Heteromysis (Heteromysis) fosteri Wittmann & Griffiths

Wittmann, Karl J. & Griffiths, Charles L., 2017, Three new species of Heteromysis (Mysida, Mysidae, Heteromysini) from the Cape Peninsula, South Africa, with first documentation of a mysid-cephalopod association, ZooKeys 685, pp. 15-47 : 21-25

Heteromysis (Heteromysis) fosteri Wittmann & Griffiths sp. n. Figs 6A, 7, 8

Type series.

Holotype, adult male with 6.7 mm body length, in vial at NHMW-25905; paratypes adult female 7.0 mm, adult male 6.6 mm, 2 subadult males 3.6, 4.6 mm in vial at SAM-MB-A067551; dissected paratypes on slides at NHMW-25906: adult female 8.0 mm, subadult female 5.9 mm, adult male 6.0 mm; sublittoral marine coastal waters, Miller’s Point, on the False Bay coastline of the Cape Peninsula, South Africa, 34°13.78'S, 18°28.47'E, 5 m depth; extracted from empty urchin and gastropod shells without hermit crabs, 25 Jan. 2017, leg. Craig Foster.

Diagnosis.

Carapace produced into well-projecting, triangular rostrum with narrow rounded apex. Eyes well developed; cornea occupies 35-50% of eye surface; eyestalks with inconspicuous, distally-directed, blunt extension of (obliquely anterior facing) inner margin. Antennular trunk with a number of smooth and barbed setae, but no particularly modified setae; inner distal corner of its terminal segment with anteriorly directed apophysis carrying two large, smooth setae. Antennal scale stout, extending to 0-10% below tip of antennular trunk; outer margin convex. First thoracic sternite with anteriorly-projecting, terminally-rounded median lobe; sternites 2-8 without lobes in both sexes. Carpopropodus of thoracic endopods 1-8 with 2, 2, 2, 3, 6, 6, 6, or 5-6 segments, respectively. Third thoracic endopod weakly dimorphic, without any spines or spine-like setae; carpus not swollen in female, slightly swollen in male (with respect to merus). Carpus of third thoracic endopod with series of three subbasally toothed setae (i.e. with modified barbs) near outer margin. Carpopropodus of fourth thoracic endopod with series of 2-3 subbasally toothed setae near outer margin; no such modified setae in endopods 5-8. Penes long and slender, twice length of merus of eighth thoracic endopod; tip with three rounded lobes, each wider than long. Pleopods reduced to small setose, bilobate plates, without any spines in both sexes. Exopods of uropods extend distinctly beyond endopods. Endopods with only one spine on inner margin, in subbasal position near statocyst. Telson subtriangular, terminally truncate; lateral margins weakly-sigmoid, along their distal 83-93% furnished with slightly discontinuous series of 17-20 spines each. Telson with apical cleft forming proximally poorly rounded ‘V’. This cleft slightly deeper than wide, its depth 14-18% telson length. Cleft densely furnished with 16-24 acute laminae all along its margins. Two latero-apical lobes of telson show narrow, transverse apical margins, each bearing a large latero-apical spine plus much smaller medio-apical spine.

Description.

As described above for H. cancelli sp. n. unless stated otherwise in the following. Cephalothorax comprises 41-44% of body length without telson, pleon 56-59%, and carapace 30-38%, when measured along dorsal median line. First thoracic sternite with median lobe showing a smooth, rounded apex. Terminal margin of sixth pleonite with lateral shields more evenly rounded in females (Fig. 7L) versus males (Fig. 7K).

Carapace (Figs 6A, 7A). Non-dimorphic, antero-lateral edges evenly rounded. Anterior pore group with 25-34 pores, in strongly flattened ‘U’ -shaped arrangement. Posterior pore group with 12-16 pores.

Eyes (Figs 6A, 7A). Anterior, basal, and posterior margins of eyestalks densely covered by scales. Ocular symphysis with broadly-rounded, smooth, subrostral process (dashed line in Fig. 7A).

Antennulae (Fig. 7A, B). Basal segment 41-48% the length of trunk, middle 14-18% and terminal segment 37-43%, when measured along dorsal midline of trunk. Trunk stouter in males, with basal segment 1.1-1.2 times longer than broad, compared to 1.3 times in females. Basal segment with three barbed and one smooth seta at its dorsal apophysis; four plumose setae at tip of outer ventral lobe (exite). Anterior margin of median segment dorsally with a smooth seta and larger barbed seta; and more laterally another smooth seta together with three barbed setae in both sexes. Two small barbed setae antero-ventrally near outer margin, visualized by dashed lines in Fig. 7B. Anterior margin of terminal segment in about median position with a lobe bearing 3-4 medium-sized barbed setae plus a dense series of short bristles. Only females with additional, large plumose setae on terminal segment of trunk, one inserting ventrally half-way near inner margin, the second, forward directed in Fig. 7A, on the ventral surface proximally from the inner flagellum at about 9-19% segment length from anterior margin of terminal segment. Outer antennular flagellum 1.5-1.7 times as thick as inner flagellum, when measured near basis.

Antennae (Fig. 7A). Length of antennal scale 2.7-3.0 times its maximum width. Basal segment 24-29% length of peduncle, second 33-39% and third 34-38%.

Mouth parts (not figured). Pars incisivus of mandibles with 3-4 large teeth, and digitus mobilis with 3-4 large plus 1-3 small teeth. Pars centralis with 4-5 spiny teeth. Distal segment of maxillula terminally with 8-10 strong, inconspicuously serrated spines, subterminally with a transverse row of 5-6 barbed setae. Endite of maxillula with three large, distally-spinose setae, and a total of 15-20 smaller, smooth or barbed setae.

Thoracopods in general (Figs 7 D–J, 8 A–F). Sizes increase from exopod 1 to 4 and then show no clear trend from 4 to 8. Homologous exopods are not clearly different between sexes. Flagellum of first to eighth exopods with 8, 9, 9, 9, 9, 9, 9, 8-9 segments. Exopods with basal plate 1.4-2.0 times longer than broad in both sexes. Claw of third endopod more strongly serrated in males (Fig. 7J) versus females (Fig. 7E), to a minor degree also in fourth endopod, not so in remaining endopods.

Maxillipeds (first and second thoracic endopods; Fig. 7C, D). First endopod with hairs on outer half of sympod. Its epipod large, leaf-like, with comparatively long field of minute scales near insertion with sympod, and subbasally with a large seta densely barbed along its distal 60-75%. Dactylus of second endopod with dense brush of setae, among these 10-15 modified ones.

Gnathopods (Figs 7E, J; 8 A–C). Carpopropodus of endopod comparatively slender, four times longer than broad in males, versus five times in females; length is 0.8-0.9 times that of merus and 0.9-1.0 times that of ischium in both sexes. Subbasally toothed setae (Fig. 8C): three on carpus plus two in (sub)apical position near outer margin on merus (Fig. 8A, B).

Pereiopods (Figs 7 F–H, 8 D–F). Carpus of fourth endopod (Fig. 8D, E) with longer, subbasally toothed setae compared to third endopod (Fig. 8 A–C). Fourth endopod with moderately small dactylus bearing long, strong, weakly-bent claw, microserrated on two opposite sides of subapical portions (Fig. 7F). Fifth to eighth endopods equipped with again smaller dactylus bearing a much shorter claw that shows slightly stronger, distally-increasing curvature; this claw unilaterally microserrated only in median portions of its inner margin (Fig. 7G, H). Sixth thoracopod of females with rudimentary oostegite representing a small lobe, on its inner margin with 0-2 proximally weakly barbed setae.

Penes (Fig. 8F) as above in diagnosis. Presence of small, barbed setae: 1-2 subterminally on exterior face plus 4-5 ones scattered anywhere between 3% and 70% penis length from basis.

Pleopods (Fig. 8G). The seta at inner terminal edge of endopod shows only minor number of barbs, all remaining setae well-barbed or plumose. Total length of pleopod 5 is 177-190% that of pleopod 1 (n = 4). Starting with pleopods 1 versus 2, length increase between subsequent pleopods is 19-32%, 0-13%, 1-18%, and 22-33%, respectively.

Uropods (not figured). The exopods reach with 21-30% of their length beyond endopods and 17-25% beyond telson, the endopods 6-11% of their length beyond telson. Exopod length 4.3-4.4 times maximum width. Statoliths composed of fluorite; diameter 145-181 µm (n = 4); statolith formula is 2 + 3 + 1 + (8-13) + (16-19) = 31-38.

Telson (Fig. 8H). Length 1.2 times that of ultimate abdominal somite or 0.7-0.8 times exopod of uropods. Length of telson 1.2-1.5 times its maximum width. Laminae of cleft show 0.6-0.8 times average length of lateral spines. Length of lateral spines distally discontinuously increasing in size by a factor of about 1.6, arming almost all outer margin.

Colour (Fig. 6A). General appearance of living specimens light red with orange tinge. The stronger orange tinge of the thorax in Fig. 6A is due to yolk in the ovarian tubes. Cornea yellow-golden; eyestalks mainly light red, except for a white ribbon along posterior, dorsal portions of the inner margin of the cornea. Red chromatophore centres scattered over eyestalks, antennae, pleon, uropods, and most densely over carapace, thoracomere 8, and telson. Two transverse series of chromatophores, one in about the middle and the second near posterior margin of pleomeres 1-2, and less regularly arranged also on pleomeres 3-6. Starting with pleomere 3, additional chromatophores are scattered with increasing density up to pleomere 6. Uropods with chromatophores only over proximal 70%. Persistence of colours as in H. cancelli sp. n.

Nauplioid stage (Fig. 7M). One female with body length 8.0 mm carried 13 nauplioid larvae at substage 3, length 1.1-1.3 mm. At that same state of development one finds the same external morphological features as in H. cancelli sp. n. (Fig. 3N shows substage 2). Each cercopod bears 10-14 acute spines with apically increasing size.

Etymology.

The species name is a noun in genitive singular, named after well-know underwater-photographer and diver Craig Foster, who has accompanied and assisted the second author in many collecting expeditions and who made all in situ photographs and sampled all specimens of both this species and the one following.

Type locality.

Sublittoral marine coastal waters at Miller’s Point, on the False Bay coastline of the Cape Peninsula, South Africa, 34°13.78'S, 18°28.47'E. This is only 5.5 km to the SSE of the type locality of H. cancelli sp. n. (above). Materials were extracted from mixed collection of dead shells mainly belonging to the whelk Argobuccinum pustulosum (Lightfood, 1786), the winkle Turbo cidaris Gmelin, 1791, and the urchin Parechinus angulosus (Leske, 1778).