Haliestes inhabited waters about 150-200 m deep in the outer shelf/upper slope area of the
Anglo-Welsh Basin, within the southern subtropics (Brett, Boucot & Jones 1993; Briggs,
Siveter & Siveter 1996). Its long walking legs, which are more typical of deeper or quiet
water, extant, pycnogonids (Vilpoux & Waloszek 2003), are consistent with this setting. The
morphology and attitude of the walking legs suggests that they functioned in a similar way
to those of Recent species (Manton, 1978; Schram & Hedgpeth 1978; Vilpoux & Waloszek
2003). Haliestes was almost certainly epibenthic like most Recent pycnogonids, possibly on
the local unconsolidated carbonate muds or perhaps on the abundant, co-existing sponges in
the way that hexactinellids harbour pycnogonids on muddy bottoms in the Indian Ocean
today (Arnaud & Bamber 1987). Living pycnogonids also prey on gastropods and
polychaetes, and they can be commensal with asterozoans, gaining shelter amongst
pedicellariae and tube feet in exchange for oral surface cleaning; these elements were also
present in the Herefordshire fauna. The setae on the walking legs may have acted as a basket
trap. By analogy with modern species the proboscis of Haliestes would have extracted soft
tissues directly. Likewise, the chelicerae probably grasped and passed food to the mouth
(King 1973), although they are directed upwards; this attitude is unknown in extant
pycnogonids and suggests a greater range of cheliceral mobility in Haliestes.
Arnaud, F. & Bamber, R. N. The biology of Pycnogonida. Adv. Mar. Biol. 24, 1-96 (1987).
Briggs, D. E. G., Siveter, David J. & Siveter, Derek J. Soft-bodied fossils from a Silurian
volcaniclastic deposit. Nature 382, 248-250 (1996).
Brett, C. E., Boucot, A. J. & Jones, B. Absolute depths of Silurian benthic assemblages.
Lethaia 26, 25-40 (1993).
King, P. E. Pycnogonids, 144 pp (Hutchinson & Co, London, 1973).
Manton, S. M. Habits, functional morphology and the evolution of pycnogonids. Zool.
Journ. Linn. Soc. 63, 1-21 (1978).
Schram, F. R. & Hedgpeth, J. W. Locomotory mechanisms in Antarctic pycnogonids. Zool.
Journ. Linn. Soc. 63, 145-170 (1978).
Vilpoux, K. & Waloszek, D. Larval development and morphogenesis of the sea spider
Pycnogonum litorale (Ström, 1762) and the tagmosis of the body of Pantopoda. Arthrop.
Struct. Devel. 32, 349-383 (2003).