Tuatara: Volume 16, Issue 3, December 1968
The New Zealand Hymenosomidae
The New Zealand Hymenosomidae
Ecologists And taxonomists have experienced difficulties in identifying these small crabs from early descriptions. Richardson (1949) provided the only workable key to date but it does have limitations. This article expands and corrects his key. For a list of relevant literature, more complete descriptions and ecological notes, the author's M.Sc. thesis, ‘Contributions to the Systematics and Ecology of the New Zealand Hymenosomidae’. M. J. Gordon, University of Auckland, 1966, may be consulted. This thesis is to be published as a monograph by the Oceanographic Institute of the D.S.I.R., Wellington.
In the Plates, the dorsal view of the carapace of each crab (drawn from the male except for a new genus), is represented 3 x normal size, except for Plate 1, which is 5 x normal size. A list of abbreviations used in labelling precedes Plate 1. Gordon (1940), and Garth (1958), emphasise the importance of the first male pleopod in identification, and Plate 7 shows a selection from the Hymenosomidae. A new monotypic genus is based on only four specimens; at present no adult male has been found so the pleopod remains unfigured. A table is provided showing the size range and known habitat of each species.
Key to the New Zealand Genera of Hymenosomidae
1 Upper carapace with a distinct gastro-cardiac groove and cervical grooves. Ischium of endopodite of third maxilliped subequal to or shorter than merus, subrectangular or subquadrangular. … Halicarcinus
(8 authenticated species)
Upper carapace without distinct grooves. Ischium of endopodite of third maxilliped longer than merus, triangular or trapezoid. … 2
2 Eyestalks entirely visible dorsally; folded antennules similarly visible. Epistome tiny, subcircular. Ischium of third maxilliped subtriangular. Dactylus of each walking leg lacking teeth. … Hombronia*
(1 species, Hombronia depressa Jacquinot (Plate 6, Fig. 3)
Cornea of eye, but not eyestalks, visible dorsally; folded antennules completely hidden. Epistome large and rectangular. Ischium of third maxilliped trapezoid, shaped like an axe-blade. Dactylus of each walking leg sparsely dentate.… 3
* This generic name is invalid and should be changed, as will be done in a later monograph.
3 Carapace and rostrum completely fused, without suture between Rostrum with a ventral keel. Epistome almost as long as broad. Endopodites of third maxillipeds almost meeting in the midline. Dactylus of each walking leg with two large teeth adjacent to the claw, lacking other dentation. … Elamena s.s. (3 species)
Distinct suture between carapace and rostrum. Rostrum without keel or ridge ventrally. Epistome only half as long as broad. Endopodites of third maxillipeds gaping in the midline. Dactylus of each walking leg with a single large tooth adjacent to the claw, lacking other dentation. … Gen. nov. (1 species) (Plate 6, Fig. 2)
Key to the New Zealand Species of Halicarcinus
(Eight of these species are represented in New Zealand collections. H. ovatus has been reported here but no specimens are now in collections in New Zealand.)
1 Rostrum trilobate or tridentate, arising below the level of the upper carapace, the carapace rim being continuous above the rostrum, and the concavities between the lobules extending below this rim. … 2
Rostrum simple, or, if trilobate, the lobes arising from the level of the upper carapace, separated from it only by a suture. … 4
2 Three rostral lobes arising some considerable distance below the carapace rim, with the lateral lobes at the same level as the median lobe and not set at an angle to it. Antero lateral border of carapace convex. Dactylus of each walking leg with a single row of teeth or tubercles. … Halicarcinus innominatus Richardson*
(Mainland, littoral) (Plate 2, Fig. 1)
Three rostral lobes arising just below the rim of the carapace, with the lateral lobes set at an oblique angle to the median lobe. Antero lateral border of carapace straight or concave. Dactylus of each walking leg with a double row of teeth. … 3
3 Rostral lobes widely separated, median rostral lobes shortest; lateral lobes sloping downward and outward. Neither of the two lateral angles of the carapace marked above by angles in the carapace rim. Dactylus of each walking leg armed with two irregular but distinctly separated rows of short, pointed teeth. … Halicarcinus planatus Fabricius
(Sub-Antarctic, littoral and deep water) (Plate 2, Fig. 2)
* The nomenclature of this species is not clear; older names may be available.
4 Rostrum distinctly trilobate or tridentate, the concavities between the lobes reaching almost to the suture beween carapace and rostrum.…
Rostrum simple, or trilobate only distally, any concavities between the lobes not reaching near the suture between rostrum and carapace. … 6
5 Rostrum extending past the eyes. Rostral lobes acute, sub-equal. Carapace longer than wide, narrowing anteriorly. Antero lateral border of the carapace straight or faintly convex. Two pairs of angles below the carapace rim, which is itself uninterrupted by the angles. Postocular lobe large. Dactylus of each walking leg with a single row of recurved large teeth. Chela of male equipped with the typical basal tooth on the movable finger. … Halicarcinus sp. nov. (deep water) (Plate 5, Fig.2)
Rostrum not projecting past the eyes. Rostral lobes rounded apically, the median one a fraction longer than the laterals. Carapace sub-circular. Antero lateral border of the carapace markedly concave. Two pairs of lateral teeth marked by angles in the carapace rim. Postocular lobe very small. Dactylus of each walking leg with two irregular rows of recurved narrow teeth. Chela of male without the typical basal tooth on the movable finger. … Halicarcinus cookii Filhol (littoral) (Plate 1, Figs. 1 & 2; Plate 3, Fig. 2)
6 Rostrum not projecting past the eyes, and forming a flat, almost horizontal platform. … * Halicarcinus varius Dana (littoral and deep water) (Plate 3, Fig. 3)
Rostrum projecting past the eyes, and downwardly deflexed anteriorly. … 7
* Note on Halicarcinus varius
This species would seem to derive its name from the fact that the rostrum is variable, showing more variety of form than any other species dealt with by the author. The rostrum is generally trilobate, with the centre lobule longer than the others. Sometimes the concavities between the lobules approach the condition shown by Halicarcinus cookii. However, the antero lateral borders of the carapace are straight or convex in Halicarcinus varius, contrasting with the markedly concave borders in Halicarcinus cookii, so that the two species may be separated by this feature if the collector finds difficulty in interpreting the key.
Rostrum simple, just projecting past the eyes. Chela of male of normal width. Dactylus of each walking leg lacking teeth or sparcely dentate. Male abdomen short, abnormal in narrowing evenly to the ultimate segment; male pleopod of unusual form. … 8
8 Rostrum deflexed only a little downward, convex from side to side above, narrowing to a blunt point anteriorly. Male first pleopod with a longitudinal row of long, sturdy setae subterminally, (as in Elamena), the tip forming a tiny knob. Dactylus of each walking leg curved, with a single blunt tooth adjacent to the claw. Everywhere covered with long, feathery hairs. … Halicarcinus pubescens Dana (Marine, littoral to deep water) (Plate 4, Fig 2; Plate 7, Fig. 2)
Rostrum strongly deflexed downward, concave from side to side above, narrowing only slightly anteriorly to a somewhat truncate but curved tip, sometimes with a scarcely visible trilobation on this tip. Male first pleopod very stout, with long, slender setae in tufts sub-terminally, the tip tapering normally. Dactylus of each walking leg straight, without teeth. Everywhere covered with short, fine setae. … Halicarcinus lacustris Chilton (fresh water) (Plate 5, Fig. 1; Plate 7, Fig. 3)
Key to the New Zealand Species of Elamena
1 Rostrum broad, rounded; sub-rostral keel blunt. Carapace rounded. Legs without teeth except for one on the merus. … 2
Rostrum narrow, produced; sub-rostral keel with a strong spine extending from it. Carapace triangular. Legs with many sturdy teeth. … Elamena longirostris Filhol* (off-shore in deep water)
2 Length of rostrum at least half as great as width. Keel deepest anteriorly, tapering behind. Prominent upwardly curved tooth on the distal end of merus of each walking leg. Carapace rim produced into two pairs of lateral angles. … Elamena producta Kirk (littoral) (Plate 5, Fig. 3)
Length of rostrum less than a third of width. Keel shallow, of equal depth throughout. Tooth on merus of each walking leg reduced, obtuse. Carapace rim without distinct angles. … Elamena sp. nov. (deep water) (Plate 6, Fig. 1)
* No specimen of this species has been seen by the author but it is apparently valid and a figure of its appears in Richardson's key.
|Species||Collecting grounds||Substrate||Degree of exposure to wave force||Size range in millimetres Males||Size range in millimetres Females|
|Ha icarcinus innominatus||intertidal, subtidal||near Mytilus canaliculus||minimum to medium exposure||1.25 — 19||3.5 — 15.5|
|H. planatus||intertidal on subantarctic Is. deep water (not on N.Z. mainland)||pools, under stones||not known||2.5 — 23.5||3.5 — 19|
|H. cookii||intertidal, subtidal||algae (red or brown)||medium exposure||1.5 — 13||3 — 8.5|
|H. varius||intertidal, subidal||algae, Zostera, sand,||shelter||2.5 — 10||2.5 — 8.5|
|H. whitei||intertidal, subtidal||Zostera, sand||shelter||2 — 12.5||3.5 — 11|
|H. pubescens||Intertidal||open reefs, wharf piles, under rocks, Corallina, algal hold-fasts||shelter or medium exposure||3 — 6.5||2.5 — 6.5|
|Halicarcinus sp. nov.||Deep water||—||—||4 — 6.5||3.5 — 6.5|
|H. lacustris||Rivers, ponds||Weed||—||2.5 — 11||2.5 — 7.5|
|Elamena producta||Intertidal pools||Under rocks in sand at bottom of pools||medium exposure||4 — 17.75||4 — 13|
|Elamena sp. nov||Deep water||Oyster beds||—||4 — 9||4.5 — 9|
|Gen. nov. sp. nov.||Intertidal, Deep water||Seaweed||medium exposure||1.3 — 1.5||6 — 6.2|
|Hombronia depressa||Intertidal, Under stones, Deep water||Wharf piles||not known||5.5 — 12||5.5 — 6.6|
Garth, J. S., 1958. Brachyura of the Pacific Coast of America Oxyrhyncha. Allan Hancock Pacif. Exped. 21 (1 and 2).
Gordon, I., 1940. On some Species of the Genus Elamena (s.s.) (Crustacea, Decapoda). Proc. Linn. Soc. Lond. 152 (1).
Richardson, L. R., 1949b. A Guide to the Oxyrhynchous Crabs. Tuatara 2 (2) pp. 58-69, 28 figs.
——, 1949c. Corrections and Additions for the Guides to the Brachyura, Ibid. 2 (3) 130.
Terms used in the Plates
aa — antenna
au — antennule
a.s. — antennal spine
a.v.d. — aperture of vas deferens
a.l.a. — anterior lateral angle
e.s. — eye stalk
k. — keel on rostrum
p.l.a. — posterior lateral angle
p.o. — postocular lobe
rm. — rostrum
r.r. — ventral ridge on rostrum
PLATE 1: Parts of hymenosomid (Halicarcinus cookii). FIG. 1: Dorsal view of the carapace and leg bases (The regions of the carapace are indistinct in many Hymenosomidae.) FIG. 2: Last segments of the male cheliped. FIG. 3: Posterior view of the left 3rd walking leg. FIG. 4: Ventral view of carapace and leg bases.
PLATE 2: FIG 1: Halicarcinus innominatus. A — dorsal view of carapace, B — dorsal view of rostrum, C — frontal view of rostrum with left antennule removed. FIG 2: Halicarcinus planatus. A — dorsal view of carapace, B — dorsal view of rostrum, C — frontal view of rostrum.
PLATE 3: FIG. 1: Halicarcinus ovatus. A — dorsal view of carapace, B — dorsal view of rostrum, C — frontal view of rostrum with left antennule removed. FIG. 2: Halicarcinus cookii (see also plate 1.) A — dorsal view of rostrum, B — frontal view of rostrum with left antennule removed. FIG. 3: Halicarcinus varius. A — dorsal view of carapace, B — frontal view of rostrum with right antennule removed, C — dorsal view of rostrum.
PLATE 4: FIG. 1: Halicarcinus whitei. A — dorsal view of carapace, B — dorsal view of rostrum, C — frontal view of rostrum with left antennule removed. FIG. 2: Halicarcinus pubescens. A — dorsal view of carapace, B — dorsal view of rostrum, C — frontal view of rostrum with right antennule removed.
PLATE 5: FIG 1: Halicarcinus lacustris. A — dorsal view of carapace, B — dorsal view of rostrum, C — frontal view of rostrum. FIG. 2: Halicarcinus sp. nov. A — dorsal view of carapace, B — dorsal view of rostrum, C — frontal view of rostrum with right antennule removed, D — angles at the side of the carapace which are usually sharp for this family. FIG. 3: Elamena producta. A — dorsal view of the carapace, B — frontal view of rostrum, C — lateral view of rostrum, D — left 3rd walking legs anterior view, E — tip of dactylus of walking leg.page 202
PLATE 6: FIG. 1: Elamena sp. nov. A — dorsal view of carapace, B — frontal view of rostrum, C — lateral view of rostrum, D — left 3rd walking leg anterior view, E — tip of dactylus of walking leg. FIG. 2: Gen. nov. sp. nov. A — dorsal view of female carapace, B — lateral view of rostrum C — left 3rd walking leg, D — dactylus of walking leg of immature male, E — tip of dactylus of female. FIG. 3: Hombronia depressa. A — dorsal view of carapace, B — dorsal view of rostrum, C — dorsal view of female abdomen (this is a typical for the family 3rd segment is folded on itself so that half is visible dorsally, half ventrally and the abdomen cannot be lifted and straightened), D — tip of dactylus of walking leg showing two longitudinal rows of long fine setae.
PLATE 7: First Male Pleopods (whole pleopod x 27, tip further enlarged). FIG. 1: Halicarcinus varius (‘normal type’). FIG. 2: Halicarcinus pubescens. FIG. 3: Halicarcinus lacustris. FIG. 4: Elamena producta. FIG. 5: Hombronia depressa. Although the male pleopod of the new genus is not available the other 3 genera can be separated by the form of this pleopod. Aperture of Vas deferens terminal and elongate Halicarcinus.
Aperture of Vas deferens markedly subterminal Elamena.
Aperture of Vas deferens terminal and encircled by a tumid lip Hombronia.page 203