Aurospio tribranchiata, Paterson, Gordon L. J., Neal, Lenka, Altamira, Iris, Soto, Eulogio H., Smith, Craig R., Menot, Lenaick, Billett, David S. M., Cunha, Marina R., Marchais-Laguionie, Claire & Glover, Adrian G., 2016

Paterson, Gordon L. J., Neal, Lenka, Altamira, Iris, Soto, Eulogio H., Smith, Craig R., Menot, Lenaick, Billett, David S. M., Cunha, Marina R., Marchais-Laguionie, Claire & Glover, Adrian G., 2016, New Prionospio and Aurospio Species from the Deep Sea (Annelida: Polychaeta), Zootaxa 4092 (1) : 19-24

Aurospio tribranchiata sp. nov. Paterson & Soto

( Figure 1 , 8 d, 10, 11, 12, Table 3 )

Minuspio sp4 Soto 2008: 89.

Material examined: 33 specimens examined in total.

Holotype: Porcupine Abyssal Plain, RRS Discovery D229, July 1997, 13200#20, 48º49.8’ N, 16º29.62’ W, 4844 m, 1–3 cm, 0.3 mm (NHMUK 2015:1199).

Paratypes: Porcupine Abyssal Plain, RRS Challenger 79, May 1991, 52701#9, 48º51.6’ N, 16º27.4’ W, 4842 m, 2 individual; 52701#25, 48º50.4’ N, 16º29.6’ W, 4844 m, 3 individuals; 52701#47, 48º50.6’ N, 16º29.9’ W 4841 m, 1 individual.

Porcupine Abyssal Plain, RRS Discovery D222, August 1996, 12930#14, 48º50.92’N, 16º30.24’W, 4837 m, 1 individual; 12930#44, 4849.95’N, 1630.2’W, 4839 m, 1 individual; 12930#59, 4850.45’N, 1630.58’W, 4837 m, 1 individual; 12930#68, 48º49.92’N, 16º29.76’W, 4840 m, 2 individual; 12930#73, 48º50.08’N, 16º29.69’W 4839 m, 2 individuals.

1) Aurospio tribranchiata sp. nov. a) Chaetiger 2; b) Chaetiger 3; c) Chaetiger 4; d) Chaetiger 5; scale bar = 100 µm. 2) Aurospio abranchiata sp. nov. from PAP a) Chaetiger 2; b) Chaetiger 3; c) Chaetiger 4; d) Chaetiger 5; e) Chaetiger 8; scale bar = 100 µm.

3) Aurospio abranchiata sp. nov. from canyons a) Chaetiger 2; b) Chaetiger 3; c) Chaetiger 4; Chaetiger 5; scale bar = µm.

Porcupine Abyssal Plain, RRS Discovery D226, March 1998, 13077#19, 4850’N, 1630.05’W, 4846 m, 4 individual; 13077#23, 4849.28’N, 1630.56’W, 4844 m, 1 individual; 13077#59, 48 49.98N, 16 29.96W, 4845 m, 1 individual; 13078#13, 48º50.00’N, 16º30.0’W, 4843 m, 1 individual.

Porcupine Abyssal Plain, RRS Discovery D229, July 1997, 13200#17, 4849.67’N, 1628.72’W, 4843 m, 2 individuals; 13200#20, 48º49.8’ N, 16º29.62’ W, 4844 m, 3 individuals; 13200#47, 4839.29’N, 1630.27’W, 4844 m, 1 individual; 13200#52, 48º49.84’N, 16º29.84’W, 4844 m, 2 individuals.

Porcupine Abyssal Plain, RRS Discovery D231, March 1998, 48 50.51’N 16 29.43’W, 4842 m, 1 individual; 13368#25, 48º 50.51’N, 16º 29.43’W, 3 individuals.

Porcupine Abyssal Plain, RRS Discovery D237 September 1998, 13627#17, 4849.9’N, 16 49.9’W, 4837 m 2 individuals.

Diagnostic features: three pairs of branchiae, first pair starting on chaetiger 3 and the last pair being much longer than the other two.

Description. Small slender species with thorax widening posteriorly then staying the same width; holotype fragment with 20 chaetigers, 3.00 mm long; 0.18 mm wide at chaetiger 1 (not including the chaetae). Colour cream to pale yellow.

Prostomium rounded to rectangular; caruncle long extending to anterior edge of chaetiger 2, well developed, then appearing to extend weakly beyond segment boundary. No eyes. Peristomium separated ventrally and laterally from chaetiger 1, fused dorsally forming a distinct rounded collar. Palps simple up to 5 chaetigers in length, no basal sheath.

Branchiae present on chaetigers 3 to 5; all apinnate, cylindrical, tapering gradually to a rounded point; branchiae on chaetigers 3 and 4 short, about the same length as the accompanying dorsal lamellae; branchiae on chaetiger 5 long, up to five chaetigers in length and two to three times the length of the accompanying dorsal lamellae (Fig. 11.1d; 12 a,c, 13a,c.

Chaetiger 1 with small rounded notopodial lamellae. Notopodial lamellae increase in size with the largest on chaetigers 4 and 5; lamellae triangular on chaetigers 2 and 3, becoming wider and more rounded on chaetigers 5 and 6. Notopodial lamellae in mid-body low and rounded. Dorsal crests low difficult to see but occur on chaetigers 9 to 12.

Neuropodial lamellae on chaetiger 1 small rounded, increasing over chaetigers 2 to 9; lamellae largest on chaetiger 3 ( Fig 12 b).

Capillaries arranged on two rows on notopodia and neuropodia, capillaries bilimbate with those in the lower row slightly granulated. Sabre chaetae robust, curved, limbate, slightly or non-granulated, starting on chaetiger 10 or 11; one per fascicle. Neuropodia hooded hooks start on chaetiger 12, up to six per fascicle; two to three pairs of small teeth above the main fang (specimens small difficult to see the exact arrangement), no inner hood; Notopodial hooded hooks not observed. Pygidium unknown.

Methyl green pattern. Band of stain across middle of prostomium or across whole prostomium, diffuse over body.

Remarks. A. tribranchiata sp. nov. is assigned to Aurospio because the branchiae start on chaetiger 3. All specimens of A. tribranchiata , were carefully examined stained with Shirlastain A (SDL international. A textile fibre identification stain - very useful in revealing features, such as scars) and were not able to detect the presence of scars on any of our specimens. As further supporting evidence there was no branchial pair on chaetiger 2 or evidence of their scars even on otherwise complete specimens which had very long branchiae of chaetiger 4 (which could be easily lost) and palps (almost always lost in spionids) still attached. Based on current evidence we have assigned this species to Aurospio until proven otherwise. Other characters such as the shape of the prostomium, lack of an internal secondary hood in the hooded hooks also are common to species in this genus (but see Remarks in the previous species for a discussion on the problems of defining this genus).

A. tribranchiata sp. nov. is similar to A. pilkena Wilson, 1990 and A. banyulensis (Laubier, 1963) , in particular the form of the prostomium, having three pairs of branchiae (see Table 4). A. banyulensis also has dorsal crests starting on chaetiger 8, hooded hooks starting on chaetiger 12 and sabre chaetae on chaetiger 10. A. tribranchiata sp. nov. differs in the arrangement of the third pair branchiae which are long whereas on A. pilkena and A. banyulensis they are all the same size. A. longibranchiata differs from A. pilkena in the starting positions of the sabre chaetae and hooded hooks and having dorsal crests (see Table 4).

Etymology. tribranchiata refers to the three pairs of branchiae found on this species. Ecology. A. tribranchiata sp. nov. is one of the dominant species of spionids found on the Porcupine Abyssal Plain, found in densities of between 4 and 24 individuals per m2. This species was found within the sediment at depths between 0–5 cm.

Distribution. This species has only been recorded from the Porcupine Abyssal Plain 48°N, 16° W (Northeast Atlantic Ocean) and from a depth of 4800 m.

Figures

FIGURE 1. Maps showing location of collecting sites and distribution of species. a. Locations of the collection sites. CCFZ- Clarion—Clipperton Fracture Zone, W = west site, E = east site, A = UK concession area; CR—Crozet Island; CVAP Cap Verde Abyssal Plain; EP—Equatorial Pacific (EqPac); MAP—Madeira Abyssal Plain; PAP—Porcupine Abyssal Plain; PC— Portuguese Canyons. b. Distribution of Prionospio amarsupiata sp. nov (blue squares), Aurospio abranchiata sp. nov (orange triangles); c. Distrubutions of Prionospio branchilucida sp nov (purple stars), P. vallensis sp. nov (blue triangle); d. Distributions of Prionospio kaplani sp. nov (solid green hexagons); P. hermesia sp. nov (yellow circle), Aurospio tribranchiata sp. nov. (inverted orange triangle)

FIGURE 8. Drawings of hooded hooks of a) Prionospio branchilucida sp. nov.; b) Prionospio kaplani sp. nov.; c) Aurospio abranchiata sp. nov.; d) Aurospio tribranchiata sp. nov. (left hook shown without hood). Bar scale = 0.001 mm (a – d). e) Prionospio amarsupiata sp. nov.; f) Prionospio hermesia sp. nov. g) Prionospio vallensis sp. nov. Bar scale = 0.001 mm (e – g).

FIGURE 12. Aurospio tribranchiata sp. nov. (Bengal 1 D 222 12390 # 59). a) Dorsal view of anterior chaetigers, showing regenerating palp on left side; scale bar = 100 µm. b) Mid body region show dorsal folds; scale bar = 100 µm. c) Second specimen dorsal view of anterior chaetigers; scale bars = 100 µm. d) Detail of anterior chaetigers of second specimen, showing detail of palp and long third branchiae; scale bar = 50 µm.

Tables

TABLE 3. Comparison of species of Aurospio. Abbreviations: Ch—Chaetiger, HH—hooded hooks. Characters taken from original descriptions.

Species	No of pairs branchiae	Size of branchiae	Sabre chaetae	Start of HH	Dorsal crests
A. abranchiata sp. nov.	absent	n/a	Ch10	Ch11–12	Ch8
A. dibranchiata	2	Ch3>Ch4	Ch9–11	Ch9–11	Ch5-10*
A. banyulsensis	3	All equal	Ch10	Ch12–13	Ch7–8
A. pilkena	3	All equal	Ch15–16	Ch18–19	absent
A. tribranchiata sp. nov.	3	Ch3<<Ch5	Ch10/11	Ch12	Ch8
A. foodbancsia	1	n/a	Ch10	Ch11	Ch9
*absent in some specimens