Sternaspidae Carus, 1863
Genus Sternaspis Otto, 1821
Sternaspis sp. 1
Voucher specimens. Sea Lion: Stations 90MFB (2 adults) and 22 MFC (adults and subadults).
Diagnosis. Small species (relative to other species of Sternaspidae); voucher complete specimens (adults), 9 mm long, 3 mm wide (at widest part of abdomen), 31 segments introvert exposed . Body colour in alcohol light brown to greyish. The body has narrow introvert, with bulbous head of 2:3 width ratio to widest part of abdomen and very narrow waist segments (the narrowest part of the body) at 1:3 width ratio to the widest part of the abdomen. Cuticular papillae evenly distributed over most of the body (can be eroded in larger specimens) especially obvious at narrowest part of the introvert.
Prostomium hemispherical, opalescent, without eyespots. Peristomium rounded, without papillae. Mouth slightly oval, completely covered by papillae. First three chaetigers with 8-13 bronze, widely separated, slightly falcate hooks per ramus, with subdistal dark areas, transparent in juveniles, opaque in larger specimens, with thin arista-like spine distally (often broken off). Genital papillae protrude ventrally from intersegmental groove between segments 7 and 8.
Ventro-caudal shield orange in juveniles, darker orange to light brown in adults; ribbed, often covered by sediment; concentric bands not obvious; anterior margins rounded; deep suture running through the shield; lateral margins straight in smaller specimens, curved in larger specimens, expanding posteriorly. Fan projecting beyond posterior corners, smooth, with a well-developed median notch .
Marginal chaetae fascicles include 10 lateral ones in an oval arrangement, and 6-7 posterior fascicles arranged in an approximately ventro-dorsal line. Lateral chaetae are longest in their most posterior position; light bronze proximally along the shafts, grading to almost clear at the distal ends; the posteriomost lateral 3-4 fascicles overlap with the short posterior chaetae, but clearly set behind these, the last lateral fascicle often present as only one or few chaetae and can be easily overlooked. Posterior chaeatal fascicle short, getting progressively longer toward the outer margin of the shield.
Branchiae stout, coiled, protruding from two oval, obliquely set plates, one on either side of anus. Many long filamentous interbranchial papillae with sediment particles attached.
Remarks. FI specimens superficially agree well with S. fossor (considered to have a distribution limited to North American Atlantic coast) in body colour, shape of caudal shield (including sediment encrustation), papillation, possession of 10 lateral shield chaetae and 6-7 posterior chaetae (this number is fixed in other species, not variable). FI specimens differ in not having obvious concentric lines in their shield unlike the S. fossor. Additionally, the two species possess different body shapes with S. fossor generally having a very thick introvert, while it is thin in FI specimens. The body shape has not been really assessed as taxonomic character so far, but given examination of several other species (see below), we suggest that there is consistency to the body shape, which varies among the species.
Sternaspis had been recorded from Southern Ocean and South America by previous authors (see reference in Sendall and Salazar-Vallejo 2013) and commonly assigned to species S. scutata (possessing 6 posterior shield chaetae). None of these authors gave a detailed description of their specimens, as given the distinctive shape of Sternaspidae, they have assumed that their material belongs to a few or even one species most notably S. scutata. Recent revision work by Sendall and Salazar-Vallejo (2013) showed this assumption to be incorrect and restricted the distribution of S. scutata to Mediterranean and Northeastern Atlantic, eventually leading to a description of two new species from the Southern Ocean S. monroi and S. sendalli (Salazar-Vallejo, 2014). Type specimens of S. monroi and S. sendalli were elected from the historical collection held at NHM London and were re-examined in here. The differences between two known species from the Southern Ocean and new FI species are summarized in table below.
Table. 1 Main morphological features of Sternaspis known from the Southern Ocean and Sternaspis sp. 1 from Falkalnd Islands.
|
Species |
Body colour; length |
Introvert |
Posterior chaetae |
Lateral chaetae |
Introvert chaetae |
Caudal shield fan |
|
S. monroi |
pale; 14mm |
relaxed (thick) |
6 |
9 |
12-14 |
truncated, median notch narrow, no lateral notches |
|
S. sendalli |
pale; 15mm |
relaxed (thick) |
5-6 |
9 |
12-14 |
slightly projecting; median notch developed; with lateral notches |
|
Sternaspis sp. 1 |
grey; 9mm |
constricted (thin) |
6-7 |
10 |
8-13 |
projecting; median notch well-developed; no lateral notches |
REFERENCES
Carus, J. Victor 1863. Vermes, in W. C. H. Peters, J.V. Carus and C.E.A. Gerstäcker eds., Handbuch der zoologie: Leipzig, Wilhelm Engelmann, p. 422-484., available online at http://biodiversitylibrary.org/page/1092677 page(s): 453
Otto, A. G. 1821. Animalium maritimorum nondum editorum genera duo. Nova Acta Physico-Medica Academiae Caesareae Leopoldino-Carolinae Naturae Curiosorum 10(2): 617-634, Plates 50-51., available online at http://biodiversitylibrary.org/page/37021183
Sendall, K., & Salazar-Vallejo, S. I. (2013). Revision of Sternaspis Otto, 1821 (Polychaeta, Sternaspidae). ZooKeys, (286), 1.
Sendall, K., & Salazar-Vallejo, S. I. (2013). Revision of Sternaspis Otto, 1821 (Polychaeta, Sternaspidae). ZooKeys, (286), 1.
Salazar-Vallejo, S. I. (2014). Three new polar species of Sternaspis Otto, 1821 (Polychaeta: Sternaspidae). Zootaxa, 3861(4), 333-344.
