Aaptos simplex

Aaptos simplex (Lambe, 1893b)

Fig. 17 A–G

Suberites simplex Lambe, 1893b, Suberites simplex Lambe, 1893b of Austin & Ott 1987.

Material examined. Holotype: CMNI 1900–2895 (previously 2708), near Comox, Strait of Georgia, BC, (approx. 49º 42′N, 124º 50′W), 73 m depth, Jun. 24, 1885, coll. G. M. Dawson.

Other material: KML 1046, off Sandspit, Hecate Strait, BC, (approx. 53º 15'N, 131º 44'W), no depth, Jul. 29, 1960, coll. D. B. Quayle; KML 1037, KML sta. 226/70, Gordon Channel, BC, (50º 54.4'N, 127º 39.1'W), 290–436 m depth, Sept. 16, 1970, coll. W.C. Austin, 1 specimen; KML 1041, KML sta. VT2/80, Dark Cove, Jervis Inlet, BC, (49º 48.8'N, 123º 57.0' W), 150 m depth, May 19, 1980, coll. V. Tunnicliffe, 1 specimen; KML 1045, 5VT19/ 81, Dark Cove, Jervis Inlet, BC, (49º 48.8'N, 123º 57.0' W), 187 m depth, Feb. 24, 1981, coll. W.C. Austin, 1 specimen on dead Aphrocallistes vastus skeleton; KML 1040, KML sta. 80/75, Junction Passage, Barkley Sd., BC, (48º 57.0'N, 125º 48.6'W), 181–201 m depth, Apr. 17, 1975, coll. W.C. Austin, 1 specimen; KML 1039, KML 55/ 75, NW of Poet Nook, Barkley Sd., BC, (48º 53.5'N, 125º 03.5'W), 26–126 m depth, Apr. 14, 1975, coll. W.C. Austin, 1 specimen; KML 1038, KML sta. 61/75, East of Soquel Bank, BC, (48º 42.5'N, 125º 10.9'W), 55 m depth, Apr. 15, 1975, coll. W.C. Austin, 1 specimen; VT16/81, KML 1043, VT10/80, Squally Reach, Saanich Inlet, BC, (48º 33.3'N, 123º 32.8'W), 63 m depth, 1980, coll. V. Tunnicliffe, 9 specimens; KML 1042, VT580, Elbow Point, Saanich Inlet, BC, (48º 32.7'N, 123º 32.5'W), 63–99 m depth, Nov. 18, 1980, coll. V. Tunnicliffe, numerous specimens; KML 1044, VT 14/80 Elbow Pt., Saanich Inlet, BC, (48º 32.7'N, 123º 32.5'W), 65 m depth, 1980, coll. V. Tunnicliffe, abundant on collected rock; KML 1036, KML sta. 67/68, off Whytecliffe Park, BC, (48º 22.2'N, 123º 17.5'W), 20 m depth, Aug. 16, 1968, coll. W. C. Austin, 2 specimens, 1 on dead Aphrocallistes vastus skeleton.

Description. Macroscopic features. Hemispherical with no obvious oscula. Often a flattened skirt around the base. Surface smooth and hard to the touch. One specimen with six small papillae, absent in others. Specimens range in size up to about 11 mm in diameter. Colour alive yellowish white (Fig. 17 A).

Microscopic features. (Based on specimen KML 1036 from Sta. 7/68 Whytecliff Park, BC). Ectosome about 800 µm thick, and clearly set off from the choanosome. Choanosome, in contrast to Suberites spp., with long megascleres aligned in well developed spicule tracts fibres radiating toward and supporting a palisade of shorter megascleres in the ectosome (Fig. 17 B).

Spicules. The megascleres of the ectosome appear to fall in long or short size categories; the long megascleres constitute less than 5% of the total. The shorter megascleres are all tylostyles, while longer megascleres are almost all fusiform subtylostyles. The megascleres in the radiating spicule tracts of the choanosome are the longest.

KML 1036 Remarks. Fusiform subtylostyles are similar to strongyloxea except that the blunt end is subtylote rather than stylote. Their fusiform shape can be seen in the tapering toward the blunt end (Fig. 17 G) as well as toward the pointed end. At least one of the megasclere classes has a blunt end which is very close to a style (Fig. 17 G) which would place it in the category of strongyloxea.

Lambe described the long megascleres as “straight, very gradually pointed, smooth tylostyli with moderately well marked elongated heads”. His figure does not suggest a fusiform shape. Otherwise, the macro and microscopic structure of our material fits well with that described by Lambe from the holotype.

Aaptos is defined as belonging to the Suberitidae with a radiate skeleton of strongyloxeas in three size classes the smallest of which form a dense ectosomal palisade. There are no microscleres (van Soest 2002). Redescription of the holotype of Aaptos aaptos (Schmidt, 1864) by Kelly-Borges & Bergquist (1994) reported strongyloxea of two size categories 1053–(1502)–1911 and 490–(705)–955. It did not mention or figure large fusiform subtylostyles. However, illustrations of the tylostyles of the type by Lendenfeld (1897) reproduced by van Soest (2002) did figure three of the four largest megascleres as fusiform subtylostyles and the fourth as a fusiform style or strongyloxea in A. aaptos from the Adriatic. The tapering of the megascleres in A. simplex is certainly not as marked as in some species of Aaptos (e.g., Aaptos niger Hoshino, 1981) but is also not qualitatively different from that in the type species as figured by Lendenfeld (1897). Suberites simplex is a synonym of A. simplex in Austin et al. (2012).

The megasclere size range in our material is not as great as that in A. aaptos with two non-overlapping size categories of strongyloxea. But the range is comparable to e.g., A. niger Hoshino, 1981 with a range of 540–1310 µm. The thick radiating fibers made up of the long megasleres in A. simplex are comparable to those in A. aaptos (Kelly-Borges & Bergquist 1994, van Soest 2002).

Lehnert et al. (2008) described Aaptos kanuux as a new species from the Bering Sea. It has ectosomal tylostyles 104–215 x 4–8 µm; choanosomal strongyloxea 794–2132 µm x 15–22 µm, and choanosomal fusiform subtylostyles 485–770 x 8–10 µm. The large maximum size of the megascleres is about twice that in A. simplex and they are strongyloxeas, not fusiform subtylostyles. The latter constitute a category of medium size megascleres. Lehnert et al. (2008) compared A. kanuux with five congeners known from the North Pacific or North Atlantic. They concluded, largely on the basis of megasclere form and size, that A. kanuux is not conspecific with any of them. Based on the table by Lehnert et al. (2008), A. simplex does not have the same spicule size range and/or complement as any of the other species of Aaptos recorded from the northern hemisphere or with A. kanuux. While the colour in life of A. simplex is yellowish white, and that of A. kanuux is mustard yellow, a dramatic colour range from white to bright yellow has been observed in at least one other hadromerid, Polymastia pachymastia.

Conclusions. Based on the tapering of the megascleres, their large size range, and the radiating skeleton, we consider that our specimens are members of the genus Aaptos and belong to the species A. simplex. The definition of the genus might be modified to encompass fusiform subtylostyles as well as fusiform styles or strongyloxea. Aaptos simplex characters do not fit descriptions for any of the six species of Aaptos recorded from the northern Hemisphere. However, megasclere size ranges are based on measurements from a 5 mm specimen of A. simplex. The A. kanuux specimens ranged from 9–19 mm.

Bathymetric range. 20–290 m depth.

Geographic distribution. Saanich Inlet to off Sandspit (BC, Canada).

Ecology. Aaptos simplex is one of the first organisms to appear above the anoxic layer in BC fjords in oxygen tensions of 0.2 ml/l (Tunnicliffe 1981).