(Figs. 1, 2)
Heteromysis (Olivemysis) sp. A.— Price et al., 2002: 48, fig. 4 N.
Type material. Holotype: —adult male (Length [L] 4.6 mm), USNM 1142938, Grand Cayman Island, BWI, Cottage Point, rock/algal washings, depth 1–2 m, W. Price, R. Heard, coll., 23 May 1998. Paratypes: — 1 adult male (L 4.4 mm), 2 ovigerous females (L 4.4, 4.3 mm), USNM 1142939, same collection data as holotype; — 1 ovigerous female (L 4.4 mm), GCRL 2997, Grand Cayman Island, Cottage Point, rock/algal washings, depth 1–2 m, R. Heard, J. Foster, M. Abney, coll., 13 Aug 1999; — 1 mature male (L 4.3 mm), — 1 non-ovigerous female (L 4.0), GCRL 2998, Grand Cayman Island, South Sound (Prospect Point), rock/algal washings, depth 1.5 m, W. Price, R. Heard, coll., 19 May 1998; — 1 ovigerous female (L 4.3 mm), GCRL 2999, Grand Cayman Island, The Edge, depth 1–2 m, W. Price, R. Heard, coll., 11 May 1998.
Additional material examined. — 1 male, same collection data as holotype; — 1 male, Grand Cayman Island, BWI, Cottage Point, rock/algal washings, depth 1–2 m, R. Heard, J. Foster, M. Abney, coll., 13 Aug 1999; — 1 male, 3 females, Grand Cayman Island, South Sound (Prospect Point), rock/algal washings, depth 1.5 m, W. Price, R. Heard, coll., 19 May 1998; — 2 males, 1 female, Grand Cayman Island, South Sound, west end, sand/seagrass, rock/sponge/algal washings, depth 1–2 m, W. Price, R. Heard, coll., 22 May 1998. Material in collection of W. W. Price.
Diagnosis. Article 3 of antennular peduncle with distomedial flagellated seta; thoracic endopod 3 with 6–7 robust flagellated setae on medial margin of carpo-propodus; male pleopod 3 with 3–5 bent, attenuated spines on distal margin; male pleopod 4 with 4–6 bent, attenuated spines on distal margin; uropodal endopod armed with 3–4 spiniform setae along medial margin; lateral margins of telson completely armed with 14–19 spiniform setae per margin (including apical setae); outer apical seta 1.6 –2.0 times longer than inner; cleft depth 0.25 times length of telson, anterior 0.75 length of cleft armed with 10–16 spinules.
Description. General body form (Fig. 1 A): small, moderately robust; carapace with anterior margin produced into a pointed triangular rostrum; posterior dorsal margin emarginated, exposing thoracic somite 8; anterolateral lobes rounded.
Antennule peduncle (Fig. 1 B): article 1 subequal in length with article 3, distolateral epiprocess with 3–4 simple setae and 1 blunt spiniform seta laterally and 4 plumose setae distally; article 2 compressed with 1 plumose and 1 simple seta distomedially; article 3 with 1 thick subapically flagellated seta, 0.6–0.7 times width of distal margin of article 3, also bears 2 long plumose setae and 1 long simple seta on distomedial margin, 3–4 plumose setae on distolateral margin, 2 simple setae on dorsolateral surface, and 1 plumose seta on medial margin; males with setose lobe on ventral surface.
Antenna (Fig. 1 C): scale extending slightly beyond peduncle, 2.7–2.9 times as long as maximum width, medial margin moderately convex, lateral margin straight, apex articulated, tip about 0.1 times scale length, all margins setose; antennal peduncle 3 -articulated; article 1 inconspicuous; article 2 is 1.2–1.3 times longer than article 3, bears 3 simple and 1 plumose setae distomedially; article 3 with 3 simple setae distomedially.
Eye (Fig. 1 A): large, oval, directed laterally, distal end of eyestalk slightly wider than cornea with ocular tooth on anteromedial margin; cornea large, oval, occupying distal third of eye.
Mandible (Figs. 1 D, E): cutting edges typical of genus; palp 3 -articulated; article 1 small, inconspicuous; article 2 about two times longer than article 3, lateral margin with a series of plumose setae along entire length, medial margin with curved row of 9–12 plumose setae; article 3 with 2 setulose setae at apex and 9–12 pennate setae on distal part, 5 setulose setae on medial surface.
Labrum and paragnaths: typical of genus.
Maxillule (Fig. 1 F): typical of genus; outer lobe of protopodite with 11–14 apical robust spiniform and 3 subapical simple setae.
Maxilla (Fig. 1 G): typical of genus; exopod with 15–17 plumose setae.
Thoracic endopods 1 and 2 as illustrated (Figs. 2 A, B). Thoracic endopod 3 (Fig. 2 C): ischium about 0.7 times length of merus; merus 1.25 times length of carpo-propodus, medial margin with a series of 12–14 short and long simple setae, lateral margin with 1 simple seta distally; medial margin of carpo-propodus with 6–7 robust flagellated setae, usually 4 arranged in pairs distally, 2–3 single setae proximally, lateral margin with 4–5 setae; dactylus with long, slightly curved, robust nail on distal end. Thoracic endopod 4 (Fig. 2 D): merus about 1.5 times length of ischium; carpo-propodus about 0.6 times length of merus, with 4 articles, distal 3 subequal in length, each about 0.5–0.7 times as long as proximal article. Thoracic endopods 5–8 (Figs. 2 E–H): merus about 0.7 times length of ischium; carpo-propodus subequal in length to merus, with 6 articles, distal 5 subequal in length, each about 0.5 times as long as proximal article; dactylus armed with slender serrated nail.
Thoracic exopods: exopod 1 with 8 articles; exopods 2–8 with 9 articles.
Thoracic sternal processes: median spiniform processes on sterna 3–8 in males and sternite 1 in females.
Pleopods: uniarticulated; male pleopods 1, 2, and 5 unmodified; pleopod 3 (Fig. 2 I) with row of 8 plumose setae on anterior surface, distal margin with 3–5 bent, attenuated spines and 1 long seta, lateral margin with 3 plumose setae, medial margin with 1 plumose seta, pseudobranchial lobe with 5 plumose setae; pleopod 4 (Fig. 2 J) with row of 7 plumose setae on anterior surface, distal margin with 4–6 bent, attenuated spines and 1 long seta, lateral margin with 3 plumose setae, medial margin with 1 plumose seta, pseudobranchial lobe with 5 plumose setae; female pleopods as unmodified male pleopods.
Uropod (Fig. 2 K): exopod about 1.3 times longer than endopod, lateral margin straight, medial margin slightly convex, all margins setose; endopod linguiform with a row of 3–4 prominent spiniform setae on medial margin in region of statocyst, all margins setose.
Telson (Fig. 2 L): 0.7–0.8 times length of uropodal exopod, 1.2–1.4 times as long as maximum width; lateral margins moderately concave, armed along entire length with 14–19 spiniform setae per margin (apical setae included); outer apical seta 1.6 –2.0 times longer than inner; cleft V-shaped, depth 0.25 times length of telson, anterior 0.75 length of cleft armed with 10–16 spinules.
Etymology. This species is named in honor of Richard Modlin in recognition of his contributions to the study of the genus Heteromysis of the northwest Atlantic.
Habitat. Heteromysis (Olivemysis) modlini collected from rock/sponge/algal washings in back reef and sand/ seagrass habitats in depths of 1– 2 m. Collecting techniques were too general to determine if the species was associated with a specific sessile host.
Distribution. This species is known only from waters immediately adjacent to the south coast of Grand Cayman Island.
Remarks. Of the 27 nominal species of Heteromysis reported from the western Atlantic, H. (Olivemysis) modlini is most closely related to H. agelas Modlin, 1987, H. bredini Brattegard, 1970, H. (Olivemysis) guitarti Bäcescu, 1968, and H. tuberculospina Modlin, 1987. These species share the following characters: article 3 of antennular peduncle with normally flagellated spiniform seta for both sexes; margins of telsonic cleft with spinules along at least 0.75 length; lateral margins of telson armed with spiniform setae along at least 0.8 length; uropodal endopod with 6 or fewer spiniform setae along medial margin; male pleopods 3 and 4 with modified setae or spines (see Table 1). Heteromysis (Olivemysis) modlini is unique among these species in having bent, attenuated spines (non-articulated cuticular extensions) on male pleopods 3 and 4 while three of the other four species are known to possess flagellated setae (articulated cuticular extensions) or spines. Males of H. bredini have not been described. The new species differs from H. agelas and H. (Olivemysis) guitarti in having the outer apical seta on the telsonic lobes two times or less the length of the inner seta rather than 2.2 times or more. It is distinguished further from H. agelas by the setation of the uropodal endopod (3–4 setae compared to 2) and from H. (Olivemysis) guitarti by having the antennal scale reaching beyond the antennal peduncle as well as more lateral setae on the telson (14–19 compared to 9–14). Heteromysis (Olivemysis) modlini is distinguished from H. bredini by having 10–16 rather than 31 spinules in the telsonic cleft and 6–7 rather than 10 flagellated setae on the carpo-propodus of thoracic endopod 3. Heteromysis tuberculospina differs from the new species in having tubercles on the flagellated seta of article 3 of the antennular peduncle, an antennal scale length:width ratio greater than 3.0 rather than less than 3.0, and 18–20 rather than 10–16 spinules in the telsonic cleft.