Comaroma simoni Bertkau

Palmgren, P., 1980, Some comments on the anatomy of spiders, Ann. Zool. Fennici 17, pp. 161-173 : 166-167

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Comaroma simoni Bertkau


2. Muscular anatomy of Comaroma simoni Bertkau , Ceratinella brevis (Wider) , and several small theridids

The genus Comaroma has been placed in the family Theridiidae by several recent authorities (Oi, Levi & Levi, Thaler), as it originally was by Bertkau. Simon considered it more or less intermediate between the Micryphantidae and Theridiidae ( Pholcomma ), Wiehle discussed Comaroma simoni in connection with the Micryphantidae , but remarked that its taxonomic position was uncertain. The extrinsic coxal musculature is very peculiar: One median tergo-coxal muscle is inserted in the middle of the superior margin of the coxa, and two lateral muscles of the same length and strength are inserted symmetrically fairly low on the lateral margins, thus preventing the development of the upper endosterno-coxalis muscles ( “promotors” and “remotors” of earlier authors, c, and c 6 in my nomenclature, Palmgren 1978a).

This muscular equipment, found in no other spiders studied by me, could theoretically be interpreted 1) as an adaptation to the very strongly sclerotized prosoma, or 2) as a character also to be found in other very small theridids. To test these hypotheses, specimens ( çç) of several genera were dissected ( Ceratinella brevis Wider , Fig. 21, Crustulina guttata (Wider) , Fig. 22, Steatoda bipunctata (L.) , Figs. 23-24, Dipoena tristis (Hahn) , Figs. 25-27, Pholcomma gibbum (Westring) , Fig. 28). Unfortunately, only material preserved in alcohol was available. The outlines of the brain, ganglia and intestinal caeca could not be clearly discerned in all cases.

The extrinsic musculature of the coxae displayed the normal features of spiders. - Comaroma is also distinguished by the replacement of book-lungs by tracheae (Figs. 19-20). Posterior tracheae appear to be absent. Comaroma might thus be related to the very heterogeneous Symphytognathidae complex, although the chelicerae are free and a pedipalp present in the female. The external resemblance to Chasmocephalon shantzi Gertsch is striking (cf. Gertsch, Fig. 4). Another observation of interest is that in general even very small species, with a cephalothorax less than 1 mm long, have the normal set of leg muscles (cf. also Minyriolus , Palmgren 1978a, fig. 19:3-4).

A few comments may be added on the special features of the above-mentioned species.

The lateral muscle (Ml) is very poorly developed in Ceratinella and Crustulina , just as in Comaroma . As I have pointed out (1978 a), strong sclerotization of the carapace and pleurae more or less excludes compression of the prosomal space, which is the supposed function of Mi, this leaves unanswered the question of the extensor mechanism of the leg joints. In Steatoda and Dipoena the Ml is strong; in Pholcomma the muscle is quite continuous, but its fibres are short.

The cheliceral and pedipalpal muscles are on the whole only weakly developed, leaving the poison gland laterally exposed for part of its length. This accords with the weak development of the chelicers and pedipalps.

The poison gland is long in all species. This is apparently a general character of theridids, whereas Ceralinella appears to be unique among the Micryphantinae in this respect (cf. Palmgren 1978a).

Ceralinella : The celebrum is high and has a lateral lobe. There seems to be no median dorsal caecal pouch (owing to competition for space with the poison glands and the cerebrum?), but the tube draining the coxal caecal branches is enlarged.

Crustulina : The tergo-coxal c, I ("anterior rotator") is very small and hidden behind c 2 I; c 2 is progressively weaker from I-IV. The poor state of preservation prevented observation of the caeca.

Slealoda : The progressively greater strength of all tergo-coxal muscles from I to IV is very striking; the plagulo-tergalis muscle (pi) is also unusually conspicuous. The cerebrum is flanked laterally by the paired parts of the dorsal caecal pouch. The branches to the coxae are wide.

Dipoena : The contrast between the long, though slender, cheliceral muscles and the extremely short tergo-pedipalpal muscles is striking; only the retro-descending muscle (rtf) to the median margin of the chelicer is strong. The tergo-coxal muscles are long and thin; only Cj IV is unusually powerful. The dorsal caecal pouch occupies the usual space between the tip of the poison gland and the dorsal apodeme. The branches to the legs form small pouches protruding between muscles c 2 an d c:i> a feature attaining its extreme development in the tetragnathids .

Pholcomma : The “dome” of the prosoma lacks muscle origins, but is filled by the poison glands and the cerebrum. It was impossible to distinguish any traces of the caecal system. The very short tergo-pedipalpal muscles could not be differentiated in this tiny spider. The tergo-coxal muscles of the first leg are unusually strong, compared with those of the other legs.