Hippomedon coecus (Holmes 1908)

Hippomedon coecus (Holmes)

Tryphosa coeca Holmes, 1908, pp. 496–497, figs. 7–8.

Hippomedon (?) coecus.—Gurjanova, 1962, pp. 96–97, fig. 21.

Hippomedon coecus.—Hurley, 1963, pp. 136–137.

NOTES ON HOLOTYPE.—Hurley (1963) has reported partially on the poorly elucidated holotype of this species, from Monterey Bay, California. I have examined the type once again and must add some further details in light of various new species described from Oregon.

There is no doubt that H. coecus is a member of Hippomedon in view of the small head and the stout spines on the outer lobe of maxilla 1, the gnathopods, the pleonal epimera, and the characteristic maxillipeds. The holotype is in poor condition, consisting of two type slides in deteriorating condition, a carcass with head, and portions of pereopods detached in alcohol.

Eyes are absent (although a faint clear space with an internal diffuse spot is present); the lateral cephalic lobes are sharp and more strongly projecting than in H. pacificus Gurjanova (1962); essentially no antennal notch is present; coxae 1–3 each have a posteroventral notch, coxa 4 is not serrate but otherwise resembles that of H. subrobustus Hurley; gnathopods, pereopod 1 and antenna 1 are as figured by Holmes; uropod 1 with 2 spines and uropod 2 with 1–2 spines on outer rami; inner ramus of uropod 1 with 1 spine, inner ramus of uropod 2 lacking spines; pleonal epimeron 1 with subquadrate but smoothly rounded posteroventral corner, epimeron 2 with very weak tooth, one-third as long as that shown for H. wecomus, epimeron 3 with tooth similar to that of H. wecomus, new species, but with a very minute notch on the dorsal base of the tooth; antenna 1 as drawn by Holmes and lacking a distal spine on article 1 of the primary flagellum; pereopods 3 and 5 generally resembling those of H. pacificus Gurjanova (1962) but posterior serrations of article 2 smaller and more numerous by about 30 percent; pereopod 4 generally similar but anterior and posterior margins of article 2 nearly parallel as in H. wirketis Gurjanova (1962) and serrations continuing down to terminus of posterior margin; thus article 2 of pereopod 5 definitely tapering distally; body covered with sculpture like that of H. pacificus, polygons each with a central sharp scale or spine; uropod 3 poorly preserved but article 2 of outer ramus determined to be 45 percent as long as article 1 of outer ramus.

Hippomedon coecus seems to be a blind relative of H. pacificus. The interantennal cephalic lobe appears to be slightly larger on H. coecus than on H. pacificus, article 2 of pereopod 4 does not taper distally, pleonal epimeron 3 has a rudimentary notch above the tooth (easily overlooked under low-power microscopy), gnathopod 2 of H. coecus does not have the small distal bulbosity of article 5 (but it is poorly preserved), the telsonic lobes are slightly wider distally and each apex has a distinct evagination in which the spine occurs and article 2 of the outer ramus of uropod 3 is much longer than it is in H. pacificus.

Hippomedon coecus also has affinities with H. denticulatus orientalis Gurjanova (1962) because of the very rudimentary epimeral notch. The pereopods are almost precisely identical to those of H. d. orientalis, in contrast to H. pacificus. Of course eyes are absent or are completely unapparent in H. coecus. The dorsal crest and distal projection on article 1 of antenna 1 are not nearly as strong as in H. d. orientalis, and article 2 of the outer ramus of uropod 3 is highly elongate in comparison to H. d. orientalis. The palm of gnathopod 1 of the latter is weakly defined in comparison to H. coecus.