Heteromysis (Olivemysis) mclellandi, Price, Wayne & Heard, Richard W., 2011

Price, Wayne & Heard, Richard W., 2011, Two new species of Heteromysis (Olivemysis) (Mysida, Mysidae, Heteromysinae) from the tropical northwest Atlantic with diagnostics on the subgenus Olivemysis Băcescu, 1968, Zootaxa 2823, pp. 32-46 : 38-43

Heteromysis (Olivemysis) mclellandi , new species

Figs. 3–5

Heteromysis sp. A.— Price & Heard, 2004:157, fig. 4I.

Type material. Holotype: —adult male (Length [L] 4.8 mm), USNM 1142940, Turks and Caicos Islands, BWI, fringing reef off Pine Cay, hard sponge, depth 24–27 m, J. McLelland, coll., 17 Nov 1989. Paratypes: — 1 adult male (L 5.3 mm), USNM 1142941, same collection data as holotype; —1 ovigerous female (L 5.1 mm), GCRL 3000, Turks and Caicos Islands, fringing reef off Pine Cay, sponge, depth 24–27 m, J. McLelland, coll., 17 Nov 1989.

Additional material examined. — 1 male, 1 female (damaged), same collection data as holotype; — 1 male, 1 female (damaged), Turks and Caicos Islands, BWI, fringing reef off Pine Cay, sponge, depth 24–27 m, J. McLelland, coll., 17 Nov 1989; — 2 males (damaged), Turks and Caicos Islands, fringing reef off Pine Cay, large yellow tube sponge, depth 21 m, J. McLelland, coll., 13 Nov 1989. Material in collection of W. W. Price.

Diagnosis. Article 3 of antennular peduncle with distomedial flagellated seta possessing small tubercles distally; thoracic endopod 3 with 7–9 robust flagellated setae with tubercles on medial margin of carpo-propodus; pleopods 1–5 of males and females uniarticulated, with 14–29 modified attenuated setae on anterior surface, lateral, distomedial, and distal margins; uropodal endopod armed with 4–5 spiniform setae along medial margin; lateral margins of telson armed along posterior 0.75 length with 13–16 spiniform setae per margin (including apical setae); outer apical seta 1.2–1.6 times longer than inner; cleft depth 0.15–0.20 times length of telson, cleft completely armed with 12–15 spinules.

Description. General body form ( Fig. 3 A): moderately slender; carapace with anterior margin produced into a triangular rostrum; posterior dorsal margin emarginated, partially exposing thoracic somite 8; anterolateral lobes rounded.

Antennule peduncle ( Fig. 3 B): article 1 subequal in length with article 3, distolateral epiprocess with 3–4 simple setae; article 2 compressed with 1 plumose and 1 attenuated simple seta distomedially, small finger-like process immediately adjacent to a cluster of 4–5 simple setae on proximodorsal surface; article 3 with 1 thick, slightly curved subapically flagellated seta with small tubercles distally, 2 plumose setae, and 1 long simple seta on distomedial margin, 4 setae on small lobe on distodorsal margin, 1 plumose seta on medial margin; outer and inner flagella with attenuated finely setulose setae along medial margins, density greatest proximally; males with moderately setose lobe on ventral surface.

Antenna ( Fig. 3 C): scale not extending beyond peduncle, 2.6–2.7 times as long as maximum width, medial margin slightly convex, lateral margin straight, apex faintly articulated, tip 0.07 times scale length, all margins setose; antennal peduncle 3-articulated; article 1 inconspicuous; article 2 is 1.1 times longer than article 3, armed with 3 simple and 1 plumose setae distomedially; article 3 with 3 short simple setae and 1 long attenuated seta distomedially, 2 plumose setae distolaterally, flagellum with attenuated setae along medial margin, density greatest proximally.

Eye ( Fig. 3 A): moderately large, oval, distal end of eyestalk slightly wider than cornea with ocular tooth on anteromedial margin; cornea large, oval, occupying distal third of eye.

Mandible ( Fig. 3 D, E): cutting edges typical of genus; palp 3-articulated; article 1 small, inconspicuous; article 2 expanded medially, about 2.5 times longer than article 3, lateral margin with a series of 19–26 simple and attenuated setae along entire length, medial margin with 9–12 simple setae; article 3 with 2 long plumose setae at apex and 12–13 shorter pennate setae on distal part, 5–6 simple setae on medial surface.

Labrum and paragnaths: typical of genus.

Maxillule ( Fig. 3 F): outer lobe apex of protopodite with 12–14 robust setulose spiniform and 3 subapical plumose setae; inner lobe apex with 3 long distally curved serrated setae, 3 subapical simple setae, 5–6 attenuated setae on inner margin, and 3 attenuated and 1 plumose setae on outer margin.

Maxilla ( Fig. 3 G): typical of genus; exopod with 15–18 plumose setae.

Thoracic endopods 1 and 2 as illustrated ( Fig. 4 A, B). Thoracic endopod 3 ( Fig. 4 C): ischium about 0.6 times length of merus; merus 1.1–1.2 times length of carpo-propodus, medial margin with a series of 9–15 short and long simple setae, lateral margin with 1 simple seta distally; medial margin of carpo-propodus with 7–9 robust flagellated setae with small tubercles or microdentations, 6–8 of these setae arranged in pairs distally, 1 single seta proximally, 1 or more simple setae at base of each single or pair of flagellated setae, lateral margin with 4–8 short simple setae; dactylus with long, slightly curved, robust nail on distal end. Thoracic endopod 4 ( Fig. 4 D, E): merus 1.1 times length of ischium; carpo-propodus 0.6–0.7 times length of merus, with 4 articles, distal 3 subequal in length, each 0.4–0.5 times as long as proximal article; Thoracic endopod 5 ( Fig. 4 F): merus about 0.8 times length of ischium; carpo-propodus 0.8 times length of merus, with 7–8 articles, distal 6–7 subequal in length, each 0.4–0.5 times as long as proximal article; dactylus armed with slender serrated nail. Thoracic endopods 6 and 8 ( Fig. 4 G, I): merus approximately 0.7 times length of ischium; carpo-propodus subequal in length to merus, with 6 articles, distal 5 are subequal in length, each 0.3–0.4 times as long as proximal article; dactylus armed with slender serrated nail. Thoracic endopod 7 ( Fig. 4 H): merus approximately 0.7 times length of ischium; carpo-propodus subequal in length to merus, with 7 articles, distal 6 subequal in length, each 0.3–0.4 times as long as proximal article; dactylus armed with slender serrated nail.

Thoracic exopods: exopods 1–8 with 9 articles; basal plates of exopods 4–8 with small rounded tooth on outer distal corner.

Thoracic sternal processes: sterna 3–8 supporting median spiniform processes in males.

Pleopods ( Fig. 5 ): uniarticulated; male and female pleopods 1–5 with 14–29 modified attenuated setae on anterior surface, lateral, distomedial, and distal margins, the attenuated setae on distal margins reaching to anterior margins of adjacent posterior somites, 1 setulose seta on distolateral margin, pseudobranchial lobe with 4 sometimes minutely setulose setae; pleopod 1 short and subtriangular with most attenuated setae on truncate distal margin, succeeding pleopods becoming more elongate posteriorly with most attenuated setae on anterior surface, distomedial, and distal margins.

Uropods ( Fig. 4 J): exopod about 1.2 times longer than endopod, lateral margin straight, inner (medial) margin slightly convex, all margins setose; endopod linguiform with a row of 4–5 spiniform setae on medial margin in region of statocyst, all margins setose.

Telson ( Fig. 4 K): 0.8 times length of uropodal exopod, 1.3 times as long as maximum width; lateral margins moderately concave, armed along anterior 0.75 length with 13–16 spiniform setae per margin (apical setae included); outer apical seta 1.2–1.6 times longer than inner; cleft depth 0.15–0.20 times length of telson, completely armed with 12–15 spinules.

new species. Subgeneric placement follows new diagnostic in this study.

Species

Character H.( O.) gomezi H.( O.) mayana H. ( O.) rubrocincta H.( O.) mclellandi Etymology. This species is named in honor of the collector, Jerry McLelland, in recognition of his many contributions to the study of the invertebrate fauna of the temperate and tropical waters of the northwest Atlantic.

Habitat. Heteromysis (Olivemysis) mclellandi was collected from unidentified sponges in depths of 21–27 m on deep fringing reefs. This species may be spongicolous, similar to H. (Olivemysis) guitarti Bäcescu, 1968 , which is another tropical northwest Atlantic species that appears to have a commensal relationship with sponges, especially with the Demospongiae genus Ircinia ( Price and Heard 2004).

Distribution. This species is known only from waters adjacent to Pine Cay, Turks and Caicos Islands.

Remarks. Heteromysis (Olivemysis) mclellandi may be separated immediately from all other nominal species of Heteromysis and, in fact, all other members of the subfamily Heteromysinae by having modified attenuated setae on pleopods 1–5 of both males and females. In an earlier study, Price and Heard (2004) characterized these modified setae of Heteromysis (Olivemysis) mclellandi (= Heteromysis sp A) as simple, leading to the report of “male pleopods 3 and 4 without modified spiniform setae”. Closer examination showed that attenuated setae were present on male and female pleopods as well as on all mouthparts of this new species.

A survey of species within the subfamily Heteromysinae reveals only three in which females possess pleopods with modified setae. Modified setae are reported for pleopods 2–5 for both sexes of Heteromysoides longiseta Bäcescu, 1983 , pleopods 2–4 for both sexes of Heteromysis (Neoheteromysis) muelleri Bäcescu, 1976 , and pleopod 2 for females of Heteromysis kushimotensis Murano and Fukuoka, 2003 .

For heteromysid males, in addition to the two species mentioned above, modified setae are present on pleopod 3 of Harmelinella mariannae Ledoyer, 1989 and on pleopod 4 of all members of Heteromysis belonging to the subgenus Olivemysis Bäcescu, 1968 . Within this subgenus the majority of species also have modified setae on pleopod 3. However, seven species have pleopods 2–4 modified: H. (Olivemysis) dardani Wittmann, 2008 , H. (Olivemysis) macrophthalma Bäcescu, 1983 , H. (Olivemysis) quadrispinosa Murano, 1988 , H. tattersalli Nouvel, 1942 , H. (Olivemysis) tenuispina Murano, 1988 , H. (Olivemysis) wirtzi Wittmann, 2008 , and H. (Olivemysis) zeylanica Tattersall, 1922 . Three additional species, H. digitata Tattersall, 1927 , H. gomezi (Olivemysis) Bäcescu, 1970, and H. (Olivemysis) mayana Brattegard, 1970 exhibit modified setae on pleopods 1–4. Although Bamber (2000) places H. (Olivemysis) meenakshiae Bamber, 2000 in the subgenus Olivemysis , and describes and illustrates male pleopods 2 and 3 as modified, no mention is made of pleopod 4. The subgeneric status of some species (i.e., H. tattersalli , H. digitata ) included in this section could not be determined. This is because their descriptions do not include or indicate the characters needed for proper subgeneric placement (see below).

Among the previously described western Atlantic species of Heteromysis , H. (Olivemysis) mclellandi most closely resembles H. (Olivemysis) gomezi , H. (Olivemysis) mayana , and H. (Olivemysis) rubrocincta Bäcescu, 1968 (see Table 2 ). Although the telsons of these four species are similar with respect to the arrangement of setae on the lateral margin and spinules in the telsonic cleft, the new species differs from its three related congeners in several aspects. Unlike H. (Olivemysis) mclellandi , females of these three species have no modified setae on their pleopods. Males have flagellated setae on pleopods 3 and 4; in addition, H. (Olivemysis) gomezi and H. (Olivemysis) mayana males have a terminal spiniform seta on pleopods 1 and 2. Heteromysis (Olivemysis) mclellandi is the only species with tubercles on the flagellated seta on the antennular peduncle as well as attenuated setae on the mouthparts. The new species has 7–9 flagellated setae on the carpo-propodus of thoracic endopod 3 rather than 0– 7 in the other species; a telson cleft depth: telson length ratio of about 1/6 rather than 1/5 or greater; and an outer: inner length ratio of apical telson setae of 1.2–1.6 rather than 1.8 or more.

Taxonomic history and classification of the subgenus Olivemysis B ă cescu, 1968

In 1968, Bäcescu revised the tribe Heteromysini Norman,1892 , by erecting a new genus Heteromysoides Bäcescu, 1968 and suggesting the first established Heteromysini genus, Heteromysis , to consist of three subgenera: Heteromysis S. I. Smith, 1873 , Gnathomysis Bonnier and Pérèz, 1902 , and Olivemysis Bäcescu, 1968 . Later, Bäcescu completed his Heteromysis classification by adding a fourth subgenus, Neoheteromysis Bäcescu, 1976 .

Despite taxonomic recognition of Olivemysis , the history of diagnostic characters defining this subgenus is somewhat confusing. Initially, Bäcescu (1968) included, as a diagnostic character, the absence of thoracic sternal processes. Later, without comment, Bäcescu (1970) placed two new species with well-developed sternal processes within Olivemysis , thus expanding the diagnosis for the subgenus. This issue, as well as another involving the spelling of Olivemysis , was addressed by Wittmann (2008). To complicate matters further, Bowman and Orsi (1992) and Bravo and Murano (1996) misinterpreted the wording in Bäcescu’s 1968 key to the genera and subgenera of the Tribe Heteromysini and, in their keys, referred to sternal processes as abdominal rather than thoracic.

Lending to the confusion, with the exception of Bäcescu’s (1968: 237) initial designation of the subgenus in a dichotomous key, no diagnostics for Olivemysis have ever been provided in the subsequent publications dealing with the group (e.g., Bäcescu 1976, Bowman & Orsi 1992, Bravo & Murano 1996). In effect, a formal diagnosis for Olivemysis is wanting. To address this problem, we provide the following formal diagnosis for the subgenus.

Figures

FIGURE 3. Heteromysis (Olivemysis) mclellandi, new species. Adult male. A, dorsal view; B, antennular peduncle and enlargement of attenuated setae on outer flagellum; Adult female: C, antennal peduncle and scale and enlargement of attenuated setae on flagellum; D, left mandible with palp; E, right mandible; F, maxillule; G, maxilla. Scale, A = 1.0 mm; B – E, G = 0.25 mm; F = 0.10 mm.

FIGURE 4. Heteromysis (Olivemysis) mclellandi, new species. Adult female. A – C, endopods of thoracic limbs 1 – 3; D, E, endopod of thoracic limb 4, medial and lateral aspects, respectively; F – I, endopods of thoracic limbs 5 – 8; J, uropod; K, telson. Scale = 0.3 mm.

FIGURE 5. Heteromysis (Olivemysis) mclellandi, new species. Adult male. A – E, pleopods 1 – 5; Adult female. F – J, pleopods 1 – 5. Scale = 0.2 mm.

Tables

TABLE 2. Common and specific morphological characters of species closely related to Heteromysis (Olivemysis) mclellandi

Flagellated seta on antennular peduncle	present	present	present, fine serra- tions distally	present, tuberculate
Antennal scale reaching beyond antennal peduncle	no	yes	no	no
Flagellated spiniform setae on medial margin of carpo-propodus of thoracic endopod 3	3	5–7, non-tuberculate or tuberculate	0	7-9, tuberculate
Modified female pleopods	none	none	none	all 5 pairs, attenuated setae
Modified male pleopods	1st, 2nd pair-terminal spiniform seta; 3rd, 4th pair-15, 17–18 flagellated setae, respectively	1st, 2nd pair-terminal spiniform seta; 3rd, 4th pair-13–22, 19–35 flagellated setae, respectively	3rd, 4th pair-6–10, 8– 15 flagellated setae, respectively	all 5 pairs, attenuated setae
Spiniform setae on uropodalen- dopod	3	1–4	4–5	4–5
Lateral spiniform setae on telson (apical setae included)	posterior 2/3, 9	posterior 1/2–2/3, 6–9	posterior 1/2, 12–13	posterior 2/3, 13–16
Telson cleft depth:telson length	0.33	0.25–0.33	0.20	0.15–0.20
Spinules in telson cleft	entire, 20–22	entire, 14–20	entire, 15–16	entire, 12–15
Outer:inner length of apical tel- son setae	2.0	1.8–3.0	2.0	1.2–1.6
References	Bäcescu 1970	Brattegard 1970, Price et al. 2002, Price & Heard 2004	Bäcescu 1968	present study