Tribrachium schmidtii Weltner 1882

Tribrachium schmidtii Weltner, 1882

Figures 51 a–g, 52a–g

Tribrachion schmidtii Weltner, 1882: 50, pl. III figs 29–41.

Tribrachium schmidtii; Ridley 1884: 479; Sollas 1888: 154, pl. XVII, pl. XLI fig. 5; Wilson 1902: 385; Van Soest & Stentoft 1988: 34; Uriz 2002: 124, figs 20–21; Hajdu et al. 2011: 78.

Kapnesolenia fisheri De Laubenfels, 1934: 6.

Tribrachium fisheri; Uriz 2002: 125, fig. 22.

Material examined. RMNH Por. 6295, Suriname, ‘Luymes’ Guyana Shelf Expedition, station 26, 7.2°N 53.9333°W, depth 86 m, bottom coarse sand, 27 August 1970 (3 specimens); RMNH Por. 6302, Suriname, ‘ Luymes O.C.P.S. ’ Guyana Shelf Expedition, station K101B, 7.3783°N 54.3583°W, depth 93 m, rectangular dredge, 17 April 1969 (13 specimens); RMNH Por. 6305, Suriname, ‘Luymes’ Guyana Shelf Expedition, station 29, 7.15°N 53.9167°W, depth 96 m, bottom muddy sand, 27 August 1970 (4 specimens); RMNH Por. 9301, 9395, 10000, Suriname, ‘ Snellius O.C.P.S. ’ Guyana Shelf Expedition, station F45, 6.4417°N 56.5467°W, depth 34 m, Van Veen grab, 7 May 1966 (3 specimens); RMNH Por. 9304, Suriname, ‘ Snellius O.C.P.S. ’ Guyana Shelf Expedition, station F41, 6.9133°N 56.4767°W, depth 55 m, Agassiz trawl, 6 May 1966 (1 specimen); RMNH Por. 9305, Suriname, ‘ Luymes O.C.P.S II.’ Guyana Shelf Expedition, station K101A, 7.4233°N 54.4317°W, depth 132 m, Van Veen grab, 17 April 1969 (2 specimens); RMNH Por. 9306, 9330, 9859, Suriname, ‘ Luymes O.C.P.S. II’ Guyana Shelf Expedition, station M98, 7.1767°N 53.845°W, depth 85 m, bottom coarse sand, rectangular dredge, 16 April 1969 (13 specimens); RMNH Por. 9307, Suriname, ‘Luymes’ Guyana Shelf Expedition, station 28, 7.2°N 53.9333°W, depth 82 m, bottom coarse sand, 27 August 1970 (4 specimens); RMNH Por. 9308, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 51, 7.6833°N 57.0333°W, depth 98 m, bottom calcareous sand, 30 August 1970 (3 specimens); RMNH Por. 9710, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 84, 7.68°N 57.2533°W, depth 70.5 m, Van Veen grab, 2 September 1970 (2 specimens); RMNH Por. 9711, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 102, 7.8833°N 57.4333°W, depth 90 m, Van Veen grab, 4 September 1970 (1 specimen); RMNH Por. 9712, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 63, 7.5833°N 57.0667°W, depth 71 m, sandy bottom, 31 August 1970 (1 specimen); RMNH Por. 9713, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 83, 7.7333°N 57.2833°W, depth 82 m, muddy sandy bottom with shells, 2 September 1970 (1 specimen); RMNH Por. 9714, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 73, 6.9167°N 57.25°W, depth 29.5 m, muddy sandy bottom with shells, 31 August 1970 (1 specimen); RMNH Por. 9715, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 87, 7.5667°N 57.2667°W, depth 59 m, sandy bottom with shells, 2 September 1970 (1 specimen); RMNH Por. 9723, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 121, 7.2167°N 57.6833°W, depth 25 m, bottom muddy sandy with shells, 7 September 1970 (2 specimens); RMNH Por. 9724, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 97, 6.8°N 57.5167°W, depth 21 m, bottom muddy sandy with shells, 5 September 1970 (1 specimen); RMNH Por. 9725, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 107, 7.7°N 57.5°W, depth 65 m, bottom mud with shells, 3 September 1970 (1 specimen); RMNH Por. 9726, Suriname, ‘Luymes’ Guyana Shelf Expedition, station 38, 7.2833°N 53.95°W, depth 100 m, bottom shell gravel, trawl, 28 August 1970 (1 specimen); RMNH Por. 9727, Suriname, ‘Luymes’ Guyana Shelf Expedition, station 2, 7.1167°N 53.6°W, depth 93 m, bottom sandy calcarenite, dredge, 24 August 1970 (2 specimens); RMNH Por. 9853, Suriname, ‘ Luymes O.C.P.S. II’ Guyana Shelf Expedition, station unknown, 1969 (1 specimen); RMNH Por. 9906, Suriname, ‘ Snellius O.C.P.S. ’ Guyana Shelf Expedition, station F38, 7.23°N 56.4067°W, depth 81 m, Agassiz trawl, 5 May 1966 (2 specimens); RMNH Por. 9908, Suriname, ‘ Snellius O.C.P.S. ’ Guyana Shelf Expedition, station A12, 7.3783°N 56.0917°W, depth 120 m, Agassiz trawl, 5 May 1966 (1 specimen); RMNH Por. 9909, Suriname, ‘ Snellius O.C.P.S. ’ Guyana Shelf Expedition, station E64, 6.9217°N 56.2017°W, depth 57 m, Agassiz trawl, 5 May 1966 (1 specimen).

Description. (Figs 51 a,a1, 52a) A perfectly spherical body is buried in the soft substratum and a single long thin-walled tube with open end extends above the substratum. Surface of the spherical body rough and occasionally encrusted by sand or pieces of shells, surface of the tube smooth. Size of spherical body variable, 3–15 mm in diameter, tube diameter 2–5 mm, length of tube up to 55 mm. Color in alcohol of spherical body pale beige, of tube white-transparent. Consistency of spherical body hard, barely compressible, of the tube parchment-like but tough.

Skeleton. The spherical body has a radiate skeleton, with cladomes of the triaenes carrying a thin layer of microrhabds at the surface. The radiate bundles consist predominantly of dicho- or plagiotriaenes and oxeas, with rarely some thin anatriaenes. Choanosomal skeleton with fewer bundles of megascleres, somewhat pulpy. The skeleton of the tubes is a beautiful tangential arrangement of orthodiaenes with both rhabdomes and cladomes aligned very regularly at opposite angles, covered by a thin but dense layer of microrhabds. No other megascleres. The tubes contain no tissue (and thus no choanocyte chambers; for a detailed description of the choanosomal arrangement cf. Sollas 1888, p. 156).

Spicules. (Figs 51 b–g, 52b–g) Oxeas, dichotriaenes/plagiotriaenes, anatriaenes, orthodiaenes, microrhabds. To support the synonymy decision and the discussion below, I present the spiculation of a selected representative specimen of ‘ Kapnesolenia fisheri’, RMNH Por. 6305 (Fig. 51) and a ditto T. schmidtii specimen RMNH Por. 9935 (Fig. 52).

Oxeas (Figs 51 b,b1, 52b,b1), fusiform, gradually tapering to thin endings, occasionally with bluntly rounded ends, 2340– 2742 –3420 x 37 – 49.3 –60 µm.

Dichotriaenes (Figs 51 c,c1), when present, of widely divergent sizes, with secondary cladi curved at right angles to the rhabdome, and with bluntly rounded apices on the cladi; rhabdomes 910– 1956 –3060 x 12 – 38.9 –78 µm, cladomes 198– 492 –1080 µm, primary cladi 62– 90 –110 x 11 – 33.8 –57 µm, secondary cladi 30– 186 –510 x 8 – 25.8 –54 µm.

Plagiotriaenes 1 (Figs 51 d, 52c,c1) when present, large and thick, with cladi often curved and curled at the bluntly rounded endings, occasionally bifid (Fig. 52 d); rhabdomes 840– 1337 –1810 x 26– 58.0 –84 µm, cladomes 186– 513 –780 µm, cladi 96– 258 –390 x 29 – 53.7 –78 µm.

Plagiotriaenes 2 (not illustrated), not common but always present, small and thin, with cladi straight, probably to be interpreted as juvenile stages of the larger dicho- and plagiotriaenes; rhabdomes (n=5) 420–600 x 6–9 µm, cladomes 69–84 µm, cladi 36– 52 x 5–8 µm.

Anatriaenes (Figs 51 e, 52e), not common, not always present, usually with reduced cladomes and stunted cladi; rhabdomes (n=4) 1020–1560 x 4–20 µm, cladomes 30–120 µm, cladi 12– 61 x 4–13 µm.

Orthodiaenes (Figs 51 f,f1, 52f,f1), with thinly tapering ending, with cladi at right angles to the rhabd and usually more or less symmetrical, usually with sharp endings; rhabdomes 504– 2429 –4680 x 6 – 31.6 –54 µm, cladomes 219– 929 –1530 µm, cladi 111– 456 –900 x 5 – 27.4 –48 µm.

Microrhabds (Figs 51 g,g1, 52g,g1), variable in length and thickness, with prominent bifid or trifid rays provided with sharp spines; no clear size or form categories were observed in the 72 specimens obtained, length 9– 11.6 –16 µm.

Distribution and ecology. Cuba, Puerto Rico, NE Brazil, Guyana Shelf, on sandy and muddy bottoms, at 12–720 m depth (Guyana Shelf 25–132 m).

Remarks. Treatment of this species by Uriz (2002) must be criticized. The holotype was declared ‘missing’, but the catalogue of the Zoological Museum of Strasbourg (MZS) lists the specimen under MZS Po0710, labeled ‘Agassiz collection, 1879, locality Morro Light, depth 250–400 fathoms’, exactly as described by Weltner (1882, p. 55). There can be little doubt that the holotype is extant and the neotype designation made by Uriz (the ‘Challenger’ specimen described by Sollas (1888), BMNH 1889.1.171D) is void. The existence of the holotype poses indeed a challenge as it lacks the basal globular main body, which contains additional spicule types not described by Weltner. Subsequently, Uriz maintained that the species is distinct from Kapnesolenia fisheri De Laubenfels, 1934 (holotype USNM 22370), considered a junior synonym of T. schmidtii by Van Soest & Stentoft (1988, p. 34), because that would have only dichotriaenes in the main body, lacking orthotriaenes (=plagiotriaenes). A further distinction between the two would be the existence of two types of sanidasters in schmidtii and only a single type in fisheri. These alleged differences cannot be properly confirmed from the holotype as it lacks the body part in which the triaenes occur. Moreover, in the many specimens studied by me, there are no clearly different sanidaster types discernible, all specimens having thinner or thicker, shorter or longer sanidasters. A slight discrepancy in sanidaster length was found between the specimens possessing dichotriaenes (9–12 µm) and those possessing plagiotriaenes (10–15 µm), but no further relationships between specimens with predominantly dichotriaenes and predominantly ortho(plagio-)triaenes and the shape of the sanidasters could be detected. Finally, Uriz suggested that the two alleged species would be separated by their depth occurrence, schmidtii occurring in shallow water, fisheri in deep water. Specimens identified as T. schmidtii occurring in deep water were suspected by her to be K. fisheri. Since the holotypes of both alleged species were collected in deep water, at respectively 450–720 m and 324–360 m, this cannot be the difference between the two, as that would mean they are the same species. The choice of a neotype from very shallow waters by Uriz was unfortunate in this respect. Extending this argument, the shallow-water specimens, represented by the ‘Challenger’ specimen, would then belong to an unnamed species. However, in my experience all the many specimens (72) I found on the Guyana shelf, between 21 and 132 m, were closely similar in habitus and measurements, with a normal continuous variation in main body sizes and length of the tubes, no distinct habitus differences are apparent.

Nevertheless, Uriz is right in the observation that some individuals have predominantly dichotriaenes (with a few plagiotriaenes present) in the basal body (the majority of my specimens, corresponding then to ‘ K. fisheri’), and others have predominantly plagiotriaenes with a few provided with one or more bifid cladi (a minority of three in my specimens, only RMNH 9395, 9725 and 9853). There is no relation with depth and triaene dominance: the specimens with dichotriaenes were collected at 21–132 m, those with predominantly plagiotriaenes from 34– 65 m.

For the time being I propose to consider the species schmidtii and fisheri as synonyms. To confirm the likely synonymy of the two forms, I present separate SEM illustrations of a fisheri form (Figs 51 b–g) and a s chmidtii form (Figs 52 b–g).