsely serrated median cutting edge; D4–D7 with finely serrated edge, associated with oval ventral plate.

Reproduction and development. Ophryotrocha alborana is hermaphroditic. The first and second chaetigers are sterile, the third and fourth are male, and the remainder are female. The chromosome number is 2n = 8. Newly laid eggs are ovoid, 190 x 150 µm. The egg case is firm and elastic, transparent, and of fusiform shape, closed at both ends. The larvae are released from the egg case at the 4- to 5-chaetiger stage. The jaw ontogeny has been described and illustrated on the basis of SEM images by Macnaughton et al. (2010). Larval maxillae are present in up to 6-chaetiger animals, juvenile (P1) maxillae are found in 7- to 11-chaetiger animals, and adult (P2) maxillae in 8-chaetiger animals onwards. Other reproductive and population parameters are listed in Table 2 and will be compared for the three species in the “Discussion” below.

Etymology. The specific name is derived from the Alboran Sea, collection site of the new species.

Remarks. The new species was originally identified through crossbreeding experiments and has been confirmed by gene sequence studies ( Dahlgren et al. 2001; Heggøy et al. 2007). It can be distinguished from the other two species of the O. diadema group by having eyes with a reddish pigment cup in addition to the silvery white crystalline platelets ( Fig. 1 ), as well as other subtle morphological differences ( Table 1 ), and differing life history parameters ( Table 2 ).

Ophryotrocha alborana was collected in February 1978 in the harbour of Algeciras, in the Alboran Sea, the westernmost portion of the Mediterranean Sea. It coexisted with O. hartmanni Huth, 1933 , O. puerilis Claparède & Mecznikow, 1869 , and O. labronica La Greca & Bacci, 1962 . A few days later it was also found in Ceuta, the Spanish enclave on the Moroccan coast, together with O. puerilis , O. rubra Paxton & Åkesson, 2010 and O. robusta Paxton & Åkesson, 2010 . Despite repeated searches, O. alborana has never been found again in either locality.

Distribution. Mediterranean Sea: Algeciras, Alboran Sea and Ceuta.

Figures

FIGURE 1. Photographs of live animals, dorsal view. A, Ophryotrocha diadema; B, Ophryotrocha alborana, sp. nov.; C, Ophryotrocha birgittae, sp. nov.

FIGURE 3. Mandibles and maxillary forceps, dorsal views. Ophryotrocha diadema (A – C). A, Mandibles of 4 - chaetiger worm; B, same of 19 - chaetiger worm; C, maxillary forceps of 19 - chaetiger worm. Ophryotrocha alborana, sp. nov. (D – F). D, Mandibles of 5 - chaetiger worm; E, same of 20 - chaetiger worm; F, maxillary forceps of 20 - chaetiger worm. Ophryotrocha birgittae, sp. nov. (G – I). G, Mandibles of 4 - chaetiger worm; H, mandibles of 19 - chaetiger worm; I, maxillary forceps of 19 - chaetiger worm.

FIGURE 4. SEM images of Ophryotrocha alborana, sp. nov.. A, complete adult, dorsal view; B, same, ventral view; C, anterior end, dorsal view; D, same, ventral view; E, posterior end, dorsal view; F, enlargement of last five chaetigers to show mammillate rosette glands, dorsal view; G, mandibles of 14 - chaetiger worm, dorsal view; H, same of 13 - chaetiger worm, ventral view; I, P 2 - maxillae of 14 - chaetiger animal, ventral view; J, same, dorsal view. G – J by M. O. Macnaughton.