S89

Dictyocoryne truncatum (Ehrenberg)

Rhopalodictyum truncatum Ehrenberg, 1861, p. 301, Haeckel, 1887, p. 589

Dictyocoryne cf. truncatum (Ehrenberg), Benson, 1966, p. 235, pl. 15, fig. 1

?Dictyocoryne sp. Ling and Anikouchine, 1967, p. 1489, pls. 191, 192, fig. 4,5

?Dictyastrum angulatum Ehrenberg, 1872b, pl. 8, fig. 17

?Euchitonia mulleri Haeckel (?), Popofsky,1912, p. 137, text. fig. 52 only

DESCRIPTION (modified from Benson, 1966) Test with three, broad, spongy arms, equally to bilaterally disposed, generally with but in several specimens without a spongy patagium between them. Central region consisting of 5-10 or more concentric latticed discoidal shells; these shells are frequently concealed by a fine spongy lattice. Arms narrow proximally for a short distance, becoming broad and thick, elliptical in section distally. In specimens without a patagium the arms have a definite margin; in those with a patagium margin of arms indefinite, often appearing to merge with patagium; in several specimens arms appear only as trianqular dark areas.

DIMENSIONS "based on 30 specimens from stations 46, 56, 60, 71 and 81; angle A 112 deg - 139 deg, mean 126 deg; angle B 92deg - 116 deg, mean 108 deg; angle C 114 deg - 144 deg, mean 127 deg; ratio of angle A to B 1.03-1.43, mean 1.17, of angle C to B 1.07-1.43, mean 1.18; diameter of outermost concentric shell of central region (11 specimens with number of shells ranging from 5-10) 68-117 mu; maximum breadth of arms 86-153 mu; length of base of triangular test 172-343 mu, of altitude 177-348 mu." (from Benson, 1966).

REMARKS

1. Dictyocoryne sp. (in Ling and Anikouchine, 1967) is tentatively included in the synonymy of this species. The arms of their figured specimens are clearly chalice-shaped, but it is not clear whether this characteristic is sufficient to erect a separate species or whether it is an allowable morphological variation of D. truncatum.

2. There is another very similar form, Euchitonia triangulum (Ehrenberg) with the following synonymy:

Stylactis triangulum Ehrenberg, 1872a, p. 320; 1872b, pl. 8, fig. 9, Stohr, 1880, p. 113, pl. 6, fig. 2

Euchitonia triangulum (Ehrenberg) Haeckel, 1887, p. 533.

Euchitonia cf. E. triangulum (Ehrenberg) Ling and Anikouchine, 1967, p. 1487, pls. 189,190, figs.8,9.

Plate 12, figures 2a,b

S90

This species closely resembles D. truncatum (cf. Ling and Anikouchine, 1967) except that the arms are not equidistant and the central region is not spongy. These features were not found to be particularly distinctive and it is suggested herein that there is only one species of this general type. The species is never as markedly bilateral as Euchitonia elegans or Euchitonia furcata.

Benson (1966) described a third species Euchitonia cf. echinata which may be valid. His description is as follows:

"Arms distinctly bilaterally disposed, an odd arm generally distinguishable. Central region circular, consisting of 5-8 concentric discoidal shells; arms generally broad proximally with broader but blunt, thicker terminations, characteristically with 1-5 or more (generally 12) conical to pyramidal terminal spines, continuous inwards as beams, lying in the plane of the disc, variable in length (4-31 mu). Internal structure of arms with distinct, regular, equally spaced, concentric, latticed rings, traceable from arm to arm, 6-20 per arm; terminations of arms appear spongy, suggestive of a structure similar to the central region, i.e., concentric shells. Test covered by a distinct latticed sheath as in the preceding species. A spongy, layered patagium between the arms generally absent or only rudimentary, thinner and more delicate proximally."

DIMENSIONS

(based on 30 specimens) "diameter of outer concentric shell of central region 68-107 mu; length of odd arm 37-129 mu, of each of the two similar arms 43-112 mu and 41-116 mu; minimum breadth of odd arm 49-79 mu, of each of the two similar arms 44-79 mu and 41-80 mu maximum breadth of odd arm 69-135 mu, of each of the two similar arms 54-119 mu and 55-121 mu length of base of triangular test 146-265 mu, of altitude 151-276 mu." (from Benson, 1966).

The distinctive features of this species are the concentric rings which may be traced from arm to arm and the consistent and well-developed terminal spines. However, the concentric ring structure of the arms is quite different from the type of chambering observed in Euchitonia furcata and Euchitonia elegans and for this reason it might be more properly assigned to another genus.

RECENT DISTRIBUTION

1. Benson, 1966; "...cosmopolitan in the Gulf [of California] but is rare at all stations where it is present... some tolerance for waters of higher than average salinity and temperature."

2. Molina-Cruz, 1975, Code S36; used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S36 at each station.