Heteromysoides stenoura, Hanamura & Kase, 2004

Hanamura, Yukio & Kase, Tomoki, 2004, Heteromysoides (Crustacea: Mysidacea: Heteromysini) from a submarine cave on Grand Cayman, the Caribbean Sea: descriptions of a new and a rare species, Journal of Natural History 38 (17), pp. 2145-2152 : 2148-2151

Heteromysoides stenoura , new species

( figures 2 , 3 )

Material examined

HOLOTYPE: NSMT-Cr 15 630, male (tl ca 2.5 mm), submarine cave named ‘Mouse Trap’ located in a coral reef approximately 400 m offshore on the west side of Grand Cayman (19‡19′14.8̎N, 81‡23′22.8̎W), 9–11 m.

PARATYPES: NSMT-Cr 15 631, two males (ca 2.5, 2.6 mm), two juveniles (1.3, 1.5 mm); NSMT-Cr 15 632, two females (2.2, 3.0 mm), six?females (2.2–2.6 mm), one juvenile (1.4 mm); NSMT-Cr 15 633, one?male (ca 2.5 mm), one female (2.5 mm); NSMT-Cr 15 634, one?male (1.7 mm), two?females (2.0, ca 2.5 mm), one juvenile (ca 1.5 mm). For all specimens, data same as holotype.

Description

Body ( figure 2a ) somewhat fragile.

Carapace ( figure 2a, b ) with anterior margin obtusely produced into wide, subtriangular rostrum; cervical groove distinct at anterior two-fifths; posterior margin excavate, leaving last thoracic somite uncovered in dorsal view, but sufficiently covered laterally: anteroventral corner rounded.

Eye ( figure 2b, d ) slightly depressed, subquadrate in dorsal aspect; cornea slightly diminished in size, situated in anterolateral part; sharp spiniform process present at anteromesial corner of stalk. Antennule ( figure 2e ) with first segment of peduncle subequal in length to the third segment, distolateral corner greatly produced anteriorly, distal end bearing a few setae, distomesial corner with one seta; second segment shortest, obliquely articulated with third segment, mesial margin with one seta each at mid-length and distal corner; third segment rather massive, with a few sensory setae distoventrally. Antenna ( figure 2f ) with long, elliptical scale, extending beyond anterior end of antennular peduncle by onequarter of its length, latter more than six times as long as wide, without suture separating distal lobe, setose all around margin.

Labrum ( figure 2g ) triangular, without anteromedial process or spine. Mouthparts as illustrated ( figure 3a–e ).

Third thoracopod ( figure 3f ) similar to posterior thoracopods and endopod not modified, but with simple termination; dactylus short, apex with long claw and a few setae; carpopropodus constituting three articles, basal segment subequal in length to distal two segments combined; merus slightly shorter than carpopropodus; ischium subequal to length of merus. Endopod of fourth thoracopod ( figure 3g ) with dactylus short, bearing long terminal claw and a few setae; carpopropodus consisting of four articles, basal article longest, second article subequal in length to third, and fourth one shortest; merus and ischium subequal in length: exopod composed of about 10 articles distal to basal plate.

Penis ( figure 3h ) long, fully reaching second thoracopod, apex without seta.

Abdomen without spine, hair or groove; first five somites subequal in length; sixth somite 1.33–1.63 (average: 1.51) times as long as fifth somite. Telson ( figure 2c ) as long as or slightly longer than sixth abdominal somite, about 1.8 times as long as basal width, rather abruptly narrowing at basal one-fifth, then width steadily decreasing distally; posterior margin nearly truncate, with two pairs of spines, lateral pair about 1.5 times longer than mesial pair; lateral margin with four or five spines subequal in length on distal half and basally unarmed.

Pleopods ( figure 3i–k ) all rudimentary, single lobes, in both sexes; fifth pleopod longest, about twice length of fourth.

Uropod ( figure 2h ) extending well beyond edge of telson; exopod subequal in length to endopod, subrectangular; endopod slightly narrowing distally, without spines near statocyst region or along mesial margin.

Egg size

Stage III embryos (in preserved specimen) measured 0.9 mm across the anterior end to the tip of the telson.

Etymology

The specific name ‘ stenoura ’ is derived from the Greek, ‘ stenos ’ (~narrow) and ‘ oura ’ (~tail), with reference to the distally narrow telson, as compared with similar species.

Habitat

For details of environmental characteristics of the sampling site, see Ohtsuka et al. (2002).

Remarks

Heteromysoides stenoura exhibits closest similarity to H. simplex , from submarine caves of Okinawa, south-western Japan, because both species have a spiniform process on the eyes and a simple termination to the endopod of the third thoracopod. However, the new species has the distal part of the telson much narrower than in its Pacific congener. Moreover, the eyes of the new species have a more developed cornea (ommatidia numerous versus about 20; for H. simplex , see Hanamura and Kase, 2001).

A simple termination to the third thoracic endopod of the present new species is also shared with Heteromysoides nana Murano, 1998 , recorded from shallow water of northern Australia, but the Australian species does not bear the ocular process on the eyes.

Heteromysoides dennisi Bowman, 1985 , from a submarine cave on Grand Bahamas Island, has an ocular process on the eyes, but the third thoracic endopod of this species possesses an entire carpopropodus with a subserrate termination.

Distribution Known only from the type locality, at depths from 9 to 11 m.

Figures

FIG. 2. Heteromysoides stenoura new species. (a–c) Paratype female, ca 2.5 mm tl; (d–h) paratype male, ca 2.5 mm tl. (a) Entire body, dorsal; (b) anterior part of carapace and cephalic appendages, dorsal; (c) telson, dorsal; (d) left eye, lateral; (e) left antennule, dorsal; (f) left antenna, ventral; (g) labrum, external.

FIG. 3. Heteromysoides stenoura new species. (a–e, i, j) Paratype male, ca 2.5 mm tl; (f–h) holotype male, ca 2.5 mm tl; (k) paratype female, 3.0 mm tl. (a) Right mandible, external, with enlarged cutting edge from lateral view; (b) right maxillule, internal, endites slightly separated; (c) right maxilla, internal; (d) right 1st thoracic endopod, lateral; (e) left 2nd thoracic endopod, lateral; (f) right 3rd thoracic endopod, lateral; (g) right 4th thoracic endopod, lateral; (h) left penis, lateral; (i) left 4th pleopod of male; (j) left 5th pleopod of male; (k) left 5th pleopod of female.