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Helotholus vema Hays, 1965

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Shell cup-shaped, of heavy construction; collar stricture often imperceptible. Cephalis hemispherical, width half that of thorax, wall thick, in some speciemens spongy, pores circular to oval, irregular in size, shape and spacing. Cephalis in some specimens one or two approximately apical spines. Thorax cylindrical, of highly variable length; wall thick, sometimes spongy. Upper horizontal portion of thorax characterized by 6 large circular pores.
Length of apical spine up to 15, of cephalis 45-50, of thorax 44-125, width of cephalis 52-60, of thorax 95-125.
Description based on 40 individuals from samples V-16-66, 920 cm; V-16-130, 450 cm; V16-116, 720 and 750 cm. The internal skeleton of this species is complex but can be reduced to the following elements (Figure A). A basal horizontal ring (BR) is connected to the thorax by 6 stout horizontal beams. Above these heavy horizontal beams occur 6 other beams rising obliquely at angles of about 45° and joining the shell wall at the junction of the cephalis and thorax. Below the horizontal ring are 4 beams wich are in turn connected vertically with the horizontal ring. These can be classified, following Popofsky, into a median bar (mb), 2 lateral spines Ll, Lr), and a dorsal spine (D). In some specimens a bar extends from the junction of the two lateral spines, bisecting the angle between them, and terminates at the basal ring. Near the junction of the two lateral spines, wich make angles up to 90° with the median bar, an axial spine up to 37 micon long projects freely into the thoracic cavity. When the shell is viewed along its main axis, these bars divide the area enclosed by the basal ring into 4 pores. The similarity between the internal structure of this species and Helotholus histricrosa Jörgensen suggests that they may be very closely related. Helotholus vema is distinguished from the the few other members of this genus by the small hemispherical cephalis and broad cylindrical thorax.
Distribution:
This species is restricted to zone ø.
Hays 1965
Helotholus vema
Distinguished by an internal ring within the thorax, connected to the thorax lattice-wall by six (rarely seven) radial beams, by the short tho­rax, and the relatively small, large-pored cephalis. Kellogg (1975) has this species evolving from an ancestral population which she included within the same species, and which Weaver (1983) subsequently defined as Helotholus praevema. This ancestral species was not identified in Leg 113 material. Chen (1975a) questionably identifies the ancestor of H. vema to be Antarctissa cylindrica Petrushevskaya, 1975. Another possi­ble ancestral species is the undescribed form which was confused with H. vema in the initial shipboard work. This undescribed form possesses the same distinctive internal ring structure of H. vema and A. cylindrica, however it is much larger than early specimens of H. vema, and has a less regular, large pored outer lattice shell with only an indistinct cephalis.
The generic assignment of this species is uncertain. The distinctive internal structures led Petrushevskaya to refer to this species as Pseudocubus vema, although she did not formally reassign the species to the genus Pseudocubus. Dumitrica refers to a species similar to H. vema as Pseudocubus cf. vema (Hays). It is not clear whether Dumitrica meant to transfer H. vema into Pseudocubus. Keany and Kennett (1972) refer to this species as Pseudocubus vema, without formally transferring the species, or citing an author for this implied revision. Keany (1979) spe­cifically rejects the assignment of H. vema to Pseudocubus. Kellogg (1975) also referred to this species as P. vema, again without formally transferring the species.

Lazarus 1990


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