Echinoderms from Southern New Zealand
Family Echinasteridae — Henricia Gray, 1840 — Henricia ralphae sp. nov. (Figures 1 to 4)
Henricia Gray, 1840
Dimensions: R, 53 mm.; r. 15 mm.; breadth of arm at base, 17 mm. R, 54 mm.; r, 17 mm.; br., 23 ram. R, 64 mm.; r, 14 mm.; br., 13 mm. (syntypes). R, 72 mm.; r, 16 mm.; br., 18 mm. (holotype).
Henricia ralphae sp. nov.
Fig. 1.—Actinal surface of arm, the furrow lying to the left. Fig. 2.—Abactinal surface of arm. Fig. 3.—Abactinal surface of disc in region of periproct and madreporite. Fig. 4.—Part of syntype, showing the inflated type of arm, abactinal view.
Abbreviations: A, anus. AB, abactinal plate. ACT, actinal spines. AD, adambulacral spines. FU, furrow-spine of adambulacral plate. MADP, madreporite covered by spines. MAG, marginal spines, arranged in comb. PAA, papular area. PAP, papula (or dermal branchia). PP, periproct.
Figs. 1 to 3 are to the lower scale; Fig. 4 to the upper scale.
On the actinal surface, three regular, longitudinal series of plates are present—namely, an adambulacral series bordering the furrow, next to it an actinal series, and next to this a prominent marginal series. The actinal, or middle, series extends from near the mouth to only about half-way along the arm. Papulae occur singly in the depressions between the adambulacral and actinal series, and between the actinal and marginal series. The armature of the plates is as follows: Each adambulacral plate bears a furrow-spine, which is placed deep in the furrow and is somewhat curved; it also bears subambulacral spines, two or three large ones at or near the furrow border, and beyond these three or four smaller spines occur. All these adambulacral spines are arranged in a more or less monoserial, transverse line. The actinal plates each bear a compact cluster of four or five similar slender spines. The marginal plates are transversely elongated; each of them carries a transverse monoserial comb of seven to ten slender, rather glassy spines with thorny tips. There are distinct intervals without spines between all these plates, so that in no case are there continuous transverse rows of spines extending from the furrow up the sides of the arm, such as occur in the other two New Zealand species, H. lukinsii and H. compacta.
Colour in life, brilliant orange-vermilion.
Holotype in the Zoology Museum, Victoria University College.
Type Locality.—Off east coast of Otago, between Taiaroa and Moeraki, three specimens trawled from 40 fathoms, collected by Miss P. M. Ralph in November, 1951. Syntypes from east coast of Canterbury, between Moeraki and Timaru, 40 fathoms, collected also by Miss Ralph in January, 1951.
Remarks.—This large and striking species of Henricia can easily be differentiated from the other two species of the genus occurring in New Zealand waters (H. lukinsii and H. compacta) by its sparse abactinal spinulation, its distinctive actinal and adambulacral armature, and by its large size. Of other species of Henricia known from the Southern Ocean, H. obesa (Sladen) resembles H. talphae in general form, including the occasional inflation of the base of the arm (cf. dimensions of second syntype listed above with those of the holotype)—but it has a different spinulation. The same may be said of the Australian "Henricia page 11 hyadesi" (Perrier), which supposed species Fisher (1940) has merged with obesa partim, and with H. sufflata and H. compacta partim. H. sufflata (Sladen) is as yet known only from the Challenger station 170, off the Kermadec Islands, 520 fathoms; it, too, has the base of the arm inflated in the type material, but the spinulation is quite different. H. simplex (Sladen) has a sparse abactinal spinulation, but its subambulacral armature differs from that of H. ralphae. H. pagen-stecheri (Studer) presents one resemblance to H. ralphae, as also does H. lukinsii, in the presence of an inter radial abactinal depression—an inconstant feature in the two former species, however—but that is the only similarity. H. diffidens (Koehler) is of the North Pacific "longispina" type, and so is not comparable.
The foregoing comparisons are given in view of the notoriously difficult systematics of Henricia. General body shape is variable and of no guide in separating species. The variation is well shown in the dimensions quoted for the present species. The pronounced inflation of the arm in one syntype is illustrated in Fig. 4.
In 1909, Benham described Echinaster farquhari from almost the same locality, namely, off Otago Heads, in 18 to 28 fathoms; only one specimen was obtained. In general facies it presents, to judge by Benham's account, a remarkable similarity to H. ralphae; in size and colour, it is similar. The conjunction of the localities caused me to wonder at first if he might have mistaken a Henricia for an Echinaster, and if the two might really be identical. It seems, however, that Benham's species must be a true Echinaster, as I think the following considerations show: Benham states that in Echinaster farquhari the abactinal armature of the plates of the arms comprises ... "here and there an isolated, short, blunt, apparently immovable spine" which ... "springs from a node in the network." His figures support the statement—which, of course, points to Echinaster. Again, although he refers to papulae on other parts of the body, he makes no reference to any between the actinal plates—a condition also diagnostic of Echinaster. There are a number of other differences between E. farquhari and H. ralphae, such as the distinctive arrangement of the spines on the lower plates, the fact that spines are sparse on the abactinal surface but become more numerous near the arm-tips; the madreporite in E. farquhari is prominent, projects above the abactinal surface, and is not surrounded by spines. We are forced to conclude that the two forms cannot be extreme variants of one and the same species, and that therefore the two related genera, Henricia and Echinaster, occur in the same area. An analogue is presented perhaps by Persephonaster and Psilaster, two related genera each represented by one species off Cape Campbell, and as yet known to be common only in that one place.