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Ericthonius brasiliensis Stebbing, 1906, p. 671 (with synonyms).
This species has not hitherto been recorded from New Zealand, but I have a few specimens collected near D'Urville Rock, Hauraki Gulf, in December, 1914, that I think undoubtedly belong to it. They agree closely with the description given by Stebbing quoted above, and with the figures of E. abditus given by Sars (1894, pl. 215), this species being considered by Stebbing to be a synonym of E. brasiliensis. I have also been able to compare the New Zealand specimens with an English one which I presume to be a specimen of E. brasiliensis (Dana), and find that they agree in all essential points. In one respect, however, the New Zealand specimens appear to differ from E. brasiliensis as defined by Stebbing and to agree with E. pugnax Dana from the “Sooloo Sea”—viz., the third peraeopod has the second joint with a narrow acute downward prolongation of the hind-margin. The same character is possessed by E. macrodactylus Dana, also from the “Sooloo Sea,” and I expect that it is one attained only in the older males, the younger ones having the joint of more normal shape as described by Stebbing. Stebbing says that E. pugnax is closely related to E. brasiliensis, and that E. macrodactylus is distinguished “from E. difformis especially by the long tooth of the fifth joint in the second gnathopod being separated from the base of the sixth joint by a very deep concavity, and by the second joint of the third peraeopod having a narrow acute prolongation of the hind-margin.” Of E. difformis M.-Edw. (a species found in the North Atlantic) he says, “possibly not distinct from E. brasiliensis.” From the fact that the species occurring in New Zealand seems to combine characters of E. brasiliensis and E. pugnax, I strongly suspect that all the forms mentioned above really belong to the one species, the differences in the gnathopods and in the third peraeopods being merely due to different stages of growth. The figures given, which were drawn by Miss Herriott independently and before it was recognized that the species was the same as E. brasiliensis, will, I think,
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Ericthonius brasiliensis.
Fig. 1.—Male, first gnathopod.
Fig. 2.—Male, second gnathopod.
Fig. 3.—Male, third peraeopod.
Fig. 4.—Female, second gnathopod.
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bear out this statement. This conclusion seems to be confirmed by the fact that Walker (1904, p. 292) has recorded E. abditus (i.e., E. brasiliensis) from Galle Harbour, where he says it is abundant, and from other localities on the coast of Ceylon; and that he also gives E. macrodactylus Dana, which is probably the same as E. difformis M.-Edw., from the Gulf of Manaar.
Ericthonius brasiliensis.
Fig. 5.—Female bearing eggs, second gnathopod (? abnormal).
While the males and females appear to agree closely with the figures given by Sars, it is to be noted that I have one specimen in which the second gnathopod has characters intermediate between that of the male and that of the female (see fig. 5). This specimen I would have considered without hesitation an immature male, but the appendage bears a well-developed brood-plate, and there are eggs in the brood-pouch.