Comprehensive Description

provided by Smithsonian Contributions to Zoology
Maera reishi

Maera inaequipes.—J. L. Barnard, 1959:25–26, pl. 5 [not Costa]; 1969a:205; 1969b:121–122.

ETYMOLOGY.—Dedicated to Dr. Donald James Reish for his numerous contributions to our knowledge of eastern Pacific lagoons and estuaries.

DIAGNOSIS.—Lateral cephalic lobes weakly mammilliform, anteroventral corner of head produced as narrow elongate tooth. Eyes ovate, brownish pink in alcohol. Article 1 of antenna 1 with 2 basoventral spines and 1 apicoventral spine. Article 3 of mandibular palp 1.2 times as long as article 2. Coxa 1 weakly extended forward, coxae 1–4 lacking posteroventral notch. Gnathopod 1 of medium stoutness, article 6 ovatorectangular, palm oblique and convex, equal in length to posterior margin of article 6, defined by spine, article 5 with several medial rows of diverse setal spines, article 4 lacking posterodistal cusp; gnathopod 2 very large, article 2 heavily spinose anteriorly, with medium-sized anterodistal lobe, article 3 with similar lobe, article 4 slightly extended posterodistally, article 5 very short, with long tumid posterior lobe, article 6 very large, subrectangular, slightly expanded distally, palm transverse, defined by large tooth, bearing spine, tooth adjacent to weak sinus, palm with one deep incision in males, occasionally in females, latter usually without main sinus, dactyl fitting palm, bearing inner acclivity near position of sinus, acclivity weak to strong, usually absent in females and juveniles. Article 2 of pereopods 3–5 narrowly ovatorectangular, with slightly extended, angular posterodistal corners, posteroproximal margins rounded; dactyls of pereopods 1–5 with strong distal constriction bearing sharp defining corner and armed with seta, sharp but stunted nail bearing accessory tooth, facial setule, constriction also bearing stout setule appressed to margin of nail, locking spines small, straight or slightly curved. Pleonal epimera 1–3 with slightly convex posterior margins, each with small sharp posteroventral tooth, ventrally spinose; pleonites dorsally smooth. Uropod 3 extending flush with other uropods, rami flat, narrow, apically truncate and spinose, inner extending to Mark 80 along outer, tiny article 2 on outer ramus. Telson deeply but not fully cleft, with strongly fixed medial gape, lobes thin, apically truncate or convex, each lobe with 4 long spines, some longer than telson. Dorsoposterior margin of urosomite 3 rounded.

JUVENILES.—Smallest available, 1.9 mm long; proportions of mandibular palp articles 2–3 similar to adult; inner ramus scarcely exceeding Mark 50 on outer ramus; each lobe of telson with 2 long spines; cephalic tooth small but distinct.

DESCRIPTION.—Upper lip and epistome fused together; outer plate of maxilla 1 with 5 bifid and 4 serrate spines; cuticle smooth extent for occasional bulbar setule and occasional seta on coxae; palmar sinus of gnathopod 2 developing before dactylar acclivity and before article 2 heavily spinose.

VARIATIONS.—At the northern end of its range, in suburban California, specimens of Maera reishi reach a length just less than 7 mm whereas their maximum length in more southerly waters of Mexico is less than 5.5 mm. In these large specimens from southern California, the gland cone of antenna 2 extends only two-thirds along article 3 of antenna 2 whereas in southerly specimens the gland cone overreaches the end of article 3. No females with a palmar sinus on gnathopod 2 have been found in the northern end of the range. The dactylar acclivity on gnathopod 2 of many, but not all, males in the north becomes extremely developed as it is in Maera chinarra.

HOLOTYPE.—USNM 142568, male “a,” 5.3 mm (illus.).

TYPE-LOCALITY.—PAZ 3, Gulf of California, Isla Espiritu Santo, 28 November 1971, 0.3–1.0 m, algae, rock wash.

VOUCHER MATERIAL.—Type-locality: female “w,” 5.4 mm (illus.); juvenile “j,” 2.6 mm (illus.). Corona del Mar, California, 6 February 1951, Sabellaria bed, male “v,” 6.5 mm (illus.).

RELATIONSHIP.—This species is distantly related to M. rathbunae Pearse (1908) from Florida, the latter bearing a distinctly oblique palm on gnathopod 2, equally extending rami of uropod 3 and sharply pointed, poorly spinose telsonic lobes. The identification of Maera rathbunae by Kunkel (1910) from Bermuda appears to be a distinct species much more similar to M. reishi than is the Floridian M. rathbunae. The Bermudan species has truncate telsonic apices with numerous “setae,” the inner ramus of uropod 3 is shortened and the palm of gnathopod 2 is transverse as in M. reishi. The absence of spines on article 2 of gnathopod 2 and the absence of all but 1 spine on the palm of gnathopod 2 appear to be good characters differentiating the Bermudan species from M. reishi. The mandibular palp and the inner plate of maxilla 1 also appear distinctive and there are possible differences in epimera and second maxillae. I reserve the naming of the Bermudan species to a person with material available who can describe this species minutely and determine whether the “setae” of the telson are thin and flexible or stout and spine-like.

Maera reishi differs from European M. inaequipes in the blunt telsonic apices each bearing 4 spines, whereas M. inaequipes has bifid apices bearing 2 spines. Actually 1 spine on each lobe in both species emerges from the ventrolateral surface of the lobe. Maera inaequipes has a very sharp anteroventral corner on coxa 1, the gnathopodal palm in both sexes slopes obliquely, and article 2 of gnathopod 2 is poorly spinose or free of spines.

Among several species of the central Pacific Ocean (J. L. Barnard, 1970:147–161), Maera reishi appears to be closest to M. pacifica Schellenberg, from which M. reishi differs in the presence of numerous stout spines on article 2 gnathopod 2 in both sexes and in the male in the shallower sinus adjacent to the defining tooth of the palm.

J. L. Barnard (1972b:107) gives a brief synopsis of species in the M. quadrimana complex, to which M. reishi belongs.

MATERIAL.—PAZ 3; GAL 108; DAW 3, 8, 27, 31.

DISTRIBUTION.—Gulf of California at Isla Espiritu Santo and Bahía de Los Angeles, 0 m; Galapagos Islands, 0–6 m; California north to Cayucos, 0–3 m.
bibliographic citation
Barnard, J. L. 1979. "Littoral Gammaridean Amphipoda from the Gulf of California and the Galapagos Islands." Smithsonian Contributions to Zoology. 1-149. https://doi.org/10.5479/si.00810282.271