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Volume 83, 1955-56
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Marine Asellote Isopods of the Genus Antias with the Description of a New Species from New Zealand*

By Robert J. Menzies and Milton A. Miller

[Received by the Editor, October 22, 1954.]

Abstract

The asellote genus Antias is revised, a key to the seven known species is given, together with locality data for each, and a new species is described from louse-like specimens found on the skin of sea cucumbers (Stichopus mollis) collected at Island Bay, Wellington, New Zealand, by Mr. W. H. Dawbin. The posterior three pairs of peraeopods in the newly-described isopods are peculiarly modified for anchoring the animals in impressed pits on the skin of the sea cucumbers, but lack of lesions on the host and the unmodified mouth-parts of the isopods indicate a commensal, rather than a parasitic, relationship.

The genus Antias was established by Richardson (1906, pp. 16–17) for Antias charcoti Richardson (1906, pp. 17–19, Pl. 1, Fig. 6, Text-fig. 21–23), which was collected from the Wandel and Wiencke Islands (intertidal to 20 metres, among Laminaria). Richardson's generic description follows:

“Corps couvert d'épines sétiformes sur la surface et le long des bords libres.

“Těte prolongée antérieurement en deux lobes étroits séparés par une profonde échancrure médiane.

“Angles latéro-antérieurs prolongés en lobes étroits; yeux situés sur un prolongement pédonculiforme des bords latéraux. Antennes de la premiére paire écourtées, s'étendant seulement jusqu'au bord antérieur du premier segment thoracique; antennes de la deuxième paire courtes, s'étendant seulement jusqu'au bord antérieur du second segment thoracique.

“Les quatre premiers segments du thorax longs et larges, plus ou moins subégaux. Les trois derniers segments courts, ayant environ la moitié de la longueur des segments précédents, et diminuant graduellement de largeur vers l'abdomen.

“Abdomen avec le bord postérieur prolongé en un grand lobe médian arrondi. Les uropodes sont biramés, aussi longs que l'abdomen et de forme plutôt tortueuse.

“Les pattes de la premiére paire sont préhensiles et courtes; les six autres paires sont ambulatoires et courtes aussi.

“Les pléopodes antérieurs du mâle ne sont pas élargis et ne présentent pas de prolongement à l'extrémité.”

Eight species, including the ones described as new in this paper, are currently known. Seven of them occur in the southern hemisphere. Only one, A. hirsutus (Menzies, 1951, California) is known from the northern hemisphere. Five species occur in the Antarctic Ocean. Two are known from the more temperate latitudes at Wellington, New Zealand (the new species described below) and Simonstown, South Africa (A. uncinatus Vanhöffen).

Since eight species are now known it is possible to make four important emendations and several additions to Richardson's generic diagnosis:

[Footnote] * Contribution from the Department of Zoology, University of California, Davis, California.

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(1)

Not all species have the body covered with setiform spines; the species A. hofsteni Nordenstam (1936) and A. marmoratus Vanhoffen having very few setae on the body.
(2)

Whether the frontal margin of the head is medially incised or emarginate seems to be a specific, rather than a generic, character because A. hofsteni Nordenstam, A. uncinatus Vanhöffen, and the new species herein described have a frontal margin which is either straight or strongly produced.
(3)

The ocular peduncles are variable in length, not always strongly produced.
(4)

Since the new species here described has uniramous uropods (but is clearly an Antias in all other respects), it obviously follows that the uropoda in this genus are not necessarily always biramous. While loss of a branch of the uropods may be a generic character in some groups of isopods, there are instances in which one branch may be reduced to a vestige in one species but both branches well developed in other species of the same genus (e.g., compare Janthopsis nodosa Vanhöffen in which the uropodal exopod is vestigial to Janthopsis ruseri Vanhöffen in which it is well developed). Furthermore, even in the same species, a branch of the uropoda may be reduced or absent in one sex but well developed in the opposite sex (e.g., in the genus Paracerceis, the uropodal endopod in the male is greatly reduced or absent, but in the female, both rami of the uropod are well developed).

Additional characters of the genus are: Mandible with a molar process and usually a three-jointed palp. Maxillipedal palp with five articles all of which are of similar width and distinctly more than one-half narrower than the maxillipedal sympod. Dactyls of all peraeopods with two claws. First maxilla with three lobes, second with two lobes. Second male pleopod with inner ramus pointed and not longer than outer ramus. Third pleopod of male with two-jointed outer branch which is much narrower than inner branch. Fourth pleopod of male with outer branch much narrower than inner branch; inner branch lacking plumose setae.

Nordenstam (1936, p. 198) places Antias in the subgroup Antiasini Nordenstam (1936) of the group Munnini (Hansen, 1916). It is the only genus known to belong to that subgroup. The grouping seems quite logical and illustrates the close similarity of Antias to the Munna-like rather than to the Ianira-like isopods with which Richardson had associated it.

A Key to the Known Species of Antias
1. Uropods biramous; cephalon (head) not strongly produced forward, being slightly convex, concave, or deeply emarginated 2
1a. Uropods uniramous; cephalon strongly produced forward A. unirameus n.sp. (Wellington, New Zealand).
2. First antenna composed of five articles ( [ unclear: ] peduncle plus three [ unclear: ] articles) 3
2a. First antenna composed of six or seven articles ( [ unclear: ] peduncle plus four or five flagellar articles) 7
3. Uropodal exopod less than one-half the length of endopod A. uncinatus Vanhoffen (1914, p. 535. abb. 62, Simonstown, South Africa).
3a. Rami of uropods subequal in length 4
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4. Frontal border of head evenly convex; rami of uropods longer than peduncle 5
4a. Frontal border of head evenly concave; rami of uropods as long as or slightly shorter than peduncle 6
5. Body covered with stout setae; lateral margins of pleotelson with several stout setae A. hispidus Vanhoffen (1914, pp. 533-534, abb. 60, St. Paul Isl., Antarctic. Stephensen, 1927, pp. 356-357, Fig, 24, Auckland Isl., Antarctic. Nordenstam, 1933, pp. 201ndash;203, Text-figs. 47a-g, Falkland Isls., and Graham Region, north of Astrolabe Isl., Antarctic).
5a. Body only with a few marginal setae, lateral margins of pleotelson each with one stout seta A. mawsoni Hale (1937, pp. 29ndash;30, Fig. 10, Main Base, Boat Harbour, Cape Denrson, Adelie Land, Antarctic).
6. Body densely covered with setae; pleotelson wider than long, laterally fringed with setae A. hirsutus Menzies (1951, pp. 143-147, Figs. 27-28, Tomales Point, [ unclear: ] Co., California, U. S. A.).
6a. Body with a few setae; pleotelson longer than wide, laterally devoid of setae A. marmoratus Vanhoffen (1914, pp. 534-535, abb. 61 a-d, St. Paul Isl., and Observatory Bay, Antarctic. Nordenstam, 1933, pp. 203-205, Pi. II, Fig. 17, Text-fig. 48 a-g, South Georgia Isl., Antarctic).
7. Front of head deeply incised medially, body densely covered with setae A. charcoti Richardson (1906, pp. 17-19, Pl. I, Fig. 6, Text-figs. 21-23, Antarctic at Wandel and Wiencke Isls. Hodgson, 1910, pp. 63-64, Pl. IX, Fig. 6, Winter Quarters Graham's Land).
7a. Front of head evenly convex, body with a few scattered setae A. hofsteni Nordenstam (1933, pp. 205-208, Pl. II, Fig. Is, Text-fig. 49 a-i, South Georgia Isl., Antarctic).

Antias unirameus n.sp. Figs. 1-2.

Holotype male. Length 0.7 mm, width 0.3 mm.

Allotype. Length 1.0 mm, width 0.5 mm, ovigerous.

Diagnosis. Eyes bulging, but not stalked. Large broadly rounded frontal lobe projecting forward, fringed with spine-like setae. Preocular lobes small, not curved outward. First antenna with [ unclear: ] peduncle and [ unclear: ] flagellum; second article of peduncle narrower but about as long as first and bearing a projection along its inferior margin at distal end; last article of flagellum longer than preceding two subequal articles together and bears a single sensory filament and two bristles at apex. Borders of peraeonal somites convex, each with a longitudinal row of spine-like setae near lateral margin. Epimera prominent in dorsal view along entire lateral margin of all peraeonal somites. Mandibular palp triarticulate. Pleotelson consists of a single segment and is fringed marginally with spine-like bristles. Dorsum of body, except for fringe of bristles, devoid of setae. Uropod with a single ramus, about as long as the peduncle.

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Picture icon

Figure 1.—Antias unirameus n.sp.; a, male, dorsal view; b, first antenna; c, peduncle of second antenna; d, mandible; e, mandibular palp; f, second maxilla; g, maxilliped; h, apex of pleotelson and right uropod. Scale shown only for entire animal; parts highly magnified but not to same scale.

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Picture icon

Figure 2.—Antias unirameus n.sp.; a, first peraeopod, ♂; b, second peraeopod, ♂; c, sixth peraeopod, ♂; d, apex of first pair of pleopoda, ♂; e, second pleopod, ♂; f, third pleopod, ♂; g, fourth pleopod, ♂; h, operculum, ♀.

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Body Characteristics. The fringe of erect spine-like setae around the animal gives it an unusual appearance. Chromatophores sparse, light brown in colour. Body appears yellowish. Bodily proportions vary but average length about twice width, gravid females somewhat wider.

Cephalon. About 1 ½ times wider than long. Eyes small, composed of about six ocelli, red or black in colour.

Peraeon. Epimera of third to sixth peraeonal somites each with at least one stout seta.

Pleon. Nearly 1 ½ times longer than wide, distal margin with a median lobe between uropodal insertions; lobe lacks the marginal setae characteristic of rest of body.

Second Antenna. Peduncle composed of six articles. First four articles subequal in length and width, fifth slightly narrower and longer than others, fourth bears an outward projection which has a stout seta at its apex. Flagellum with six articles.

Maxilliped. With two coupling hooks. Endite narrower than sympod.

Maxillae. Typical, first with two lobes, second with three lobes. Apices of lobes with setae.

Mandible. Palp triarticulate, first article shortest and middle the longest, being twice as long as first. Left molar process cylindrical, truncate apex with several teeth, incisor with four teeth, lacinia with three teeth, setal row with three setae. Right mandible incisor with four teeth, setal row with four setae, molar process similar to that of left mandible.

First Peraeopod. Dactyl with two unequal claws, unguis about ⅓ length of subunguis. Propod with two stout setae on inferior margin. Carpus with two stout setae on inferior margin. Merus with one stout seta at superior distal angle (male).

Second Peraeopod. Dactyl with two nearly equal claws. Propod lacking stout setae. Carpus with five stout setae on distal margin and one such seta on inferior margin. Merus with one stout seta at superior distal angle. Third and fourth peraeopods similar to second (male).

Sixth Peraeopod. Dactyl and propod recurved to close over the stout setae on the inferior margin of carpus thus forming a “claw-like” structure.g Dactyl biunguiculate, unguis ⅔ length of subunguis. Carpus with five stout setae along distal margin and two such setae along inferior margin. Merus with two stout setae at superior distal angle. Fifth and seventh peraeopods markedly similar to sixth (male).

Uropod. Peduncle widest at distal end which bears three stout setae. Ramus slightly longer than peduncle and bears two stout setae at apex in addition to the usual sensory bristles.

Pleopoda. Each first pleopod of male widest proximally with three simple setae at trilobate apex. Female operculum wider than long, with wide lobe at apex. Third pleopod of male with three plumose setae on endopod and one on exopod. Fourth pleopod of male with one plumose seta on exopod and none on endopod.

Types. Holotype, allotype, and eight male, fourteen female (six gravid), and four young paratypes. Type material has been deposited as follows: Holotype, allotype and all paratypes (except one male in the author's collection) in the Dominion Museum, Wellington, New Zealand.

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Remarks. This curious and new asellote was collected “4/9/51” by Mr. W. H. Dawbin from the sea cucumber Stichopus mollis at Island Bay, Wellington, New Zealand The specimens were sent to us for identification by Dr. Desmond E. Hurley, Portobello Marine Laboratory, Port Chalmers, New Zealand.

The new isopod superficially resembles a small louse. Samples of Stichopus flesh showed that the isopod impresses itself into the surface of the sea cucumber, leaving only its dorsal surface exposed. The hinder three pairs of legs are curiously modified to curve up around the body of the isopod and to attach like grapples to the flesh of the Stichopus. There was no evidence that the isopod penetrated the tissue of the sea cucumber. Lack of lesions and the fact that the mouth-parts of the isopod are not modified suggest that the animal is a commensal of the sea cucumber and not a parasite. In any event, the collector reports these isopods to be quite common on the host. The only other ectocommensals on holothurians, to our knowledge, are scale-worms such as Arctonoe pulchra which lives on the sea cucumber, Stichopus californicus, clinging to the host by hook-like parapodial setae. Several endocommensals that live in the cloacal chamber of various holothurians have been reported including a pea crab, Opisthopus transversus, often found in Stichopus, and a small fish occurring in large West Indian sea cucumbers.

The [ unclear: ] females had an average of four eggs in their pouch (range 1-7). One interesting feature of gravid females was the presence of only three pairs of oostegites (on somites two, three, and four).

Literature Cited

Hale, Herbert M, 1937 Isopoda and Tanaidacea [ unclear: ] Antarctic Expedition, 1911-1914, [ unclear: ] Repts, [ unclear: ] . C-Zool. and Bot, 2 (2). 1-45

Hansen. H. J. 1916 Crustacea Malacostraca. III Isopoda, The Danish Ingolf-Expedition, Vol III B, pp. 1-262, 16pls, Copenhagen. H. Hagerup

Hodgson, T. V. 1910 Crustacea. IX. Isopoda National Antarctic Expedition 1901-1904, Natural History, Zoology and Botany. 5. 1-77, 10 pls, London

Menzies Robert J, 1951 New [ unclear: ] Isopods, Chiefly from Northern California. with Notes on Related Forms Proc U. S. Nat Mus, 101 (3273). 105-156

Nordenstam, ÅKe, 1933 [ unclear: ] Isopoda of the Families, Seiolidae. Idotheidae Pseudidotheidae, [ unclear: ] . Parasellidae and [ unclear: ] Mainly from the South Atlantic Further Zoological Results of the Swedish Antarctic Expedition 1901-1903. 3 (1) 1-284, 2 pls., Stockholm.

Richardson, Harriet, 1906 Isopodes In: Dr. Jean Charcot. Expédition Antarctique Français (1903-1905), Vol 4, Crustacés, pp. 1-22, 1 pl

Stephensen, K, 1927. Papers from Dr. Th. Mortensen's Pacrfic Expedition 1914-1916, XL. Crustacea from the Auckland and Campbell Islands. Videnskabelige meddelelser fra Dansk naturhistorisk Forening [ unclear: ] Kobenhavn, 83 289-390

Vanhoffen, E, 1914 Die Isopoden der Deutschen Sudpolai-Expedition 1901-1903. Vol. 15, Zool, [ unclear: ] 449-598, 132 abb Ed Erich von Diygalski. Beilin, G. Reimei

Dr. Robert J. Menzies


Scripps Institution of Oceanography
University of California
La Jolla, California, U. S. A.

Professor Milton A. Miller


Department of Zoology
University of California
Davis, California, U. S. A.

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